Synthesis and crystal structure of three new cadmium tartrates with open frameworks

Abstract

Four metal–organic coordination polymers: {[Cd₃(C₄H₄O₆)₃(H₂O)]·H₂O}_nI, {[Cd₃(C₄H₃O₆)₂(H₂O)₂]·5.5H₂O}_nII, {[Cd₂(C₄H₄O₆)₂(H₂O)]·3H₂O}_nIII, and [Cd(C₄H₄O₆)]_nIV were obtained under hydrothermal conditions and characterized by IR spectroscopy and single crystal X-ray diffraction. The structural analysis reveals that compounds I–III exhibit new 3D open frameworks filled with water molecules, which according to thermogravimetric analysis evolve at temperatures significantly lower than onset temperatures for decomposition. Compound I exhibits an 8-c net; uninodal net (eci net) with Schläfli symbol {3⁶·4¹²·5¹⁰}, where Cd atoms are connected by μ₄,κ⁶-mode and μ₄,κ⁵-mode tartrate ligands. Compound II is a rare example of a tartrate trianion complex formed by μ₅,κ⁶-mode ligands creating a (6,3)-connected net with Schläfli symbol (4·6²)₂(4²·6¹⁰·8³). Compound III exhibits a 3,3,4,4-connected, 4-nodal net with Schläfli symbol {4·8²}{4·8⁴·10}, built up by dimers of two octahedral Cd atoms linked by μ₄,κ⁶-mode and μ₃,κ⁵-mode tartrate ligands. Compound IV was previously reported although being obtained under different synthetic conditions and can be described as a 5,5,11-connected, 3-nodal net with the Schläfli symbol of {3²·4⁶·5²}2{3⁴·4¹⁴·5¹⁶·6¹⁸·7²·8}{3⁴·4³·5²·6}. None of the compounds reported here are topologically related, evidencing the versatility of the tartrate ligand for the framework formation of coordination polymers.