Deprotonation of [Ni(II)H(2)L(1))]I . 0.5CH(3)OH (1), where (H(2)L(1))- represents the ligand pentane-2,4-dione bis(S-methylisothiosemicarbazonate(-), in an ethanol solution of aqueous ammonia under argon affords air-sensitive red-brown [Ni-II(HL(1))]. C2H5OH (2). Air oxidation of 2 in ethanol/NH3 yields the paramagnetic green-black dinuclear species [Ni(L(1)-L(1))Ni] (3) where the ligand (L(1)-L(1))(6-) is formed by oxidative C-C coupling at the methine carbon atoms of (L(1))3-. I, this formulation the nickel ions are trivalent. Reaction of 3 in ethanol with concentrated HCl affords red diamagnetic [Ni-II(H(2)L(1)-L(1)H(2))Ni1I(I)]Cl-2 . O.5C(2)H(5)OH (4). This reaction is a 2 electron reduction of 3 with concomittant protonation at the ligand. Deprotonation of 4 in C2H5OH/ammonia under argon gives red-brown [Ni-II(HL(1)-L(1)H)Ni-II] C2H5OH (5). Replacement of the S-methyl groups in (H(2)L(1))(-) by two dodecyl groups, (CH2)(11)CH3, gives the ligand (H(2)L(2))(-); the complexes [Ni-II(H(2)L(2))I (6) and their dinuclear, oxidized forms [Ni(L(2)-L(2))Ni] (7) have been prepared analogously. The molecular structure of 3 (C18H28N12Ni2S4) has been determined by X-ray crystallography. Crystal data for 3 : space group P (1) over bar with a 11.475(2) Angstrom, b = 13.615(1) Angstrom, c = 18.207(6) Angstrom, alpha = 83.87(1)degrees, beta = 88.36(1)degrees, gamma = 72.58(1)degrees, V=2698.7(10) Angstrom(3), and Z = 2. The structure refinement converged to R = 0.066 for 8865 unique reflections. Electronic and NMR spectra, the magnetism, and electrochemistry of new compounds are reported. It is shown that 3,4-diacetyl-2,5-hexanedione-tetrakis(S-alkylisothiosemicarbazonates) are noninnocent ligands in 3 and 7.