Metal-to-Ligand Ratio As a Design Factor in the One-Pot Synthesis of Coordination Polymers with [MS4Cun] (M = W or Mo, n = 3 or 5) Cluster Nodes and a Flexible Pyrazole-Based Bridging Ligand

Abstract

Two complexes, [WS4Cu5I3(bbd)2]n (1) and [(WS4Cu3I)2(bbd)3]n·n(DMF) (2), with one-dimensional polymeric chain structures containing hexanuclear and tetranuclear clusters linked by flexible 1,4-bis(3,5-dimethylpyrazol-1-yl)butane (bbd) ligands have been synthesized in facile one-pot reactions at room temperature, together with the molybdenum analogue of 2. The only significant difference in the syntheses of the two tungsten complexes is the 5:1 or 3:1 molar ratio of copper(I) to [WS4]2–, the other experimental factors being kept constant. The observed products reflect the stoichiometric Cu:W ratio used. All three complexes were characterized by IR and UV–vis spectroscopy, thermal and elemental analyses, and single-crystal X-ray diffraction. Complex 1 contains an unusual and surprisingly unsymmetrical WS4Cu5I3 cluster in which five Cu atoms bridge all but one of the six S···S edges of the WS4 tetrahedron and the three I atoms all have different coordination modes (terminal, μ2 and μ3); it consists of two face-sharing WS3Cu3I distorted cubes, in one of which a Cu···I edge is opened up instead of being bonded, this Cu atom (shared by the two cubes) having an additional terminal iodo ligand. Complex 2 is the first reported example of a polymer containing (S=)MS3M′3X cubes linked by organic ligands; pairs of these cube clusters are connected by pairs of bbd ligands, and the (cluster)2(bbd)2 units are assembled into chains by single bbd bridges. In these and previously reported complexes, the bbd bridging ligand displays considerable flexibility, enabling it to support a range of discrete oligomeric and polymeric structures. X-ray powder diffraction shows that 2 is consistently obtained as a mixture of two polymorphs, and the same has been found for the corresponding molybdenum complex [(MoS4Cu3I)2(bbd)3]n·n(DMF) (3), for which the second polymorph has been structurally characterized by single-crystal diffraction using synchrotron radiation. The two polymorphs have essentially identical polymer chain structures, with different packing arrangements of the chains and different symmetry properties.