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Abstract:
Bi2Pt(hP9) or -Bi2Pt is a high-temperature modification, which is
metastable below 420 degrees C. We obtained Bi2Pt(hP9) by reducing the
layered bismuth subiodide Bi13Pt3I7 with a high excess of n-butyllithium
at 70 degrees 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.
