2978 Inorganic Chemistry, Vol. 39, No. 14, 2000
Vlahos et al.
namely, amides, amino acid amides, and peptides. These systems
serve as models of the interaction between metal centers of
metalloenzymes and the amide group of their peptide substrates.
Our studies are undertaken in the hope that a better understand-
ing of the interaction between vanadium species, and more
generally transition metal ions, and proteins will be achieved.
A literature survey, for the diamidate ligand H2bpb, revealed
that in almost all the crystallographically characterized H2bpb-
metal compounds, the ligand acts as a dianionic planar bis[N-
amidate-N-pyridine] chelator.13 To this trend, there are only two
exceptions.14 Metal-bpb2- compounds have been used as
epoxidation13d,15 or hydroxylation16 catalysts. Herein, we wish
to report the synthesis and structural characterization of novel
vanadium(III) and oxovanadium(IV) compounds with H2bpb,
Hbpb-, and bpb2-. In addition, infrared and variable temperature
magnetic susceptibility properties of the complexes are reported.
Furthermore, an ab initio study of the Hbpb- ligand and of the
two model complexes of the general formula [VCl2(NH3)2-
(Hbpb)] is reported. A special emphasis is placed on under-
standing the energetics of the ligation of Hbpb- in its η2-
(Npy,Oam) or η2-(Npy,Nam) coordination modes. The structures
of 1, 2‚2CHCl3, and 3‚2CH3NO2 (vide infra) have previously
been communicated.17
Experimental Section
Materials. Reagent grade chemicals were obtained from Aldrich
and used without further purification. Dichlorobis(tetrahydrofuran)-
oxovanadium(IV), [VOCl2(thf)2],18 tris(acetonitrile) trichlorovanadium-
(III), [VCl3(CH3CN)3],19 bis(acetato)oxovandium(IV), [VO(CH3COO)2]x,20
and 1,2-bis(2-pyridinecarboxamide)benzene, H2bpb,21 were prepared
according to literature procedures. The purity of the above molecules
was confirmed by elemental analyses (C, H, N, and V for vanadium
compounds) and infrared spectroscopy. Reagent grade dichloromethane,
chloroform, acetonitrile, nitromethane, thiethylamine, isopropyl alcohol,
and dimethylformamide were dried and distilled (dimethylformamide
was distilled under reduced pressure) over calcium hydride, while
toluene, diethyl ether, and tetrahydrofuran were dried and distilled over
sodium wire. Methyl alcohol was dried by refluxing over magnesium
methoxide. Syntheses, distillations, crystallization of the complexes,
and spectroscopic characterization were performed under high-purity
argon using standard Schlenk techniques.
C, H, and N analyses were conducted by the University of Ioannina’s
microanalytical service. Vanadium was determined gravimetrically as
vanadium pentoxide or by atomic absorption, and chloride analyses
were carried out by potentiometric titration.
(9) (a)Shaver, A.; Ng, J. B.; Hall, O. A.; Lum, B. S.; Posner, B. I. Inorg.
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A.; Bonas, G.; Makriyannis, A.; Raptopoulou, C. P.; Terzis, A. Inorg.
Chem. 1996, 35, 357. (b) Tasiopoulos, A. J.; Vlahos, A. T.; Keramidas,
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C. R.; Terzis, A.; Deligiannakis, Y.; Kabanos, T. A. Chem.sEur. J.
1999, 5, 910.
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Triethylammonium trans-Dichloro{1,2-bis(2-pyridinecarbox-
amide)benzenato(-2)-η4-Npy,Nam,Nam,Npy}vanadate(III), NHEt3-
{trans-[VCl2(bpb)]} (1). Method A. A stirred mixture of vanadium-
(III) chloride (0.428 g, 2.73 mmol), H2bpb (0.868 g, 2.73 mmol), and
triethylamine (1.38 g, 13.6 mmol) in toluene (50 mL) was refluxed
overnight. The resulting brick-red precipitate, which is a mixture of 1,
[VO(bpb)]x, and NHEt3Cl, was filtered off and washed with diethyl
ether (3 × 10 mL) and dried in vacuo. The solid was extracted with
dichloromethane (∼50 mL) and then the solvent removed to give a
red solid. The residual solid was redissolved in chloroform (∼40 mL)
and filtered, and 40 mL of diethyl ether was very carefully layered on
top of the filtrate and cooled to -20 °C for 3 days to give dark-red
and white crystals that were filtered off and dried in vacuo. The dark-
red crystals were manually separated readily under a microscope.
Yield: 0.148 g (10%). Anal. Calcd for C24H28Cl2N5O2V: C, 53.35; H,
5.22; Cl, 13.12; N, 12.96; V, 9.43. Found: C, 53.30; H, 5.19; Cl, 13.00;
N, 13.02; V, 9.40. µeff ) 2.75 µB at 298 K. Electronic spectrum in
CH2Cl2, λmax, nm (ꢀM, L mol-1 cm-1): 220 (22 900), 261 (17 700),
290(sh) (9200), 349 (7700); in CH3CN, 197 (39 000), 204(sh) (36 000),
259 (20 400), 284(sh) (9000), 350 (9300).
Method B. To a stirred solution of [VCl3(CH3CN)3] (1.340 g, 8.540
mmol) in acetonitrile (60 mL) was added in one portion solid H2bpb
(2.730 g, 8.540 mmol). The color immediately changed from dark-
green to very light-green, and a light-green solid precipitated. The
mixture was stirred for ∼5 min before thiethylamine (1.980 g, 19.60
mmol) was added to it. The color of the solution immediately changed
to dark-brown. After about 2 h of stirring at ambient termperature, the
solution was filtered off. The residue was extracted with CH3CN (∼30
mL). The extract was combined with the filtrate and was evaporated
in vacuo to dryness. The residual solid was redissolved in dichlo-
romethane (∼45 mL), the solution filtered and concentrated (∼15 mL),
diethyl ether (∼45 mL) was added dropwise to the stirred filtrate, and
the resulting precipitate was filtered off, washed with diethyl ether (2
× 10 mL), and dried in vacuo. The precipitate was triturated with cold
isopropyl alcohol (2 × 30 mL) at ambient temperature, filtered off,
washed with diethyl ether (2 × 10 mL), and dried in vacuo. Yield:
2.77 g (60%).
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Vlahos, Antonis T.
