Synthesis and crystal structure of sodium copper tetrametaphosphimate heptahydrate Na 2Cu(PO 2NH) 4·7H 2O and sodium potassium copper tetrametaphosphimate heptahydrate K xNa 2− xCu(PO 2NH) 4·7H 2O

Abstract

Na 2Cu(PO 2NH) 4·7H 2O and K x Na 2− x Cu(PO 2NH) 4·7H 2O ( x ≈ 0.5) were synthesized by gel crystallization in sodium silicate gels. The crystal structures were solved by single-crystal X-ray methods and found to be isotypic ( Pnma, Z = 4; Na 2Cu(PO 2NH) 4·7H 2O: a = 627.5(2) pm, b = 1456.0(3) pm, c = 1900.5(4) pm, R1 = 0.0352; K 0.47Na 1.53Cu(PO 2NH) 4·7H 2O: a = 632.2(2) pm, b = 1460.0(3) pm, c = 1936.4(4) pm, R1 = 0.0345). The P 4N 4 rings of the tetrametaphosphimate anion exhibit a distorted chair-2 conformation with admixtures of saddle and crown conformation. The M + ions are six- and sevenfold coordinated by oxygen atoms, the Cu 2+ ions are fivefold coordinated, respectively. The MO 7 and the CuO 5 units form pairs of face-sharing polyhedra, which are connected by common corners forming chains and are further interconnected by tetrametaphosphimate anions, forming a three-dimensional network structure with channels along [100] and [010]. The MO 6 units form chains of face-sharing polyhedra, which are situated in the channels along [100]. Extended hydrogen bonding reinforces the three-dimensional framework structure of the compounds. 23Na-MAS NMR experiments were conducted to verify the K/Na distribution on the M sites derived from the X-ray crystal structure refinement.