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American Chemical Society, Inorganic Chemistry, 20(37), p. 5180-5188, 1998

DOI: 10.1021/ic980302q

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Molecular and Electronic Structure of Nitridochromium(V) Complexes with Macrocyclic Amine Ligands

This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

Photolysis of red cis- and trans-[CrIII(cyclam)(N3)2](ClO4) (1a, 2a) (cyclam = 1,4,8,11-tetraazacyclotetradecane) in the solid state or aqueous solution by light affords the nitridochromium(V) complexes of cis- or trans-[CrV(N)(cyclam)(N3)](ClO4) (3a) and dinuclear [{trans-[CrV(N)(cyclam)]}2(μ-N3)](ClO4)3·3.5H2O (4a), respectively. 4a was converted to the bis(tetraphenylborate)−azide−2C2H5OH salt (4b). Crystallization of 4a from acetonitrileafter addition of AgClO4 and removal of AgN3yields octahedral trans-[CrV(N)(cyclam)(NCCH3)](ClO4)2 (5a). The crystal structures of 1a, 2b (which is the tetraphenylborate salt of 2a), 4a,b, 5a,b have been determined by single-crystal X-ray crystallography. All nitridochromium(V) compounds contain the trans-[CrV(N)(cyclam)]2+ fragment with an NCrV moiety (1.56 ± 0.01 Å). The electronic spectra of d1 configurated complexes display three low-intensity d−d bands which have been assigned in C4v symmetry as (xy) ((xz,yz) 2B2 → 2E, (xy) → (x2 − y2) 2B2 → 2B1, and (xy) → (z2) 2B2 → 2A1, where the molecular z-axis coincides with the NCr vector. Ligand-field parameters within the angular overlap model (AOM) of eσcyclam = 7300−8600, eσax = 22 000, eσax = 21300−25000 cm-1 have been determined which reproduce the experimental electronic spectra well. Temperature-dependent magnetic susceptibility measurements and X-band EPR spectroscopy on solid samples of 4a containing a linear CrV−NNN−CrV moiety revealed a weak intramolecular antiferromagnetic exchange coupling which is nearly absent in 4b containing a bent azido bridge. A mechanism for this unexpected coupling in 4a is proposed.