Five New Zinc Phosphite Structures:  Tertiary Building Blocks in the Construction of Hybrid Materials

The syntheses and structures of five new zinc phosphites [Zn(HPO₃)(C₄H₆N₂)] (1), [Zn₂(HPO₃)₂(C₁₀H₁₀N₂)₂]₂ (2), [Zn(HPO₃)(C₁₄H₁₄N₄)_0.5] (3), [Zn₂(HPO₃)₂(C₁₄H₁₄N₄)]·0.4H₂O (4), and [Zn₂(HPO₃)₂(C₁₄H₁₄N₄)] (5) are reported. In compounds 1−3, the zinc atoms are ligated by 1-methylimidazole, 1-benzylimidazole, and 1,4-bis(imidazol-1-ylmethyl)benzene, respectively, while compounds 4 and 5 are synthesized in the presence of the same bifunctional ligand, 1,3-bis(imidazol-1-ylmethyl)benzene. The inorganic framework of compound 1 is composed of vertex-shared ZnO₃N and HPO₃ tetrahedra that form 4-rings, which, in turn, are linked to generate a one-dimensional ladder structure. In 2, the inorganic framework is composed of 4-rings and 8-rings to form the well-known 4.8² 2D network. This is connected via C−H···π interactions between 1-benzylimidazole ligand to generate a pseudo-pillared-layer structure. In 3, the inorganic framework again has the 4.8² topology pillared by the bis(imidazole) ligand, 1,3-bis(imidazol-1-ylmethyl)benzene. In 4, a new layer pattern is observed. Specifically, three edge-sharing 4-rings form triple-fused 4-rings. These tertiary building units are further connected to form 12-rings. The alternating triple 4-rings and 12-rings form a previously unknown 2D inorganic sheet. The sheets are joined together by the bis(imidazole) ligand, 1,3-bis(imidazol-1-ylmethyl)benzene, to generate a 3D pillared-layer structure. In 4, benzene rings and imidazole rings stack in a zigzag pattern in the interlayer space. A significant role for the triple 4-ring tertiary building unit in the formation of hybrid inorganic/organic metal phosphite structures is proposed for 4 and 5. In 5, the triple 4-rings fuse to give a 1D stair-step structure. Calculations show that the triple 4-ring pattern observed in the linear ladder structure of 1 is more stable than that in the stair step pattern of 5.