Bi2Pt(hP9) by Lowerature Reduction of Bi13Pt3I7: Reinvestigation of the Crystal Structure and Chemical Bonding Analysis

Abstract

Bi2Pt(hP9) or γ-Bi2Pt is a higherature modification, which is metastable below 420 C. We obtained Bi2Pt(hP9) by reducing the layered bismuth subiodide Bi13Pt3I7 with a high excess of n-butyllithium at 70 C. The crystals endure the heterogeneous reaction and the enormous mass loss. X-ray diffraction on a small single-crystal revealed that Bi2Pt(hP9) crystallizes in the acentric trigonal space group P31m (no. 157) with a = 657.30(7) pm and c = 616.65(7) pm. Although structure and stacking of the layers of edge-sharing [PtBi6/3] octahedra resemble the 1H-polytype of CdI2, Pt-Pt bonding interactions cause distortions that introduce polarity to the structure. Quantum chemical calculations followed by real-space bonding analysis reveal polar covalent bonding between bismuth and platinum atoms that is not limited to nearest neighbor atoms but is essentially delocalized. The Pt-Pt bond strength in Bi2Pt(hP9) is not much weaker than in the element.