Synthesis, crystal structure and electrical properties of two new palladium complexes of selenium and sulfur ligands: [NMe4][Pd(C3S3Se2)2]2 and [PMe4][Pd(C3S5)2]2
Abstract
The compounds [NMe4][Pd(C3S3Se2)2]2 and [PMe4][Pd(C3S5)2]2[C3S3Se2= 4,5-bis(hydroseleno)-1,3-dithiole-2-thionate; C3S5= 4,5-dimercapto-1,3-dithiole-2-thionate] have been prepared by electrochemical oxidation of [NBu4]2[Pd(C3S3Se2)2] and [NBu4][Pd(C3S5)2] in the presence of a large excess of NMe4PF6 and PMe4I, respectively. Their structures have been determined by X-ray crystallographic methods. Both compounds, with space group C2/c, are isostructural to the superconducting phase β-[NMe4][Pd(C3S5)2]2. The PdL2(L = C3S3Se2 or C3S5) entities are paired, forming [(PdL2)2] dimmers with a Pd–Pd bond length of 3.174 and 3.177 Å, respectively. The structure consists of [(PdL2)2] dimer layers in the (001) plane separated from each other by sheets of cations. The dimers are stacked along [110] and [1![[1 with combining macron]](https://www.rsc.org/images/entities/char_0031_0304.gif)
0]. Both compounds show similar electrical properties: the room-temperature conductivities are ≈ 50 and ≈ 20 S cm–1, respectively; at high temperature the conductivity is weakly temperature dependent, but abruptly decreases at low temperatures; the conductivity increases when applying pressure. A broad dispersion of optical excitations was observed in the reflectance spectra of [NMe4][Pd(C3S3Se2)2]2, indicating an overlap of the highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO) bands and a HOMO-type conduction band.
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