Nickel monovalent, complexes

K2[Fe(NO)2(CN)2]. My former co-worker R. Nast (83) showed that the reaction of carbon monoxide with K4[Ni2I(CN)6] and K4[Ni°(CN)4] in liquid ammonia gave nickel cyanocarbonyl complexes with monovalent and zero-valent metal atoms. The isoelectronic hexacyanoiron(III) or tetra-cyanonickel(II) complexes correspond to the cyanocarbonyls [Feu(CN)5 CO]3-, [Ni (CN)3CO]2-, or [Ni°(CN)2(CO)2]2-. Cobalt is analogous to nickel in forming the complex [Co(CN)3CO]2-. According to our earlier work, [Fe"(CN)5CO]3- and [Fem(CN)6]3- are isosteric (87). Other structural investigations were concerned with tetracyano and tetracarbonyl complexes (88). 

A surprising stabilization of monovalent nickel occurs by coordination to 5. In CH3CN, the redox potential of the Ni +/+ couple is -0.18 V. The same explanation as that put forward for Co complexes applies here to account for the stabilization of Ni complex of 5. The potential stability range of the Ni -catenate (—1.32 to —0.18 V) is remarkably broad. The behavior of Ni.5 + is strikingly different from that of bpy nickel(Il) complexes [40-42]. In the case of unsubstituted bipy ligands, electrochemical reduction of [Ni( >py)3] + leads directly to [Ni(6py)3] in a two-electron process (E1/2 = -1-3 V) [40], and monovalent nickel is not observed. 

Among the electrochemical syntheses related to the change of metal oxidation number, we emphasize obtaining acetylacetonates of divalent iron, cobalt, and nickel [551,623]. The method of alternating-current electrochemical synthesis was applied to isolate Ji-complexes of monovalent copper with allylamines, allylimines, and ally-lurea from the salts of divalent copper [624-628], We note that the same method was used for preparation of analogous ji-complexes with copper(II) halides (X = Cl, Br) [629a]. Other electrochemical syntheses with participation of metal salts and complexes are described in monographs [201,202] and literature cited therein. 

Nickel, on the other hand, bears a close similarity to copper. It does not, like copper, yield well-defined monovalent salts, but. the divalent salts of the two metals are similar. Both have a bluish or greenish colour, which is enhanced by the addition of ammonia owing to the formation of complex ammoniat.es. Pickering1 has drawn attention to the fact that the colour intensity of organic salts of nickel decreases with dilution in a similar manner to that of copper derivatives. The organic salts dissolve in caustic alkali to form compounds resembling those yielded by copper. In some cases jellies are produced, as with copper. For example, potassium nickelo-citrate yields, with potassium hydroxide, a permanent dark green jelly. 

The reactivity of [Ni(l)2] + is much more pronounced than that of nickel(I) catenate. In CH2CI2, the bimolecular rate constants corresponding to the reaction of the monovalent nickel complex with O2 are as follows ... 

Platinates, bis(oxalato)-, 139 cadmium complexes superstructure, 142 cobalt complexes, 140 electrical conductivity, 14] superstructure, 141 thermopower, 141 divalent cation salts, 140 iron complexes structure, 142 lead complexes superstructure, 142 magnesium complexes, 140 electrical conduction, 142 structure, 142 thermopower, 142 modulated superstructure, 139 monovalent cation salts, 139 nickel complexes structure, 141 partially oxidized, 139 Platinates, tetracyano-, 136 anion-deficient salts, 136 electrical conduction, 138 optical properties, 138 cation-deficient salts, 138 oxidation states, 136 partially oxidized, 138 semiconductors, 134 Platinum colloidal... 

Zilbermann, L, M. Winnik, D. Sagiv, A. Rotman, A.H. Cohen, and D. Meyerstein (1995). Rroperties of monovalent nickel complexes with tetraaza-macrocyclic ligands in aqueous solutions. Inorg. Chim. Acta 240(1-2), 503-514. 

---