Oxidative-addition reaction of platinum acetylacetonate with iodine in solid state and solution. Crystal structure and equilibrium studies of trans-bis(acetylacetonato)di-iodoplatinum(IV)

Abstract

Pt(acac)₂(acac = acetylacetonate) undergoes an oxidative-addition reaction with molecular iodine both in solution and in the solid state to yield trans-Pt(acac)₂I₂. In solution the reaction is readily reversible, and data for the equilibrium were determined spectrophotometrically. Mass spectral data of volatilized Pt(acac)₂I₂ indicate that the same equilibrium also occurs in the gas phase. A three-dimensional X-ray diffraction study from diffractometer data has established the stereochemistry of Pt(acac)₂I₂. Crystals are triclinic, space group P, with Z= 1 in a unit cell of dimensions a= 7·802, b= 8·703, c= 7·646, α= 95·866°, β= 116·321°, γ= 114·844°. The structure was solved by Patterson and Fourier methods and refined by least squares to R 4·0% for 654 independent observations. The molecule lies on a crystallographic centre of symmetry. Each Pt^IV is octahedrally co-ordinated by two oxygen-chelated acetylacetonate ligands and by two iodine atoms in a trans-configuration which deviates only slightly from D_2h symmetry. The molecules are identically oriented in layers such that each iodine ligand has one unusually close intermolecular I ⋯ I contact of 3·559(2)Å. This short distance is indicative of weak intermolecular bonds leading to infinite chains of weakly linked molecules. The readily occurring solid-state reaction of crystalline Pt(acac)₂ with solid I₂ may involve diffusion by molecular iodine into the crystalline lattice of Pt(acac)₂, followed by electron transfer from the Pt^II to the I₂ molecule with concomitant cleavage of the molecular iodine bond to give Pt^IV–I formation.