31P and 195Pt NMR studies on the clusters [Pt 4(μ 2-CO) 5L 4]. L = PEt 3, PMe 2Ph, PMePh 2, PEt 2Bu t. The molecular structure of a monoclinic modification of [Pt 4(μ 2-CO) 5(PMe 2Ph) 4

Abstract

Several clusters complexes of composition [Pt 4(μ 2-CO) 5L 4] have been synthesized and characterized, using 31P and 195Pt NMR. L = PEt 3, PMe 2Ph, PMePh 2, PEt 2Bu t. The molecular structure of a new monoclinic modification of the PMe 2Ph derivative has been determined: space group P2 1/n with a = 19.698(4), b = 10.9440(20), and c = 21.360(6) Å, β = 112.432(18)°, Z = 4. Using 4751 reflections measured at 290 ± 1 K on a four-circle diffractometer the structure has been refined to R = 0.0846. The molecule has no imposed symmetry, but the central Pt 4(CO) 5P 4 core has the approximate C 2v architecture established for the previously known orthorhombic modification. The Pt 4 unit is thus a highly distorted, edge-opened (3.3347 Å) tetrahedron, with five edge-bridging carbonyl and four terminal phosphine ligands. In contrast to the crystallographic results 31P and 195Pt NMR spectra reveal equivalent 31P and 195Pt spins, which can be interpreted in terms of a tetrahedral arrangement of platinum atoms. It is suggested that this equivalence arises from time-averaging of all possible isomeric edge-opened tetrahedra.