TY - JOUR

T1 - Molecular and Electronic Structure of Nitridochromium(V) Complexes with Macrocyclic Amine Ligands

AU - Meyer, Karsten

AU - Bendix, Jesper

AU - Bill, Eckhard

AU - Weyhermüller, Thomas

AU - Wieghardt, Karl

PY - 1998/12/1

Y1 - 1998/12/1

N2 - 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) 2B2 → 2E, (xy) → (x2 - y2) 2B2 → 2B1, and (xy) → (z2) 2B2 → 2A1, 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.

AB - 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) 2B2 → 2E, (xy) → (x2 - y2) 2B2 → 2B1, and (xy) → (z2) 2B2 → 2A1, 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.

UR - http://www.scopus.com/inward/record.url?scp=0001136257&partnerID=8YFLogxK

M3 - Journal article

AN - SCOPUS:0001136257

VL - 37

SP - 5180

EP - 5188

JO - Inorganic Chemistry

JF - Inorganic Chemistry

SN - 0020-1669

IS - 20

ER -