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

Novel vanadium(III) and oxovanadium(IV) compounds with the diamidate ligand 1,2-bis(2-pyridinecarboxamide)benzene (H(2)bpb) were synthesized and struc turally characterized. H(2)bpb is capable of binding to vanadium in either its anionic (dianionic-monoanionic) or its neutral form, resulting in compl exes 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 b is[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 [V OCl(Hbpb)](2).2CH(3)NO(2) (3.2CH(3)NO(2)), while the neutral H(2)bpb behave s 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)O H.1.23thf.0.74H(2)O crystallizes in the triclinic system P (1) over bar. wi th (at 25 degrees C) a 9.140(2) Angstrom, b = 11.058(2) Angstrom, c = 14.17 5(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 6.0.5dms o.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 compoun ds 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 sma ll antiferromagnetic coupling between the two vanadium(IV) centers. Ab init io calculations were also carried out, providing results concerning the eff ect 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 Hbp b(-) to vanadium.