Synthesis, structures, and electrochemical properties of nickel complexes of macrocyclic N2S2 aminothioethers
Academic Article
Overview
Identity
Additional Document Info
Other
View All
Overview
abstract
Macrocyclic complexes derived from the template synthesis of the cis-dithiolate nickel(II) complex [1,5-bis(mercaptoethyl)-1,5-diazacyclooctanato]nickel(II), I, and [NN'-bis(2,2-dimethyl-2-mercaptoethyl)-1,5-diazacy-clooctanato]nickel(II), I*, with S to S linkers of C2, II*Br2, C3, III*Br2, and C44, IV*Br2, were synthesized and fully characterized as square planar complex ions. The systematic enlargement of the N2S2 cavity size correlates with electrochemical measurements which find the NiII/I couple to be more accessible through the series, while the NiIII oxidation state is stabilized in the smaller cavities, maintaining an approximate 2 V difference between the NiIII/II and NiII/I couples. The dithioether compound [I*Me2]I2 shows the most positive NiII/I potential (-412 mV vs NHE, in CH3CN solution), consistent with the greater flexibility of the open-chain N2S2 ligand. While the reduced macrocycles show little tendency to react with carbon monoxide, EPR, electrochemical, and infrared spectroscopic studies of the NiI state of the open chain ligand complex support the reversible binding of CO in CO-saturated solutions. Cyclic voltammetry shows EC' activity in the production of H2 from HBF4 solutions in the presence of the macrocycle complexes and is interpreted in terms of an inner-sphere NiIII-H intermediate Crystal data for II*Br2, III*Br2, and IV*Br2 are as follows: II*Br23/2H2O crystallizes in the monoclinic system. space group P21/c with cell constants a = 7.900(5), b = 18.41(2) , c = 15.612(14) , = 97.53(6), V = 2251(3) 3, and Z = 4, R = 0.0972, Rw = 0.1886; for III*Br25/2H2O, monoclinic system, space group P21/c with cell constants a = 18.821(5) , b = 7.844(2) , c = 32.968(8) , = 97.84(2), V = 4824(2) 3, and Z = 8 and R = 0.077, Rw = 0.125; for IV*Br?*H?O, orthorhombic system, space group Pnma with cell constants a = 18.562(3) , b = 15.140(3) , c = 9.703(3) , V = 2726.8(11) 3, and Z = 4 and Rw = 0.044, Rw = 0.099.
