Structural and spectroscopic study of cobalt(III) ternary complexes

The trans-diazidobis(ethylenediamine)cobalt(III)perchlorate complex with the formula [Co(en)(2)(N-3)(2)]center dot ClO4 (1) (en = ethylenediamine) crystallises in the centrosymmetric space group C2/c of the monoclinic system. The almost ideal octahedral geometry of the cobalt atom is created by six nitrogen atoms of two ethylenediamine molecules and two azide ions, which form the trans-[CoN4N2'] chromophore. The crystal of 1 is built up of [Co(en)(2)(N-3)(2)](+) cations and non-coordinated ClO4- anions. The lattice perchlorate ions adopt an atypical C-2v symmetry. A hydrogen bonded system is created by the O1 and O2 perchlorate atoms and atoms of the NH2 groups, which generate the 3D-structure. The vibrational and electronic spectra of 1, [Co(en)(2)CO3]center dot ClO4 (2) and [Co(bpY)(2)CO3]center dot NO3 center dot 5H(2)O (3) (2,2'bpy or bpy = 2,2'bipyridine) have been also studied. The Co(III) ion in all the complexes is in the typical low-spin state. Bands centered at ca. 18030 and 24120 cm(-1) are characteristic for the trans-[CoN4N2'] chromophore of 1 and are assigned to the spin-allowed (1)A(1g) -> T-1(1g) and (1)A(1g) -> T-1(2g) transitions. The spectra of the cis-[CoN4O2] chromophore (2 and 3) exhibit an absorption at ca. 19500 cm(-1), which arises from the spin-allowed (1)A(1g) -> E-1(g) + (1)A(2g) transitions in a D-4h symmetry. The descending spin-allowed (1)A(1g) -> B-1(2g) and (1)A(1g) -> E-1(g) transitions are correlated with bands at ca. 25500 and 29000 cm(-1), respectively. (C) 2012 Elsevier Ltd. All rights reserved.