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Synthesis, Crystal Structure, and Properties of Multicomponent Bis(ethylenedithio)tetrathiafulvalene Charge-Transfer Salts of the [Mo3S7Br6]2- Cluster

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journal contribution
posted on 07.03.2005 by Rosa Llusar, Sonia Triguero, Santiago Uriel, Cristian Vicent, Eugenio Coronado, Carlos J. Gomez-Garcia
A new family of bis(ethylenedithio)tetrathiafulvalene (ET) radical salts has been prepared in the presence of a triangular molybdenum sulfide cluster of formula [Mo3S7Br6]2-, which contains highly electrophilic axial sulfur atoms. A systematic change in the experimental conditions yields five different salts, namely (ETA)2(ETB)[Mo3S7Br6]2· CH2Br2 (1), (ETA)(ETB)[Mo3S7Br6]·1.1CH2Br2 (2), (ETA)(ETB)(ETC){[Mo3S7Br6]Br}·0.5C2H4Cl2 (3), (ET)((n-Bu4)N)[Mo3S7Br6] (4), and (ET)(Ph4P)[Mo3S7Br6]·0.5CH3CN (5), where the ET subscript denotes crystallographically independent molecules. The five compounds have been structurally characterized, and all of them crystallize in the triclinic space group P1̄ with Z = 2. Lattice parameters (Å, deg) are the following:  a = 11.762(4), b = 12.246(4), c = 16.813(6), α = 107.572(9), β = 99.133(7), and γ = 102.856(8) for 1; a = 12.643(3), b = 13.370(4), c = 17.936(4), α = 103.884(8), β = 95.013(7), and γ = 114.396(6) for 2; a = 11.907(6), b = 12.742(6), c = 22.905(12), α = 90.053(15), β = 79.063(14), and γ = 75.802(15) for 3; a = 12.787(6), b = 13.653(6), c = 17.543(8), α = 68.398(10), β = 69.911(12), and γ = 62.377(10) for 4; a = 12.467(5), b = 13.553(6), c = 18.913(8), α = 85.378(11), β = 78.576(11), and γ = 65.858(9) for 5. Structural data combined with Raman spectral analysis shows that, in salt 1, one-third of the ET molecules, those marked as ETB, are incorporated into the structure as ET2+ and two-thirds as ET+. Bonds distances and Raman frequencies for donor molecules in compounds 25 suggest a 1+ charge for all ET molecules, in agreement with the stoichiometries and IR and electronic spectra of these salts. In all cases the various donor−cluster, donor−donor, and cluster−cluster interactions and those involving the solvent molecules give rise to unique arrangements of the donor molecules. A general feature of structures 15 is the presence of alternating layers of dimerized organic donor molecules (ET+:ET+) and of inorganic clusters, where the long axis of the donor dimers runs almost parallel to the cluster layer. There is a strong tendency of the combination {[Mo3S7Br6]:ET} to accommodate a third bulky component. Compounds 4 and 5 incorporate [(n-Bu4)N]+ or [Ph4P]+, respectively, with no apparent interactions with the ET layers in the solid state. Compound 2 and 4 are semiconductors, while the remaining salts are insulators.

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