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 [Ni-II(R(2)timdt(-))(2)] (R(2)timdt = 1,3-dialkylmidazolidine-2,4,5-trithione). These complexes belong to a new class of nickel-dithiolenes, showing remarkably high absorption (epsilon approximate to 80000 dm(3) mol(-1) cm(-1), lambda approximate to 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’]diimdazolyl-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 = Pr-i 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 I-2 leads to a variety of products, and among them the following derivatives have been characterized : [Ni-II(Pr(2)(i)timdt(-))(2)]. 2I(2) (6) a neutral adduct in which each I-2 molecule interacts with each peripheral thione sulfur atom of 5; [Ni-II(Pr(2)(i)timdt(-))(2)]. 2I(2) . 1/2I(2) (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 [Ni-II(Pr(2)(i)timdt(-))(2)] [Ni-II(I)(2)(Pr(2)(i)timdt)(2)]. 5I(2) (8) is formed, a ligand mixed-valence compound in which the square-planar complex 5 and the octahedral complex [Ni-II(I)(2)(Pr(2-)(i)timdt)(2)] (the ligand in neutral form) are bound by diiodine molecules in such a way that a sequence of 12 iodine atoms (S . I-2 ... I-2 ... I-... I-2 ... I-... I-2 ... I-2 . S) is formed. Spectroscopic and X-ray diffractometric studies of 3 (monoclinic, space group P2(1)/n, a = 13.104(6) Angstrom, b = 15.091(6) Angstrom, c = 6.067(7) Angstrom, beta = 103.00(2)degrees, Z = 2), 4 (monoclinic, space group C2/c, a = 18.717(5) Angstrom, b = 8.846(5) Angstrom, c = 14.475(5) Angstrom, beta = 97.78(2)degrees, Z = 4), 5 (orthorhombic, space group Pna2(1), a = 18.806(5) Angstrom, b = 5.628(7) Angstrom, c = 23.665(5) Angstrom, Z = 4), 7 (triclinic, space group , a = 9.126(7) Angstrom, b = 9.153(7) Angstrom, c = 12.924(6) Angstrom, alpha = 82.11(2), beta = 70.14(2), gamma = 72.51(2)degrees, Z = 1), and 8 (monoclinic, space group C2/c, a = 21.971(6) Angstrom, b = 28.081(5) Angstrom, c = 12.207(8) Angstrom, beta = 93.57(2)degrees, Z = 4) are given.