By means of high-resolution neutron powder diffraction (sample-limited resolution δd/d ≥ 10-3, d = lattice spacing) the temperature dependence of the orthorhombic structure of the pseudosymmetric layer compound TlAu(CN)2 was investigated in the range from 5 to 300 K in connection with optical measurements. No phase transition occurs, but similar to KAu(CN)2, the longest lattice parameter b increases anomalously with decreasing temperature, from 30.460 Å at 300 K to 30.851 Å at 5 K. When the [Au(CN)2]- ions are constrained to be linear, the b-lattice parameter increase is found to be due to the reduction of the angle between the [Au(3)(CN)2]- ion and the b-axis, from 50.7° at 300 K to 47.6° at 5 K. Apart from these essential changes the results confirm the structure model of Blom et al., corresponding to space group Pbcn as derived previously from a single-crystal neutron diffraction measurement at room temperature. Short interatomic distances Au-Au approaching 3 Å at 5 K indicate significant Au-Au overlap, causing (with Au-Tl covalent overlap) the particular yellow color of TlAu(CN)2.
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Fischer et al. (1994) studied this question.