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Synthesis, Characterization, and Calculated Electronic Structure of the Crystalline Metal–Organic Polymers [Hg(SC6H4S)(en)]n and [Pb(SC6H4S)(dien)]n

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journal contribution
posted on 02.01.2012, 00:00 by Dayna L. Turner, Kevin H. Stone, Peter W. Stephens, Aron Walsh, Mayank Pratap Singh, Thomas P. Vaid
The reaction of Hg­(OAc)2 with 1,4-benzenedithiol in ethylenediamine at 80 °C yields [Hg­(SC6H4S)­(en)]n, while the reaction of Pb­(OAc)2 with 1,4-benzenedithiol in diethylenetriamine at 130 °C yields [Pb­(SC6H4S)­(dien)]n. Both products are crystalline materials, and structure determination by synchrotron X-ray powder diffraction revealed that both are essentially one-dimensional metal–organic polymers with -M-SC6H4S- repeat units. Diffuse reflectance UV–visible spectroscopy indicates band gaps of 2.89 eV for [Hg­(SC6H4S)­(en)]n and 2.54 eV for [Pb­(SC6H4S)­(dien)]n, while density functional theory (DFT) band structure calculations yielded band gaps of 2.24 and 2.10 eV, respectively. The two compounds are both infinite polymers of metal atoms linked by 1,4-benzenedithiolate, the prototypical molecule for single-molecule conductivity studies, yet neither compound has significant electrical conductivity as a pressed pellet. In the case of [Pb­(SC6H4S)­(dien)]n calculations indicate fairly flat bands and therefore low carrier mobilities, while the conduction band of [Hg­(SC6H4S)­(en)]n does have moderate dispersion and a calculated electron effective mass of 0.29·me. Hybridization of the empty Hg 6s orbital with SC6H4S orbitals in the conduction band leads to the band dispersion, and suggests that similar hybrid materials with smaller band gaps will be good semiconductors.