Tl 4(PO 2NH) 4·H 2O – A commensurately modulated tetrametaphosphimate

Abstract

Tetrathallium(I) tetra-μ-imidocyclotetraphosphate monohydrate, Tl 4(PO 2NH) 4·H 2O, was obtained by evaporation of combined aqueous solutions of K 4(PO 2NH) 4·4H 2O and TlOOCCH 3 corresponding to the molar ratio of 1:4. The structure determination of Tl 4(PO 2NH) 4·H 2O was performed by single-crystal X-ray diffraction methods. In addition to the basic structure ( P 1 ¯ , no. 2, a = 928.3(2), b = 974.6(2), c = 1018.0(2) pm, α = 74.47(3)°, β = 64.68(3)°, γ = 78.81(3)°, Z = 2), satellite reflections indicate a fourfold superstructure ( A 1 ¯ , a = 928.0(2), b = 3897.1(8), c = 2035.4(4), α = 74.47(3)°, β = 64.68(3)°, γ = 78.81(3)°, Z = 16) that is described by an a × 4 b × 2 c, A-centered supercell which mainly concerns one thallium site of the basic structure. In order to reduce the number of parameters, this superstructure was handled as a commensurate occupancy modulation using the structural description in (3 + 1)-dimensional superspace ( P 1 ¯ ( α β γ ) , q = 0.25 b ∗ + 0.5 c ∗). The crystal structure of Tl 4(PO 2NH) 4·H 2O consists of infinite columns of the cyclic [(PO 2NH) 4] 4− anions (saddle conformation) which are interconnected by four N–H⋯O hydrogen bonds. By coordination to the Tl + ions the [(PO 2NH) 4] 4− columns form a three-dimensional network with channels along [100] wherein the thallium ions that are mainly affected by the modulation are located. The commensurate occupancy modulation of these Tl + ions has been described with a single harmonic wave function. The modulation is verified by 31P NMR spectroscopy. The thermal behavior of Tl 4(PO 2NH) 4·H 2O and the IR data are discussed as well.