Platinum(II) complexes with four ligating Phosphorus atoms crystal and molecular structure of [Pt(PEt 3) 4](ClO 4) 2. Discussion of electronic spectra of planar and tetrahedrally distorted PtP 4 chromophores

Abstract

The crystal and molecular structure of [Pt-(PEt 3) 4](ClO 4) 2 has been determine by X-ray diffraction. The compound crystallizes in the orthorhombic space group P bca with cell constants a = 26.839(4) Å b = 13.762(3) Å, c = 19.568(6) Å, z = 8. The structure was solved by the heavy-atom-method and refined to a final R-value of 0.053 As a consequence of ligand repulsion the expected square-planar PtP 4 coordination exhibits a strong tetrahedral distortion. The PPtP trans angle are 150.3° and 150.9°, respectively (instead of 180° for a square-planar structure). The PtP bond lengths of 2.33 Å to 2.35 Å are similar to those found in other platinum(II) compounds containing phosphine ligands in trans-position. Electronic spectra of the cations [Pt(PR 3) 4] 2+ (R = Me, Et) have been discussed and compared with those of the related ions [Pt(R 2PCh 2CH 2PR 2) 2] 2+, which have recently [1] been shown to be planar. SCCC-EHMO calculations have been carried out for various geometries of the PtP 4 chromophore in order to support the band assignments.