Synthesis and Characterization of a New Series of Zinc Phosphites

Several new zinc phosphites have been synthesized in aqueous solution by reactions of Zn²⁺ with H₃P0₃ and either Na⁺, K⁺, or Ba²⁺. The structures were determined by single-crystal X-ray diffraction techniques. Zn(H₂PO₃)₂⋅3H₂O; R₃ a = 21.128 (2) Å, c = 7.769 (6) Å, V = 3003 (2) ų, Z = 18, R(F) = 0.073 for 494 observations (I > 3σ(I)), 82 variables. Zn₂(HPO₃)₂-(H₂O)₄⋅H₂O: PĪ, a = 7.670 (2) Å, b = 9.454 (1) Å, c = 7.554 (1) Å, α = 90.83 (1)°, β = 92.90 (1)°, y = 88.54 (2)°, V= 546.9 (2) ų, Z = 2, R(F) = 0.022 for 1430 observations ( I > 3σ(I)) 175 variables. Zn₃Na₂(HPO₃)₄: Pnma, a= 8.331 (2) Å, b = 12.243 (2) Å, c = 12.669 (1) Å, V = 1292.2 (6) ų, Z = 4, R(F) = 0.038 for 704 observations (I > 3σ(I)), 103 variables. Zn₃K₂(HPO₃)₄: P2₁/c,a = 12.373 (2) Å, b = 13.635 (2) Å, c = 8.571 (2) Å, β = 90.24 (1)°, V= 1445.9 (4) ų, Z = 4, R(F) = 0.037 for 1525 observations ( I > 3σ(I)), 206 variables. Zn₃Ba(HPO₃)₄(H₂O)₆: C2/c, a = 22.707 (2) Å, b = 5.302 (3) Å, c = 15.029 (1) Å, β = 105.28 (1)°, V= 1745 (1) ų, Z = 4, R(F) = 0.054 for 1530 observations (I> 3σ(I))_t141 variables. Each of the five structures is a new type with the Zn atoms in either octahedral or tetrahedral coordination bridged by phosphite groups to produce a framework of zinc and phosphorus-centered oxygen polyhedra. Several of the frameworks have open channels lined with phosphite H atoms or coordinated water molecules. In some cases, these polyhedra are bridged by alkali-metal or alkaline-earth-metal ions to produce different frameworks. The exact nature of each structure is highly dependent on the identity of the second metal as each adopts a different coordination environment. The coordination numbers of the Na⁺, K⁺, and Ba²⁺ ions are 6, 7, and 12, respectively. The role of the alkali and alkaline-earth metals in the structures is discussed, and the phosphite structures are compared with similar known phosphates.