hide
Free keywords:
-
Abstract:
From the reaction of Ni(COD)2 (COD = cyclooctadiene) in dry diethylether with 2 equiv of 2-phenyl-1,4-bis(isopropyl)-1,4-diazabutadiene (LOx)0 under an Ar atmosphere, dark red, diamagnetic microcrystals of [NiII(L•)2] (1) were obtained where (L•)1- represents the π radical anion of neutral (LOx)0 and (LRed)2- is the closed shell, doubly reduced form of (LOx)0. Oxidation of 1 with 1 equiv of ferrocenium hexafluorophosphate in CH2Cl2 yields a paramagnetic (S = 1/2), dark violet precipitate of [NiI(LOx)2](PF6) (2) which represents an oxidatively induced reduction of the central nickel ion. From the same reaction but with 2 equiv of [Fc](PF6) in CH2Cl2, light green crystals of [NiII(LOx)2(FPF5)](PF6) (3) (S = 1) were obtained. If the same reaction was carried out in tetrahydrofuran, crystals of [NiII(LOx)2(THF)(FPF5)](PF6)·THF (4) (S = 1) were obtained. Compounds 1, 2, 3, and 4 were structurally characterized by X-ray crystallography: 1 and 2 contain a tetrahedral neutral complex and a tetrahedral monocation, respectively, whereas 3 contains the five-coordinate cation [NiII(LOx)2(FPF5)]+ with a weakly coordinated PF6- anion and in 4 the six-coordinate monocation [NiII(LOx)2(THF)(FPF5)]+ is present. The electro- and magnetochemistry of 1−4 has been investigated by cyclic voltammetry and SQUID measurements. UV−vis and EPR spectroscopic data for all compounds are reported. The experimental results have been confirmed by broken symmetry DFT calculations of [NiII(L•)2]0, [NiI(LOx)2]+, and [NiII(LOx)2]2+ in comparison with calculations of the corresponding Zn complexes: [ZnII(tLOx)2]2+, [ZnII(tLOx)(tL•)]+, [ZnII(tL•)2]0, and [ZnII(tL•)(tLRed)]- where (tLOx)0 represents the neutral ligand 1,4-di-tert-butyl-1,4-diaza-1,3-butadiene and (tL•)1- and (tLRed)2- are the corresponding one- and two-electron reduced forms. It is clearly established that the electronic structures of both paramagnetic monocations [NiI(LOx)2]+ (S = 1/2) and [ZnII(tLOx)(tL•)]+ (S = 1/2) are different.
