Synthesis and crystal structure of sodium copper tetrametaphosphimate heptahydrate Na2Cu(PO2NH)4•7H2O and sodium potassium copper tetrametaphosphimate heptahydrate KxNa2-xCy(PO2NH)4•7H2O

Na2Cu(PO2NH)(4) center dot 7H(2)O and K2Na(2-x)Cu(PO2NH)(4) center dot 7H(2)O (X approximate to 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 Na2Cu(PO2NH)(4) center dot 7H(2),O: a = 627.5(2) pm, b=1456.0(3)pm, c=1900.5(4)pm, R1=0.0352; K0.47Na1.53CU(PO2NH)(4) center dot 7H(2)O: a=632.2(2)pm, b=1460.0(3)pm, c=1936.4(4)pm, R1 = 0.0345). The P4N4 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 Cu2+ ions are fivefold coordinated, respectively. The MO7 and the CUO5 units form pairs of face-sharing polyhedra, which are connected by common comers forming chains and are further interconnected by tetrametaphosphimate anions, forming a three-dimensional network structure with channels along [100] and [010]. The MO6 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. Na-23-MAS NMR experiments were conducted to verify the K/Na distribution on the M sites derived from the X-ray crystal structure refinement. (c) 2007 Elsevier Masson SAS. All rights reserved.