# Refs for melonate, hydromelonic acid, cyameluric acid, and cyameluraee

<ref name=beach1954>Norman F Beach and Fred W Spangler (1954): "Melonate and cyamelurate stabilizers for photographic emulsions sensitized with alkylene oxide polymers". US patent 2704716A <!--This invention relates to fog inhibiting agents and stabilizers for photographic emulsions and to photo graphic emulsions containing them. It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called "fog,' and sometimes called "chemical fog where it is necessary to distinguish be tween it and the effects of accidental exposure to radia E. in this invention, we are not concerned with the latter.  Fog depends both on the emulsion and the conditions ... These objects are accomplished in general by adding to the emulsion sensitized with alkylene oxide polymers, derivatives of melon and cyameluric acid, particularly alkali metal salts of hydromelonic acid and cyameluric acid. Specific examples of compounds which we may use are potassium melonate, sodium melonate, potassium cyamelurate and sodium cyamelurate. The preparation of melon and --></ref>
<ref name=bord2004>Elisabeta Horvath-Bordon, Edwin Kroke, Ingrid Svoboda, Hartmut Fueß, Ralf Riedel, Sharma Neeraj and Anthony K. Cheetham (2004): "Alkalicyamelurates, M3[C6N7O3]·xH2O, M = Li, Na, K, Rb, Cs: UV-luminescent and thermally very stable ionic tri-s-triazine derivatives". ''Dalton Transactions'', volume 2004, issue 22, 3900-3908.  <!--Cyamelurates are salts of cyameluric acid, a derivative of tri-s-triazine (1,3,4,6,7,9-hexaazacyclo[3.3.3]azine or s-heptazine). These compounds are thermally very stable and possess interesting structural and optical properties. Only very few tri-s-triazine derivatives have been reported in the literature. The water-soluble alkali cyamelurates were extensively characterized using NMR, FTIR, Raman, UV, luminescence spectroscopy and elemental analysis. In addition, the single crystal X-ray structure analyses of the four hydrates of lithium, sodium, potassium and rubidium cyamelurates (Li3[C6N7O3]·6H2O; Na3[C6N7O3]·4.5H2O; K3[C6N7O3]·3H2O; Rb3[C6N7O3]·3H2O) are presented. Thermogravimetric analysis shows that the dehydrated salts start to decompose at temperatures above 500 °C. The thermal stability does not depend on the cations which is in contrast to the analogous s-triazine salts, i.e. the alkali cyanurates M3[C3N3O3]. The photoluminescence spectra indicate a very strong solid state UV-emission with maxima between 280 and 400 nm.--> {{doi|10.1039/B412517G}}</ref>
<ref name=braml2012>Nicole E. Braml and Wolfgang Schnick (2012): "New Heptazine Based Materials with a Divalent Cation – Sr[H2C6N7O3]2·4H2O and Sr[HC6N7(NCN)3]·7H2O". ''Zeitschrift für anorganische und allgemeine Chemie'', volume 639, issue 2, pages 275-279.  <!--The new heptazine based compounds Sr[H2C6N7O3]2·4H2O and Sr[HC6N7(NCN)3]·7H2O have been synthesized by metathesis reactions in aqueous solution. Crystal structures were studied by single‐crystal X‐ray diffraction and Rietveld refinement. Strontium cyamelurate tetrahydrate exhibits distorted zigzag strands embedding Sr2+ ions surrounded by crystal water molecules (Fdd2, a = 1194.0(17), b = 6358.14(97), c = 602.73(89) pm, Z = 8, GOF = 1.034, Rp = 0.033, wRp = 0.042, RB = 0.84). Strontium melonate heptahydrate crystallizes in a layer‐like structure characteristic for heptazine‐based compounds (Pequation image, a = 660.76(13), b = 1080.7(2), c = 1353.8(3) pm, α = 101.67(3), β = 101.40(3), γ = 94.60(3)°, Z = 2, R1 = 0.032, wR2 = 0.072). Additionally, the thermal behavior has been studied by DTA/TG measurements and FTIR spectroscopy data are presented.--> {{doi|10.1002/zaac.201200345}}</ref>
<ref name=brown1962>Harvey A. Brown, John G. Erickson, Donald R. Husted, and Charles D. Wright (1962): "Fluorinated sym-triazine derivatives". US PAtent  3515603.   <!--A number of synthetic pyrolytic methods which are known to the art lead to the formation of a complex material known as melon which is believed to comprise, inter alia, condensed derivatives of tri-s-triazine. The components of this mixture, like melem, are insoluble and melon is thus an unresolvable mixture including substances such as those represented--></ref>
<ref name=clauss2010a>Corinna Clauss,  Jörg Wagler, Marcus Schwarz, Anke Schwarzer, and Edwin Kroke (2010): "Lithium Melonate, Li3[C6N7(NCN)3]·6H2O – Synthesis, Crystal Structure and Thermal Properties of a Novel Precursor for Graphitic Carbon Nitrides". ''Zeitschrift für anorganische und allgemeine Chemie'', volume 636, issue 1, pages 196-200. <!--A new s‐heptazine derivative, lithium melonate Li3[C6N7(NCN)3] (2), has been prepared from potassium melonate by using an ion exchanger resin. The crystal structure of the hexahydrate Li3[C6N7(NCN)3]·6H2O (2a) has been determined by X‐ray diffraction analysis (hexagonal, P63/m, a = b = 12.2263(6), c = 6.8854(6) Å, V = 891.35(10) Å3). The results show that this s‐heptazine derivative adopts ideal C3h symmetry, thus comprising 1/6 of the formula moiety in the asymmetric unit. 13C NMR spectroscopic data indicate that no melonate‐lithium interaction occurs in solution, whereas lithium is tetrahedrally coordinated by two oxygen and two nitrogen atoms in 2a in the solid. The title compound 2 was further characterised by FTIR, Raman spectroscopy, TG/DTA and elemental analysis. In spite of the high nitrogen content, compound 2 proved to be thermally stable up to ~500 °C. The latter observation is typical for melonates and has been reported for other s‐heptazine derivatives as well.--> {{doi|10.1002/zaac.200900326}}</ref>
<ref name=clauss2010b>Corinna Clauss, Marcus Schwarz, and Edwin Kroke (2010): "Microwave-induced decomposition of nitrogen-rich iron salts and CNT formation from iron(III)–melonate Fe[C9N13]". ''Carbon'', volume 48, issue 4, pages 1137-1145. <!--Two nitrogen-rich iron salts, ferric ferrocyanide (Fe4[Fe(CN)6]3, Prussian Blue, “PB”) and iron melonate (Fe[C6N7(NCN)3], “FeM”), were thermally decomposed. A household microwave oven was used to heat a molybdenum wire after being coated with the precursor and protected from ambient atmosphere. The nanostructured products obtained were characterised with FTIR- and Raman-spectroscopy, XRD, SEM, EDX, EELS and TEM. While the PB-precursor did not give any nanotube-containing products, the FeM-precursor furnished tubular carbon nanostructures in a reproducible manner. This result may be due to the graphite-like nature of the [C6N7(NCN)3]3−-anions present in FeM. The C6N7-unit is aromatic and completely planar, while the cyanide anions in PB do not provide similar structures. Another significant difference is the high Fe:C-ratio in PB, which might prevent CNT-formation when this precursor is used. The nitrogen content of the tubes was found to be below the detection limit of EELS. This indicates that the synthesis temperatures were too high resulting in complete evaporation of all nitrogen present in the FeM-precursor forming volatile species such as N2 or (CN)2.--> {{doi|10.1016/j.carbon..11.036}}</ref>
<ref name=clauss2011>Corinna Clauss, Horst Schmidt, Anke Schwarzer, and Edwin Kroke (2011): "Copper(II) Melonates Cu3[C6N7(NCN)3]2·8H2O and [Cu(C2H8N2)2]3[C6N7(NCN)3]2·4H2O – Using the Terminal Cyano Group of the[C6N7(NCN)3]3– Ion for Complexation". ''Zeitschrift für anorganische und allgemeine Chemie'', volume 637, issue 14‐15, pages 2246-2251.  <!--Abstract. Copper melonate Cu3[C6N7(NCN)3]2·8H2O (2a) was synthesized by a metathesis reaction of potassium melonate with copper(II) in aqueous solution. A related copper melonate [Cu(C2H8N2)2]3[C6N7(NCN)3]2·4H2O (2b) was obtained from an aqueous potassium melonate solution containing copper(II) and ethylenediamine. The crystal structure of 2b was determined by X‐ray diffraction analysis (triclinic, Pequation image, a = 6.8035(5), b = 12.6931(8), c = 14.9636(10) Å,α = 67.215(5), β = 79.273(6), γ = 87.206(6)°, V = 1170.17(14) Å3). In contrast to already reported crystal structures of melonates copper ions are coordinated only to the terminal nitrogen atoms of the cyanamide functionality of the melonate anion. Both copper(II) melonates 2a and 2b were further characterized by FT‐IR and 13C MAS NMR spectroscopy, TG/DTA, and elemental analysis. Whereas dehydrated 2a is stable up to 500 °C, 2b shows less thermal stability.--> {{doi|10.1002/zaac.201100224}}</ref>
<ref name=clauss2012>Corinna Clauss, Uwe Böhme, Anke Schwarzer, and Edwin Kroke (2012): "Silver Melonates and Coordination Modes of the Multidentate [C6N7(NCN)3]3– Anion". ''European Journal of Inorganic Chemistry'', volume 2012, issue 6, pages 978-986.  <!--Three different silver melonates, Ag3[C6N7(NCN)3]·H2O (2a), Ag3[C6N7(NCN)3]·0.5NH3 (2b) and Ag3[C6N7(NCN)3]·2C2H8N2 (2c), and a nickel melonate, Ni3[C6N7(NCN)3]2·10NH3·6H2O (3), have been synthesised by the reaction of potassium melonate with silver nitrate either in an aqueous solution (2a), aqueous ammonia solution (2b) or an aqueous solution of ethylenediamine (2c) and with nickel nitrate in an aqueous ammonia solution (3). The crystal structure of 2c was determined by XRD [triclinic, Pequation image, a = 7.5499(4), b = 11.3438(6), c = 12.5741(7) Å, α = 72.138(4), β = 80.148(4), γ = 75.945(4)°, V = 984.90(9) Å3]. Silver atoms are coordinated to the terminal nitrogen atom of the cyanamide substituent as well as directly to the N atoms of the s‐heptazine core. Complex 2c crystallises in a layered structure. Adjacent Ag–melonate cation–anion units are connected by Ag–Ag interactions. The preferred coordination mode of metal ions at the melonate anion has been considered by quantum chemical calculations. Natural atomic charges calculated for the four nonequivalent, nucleophilic N atoms of the [C6N7(NCN)3]3– anion are (a) –0.596, (b) –0.619, (c) –0.675 and (d) –0.644. The metal coordination found experimentally in the melonates correlates with these relatively small charge differences and with the hard‐soft acid–base concept. However, (mono)protonation of the [C6N7(NCN)3]3– anion exclusively occurs at the terminal N atoms (b) of the s‐heptazine core, which is indicated experimentally and theoretically. Silver melonates 2a, 2b and 2c and nickel melonate 3 were further characterised by FTIR and 13C solid‐state magic‐angle spinning NMR spectroscopy, thermogravimetric/differential thermal analysis and elemental analysis. Solvent‐free complexes 2a and 2b, i.e. Ag3[C6N7(NCN)3], are thermally stable up to 500 °C. In contrast, 2c and 3 are thermally less stable.--> <!--Silver melonates were synthesised, and their spectroscopic, structural and thermal properties were investigated. Theoretical and experimental data that concern the regioselective coordination of the trianion indicate that all four different terminal N atoms are able to interact with metal cations.--> {{doi|10.1002/ejic.201101254}}</ref>
<ref name=elga2007>Nadia E. A. El‐Gamel, Lena Seyfarth, Jörg Wagler, Helmut Ehrenberg, Marcus Schwarz, Jürgen Senker, and Edwin Kroke (2007): "Tri‐s‐triazine derivatives, Part 4: The Tautomeric Forms of Cyameluric Acid Derivatives". ''Chemistry – A European Journal'' volume 13, issue 4, pages 1158-1173.  <!--The tautomerism of cyameluric acid C6N7O3H3 (1 a), cyamelurates and other heptazine derivatives has recently been studied by several theoretical investigations. In this experimental study we prepared stannyl and silyl derivatives of cyameluric acid (1 a): C6N7O3[Sn(C4H9)3]3 (3 a), C6N7O3[Sn(C2H5)3]3 (3 b), and C6N7O3[Si(CH3)3]3 (4). In order to investigate the structure of 1 a the mono‐ and dipotassium cyamelurate hydrates K(C6N7O3H2)⋅2 H2O (5) and K2(C6N7O3H)⋅1 H2O (6) were synthesized by UV/Vis‐controlled titration of a potassium cyamelurate solution with aqueous hydrochloric acid. Compounds 3–6 were characterized by FTIR and solid‐state NMR spectroscopy as well as simultaneous thermal analysis (TGA, DTA). The single crystal X‐ray structures of the salts 5 and 6 show that the hydrogen atoms in both anions are localized on the peripheral nitrogen atoms. This indicates—in combination with the solid‐state NMR studies—that the most stable tautomer of solid 1 a is the triketo form with C3h symmetry. However, derivatives of both the hydroxyl and the amido tautomers may be formed depending on the substituent atoms: The spectroscopic data and single crystal structures of compounds C6N7O3[Si(CH3)3]3 (4) and the solvate C6N7O3[Sn(C2H5)3]3⋅C2H4Cl2 (3 b′) show that the former is derived from the symmetric trihydroxy form of 1 a, while 3 b′ crystallizes as a chain‐like polymer, which contains the tin atoms as multifunctional building blocks, that is, bridging pentacoordinated Et3SnO2 and Et3SnON units as well as non‐bridging four‐coordinated Et3SnN units. The cyameluric nucleus is part of the polymeric chains of C6N7O3[Sn(C2H5)3]3⋅C2H4Cl2 (3 b′), by the action of both tautomeric forms of cyameluric acid, the amide and the ester form.--> {{doi|10.1002/chem.200600435}}</ref>
<ref name=fink1964>A. I. Finkel'shtein and N. V. Spiridonova (1964) "Chemical properties and molecular structure of derivatives of sym-heptazine [1,3,4,6,7,9,9b-heptaazaphenalene, tri-1,3,5-triazine]". ''Russian Chemical Reviews'', volume 33, issue 7, pages 400--405. <!-- --> {{doi|10.1070/RC1964v033n07ABEH001443}}</ref>
<ref name=grac2009>J. Gracia and P. Kroll (2009): "Corrugated layered heptazine-based carbon nitride: the lowest energy modifications of C3N4 ground state".  ''Journal of Materials Chemistry'', volume 19, issue 19, pages 3013-3019. <!--We systematically investigate trends in carbon nitride structures targeting the lowest energy configuration of C3N4. Layered conformations, sp2-bonded, turn out to be more favorable than denser, sp3-bonded, networks. Among layered structures, those comprising the heptazine motif are consistently lower in energy when compared to triazine-based models. Additional decrease of energy is achieved by corrugation of the layers, driven by avoiding repulsive interactions between nitrogen lone-pairs. Consequences of such curvature are for one the necessity to approximate the lowest energy configuration of C3N4 with very large unit cells, as indicated through ab-initio molecular dynamic simulations. Secondly, curvature favors the genesis of confined structures of carbon nitride: the energy difference between “one-dimensional” nanostructures and the layered state is at least smaller for C3N4 than for pure carbon.--> {{doi|10.1039/B821568E}}</ref>
<ref name=hill2011>Michael S. Hill (2011): "Alkaline and alkaline earth metals". ''Annual Reports Section "A" (Inorganic Chemistry)'', Royal Society of Chemistry, volume 107, pages 46-53. <!--Advances in the coordination and inorganic chemistry of the elements of Groups 1 and 2 of the periodic table from the calendar year 2010 are summarised in this non-critical review. As was the case in previous years, coverage concentrates on topics centred around the synthesis, structures and applications of coordination compounds and the organometallic chemistry of these elements.--> {{doi|10.1039/C1IC90016A}}</ref>
<ref name=irran2001>Elisabeth Irran, Barbara Jürgens, and Wolfgang Schnick (2001): "Trimerization of Alkali Dicyanamides M[N(CN)2] and Formation of Tricyanomelaminates M3[C6N9] (M=K, Rb) in the Melt: Crystal Structure Determination of Three Polymorphs of K[N(CN)2], Two of Rb[N(CN)2], and One of K3[C6N9] and Rb3[C6N9] from X‐ray Powder Diffractometry". ''Chemistry – A European Journal'' volume 7, issue 24, pages 5372-5381. <!--The alkali dicyanamides M[N(CN)2] (M=K, Rb) were synthesized through ion exchange, and the corresponding tricyanomelaminates M3[C6N9] were obtained by heating the respective dicyanamides. The thermal behavior of the dicyanamides and their reaction to form the tricyanomelaminates were investigated by temperature‐dependent X‐ray powder diffractometry and thermoanalytical measurements. Potassium dicyanamide K[N(CN)2] was found to undergo four phase transitions: At 136 °C the low‐temperature modification α‐K[N(CN)2] transforms to β‐K[N(CN)2], and at 187 °C the latter transforms to the high‐temperature modification γ‐K[N(CN)2], which melts at 232 °C. Above 310 °C the dicyanamide ions [N(CN)2]− trimerize and the resulting tricyanomelaminate K3[C6N9] solidifies. Two modifications of rubidium dicyanamide have been identified: Even at −25 °C, the α form slowly transforms to β‐Rb[N(CN)2] within weeks. Rb[N(CN)2] has a melting point of 190 °C. Above 260 °C the dicyanamide ions [N(CN)2]− of the rubidium salt trimerize in the melt and the tricyanomelaminate Rb3[C6N9] solidifies. The crystal structures of all phases were determined by powder diffraction methods and were refined by the Rietveld method. α‐K[N(CN)2] (Pbcm, a=836.52(1), b=646.90(1), c=721.27(1) pm, Z=4), γ‐K[N(CN)2] (Pnma, a=855.40(3), b=387.80(1), c=1252.73(4) pm, Z=4), and β‐Rb[N(CN)2] (C2/c, a=1381.56(2), b=1000.02(1), c=1443.28(2) pm, β=116.8963(6)°, Z=16) represent new structure types. The crystal structure of β‐K[N(CN)2] (P21/n, a=726.92(1), b=1596.34(2), c=387.037(5) pm, β=111.8782(6)°, Z=4) is similar but not isotypic to the structure of α‐Na[N(CN)2]. α‐Rb[N(CN)2] (Pbcm, a=856.09(1), b=661.711(7), c=765.067(9) pm, Z=4) is isotypic with α‐K[N(CN)2]. The alkali dicyanamides contain the bent planar anion [N(CN)2]− of approximate symmetry C2v (average bond lengths: C−Nbridge 133, C−Nterm 113 pm; average angles N‐C‐N 170°, C‐N‐C 120°). K3[C6N9] (P21/c, a=373.82(1), b=1192.48(5), c=2500.4(1) pm, β=101.406(3)°, Z=4) and Rb3[C6N9] (P21/c, a=389.93(2), b=1226.06(6), c=2547.5(1) pm, β=98.741(5)°, Z=4) are isotypic and they contain the planar cyclic anion [C6N9]3−. Although structurally related, Na3[C6N9] is not isotypic with the tricyanomelaminates M3[C6N9] (M=K, Rb).--> {{doi|10.1002/1521-3765(20011217)7:24<5372::AID-CHEM5372>3.0.CO;2-%23}}</ref>
<ref name=jones1957>Jean E. Jones (1957): "Supersensitization of optical sensitization". US Patent 2801172.  <!--This invention relates to photographic silver halide emulsions containing dicarbocyanine dyes and in super sensitizing combination there with, hydromelonic acid, cyameluric acid, or an alkali metal salt thereof. It is known in the art of making photographic emulsions that certain dyes of the cyanine class alter the sensi tivity of photographic emulsions of the gelatino-silver halide kind, when the dyes are incorporated in the emulsions. It is also known that the sensitization produced by a given dye varies somewhat with the type of emulsion in which the dye is incorporated. Furthermore, the sensitization of a given emulsion by a given dye may be altered by varying the conditions in the emulsion. For example, the sensitization may be increased by increasing the silver ion concentration or decreasing the hydrogen ion concentration (i. e., increasing the alkalinity) or both.  Thus, sensitization can be increased by bathing plates, coated with a spectrally sensitized emulsion, in water or in aqueous solutions of ammonia. Such a process of al tering the sensitivity of a sensitized emulsion by increasing the silver ion concentration and/or by decreasing the hydrogen ion concentration is commonly called "hyper sensitization'. Hypersensitized emulsions have generally poor keeping qualities. I have now found another means of altering the sensi tivity in emulsions containing dicarbocyanine dyes. Since the conditions in the emulsion, i. e., the hydrogen ion and/or the silver ion concentration undergo little or no change in my method, I shall designate my method as a kind of supersensitization. It is, therefore, an object of my invention to provide photographic emulsions containing dicarbocyanine dyes and as supersensitizers therefor, certain derivatives of melon and cyameluric acid, particularly hydromelonic acid, cyameluric acid, or an alkali metal salt of these acids. Another object is to provide a means for prepar ing these supersensitized emulsions. Other objects will be come apparent from a consideration of the following de scription and examples. While the derivatives of melon and cyameluric acid em ployed in my invention have been previously employed in photographic emulsions which have been optically sensi tized with “cyanine" and "merocyanine" dyes, the effects observed in the instant invention are not general. That is, it has been found that no significant (or measureable) supersensitizing effect is observed with many simple cyanine and carbocyanine dyes. It was not expected, therefor, that the useful results illustrated below could be obtained with dicarbocyanine dyes. The dicarbocyanine dyes which are useful --></ref>
<ref name=juer2000>Barbara Jürgens, Elisabeth Irran, Julius Schneider, and Wolfgang Schnick (2000): "Trimerization of NaC2N3 to Na3C6N9 in the Solid:  Ab Initio Crystal Structure Determination of Two Polymorphs of NaC2N3 and of Na3C6N9 from X-ray Powder Diffractometry". ''Inorganic Chemistry'', volume 39, issue  4, pages 665-670. <!--Sodium dicyanamide NaC2N3 was found to undergo two phase transitions. According to thermal analysis and temperature-dependent X-ray powder diffractometry, the transition of α-NaC2N3 (1a) to β-NaC2N3 (1b) occurs at 33 °C and is displacive. 1a crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 647.7(1), b = 1494.8(3), c = 357.25(7) pm, β = 93.496(1)°, and Z = 4. The structure was solved from powder diffraction data (Cu Kα1, T = 22 °C) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.072, Rp = 0.053, and RF = 0.074. 1b crystallizes in the orthorhombic system, space group Pbnm (no. 62), with a = 650.15(5), b = 1495.1(2), c = 360.50(3) pm, and Z = 4. The structure was refined by the Rietveld method using the atomic coordinates of 1a as starting values (Mo Kα1, T = 150 °C). The final agreement factors were wRp = 0.044, Rp = 0.034, RF = 0.140. The crystal structures of both polymorphs contain sheets of Na+ and N(CN)2- ions which are in 1a nearly and in 1b exactly coplanar. Above 340 °C, 1b trimerizes in the solid to Na3C6N9 (2). 2 crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 1104.82(1), b = 2338.06(3), c = 351.616(3) pm, β = 97.9132(9)°, and Z = 4. The structure was solved from synchrotron powder diffraction data (λ = 59.733 pm) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.080, Rp = 0.059, and RF = 0.080. The compound contains Na+ and the planar tricyanomelaminate C6N93-. The phase transition from 1b to 2 is reconstructive. It occurs in the solid-state without involvement of other phases or intermediates. The crystal structures of 1b and 2 indicate that there is no preorientation of the N(CN)2- in the solid before their trimerization to C6N93-.--> {{doi|10.1021/ic991044f}}</ref>
<ref name=koma2001>Tamikuni Komatsu and Takako Nakamura (2001), "Polycondensation/pyrolysis of tris-s-triazine derivatives leading to graphite-like carbon nitrides".  ''Journal of Materials Chemistry'', volume 11, issue 2, pages 474-478. <!--Polycondensation/pyrolysis of 2,5,8-tricarbodiimide-tris-s-triazine and its derivatives gave hexagonal graphite-like pseudo carbon nitrides, CH0.3–0.08N1.0–0.63, composed of tris-s-triazine nuclei. The materials were stable up to 600–800 °C under an inert atmosphere depending on their nitrogen content.--> {{doi|10.1039/B005982J}}</ref>
<ref name=lau2016>Vincent Wing-hei Lau, Igor Moudrakovski, Tiago Botari, Simon Weinberger, Maria B. Mesch, Viola Duppel, Jürgen Senker, Volker Blum  and  Bettina V. Lotsch (2016): "Rational design of carbon nitride photocatalysts by identification of cyanamide defects as catalytically relevant sites". ''Nature Communications'',  volume 7, article 12165. <!--The heptazine-based polymer melon (also known as graphitic carbon nitride, g-C3N4) is a promising photocatalyst for hydrogen evolution. Nonetheless, attempts to improve its inherently low activity are rarely based on rational approaches because of a lack of fundamental understanding of its mechanistic operation. Here we employ molecular heptazine-based model catalysts to identify the cyanamide moiety as a photocatalytically relevant ‘defect’. We exploit this knowledge for the rational design of a carbon nitride polymer populated with cyanamide groups, yielding a material with 12 and 16 times the hydrogen evolution rate and apparent quantum efficiency (400 nm), respectively, compared with the unmodified melon. Computational modelling and material characterization suggest that this moiety improves coordination (and, in turn, charge transfer kinetics) to the platinum co-catalyst and enhances the separation of the photogenerated charge carriers. The demonstrated knowledge transfer for rational catalyst design presented here provides the conceptual framework for engineering high-performance heptazine-based photocatalysts. --> {{doi|10.1038/ncomms12165}}</ref>
<ref name=mako2009>Sophia J. Makowski and Wolfgang Schnick (2009): "Rb3[C6N7(NCN)3]·3H2O and Cs3[C6N7(NCN)3]·3H2O – Synthesis, Crystal Structure and Thermal Behavior of Two Novel Alkali Melonates". ''Zeitschrift für anorganische und allgemeine Chemie'', volume 635, issue 13‐14, pages 2197-2202.  <!--Rubidium melonate trihydrate Rb3[C6N7(NCN)3]·3H2O and cesium melonate trihydrate Cs3[C6N7(NCN)3]·3H2O were obtained by ion exchange reactions in aqueous solution. The structure of the cesium salt was determined by single‐crystal X‐ray diffraction (Pna21, a = 687.34(14), b = 2196.5(4), c = 1232.6(3) pm, V = 1860.9(7)·106 pm3, Z = 4, T = 200 K). The crystal structure of the isotypic rubidium salt was refined from X‐ray powder diffraction data by the Rietveld method (Pna21, a = 674.48(2), b = 2146.4(1), c = 1207.5(1) pm, V = 1753.4(6)·106 pm3, Z = 4, T = 298 K). In the crystal structure planar melonate ions and alkali cations as well as water molecules are arranged in alternating layers. The melonate entities are interconnected by a dense hydrogen bonding network. Rb3[C6N7(NCN)3]·3H2O and Cs3[C6N7(NCN)3]·3H2O were investigated by FT‐IR spectroscopy, TG and DTA measurements.-> {{doi|10.1002/zaac.200900232}}</ref>
<ref name=mako2009>Sophia J. Makowski, Daniel Gunzelmann, Jürgen Senker, and Wolfgang Schnick (2009): "Protonated Melonate Ca[HC6N7(NCN)3]·7H2O – Synthesis, Crystal Structure, and Thermal Properties". ''Zeitschrift für anorganische und allgemeine Chemie'', volume 635, issue 15, pages 2434-2439. <!--Calcium hydrogenmelonate heptahydrate Ca[HC6N7(NCN)3]·7H2O was obtained by metathesis reaction in aqueous solution. The structure of the molecular salt was elucidated by single‐crystal X‐ray diffraction. The crystal structure consists of alternating layers of planar monopronated melonate ions, Ca2+ and crystal water molecules. The anions of adjacent layers are staggered so that no π–π stacking occurs. The melonate entities are interconnected by hydrogen bonds within and between the layers. Ca[HC6N7(NCN)3]·7H2O was investigated by solid‐state NMR and FTIR spectroscopy, TG and DTA measurements.--> {{doi|10.1002/zaac.200900231}}</ref>
<ref name=mako2012>Sophia J. Makowski, Arne Schwarze, Peter J. Schmidt, and Wolfgang Schnick (2012): "Rare‐Earth Melonates LnC6N7(NCN)3·xH2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb; x = 8–12): Synthesis, Crystal Structures, Thermal Behavior, and Photoluminescence Properties of Heptazine Salts with Trivalent Cations". ''European Journal of Inorganic Chemistry'', volume 2012, issue 11, pages 1832-1839. <!--The rare‐earth melonates LnC6N7(NCN)3·xH2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb; x = 8–12) have been synthesized by metathesis reactions in aqueous solution and characterized by single‐crystal and powder XRD, FTIR spectroscopy, thermal analysis, and photoluminescence studies. Powder XRD patterns revealed isotypism of the La–Sm compounds. The structure of LaC6N7(NCN)3·8H2O has been solved and refined from single‐crystal diffraction data and those of the remaining salts have been refined from powder XRD data by Rietveld refinement. In the crystal structures, the melonate entities are arranged in corrugated layers, which alternate with layers of crystal water molecules. The lanthanide ions are coordinated by two melonate and six water molecules. LnC6N7(NCN)3·xH2O (Ln = Eu, Tb; x = 9–12) have also been investigated by photoluminescence studies. Neither hydrated nor dehydrated europium melonate exhibits luminescence under UV excitation, whereas photoluminescence studies of terbium melonate showed green emission with a maximum at 545 nm due to the 5D4→7F5 transition. Thermal analysis revealed rather low thermal stability of the rare‐earth melonates, which is probably due to the tight binding of crystal water that results in hydrolytic decomposition at elevated temperatures.--> <!--New rare‐earth melonates LnC6N7(NCN)3·xH2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb; x = 8–12) have been synthesized by metathesis reactions. In the crystal structures, melonate units and rare‐earth ions form 1D strands. The compounds were further characterized with respect to their thermal behavior and the luminescent properties of the europium and terbium salts.--> {{doi|10.1002/ejic.201101251}}</ref>
<ref name=mill2004>Dale R. Miller, Dale C. Swenson, and Edward G. Gillan (2004): "Synthesis and Structure of 2,5,8-Triazido-s-Heptazine:  An Energetic and Luminescent Precursor to Nitrogen-Rich Carbon Nitrides". ''Journal of the American Chemical Society'', volume 126, issue 17, pages 5372-5373. <!--Derivatized s-triazine (C3N3) precursors have seen significant recent use in the production of carbon nitride materials. Larger polycyclic molecular precursors, such as those containing an s-heptazine core (C6N7 or tri-s-triazine), may improve stability and order in carbon nitride products. In this Communication, we describe the synthesis and crystal structure of 2,5,8-triazido-s-heptazine (2). Synthesis of 2 was achieved from melon, an oligomeric s-heptazine synthesized by the pyrolysis of NH4SCN. Melon was converted to molecular 2,5,8-trichloro-s-heptazine, which was then transformed to the triazide upon reaction with (CH3)3SiN3. The crystal structure of 2 verifies that the s-heptazine is planar and the azides adopt a pinwheel-like C3h arrangement around the periphery. The s-heptazine core shows π delocalization in the C−N bonds around the periphery (av. 1.33 Å), while the internal planar C−N bonds are longer (1.40 Å). The heptazine units pack into parallel, but offset, layered sheets in the crystal. The triazide 2 exhibits photoluminescence at 430 nm and rapidly and exothermically decomposes upon heating at 185 °C to produce a tan thermally stable carbon nitride powder with a formula near C3N4.--> {{doi|10.1021/ja048939y}}</ref>
<ref name=qdou2008>Qiang Dou, Qu-Liang Lu, and Huai-Dong Li (2008): "Effect of Metallic Salts of Malonic Acid on the Formation of β Crystalline Form in Isotactic Polypropylene". ''Journal of Macromolecular Science, Part B'', volume 47, issue 5, pages 900-912.  <!--The effects of malonic acid and the lithium, sodium, potassium, zinc, magnesium, calcium, strontium, and barium salts of malonic acid on the formation of β crystalline form in isotactic polypropylene at the crystallization temperatures 120 and 130°C have been investigated. It was found that malonic acid and the lithium, sodium, and potassium salts of malonic acid inhibit the formation of β crystalline form in polypropylene. Zinc malonate has a limited positive effect on the formation of β crystalline form, while magnesium, calcium, strontium, and barium salts are β nucleating agents, in descending order. The decreased β nucleation abilities of the alkaline earth metallic salts of malonic acid are attributed to the increasing atomic radii of the combined metals and decreasing crystallization temperatures--> {{doi|10.1080/00222340802216053}}</ref>
<ref name=rede1939>C. E. Redemann and H. J. Lucas (1939): "Ionization Constants and Hydrolytic Degradations of Cyameluric and Hydromelonic Acids". ''Journal of the American Chemical Society'', volume 61, issue  12, pages 3420-3425. <!--Recently the question of the structure of cyameluric and hydromelonic acids has been reopened by Pauling and Sturdivant.1 It is rather surprising that cyameluric acid and related compounds, for example melon, melam, melem, and hydromelonic acid, should have received so little attention at the hands of organic chemists. With the exception of a limited amount of work by E. C. Franklin2 and students, the problems in this field have been neglected for many years. Since most of these compounds are insoluble both in organic solvents and in water, show neither melting nor boiling points, are inert chemically with the exception that they undergo hydrolytic cleavage, and do not yield derivatives which are readily identified, it is probable that the reasons for this neglect bear some relation to their physical and chemical properties.  Tripotassium melonate, the potassium salt of hydromelonic acid, first described by Gmelin8 as an undesirable by-product when too high a temperature was used in the preparation of potassium thiocyanate by the fusion of sulfur, potassium ferrocyanide and potassium carbonate, was obtained also by Liebig, who dissolved melon in fused potassium thiocyanate.4,5 Potassium melonate is formed also by heating antimony or bismuth trichloride with potassium thiocyanate. ... --> {{doi|10.1021/ja01267a056}}</ref>
<ref name=satt2009>Andreas Sattler and Wolfgang Schnick (2009): "On the Formation and Decomposition of the Melonate Ion in Cyanate and Thiocyanate Melts and the Crystal Structure of Potassium Melonate, K3[C6N7(NCN)3]". ''European Journal of Inorganic Chemistry'', volume 2009, issue 33, pages 4972-4981. <!--The synthesis of potassium melonate, K3[C6N7(NCN)3], by reaction of a potassium thiocyanate melt with the polymer melon [C6N7(NH)(NH2)]n is an established, though poorly understood, reaction. We have modified the original approach by using salt melts containing Na+ ions and/or cyanate ions to yield the respective melonate salts. These melonates, however, are not the final reaction products. We have identified them to decompose in cyanate melts to formtricyanomelaminates at higher temperatures and prolonged reaction times. This is the first selective decomposition reaction leading from heptazines to triazines. The progress of the reactions was studied by using thermal analysis, thus allowing the exact determination of reaction temperatures and weight losses. With the data at hand we are now able to gain better insight into the formation and properties of alkali melonates while establishing new synthetic routes to these compounds. We were able to isolate crystals of anhydrous potassium melonate directly from a thiocyanate melt. The structure of this compound was solved by single‐crystal X‐ray‐diffraction. The new reaction conditions involving cyanates on the one hand avoid the release of CS2 and are no longer highly corrosive to most metallic reaction vessels and on the other hand these reagents provide new, cheap, and convenient access to melonates and tricyanomelaminates. --> {{doi|10.1002/ejic.200900585}}</ref>
<ref name=schlo2019>Hendrik Schlomberg, Julia Kröger, Gökcen Savasci, Maxwell W. Terban, Sebastian Bette, Igor Moudrakovski, Viola Duppel, Filip Podjaski, Renée Siegel, Jürgen Senker, Robert E. Dinnebier, Christian Ochsenfeld, and Bettina V. Lotsch (2019): "Structural Insights into Poly(Heptazine Imides): A Light-Storing Carbon Nitride Material for Dark Photocatalysis". ''Chemistry of Materials'', volume 31, issue  18, pages 7478-7486 <!--Solving the structure of carbon nitrides has been a long-standing challenge due to the low crystallinity and complex structures observed within this class of earth-abundant photocatalysts. Herein, we report on two-dimensional layered potassium poly(heptazine imide) (K-PHI) and its proton-exchanged counterpart (H-PHI), obtained by ionothermal synthesis using a molecular precursor route. We present a comprehensive analysis of the in-plane and three-dimensional structure of PHI. Transmission electron microscopy and solid-state NMR spectroscopy, supported by quantum-chemical calculations, suggest a planar, imide-bridged heptazine backbone with trigonal symmetry in both K-PHI and H-PHI, whereas pair distribution function analyses and X-ray powder diffraction using recursive-like simulations of planar defects point to a structure-directing function of the pore content. While the out-of-plane structure of K-PHI exhibits a unidirectional layer offset, mediated by hydrated potassium ions, H-PHI is characterized by a high degree of stacking faults due to the weaker structure directing influence of pore water. Structure–property relationships in PHI reveal that a loss of in-plane coherence, materializing in smaller lateral platelet dimensions and increased terminal cyanamide groups, correlates with improved photocatalytic performance. Size-optimized H-PHI is highly active toward photocatalytic hydrogen evolution, with a rate of 3363 μmol/gh H2 placing it on par with the most active carbon nitrides. K- and H-PHI adopt a uniquely long-lived photoreduced polaronic state in which light-induced electrons are stored for more than 6 h in the dark and released upon addition of a Pt cocatalyst. This work highlights the importance of structure–property relationships in carbon nitrides for the rational design of highly active hydrogen evolution photocatalysts.--> {{doi|10.1021/acs.chemmater.9b02199}}</ref>
<ref name=schr1962>Hansjuergen Schroeder and Ehrenfried Kober (1962): "Some Reactions of Cyameluric Chloride". ''Journal of Organic Chemistry'', volume 27, issue  12, pages 4262-4266. <!--In contrast to the concept generally presented in the literature, cyameluric chloride was found to undergo nucleophilic displacement reactions readily, and therefore was utilized as the starting material for the synthesis of various tri-s-triazine derivatives. All three chlorine atoms can be easily replaced by means of sodium alkylates, phenols, or amines to give the respective trialkylcyamelurates, triarylcyamelurates, and melem (triaminotri-s-triazine) derivatives. Difficulties were encountered in the synthesis of unsymmetrical tri-s-triazines, since in most reactions cyameluric chloride trisubstitution predominated regardless of the ratio of the reactants. Only four unsymmetrical compounds could be obtained. A series of triaryl tri-s-triazines was prepared by subjecting cyameluric chloride to a modified Friedel-Crafts reaction with benzene or alkylbenzenes. While s-triazine derivatives show ... --> {{doi|10.1021/jo01059a032}}</ref>
<ref name=schw2013>Anke Schwarzer, Tatyana Saplinova, and Edwin Kroke (2013): "Tri-s-triazines (s-heptazines)—From a “mystery molecule” to industrially relevant carbon nitride materials". ''Coordination Chemistry Reviews'', volume 257, issues 13–14, pages 2032-2062. <!--This review provides a comprehensive overview about the fascinating history and chemistry of s-heptazines in its ionic, molecular and polymeric forms – their synthesis, structure, properties and (potential) applications. The very stable aromatic s-heptazine (tri-s-triazine) C6N7 moiety has been discovered as early as in the 1830s, when Liebig, Berzelius and Gmelin independently synthesized the first s-heptazine derivatives. However, the correct tricyclic molecular structure was first proposed by L. Pauling about 100 years later. He obviously was intrigued by selected C6N7-derivatives until he died since the structure of a so-called “mystery molecule” C6N7(OH)2N3, which has not been synthesized so far, was later found on the chalkboard in his office. Very few s-heptazines including the parent molecule C6N7H3 (6) were synthesized and unambiguously analysed until the beginning of the 21st century. Due to the proposed ultrahardness of 3D carbon(IV) nitride networks C3N4 in the 1980/90s several researchers became interested in s-heptazines as precursors for novel carbon(IV) nitrides. Besides, in the patent literature numerous claims for the application of s-heptazines (and s-triazines C3N3X3) as flame retardants and for other applications are found. Thus, the formation, structure and properties of key molecular derivatives such as cyameluric chloride C6N7Cl3 (4), melem C6N7(NH2)3 (1), cyameluric acid C6N7(OH)3 (2), selected symmetric and asymmetric amides C6N7(NR1R2)3 − x(NR3R4)x, cyameluric esters C6N7(OR)3 and s-heptazine triazide C6N7(N3)3 (5) have been reported in recent years. In addition, various metal melonates M(I)3[C6N7(NCN)3], metal cyamelurates M(I)3[C6N7(O)3], s-heptazine-based metal-organic frameworks (MOFs) and melon [C6N7(NH2)(NH)]n were analysed in detail. Also, numerous reports on so-called carbon nitrides, which are in fact melon-related C/N/H-oligomers and polymers, have been reported recently. Although the structure of these materials is not known in detail, their properties as well as the properties of the above mentioned thoroughly analysed compounds provide a very promising outlook for various applications of carbon nitrides and C/N/H materials including s-heptazines, especially in the field of novel semiconducting materials, (photo)catalysts e.g. for hydrogen generation and carbon dioxide fixation, luminescent and in other ways optically active materials. Many of the latter characteristics have been investigated very recently and in most cases supported by experimental and theoretical studies.--> {{doi|10.1016/j.ccr.2012.12.006}}</ref>
<ref name=xbli2019>Xiaobo Li, Stuart A. Bartlett, James M. Hook, Ivan Sergeyev, Edwin B. Clatworthy, Anthony F. Masters, and  Thomas Maschmeyer (2019): "Salt-enhanced photocatalytic hydrogen production from water with carbon nitride nanorod photocatalysts: cation and pH dependence". ''Journal of Materials Chemistry A'', volume 7, issue 32, pages 18987-18995.  <!--Carbon nitride polymeric semiconductors with nanorod morphology are explored as photocatalysts for efficient hydrogen evolution from water. Their composition, structure, optical properties and photocatalytic performance are found to be highly sensitive to the presence of added salts in the photocatalytic reaction solution. In potassium-incorporated carbon nitride (CNK), the photocatalytic hydrogen evolution activity is significantly enhanced with the addition of salts into the reaction solution by up to ∼9 times, depending on the salt added. Similarly, cation-dependent red-shifts in the UV-vis absorbance of CNK are observed. We find that the effect of the salts on the photocatalytic activity and optical properties of CNK is further modulated by the solution pH. The CNK nanorods form a compact layer stacking structure for certain cations, such as for K+ but not Li+. The enhancement of the photoactivity of CNK in the presence of salts is attributed to improved light harvesting ability, a dielectric screening effect, and the nanorod structure. An obvious and consistent potassium–potassium interaction is observed via EXAFS, indicating a high degree of order, likely in the form of a potassium channel or ordered layer. The strong sensitivity of CNK materials to the photocatalytic environment yields dramatic changes in structure, optical properties and photoactivity, thus providing a new experimental variable for photocatalyst material development and optimization.--> {{doi|10.1039/C9TA04942H}}</ref>
<ref=bord2005>Elisabeta Horvath-Bordon, Edwin Kroke, Ingrid Svoboda, Hartmut Fuess and Ralf Riedel (2005): "Potassium melonate, K3[C6N7(NCN)3]·5H2O, and its potential use for the synthesis of graphite-like C3N4 materials". ''New Journal of Chemistry'', volume 29, issue 5, pages 693-699.  <!--Melonates, Mx3/x[C6N7(NCN)3], contain the aromatic and planar tricyanamino-s-heptazine anion. Only one example, the potassium derivative, has been isolated in pure form so far, but it has never been characterised comprehensively. Potassium melonate is obtained from a reaction of the polymer melon, [C6N9H3]n, with KSCN. 13C NMR, FTIR, Raman, UV-vis and luminescence spectroscopy support the proposed molecular structure. The crystal structure of the hydrate K3[C6N7(NCN)3]·5H2O was determined by single crystal X-ray analysis (MoKα: Pbca (no. 161), a = 6.538(2), b = 24.033(6), c = 23.684(6) Å and Z = 8). Thermogravimetric analysis shows that the dehydrated salt starts to decompose at temperatures above 500 °C. The [C6N7(NCN)3] unit is an ideal molecular building block for carbon(IV) nitrides, especially s-heptazine based graphite-like C3N4 networks.--> {{doi|10.1039/B416390G}}</ref>