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

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  • Karsten Meyer
  • Bendix, Jesper
  • Eckhard Bill
  • Thomas Weyhermüller
  • Karl Wieghardt

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)](ClO 4)3·3.5H2O (4a), respectively. 4a was converted to the bis(tetraphenylborate)-azide-2C2H5OH salt (4b). Crystallization of 4a from acetonitrile-after addition of AgClO4 and removal of AgN3-yields 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 N≡CrV 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) 2B22E, (xy) → (x2 - y2) 2B22B1, and (xy) → (z2) 2B22A1, where the molecular z-axis coincides with the N≡Cr 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-N=N=N-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.

Original languageEnglish
JournalInorganic Chemistry
Issue number20
Pages (from-to)5180-5188
Number of pages9
Publication statusPublished - 1 Dec 1998

ID: 240002778