Interpenetrating copper-silver cyanometallate networks: polymorphs and topological isomers.
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Biomedical subjects
Simon M Cheyne
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Structure of AuCN determined from total neutron diffraction.
The structure of gold cyanide, AuCN, has been determined at 10 and 300 K using total neutron diffraction. The structure consists of infinite [bond]Au[bond](CN)[bond]Au[bond](CN)[bond] linear chains, hexagonally packed, with the gold atoms in sheets. The Au-C and Au-N bond lengths are found to be identical, with d(Au(-C/N) = 1.9703(5) A at 300 K. This work supersedes a previous study, by others, which used Rietveld analysis of neutron Bragg diffraction in isolation, and found these bonds to have significantly different lengths (Delta d = 0.24 A) at 300 K. The total correlation function, T(r), at 10 and 300 K, has been modeled using information derived from total diffraction. The broadening of inter- and intrachain correlations differs markedly due to random displacements of the chains in the direction of the chain axes. This is a consequence of the relatively weak bonding between the chains. An explanation for the negative thermal expansion in the c-direction, which occurs between 10 and 300 K, is presented.
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CuCN: a polymorphic material. Structure of one form determined from total neutron diffraction.
CuCN has been found to be polymorphic. The structure of one form, which is isomorphous with AgCN, has been determined using the information provided by Bragg and diffuse neutron scattering. The polymorph of CuCN formed has been found to depend on the Cu/CN ratio used in its preparation.
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Beyond Bragg scattering: the structure of AgCN determined from total neutron diffraction.
Total neutron diffraction has yielded accurate bond lengths, Ag-C = Ag-N = 2.06 A and C-N = 1.16 A, for the disordered crystalline solid AgCN. This information cannot be obtained from analysis of Bragg scattering studies, because the (-Ag-CN-)(n) chains are randomly displaced along the chain axis relative to each other by a root-mean-square displacement of 0.24 A at 10 K. These results show the power of total neutron diffraction for determining structure in disordered systems.
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