Vanadium complexes diamagnetism

Vanadium, a typical transition element, displays weU-cliaractetized valence states of 2—5 in solid compounds and in solutions. Valence states of —1 and 0 may occur in solid compounds, eg, the carbonyl and certain complexes. In oxidation state 5, vanadium is diamagnetic and forms colorless, pale yeUow, or red compounds. In lower oxidation states, the presence of one or more 3d electrons, usually unpaired, results in paramagnetic and colored compounds. All compounds of vanadium having unpaired electrons are colored, but because the absorption spectra may be complex, a specific color does not necessarily correspond to a particular oxidation state. As an illustration, vanadium(IV) oxy salts are generally blue, whereas vanadium(IV) chloride is deep red. Differences over the valence range of 2—5 are shown in Table 2. The stmcture of vanadium compounds has been discussed (6,7). 

In diamagnetic vanadium complexes, information on the mode of coordination of the ligand(s) can be obtained from magnetic nuclei in the coordination sphere by both one-and two-dimensional (homo- and heteronuclear) methods. In model complexes for biorelevant vanadium compounds, informative spin probes are the spin-i/2 nuclei H, and (the last preferably in N-enriched samples), and the quadrupolar nuclei H (7 = 1), (7 = 1) and (7 = 72). NMR is a powerful tool in characterising... 

In contrast to Vcp2, fulvalene vanadium complexes (9.82) are diamagnetic and... 

The neutral complexes of chromium, molybdenum, tungsten, and vanadium are six-coordinate and the CO molecules are arranged about the metal in an octahedral configuration as shown in stmcture (3). Vanadium carbonyl possesses an unpaired electron and would be expected to form a metal—metal bond. Steric hindrance may prevent dimerization. The other hexacarbonyls are diamagnetic. 

Electrochemically characterized V(V) complexes which lack oxo ligands are somewhat rare. Many of those which are known are the result of preparative studies guided by CV results on V(IV) systems. For example, a series of imidovanadium(IV) complexes containing the tetradentate dianionic 5,7,12,14-tetramethyldibenzo[b, i] [1, 4, 8, 11] tetraazacyclotetradecinato moiety (TMTAA ) was reported [73], and diamagnetic vanadium(V) cations [(TMTAA)V = NR]+ (4) were prepared by oxidation of... 

Carbonyl and other Low Oxidation State Compounds.—Tris-(2,2 -bipyridyl)vana-dium(O) solutions in DMF exhibit three one-electron reduction waves corresponding to VL3 - VL3 (L = 2,2 -bipyridyI) VLJ -> VL " and VLf -VL, and two oxidation waves corresponding to VL3-> VL3 and VLJ ->VL3+ whose half-wave potentials differ by only 0.10 V.342 The difference for the isoelectronic chromium complexes is 0.49 V. An explanation has been offered for the small difference between the vanadium potentials in terms ol the possible diamagnetism of the d4VL3 species arising from a substantial splitting of the l2g orbitals. 

In a later article, complexes of Ni(II), Cu(II), Pd(II), and V02+ ions with the same tetra-substituted porphyrin were reported. Stepwise oxidation of these complexes gave products for which the authors proposed quinonoid, monoradical, and diradical structures. The most prolonged oxidations yielded the diradical products, which were isolated as dark purple crystals, relatively stable in air (40). The monoradical vanadyl complex was observed to be diamagnetic, suggesting antiferromagnetic coupling between the phenoxyl radical and unpaired electron on vanadium, whereas in the copper complex no such coupling was observed. More detailed studies of these systems seem warranted. 

Complexes containing vanadium in low oxidation states, apart from organometallic compounds, are known with ligands such as bipy, phen, nitric oxide, and tertiary phosphines, which stabihze such oxidation states. Depending on their electronic structure, V and V complexes may be diamagnetic, which permits study by NMR spectroscopy, and EPR spectroscopy has been used to study paramagnetic V complexes. 

Molecular nitrogen (N2) can act as a ligand in certain coordination complexes. Predict the structure of [V(N2)g], which is isolated by condensing V with N2 at 25 K. Is this compound diamagnetic or paramagnetic What is the formula of the carbonyl compound of vanadium that has the same number of electrons ... 

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