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Abstract:
Black shiny platelets of Bi8Pt5I3 and Bi16Pt11I6 were crystallized from
melts of the metals and BiI3. Despite very similar compositions and
close peritectics, a protocol for targeted synthesis could be developed
based on differences of the decomposition pressures. Bi8Pt5I3 has a
monoclinic crystal structure [space group C2/m; a = 1850.7(2) pm, b =
391.46(3) pm, c = 1340.5(1) pm, = 113.28(1)degrees], in which corrugated
intermetallic layers alternate with monolayers of non-coordinating
iodide ions. The platinum atoms are in square, trigonal-prismatic, or
capped trigonal-prismatic coordination by bismuth atoms. Additional
covalent bonding between platinum atoms defines flat stripes of five
atoms width inside the intermetallic layer. Bi16Pt11I6 crystallizes in
the acentric tetragonal space group P42(1)2 with a = 1386.6(1) pm and c
= 924.5(1) pm. Corresponding to the higher transition-metal content, the
covalent network of platinum atoms is two-dimensional. The node
connectivity in the network is three or four; the total coordination
number of all platinum atoms is ten. Single layers of iodide ions
separate the intermetallic layers. Two-thirds of the iodide ions are
coordinating bismuth atoms that protrude from the intermetallic layer,
forming [BiI4] squares. Temperature-dependent electrical resistivity and
magnetic susceptibility measurements on polycrystalline powders indicate
that Bi8Pt5I3 and Bi16Pt11I6 are diamagnetic metals. The calculated
electronic band structures confirm pseudo two-dimensional metallic
character only for Bi8Pt5I3.
