ISSN:
1434-1948
Keywords:
Hexadentate N/S-ligand
;
Dinuclear complexes
;
Nickel
;
Redox chemistry
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A discrete dinickel complex with a central N2NiII(μ2-SR)2NiIIN2 core has been synthesized and investigated in the context of ligand binding and oxidation state changes. Reaction of the hexadentate amine-thiolate ligand N,N′-bis-[2-thio-3-aminomethyl-5-tert-butylbenzyl]propane-1,3-diamine (8) with Ni(ClO4)2 · 6 H2O in methanol affords [NiII28][ClO4]2 · 3 CH3OH (9), the structure of which has been determined by X-ray crystallography. Complex 9 contains a central N2Ni(μ2-SR)2NiN2 core with two approximately planar cis-N2S2Ni coordination polyhedra bridged at the thiolate sulfur atoms. The cis-N2S2Ni units differ in that one nickel atom forms a six-membered chelate ring with the two secondary amine nitrogen atoms of 8 whereas the other nickel atom is bound to the remaining primary nitrogen atoms. Complex 9 binds a variety of substrates. Binding of anions to the N2Ni(μ2-SR)2NiN2 core in 9 occurs selectively at the Ni atom bound to the secondary nitrogen atoms because of a slightly weaker ligand-field strength. This is demonstrated by X-ray structure determination of the isothiocyanate complex [NiII28(NCS)2] · MeOH (10) formed by the reaction of 9 with 2 equiv. of KSCN in methanol. Complex 10 is the first example of a complex with adjacent octahedral cis-N4S2Ni and planar cis-N2S2Ni sites. The overall dinuclear structure of the parent complex 9 is retained in 10, except for trans-axially bound isothiocyanate ions at Ni(1) and an as yet unexplained inversion of configuration at both secondary amine nitrogen atoms. In DMF solution both complexes undergo two successive reductions at potentials of -0.95 V and -1.53 V vs SCE, assigned to the formation of mixed-valent [NiINiII8]1+ and [NiI28]0 species, respectively. The similar electrochemical properties of 9 and 10 suggest that the trans-axially bound isothiocyanate ions in 10 are replaced by DMF molecules in DMF solution. Upon reduction, these solvent molecules decoordinate to produce an unsolvated [NiINiII8]1+ species with two planar N2S2Ni units.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
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