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

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 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 C 4 v symmetry as (xy) ((xz,yz) 2B2 → 2E, (xy) → (x 2 − y 2) 2B2 → 2B1, and (xy) → (z 2) 2B2 → 2A1, where the molecular z-axis coincides with the N⋮Cr vector. Ligand-field parameters within the angular overlap model (AOM) of e σ cyclam = 7300−8600, e σ ax = 22 000, e σ ax = 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.

Crystal structures and nitrosation reactions of triazido complexes of chromium(III)

“…The packing of the unit cell is shown in figure 2. The Cr-N(amine) and Cr-N(azide) distances are in good agreement with those found in other amine and azide complexes of chromium(III) [2,8,17]. The coordination geometry in 2 is similar, with a facially coordinated tacn ligand as seen in figure 1.…”

“…Preliminary work has shown that dmso solutions of 1 and 2 are light sensitive with the violet solution eventually becoming yellow upon irradiation with UV-light (figure 3). Wieghardt [2,3] has observed a photorelease of dinitrogen from azidochromium(III) complexes with formation of chromium(V) nitrido complexes (equation (3)). …”

“…Since then a rich [Cr V N] 2þ chemistry has emerged with special focus on the optical properties of the complexes. Moreover, having a d 1 configuration, the electronic structure of the complexes has been investigated by use of EPR spectroscopy [2,3]. Another characteristic reaction of a coordinated azide ligand is nitrosation.…”

The chromate resistance phenotype of some yeast mutants correlates with a lower level of Cr(V)-species generated in the extra-cellular medium

“…The formation of paramagnetic Cr(V)-species in the extra-cellular medium was discovered for all tested cultures that supports our hypothesis about the crucial role of extra-cellular Strains: parental (''wild type'') L2 and Crt r -mutants L2-9 and L2-11. EPR spectrometer: Radiopan SE/X2544 Table 2 The comparison of g-factors for Cr(V)-species described in this paper with the data available in literature Reference Substance g-Factor Krumpolc and Rocek (1979) Cr(V)-EHBA complex (EHBA = 2-ethyl-2-hydroxybutyric acid) g = 1.980 Shi and Dalal (1994) Product of reaction of Cr(VI) with vitamin B 2 g = 1.9795 Meyer et al (1998) trans-[Cr V (N)(cyclam)(NCCH 3 )](ClO 4 ) 2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) g \ = 1.997 g k = 1.965 Codd and Lay (1999) K reduction in chromate detoxification. It has been demonstrated for the first time that the chromateresistant phenotype of mutants is related to a lower stationary lever of the extremely toxic intermediate, Cr(V), in the extra-cellular medium.…”

Synthesis, characterization and charge-transfer photochemistry of trans-aquo azido-N,N?-trimethylenebis(naphthylideneiminato)chromium(III)

“…As part of our efforts to stabilize the unusual oxidation state like chromium(IV) and chromium(V) [8,9], we carried out the synthesis of a few chromium(III) Schiff base complexes [10,11]. The photolysis of chromium(III) azides has been reported to produce Ôcoordinated nitreneÕ complexes [12,13] as shown in the following equation, ½Cr III ðLÞðN 3 ÞðH 2 OÞ À! hm ÀN 2 ½Cr V ðNÞðLÞ þ N 2 where (L) represents the coordinated ligand.…”