Structural, electron paramagnetic resonance and electron spin echo envelope modulation studies of oxovanadium(iv)–amidate compounds containing monoanionic axial ligands: effect on the 51V-hyperfine coupling constants

Abstract

Reaction of the amidate ligand N-{2-[(2-pyridylmethylene)amino]phenyl}pyridine-2-carboxamide (Hcapca) with [VOCl 2 (thf) 2 ] and MeONa in 1+1+1 molar ratio in MeCN affords the compound trans-[VOCl(capca)] 1, while reaction of 1 with NEt 4 NCS, MeCO 2 NHEt 3 and imidazole yields the complexes trans-[VO(NCS)(capca)] 2, trans-[VO(Me-CO 2 )(capca)] 3 and trans-[VO(im)(capca)]2 4 respectively; the X-ray crystal structure of 1 is reported; Cw EPR studies of compounds 1-3 reveal a novel phenomenon of the reduction of their A z components by ca. 10% compared to N 4 reference compounds.

Mononuclear metal complexes with Piroxicam: Synthesis, structure and biological activity

“…In the present case, the ligands involved are two O amide , two N pyr of piroxicam ligands and one O water atoms. From the literature, we obtained A i (N pyr ) = 40.3 · 10 À4 cm À1 and A i (O water ) = 45.7 · 10 À4 cm À1 [121,122]. For A i (O amide ), there is only one report with A i (O amide ) = 43.7 · 10 À4 cm À1 derived for a vanadyl complex with an aliphatic amide [121].…”

Binding of Oxovanadium(IV) to Dipeptides Containing Histidine and Cysteine Residues

“…The rather low contribution for an amide group in complexes with TEC = -1 could partially explain the anomalous reduction of the parallel hyperfine coupling constant observed by Kabanos and coworkers and mentioned above. [46] The wide range of the A z (amide) contribution was explained [37,44] by assuming two limit resonance structures for an amide group coordinated through the nitrogen atom: one "amide-like", with the nitrogen atom negatively charged and a double bond between the carbon and oxygen atoms of the carbonyl group (a in Scheme 3), and another "imine-like", with the carbonyl oxygen atom negatively charged and a double bond between the carbon and nitrogen atoms (b in Scheme 3). The predominance of one of these structures depends on the electronic density of the metal ion: particularly, the importance of the a form should increase with decreasing the density (and hence TEC value).…”

“…-(Cl -, SCN -, CH 3 COO -and PhCOO -) is an axial ligand, [46] because the authors noticed an anomalous reduction of A z of about 10 % due to the effect of X -.…”

Synthesis, characterisation and insulin-mimetic activity of oxovanadium(IV) complexes with amidrazone derivatives

“…This is one of the few exceptions from the additivity rule reported in the literature. Other cases are represented by the three octahedral complexes [VOX(capca)] [58,59], where Hcapca is N-{2-[(2-pyridylmethylene)amino]phenyl}pyridine-2-carboxamide and X (Cl À , SCN À or CH 3 COO À ) is the ligand occupying the axial position, and by the bis-chelated complex formed by 6-methylpicolinic acid, [VO(6-methylpicolinato) 2 ] [60]. The A z values are 144-148 · 10 À4 cm À1 for [VOX(capca)] derivatives and 149 · 10 À4 cm À1 for [VO(6-methylpicolinato) 2 ], $10% lower than expected [54,55].…”