Two Light‐Metal Dihydrogenisocyanurate Hydrates Linked by Diagonal Relationship: Syntheses, Crystal Structures, and Vibrational Spectra of Li[H₂N₃C₃O₃]·1.75 H₂O and Mg[H₂N₃C₃O₃]₂·8 H₂O

Abstract

Single‐crystalline materials of Li[H2N3C3O3]·1.75 H2O and Mg[H2N3C3O3]2·8 H2O were obtained by dissolving stoichiometric amounts of the respective carbonates with cyanuric acid in boiling water followed by gentle evaporation of excess water after cooling to room temperature. Even though both of these compounds crystallize in the triclinic space group P1 according to X‐ray structure analyses of their colorless and transparent single crystals, they adopt two new different structure types. Li[H2N3C3O3]·1.75 H2O exhibits the unit‐cell parameters a = 884.71(6) pm, b = 905.12(7) pm, c = 964.38(7) pm, α = 67.847(2)°, β = 62.904(2)° and γ = 68.565(2)° (Z = 4), whereas the lattice parameters for Mg[H2N3C3O3]2·8 H2O are a = 691.95(5) pm, b = 1055.06(8) pm, c = 1183.87(9) pm, α = 85.652(2)°, β = 83.439(2)° and γ = 79.814(2)° (Z = 2). In both cases, the singly deprotonated isocyanuric acid forms monovalent anions consisting of cyclic [H2N3C3O3]– units, which are arranged in ribbons typical for most hitherto known monobasic isocyanurate hydrates. The structures are governed by the oxophilic strength of the respective cation which means that they fulfil their oxophilic coordination requirements either solely with water molecules ([Mg(OH2)6]2+ for Mg2+) or with crystal water and one or two direct coordinative contacts to carbonyl oxygen atoms (O(cy)) of [H2N3C3O3]– anions ([(Li(OH2)2–3(O(cy)1–2]+ for Li+). In both structures occur dominant hydrogen bonds N–H···O within the anionic [H2N3C3O3]– ribbons as well as hydrogen bonds O–H···O between these ribbons and the hydrated Li+ and Mg2+ cations.

Investigating the Competitive Factors of Metal–Anion Coordination, Coordination by Water, and Hydrogen Bonding in Complexes of Cyanuric Acid with the Alkaline Earth Metals

“…There are only two previously reported structures of complexes of magnesium with cyanuric acid and no other metals; one of them has been the subject of two independent studies [26,27] and is the same as our compound 1, while the other, prepared hydrothermally, has the same ionic components but no uncoordinated water molecules [27]. The main structural feature of compound 1 is that CY − does not coordinate to the Mg 2+ centre at all, but serves as a counterion to the [Mg(OH 2 ) 6 ] 2+ cation.…”

“…Although these structures have been reported previously by others [26][27][28][29][30], those studies have been directed primarily at properties such as optical anisotropy, second harmonic generation, and corrosion inhibition, and the structural trends have not generally been noted. In the case of the strontium complex 3, the two previously reported structures [28,29] had inappropriate (and different) treatments of their hydrogen atoms, as discussed below.…”