It is well established that ions, such as Bi 3+ and Pb 2+ , often generate a distorted structure due to an electrostatic effect of a lone pair of electrons. The compounds formed by the combination of such ions may be non-centrosymmetric with potential applications as NLO materials.The title compound was obtained in air by a solid-state reaction of K2CO3, Bi2O3 and NH4H2PO4 in the molar ratio K:Bi:P = 5:1:4. The mixture, intimately mixed, was heated in an alumina crucible at 623 K for 12 h in order to eliminate CO2, NH3 and H2O. These ingredients were then kept for 20 days at 873 K. Slow cooling to room temperature led to colorless plate crystals of BiPO4 (high temperature form [1]) together with colorless parallelepiped crystals (0.12 × 0.09 × 0.07 × mm 3 of K6Bi2(P2O7)3. The crystal structure was determined using single-crystal XRD data. The crystal data, details of data collection and the structure determination are given in Table 1. The Bi, K, P and O atoms were refined with isotropic temperature factors in order to decrease the data to the parameter ratio.The structure of K6Bi2(P2O7)3 is built up from BiO6 octahedra and P2O7 groups sharing corners to form a three-dimensional framework enclosing interconnecting tunnels where K + cations reside. It can be decomposed in layers, parallel to the (010) plane, constituted of P(1)P(2)O7, Bi(1)O6, P(3)P(4)O7 and Bi(2)O6 polyhedra. The layers are linked together by an oxygen vertex shared with eclipsed P(5)P(6)O7 diphosphate, giving rise to P-O-Bi bridges. The layers are centrosymmetric. The noncentrosymmetric character of the structure is due to the P(5)P(6)O7 diphosphate and K(5), K(6′) and K(6″) atoms, which do not obey to an inversion center. Both Bi(1) and Bi(2) oxygen polyhedra consist of six atoms forming a distorted octahedra. This low-symmetry environment is usual for Bi 3+ cations and is in fact to be completed by the important 6s 2 stereoactive lone-pair E. This effect is especially around Bi(2), A new, noncentrosymmetric, potassium bismuth phosphate K6Bi2(P2O7)3 has been synthesized by a solid state reaction, and structurally characterized by single-crystal X-ray diffraction methods. This compound crystallizes in the triclinic space group P1 with a = 6.985(2)Å, b = 9.045(2)Å, c = 10.256(4)Å, α = 111.87(2)˚, β = 104.25(3)˚, γ = 102.00(3)˚ and Z = 1. The structure can be described as infinite anionic layers parallel to the (010) plane connected via P-O-Bi bridges to form a three-dimensional framework enclosing interconnecting tunnels where K + cations reside.
