Kinetic control of zinc cyamelurate crystal formations

Metal cyamelurates: structural diversity caused by kinetic and thermodynamic controls

“…In this synthesis, a hot aqueous solution of potassium cyamelurate was poured into a hot solution of manganese nitrate and the mixture was boiled with stirring for about 10 minutes. The increased reaction temperature inevitably led to an equilibrium crystalline form of manganese cyamelurate, which confirms our opinion on the thermodynamic equilibrium of the compounds synthesized in [4], stated earlier [3].…”

“…Solution of 0. (M=Ni(II), Zn(II)) described in [4] were unsuccessful and led to the phases we already received [3]. However, in one of our experiments with manganese cyamelurate, we found a phase identical to [Mn(H…”

“…The crystal structures of poorly soluble salts of cyameluric acid have hardly been studied as well. It was previously shown [3] that the formation of a thermodynamically stable crystalline modification of zinc cyamelurate, [Zn(H 2 O) 6 ][Zn(H 2 O) 4 (C 6 N 7 O 3 H) 2 ] [4], proceeds in several stages: (i) formation of the initial metastable phase, [ZnK 2 (H 2 O) 8 (C 6 N 7 O 3 H) 2 ], from building blocks existing in aqueous solutions of precursors; (ii) transformation of the initial metastable phase into the second phase, [Zn(H 2 O) 5 (C 6 N 7 O 3 H)], via complexation reaction; (iii) hydrate isomerization of the latter into the final thermodynamically stable product. It was suggested [3] that the synthesis of zinc, nickel, and iron cyamelurates occurs in double electric micelles, which act as nanoreactors.…”

“…It was found [3] that cyamelurate ligands donate only oxygen atoms to the inner spheres of metal complexes, despite the potential for the formation of bonds of nickel or zinc with nitrogen atoms of cyamelurate ions. This possibility follows from the tautomerism of cyameluric acid [5][6][7], the widespread occurrence of nickel or zinc amino complexes, and the ability to form chelate cycles with the simultaneous participation of oxygen and nitrogen atoms.…”

“…, where M=Mn(II), Co(II), Ni(II), Zn(II) (all four compounds are isostructural), are described in [4]. We classified them as thermodynamically stable for the reasons stated in our previous article [3]. The crystal structures described below are metastable and obtained under kinetic control with rare exceptions (see below).…”