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Syntheses, X-ray Crystal Structures, and Spectroscopic Properties of New Nickel Dithiolenes and Related Compounds

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posted on 1997-03-12, 00:00 authored by Francesco Bigoli, Paola Deplano, Francesco A. Devillanova, John. R. Ferraro, Vito Lippolis, Peter J. Lukes, Maria Laura Mercuri, Maria Angela Pellinghelli, Emanuele F. Trogu, Jack M. Williams
The direct addition of nickel powder to the reaction mixtures of 1,3-dialkyl-4,5-dioxoimidazolidine-2-thione (1) with the thionation Lawesson reagent produces [NiII(R2timdt-)2] (R2timdt = 1,3-dialkylmidazolidine-2,4,5-trithione). These complexes belong to a new class of nickel−dithiolenes, showing remarkably high absorption (ε ≈ 80 000 dm3 mol-1 cm-1, λ ≈ 1000 nm) in the near-infrared region (near-IR), accompanied by high photochemical stability that makes these complexes promising near-IR dyes. In the absence of nickel the reaction yields generally the compounds 4,5,6,7-tetrathiocino[1,2-b:3,4-b‘]diimidazolyl-1,3,8,10-tetraalkane-2,9-dithione (2) instead of the expected 1,3-dialkylimidazolidine-2,4,5-trithione. However, with bulky substituents on the nitrogen atoms, well-characterized reaction products have not been obtained until now. Only in the R = Pri case, the new tetrathiocino isomer (4,5,9,10-tetrathiocino[1,2-b:5,6-b‘]diimidazolyl-1,3,6,8-tetraisopropane-2,7-dithione (3) in trace amounts and the bis(1,3-diisopropyl-2-thioxoimidazolin-4-yl) disulfide (4) were isolated from the reaction with the Lawesson reagent and P4S10, respectively. Reaction of 5 with different amounts of I2 leads to a variety of products, and among them the following derivatives have been characterized:  [NiII(Pri2timdt-)2]·2I2 (6) a neutral adduct in which each I2 molecule interacts with each peripheral thione sulfur atom of 5; [NiII(Pri2timdt-)2]·2I2·1/2I2 (7), which differs from 6 with the presence of half diiodine as a guest; with a larger diiodine excess (starting from a 1:10 molar ratio) a partial oxidation of 5 is achieved and [NiII(Pri2timdt-)2] [NiII(I)2(Pri2timdt)2]·5I2 (8) is formed, a ligand mixed-valence compound in which the square-planar complex 5 and the octahedral complex [NiII(I)2(Pri2timdt)2] (the ligand in neutral form) are bound by diiodine molecules in such a way that a sequence of 12 iodine atoms (S·I2···I2···I-···I2···I-···I2···I2·S) is formed. Spectroscopic and X-ray diffractometric studies of 3 (monoclinic, space group P21/n, a = 13.104(6) Å, b = 15.091(6) Å, c = 6.067(7) Å, β = 103.00(2)°, Z = 2), 4 (monoclinic, space group C2/c, a = 18.717(5) Å, b = 8.846(5) Å, c = 14.475(5) Å, β = 97.78(2)°, Z = 4), 5 (orthorhombic, space group Pna21, a = 18.806(5) Å, b = 5.628(7) Å, c = 23.665(5) Å, Z = 4), 7 (triclinic, space group P1̄, a = 9.126(7) Å, b = 9.153(7) Å, c = 12.924(6) Å, α = 82.11(2), β = 70.14(2), γ = 72.51(2)°, Z = 1), and 8 (monoclinic, space group C2/c, a = 21.971(6) Å, b = 28.081(5) Å, c = 12.207(8) Å, β = 93.57(2)°, Z = 4) are given.