Model investigations of vanadium-protein interactions:: Novel vanadium(III) and oxovanadium(IV) compounds with the diamidate ligand 1,2-bis(2-pyridinecarboxamide)benzene (H2bpb)

Novel vanadium(III) and oxovanadium(IV) compounds with the diamidate ligand 1,2-bis(2-pyridinecarboxamide)benzene (H(2)bpb) were synthesized and structurally characterized. H(2)bpb is capable of binding to vanadium in either its anionic (dianionic-monoanionic) or its neutral form, resulting in complexes of various geometries and stoichiometries. The dianionic form (bpb(2-)), in NHEt3{trans-[VCl2(bpb)]} (1) and [VO(bpb)(H2O)].0.5dmso.0.36CH(3)OH.0.13H(2)O (6.0.5dmso.0.36CH(3)OH.0.13H(2)O), acts as a planar tetradentate bis[N-amidate-N-pyridine] equatorial ligand. The monoanionic form (Hbpb(-)) behaves as an (N-py,O-am) or (N-py,N-am) chelator in [V(Hbpb)(3)].2CHCl(3) (2.2CHCl(3)) as well as a mu(2)-bridging-eta(4)-(N-py,O-am-N-py,N-am) in [VOCl(Hbpb)](2).2CH(3)NO(2) (3.2CH(3)NO(2)), while the neutral H(2)bpb behaves as a mu(2)-bridging-eta(4)-bis(N-py,O-am) in [VOCl(H2bpb)](2).1.04CH(3)OH.1.23thf.0.74H(2)O (4.1.04CH(3)OH.1.23thf.0.74H(2)O). Compound 4.1.04CH(3)OH.1.23thf.0.74H(2)O crystallizes in the triclinic system P (1) over bar. with (at 25 degrees C) a 9.140(2) Angstrom, b = 11.058(2) Angstrom, c = 14.175(2) Angstrom, alpha = 99.013(5)degrees, beta = 104.728(7)degrees, gamma = 102.992(7)degrees, V= 1314.9(4) Angstrom(3): Z = 1, while compound 6.0.5dmso.0.36CH(3)OH.0.13H(2)O crystallizes in the monoclinic space group P2(1)/n with (at 25 degrees C) a = 11.054(5) Angstrom, b = 11.407(5) Angstrom, c = 16.964(7) Angstrom, beta = 93.2(1)degrees, V = 2136(2) Angstrom(3), Z = 4. Variable temperature magnetic susceptibility studies of the dimeric compounds 3.2CH(3)NO(2) and 4.1.03CH(3)OH show g values for the V(IV) centers that are slightly smaller than 2.0 (as expected for d(1) ions) and indicate small antiferromagnetic coupling between the two vanadium(IV) centers. Ab initio calculations were also carried out, providing results concerning the effect of the relative strength and the deformation energy involved in the eta(2)-(N-py,N-am) and eta(2)-(N-py,O-am) bonding modes in the ligation of Hbpb(-) to vanadium.