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)
Antonis T. Vlahos,
²
Evagelos I. Tolis,
²
Catherine P. Raptopoulou,
‡
Alexandros Tsohos,
‡
Michael P. Sigalas,*
,§
Aris Terzis,*
,‡
and Themistoklis A. Kabanos*
,²
Department of Chemistry, Section of Inorganic and Analytical Chemistry, University of Ioannina,
451 10 Ioannina, Greece, NCSR “Demokritos”, Institute of Materials Science, 15310 Aghia Paraskevi
Attikis, Greece, and Laboratory of Applied Quantum Chemistry, Department of Chemistry,
Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece
ReceiVed July 14, 1999
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 NHEt
3
{trans-[VCl
2
(bpb)]} (1) and [VO(bpb)(H
2
O)]‚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 µ
2
-bridging-η
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 µ
2
-bridging-η
4
-bis(N
py
,O
am
) in [VOCl(H
2
bpb)]
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
P1 h, with (at 25 °C) a ) 9.140(2) Å, b ) 11.058(2) Å, c ) 14.175(2) Å, R) 99.013(5)°, ) 104.728(7)°,
γ ) 102.992(7)°, V ) 1314.9(4) Å
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 °C) a ) 11.054(5) Å, b ) 11.407(5) Å, c ) 16.964(7) Å, )
93.2(1)°, V ) 2136(2) Å
3
, Z ) 4. Variable temperature magnetic susceptibility studies of the dimeric compounds
3‚2CH
3
NO
2
and 4‚1.04CH
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 η
2
-(N
py
,N
am
) and η
2
-(N
py
,O
am
) bonding modes in the ligation of Hbpb
-
to vanadium.
Introduction
Vanadium is a bioessential element that is found in remark-
ably high concentrations in marine ascidians,
1
in certain mush-
rooms,
2
and in polychaete worms,
3
but its role is still a mystery,
although quite a few hypotheses have been presented. Moreover,
the isolation and characterization of two families of vanadium-
dependent enzymes, namely, of the nitrogenases
4
and the
haloperoxidases,
5
as well as the ability of vanadium to produce
significant physiological effects,
6
such as the increment in the
cytosolic reduced glutathione
7
and glutathione S-transferase,
7
anticancer activity,
8
and in particular its insulin-like properties,
etc.,
9
have stimulated further efforts in the development of the
coordination chemistry and biochemistry of vanadium.
10
The
synthesis as well as the structural and spectroscopic character-
ization of low molecular weight model complexes with the
biologically important oxidation states (+II to +V) of vanadium
will help in making further progress in the elucidation of
biological role of vanadium.
Currently, we,
11
as well as others,
12
have been studying the
interaction between vanadium and constituents of proteins, ²
University of Ioannina.
‡
Institute of Materials Science.
§
Aristotle University of Thessaloniki.
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2977 Inorg. Chem. 2000, 39, 2977-2985
10.1021/ic990837z CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/17/2000