Synthesis and characterisation of novel heterobimetallic halide isopropoxides based on M2(OPri)9–(M = Sn, Zr or Ti) anions: crystal and molecular structures of [CdI{Sn2(OPri)9}] and [{SnI[Zr2(OPri)9]}2]

Abstract

New heterobimetallic halide isopropoxides based on the interaction of M₂(OPrⁱ)₉^–(M = Sn^IV, Zr^IV or Ti^IV) units with Cd^II, Sn^II and Pb^II have been prepared. These complexes have been characterised by multinuclear solution and solid-state cross polarisation magic angle spinning (CP MAS) NMR spectroscopy, elemental analyses and cryoscopy. Single-crystal X-ray diffraction studies have been performed for [CdI{Sn₂(OPrⁱ)₉}]1 and [{SnI[Zr₂(OPrⁱ)₉]}₂]2. Compound 1 consists of a face-sharing bioctahedral Sn₂(OPrⁱ)₉^– unit which interacts with the central metal atom, cadmium, using two µ- and two terminal OPrⁱ groups. The cadmium atom is within a distorted trigonal bipyramid of oxygen and iodine atoms. The ¹¹³Cd chemical shifts in the solution and solid-state CP MAS NMR spectra of 1 are consistent with the retention of its heterometallic nature in solution. In contrast to the monomeric form of 1, compound 2 exists as an iodo-bridged dimer in the solid state. Cryoscopic measurements for 2 indicate a monomer–dimer equilibrium (η= 1.6) in solution which has been confirmed by variable-temperature ¹¹⁹Sn NMR studies. In the solid state the ligating mode of the Zr₂(OPrⁱ)₉^– unit in 2 is different from isostructural Sn₂(OPrⁱ)₉^– and it binds to tin via only three OPrⁱ groups, the fourth M–OPrⁱ interaction being hindered by the stereochemically active lone pair of electrons present at Sn^II. The central SnI₂O₆ core in 2 can be viewed as two SnI₂O₃ octahedra fused along a common axial–equatorial edge where one of the axial co-ordination sites in each is occupied by the non-bonding electron pair of Sn^II.