Synthesis, Structure, Magnetism, and Spectroscopic Properties of Some Mono- and Dinuclear Nickel Complexes Containing Noninnocent Pentane-2,4-dione Bis(S-alkylisothiosemicarbazonate)-Derived Ligands

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Abstract

Deprotonation of [NiII(H2L1)]I·0.5CH3OH (1), where (H2L1)- represents the ligand pentane-2,4-dione bis(S-methylisothiosemicarbazonate(−), in an ethanol solution of aqueous ammonia under argon affords air-sensitive red-brown [NiII(HL1)]·C2H5OH (2). Air oxidation of 2 in ethanol/NH3 yields the paramagnetic green-black dinuclear species [Ni(L1−L1)Ni] (3) where the ligand (L1−L1)6- is formed by oxidative C−C coupling at the methine carbon atoms of (L1)3-. In this formulation the nickel ions are trivalent. Reaction of 3 in ethanol with concentrated HCl affords red diamagnetic [NiII(H2L1−L1H2)Ni1II]Cl2·0.5C2H5OH (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 [NiII(HL1−L1H)NiII]·C2H5OH (5). Replacement of the S-methyl groups in (H2L1)- by two dodecyl groups, (CH2)11CH3, gives the ligand (H2L2)-; the complexes [NiII(H2L2)I (6) and their dinuclear, oxidized forms [Ni(L2−L2)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 P1̄ with a = 11.475(2) Å, b = 13.615(1) Å, c = 18.207(6) Å, α = 83.87(1)°, β = 88.36(1)°, γ = 72.58(1)°, V = 2698.7(10) Å3, 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.

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