Structural and Electron Self-Exchange Rate Variations in Isomeric (Hexaamine)cobalt(III/II) Complexes.
The syntheses and characterisation of the new macrocyclic hexaamine trans-(5(S),7(S),12(R),14(R)-tetramethyl)-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L(6)) and its Co(III) complex are reported. The X-ray crystal structural analyses of [CoL(6)]Cl(2)(ClO(4)) [monoclinic, space group C2/c, a = 16.468(3) Å, b = 9.7156(7) Å, c = 15.070(3) Å, beta = 119.431(8) degrees, Z = 4] and the closely related cis-diamino-substituted macrocyclic complex [CoL(2)](ClO(4))(3). 2H(2)O (L(2) = cis-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine) [orthorhombic, space group Pna2(1), a = 16.8220(8) Å, b = 10.416(2) Å, c = 14.219(3) Å, Z = 4] reveal significant variations in the observed Co-N bond lengths and coordination geometries, which may be attributed to the trans or cis disposition of the pendent primary amines. The Co(III/II) self-exchange electron transfer rate constants for these and other closely related hexaamines have been determined, and variations of some 2 orders of magnitude are found between pairs of trans and cis isomeric Co(III) complexes.
Bernhardt
Paul V.
PV
Department of Chemistry, University of Queensland, Brisbane 4072, Australia.
Jones
Lathe A.
LA
Sharpe
Philip C.
PC