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~Thls Week’s Citation ClassIc B OCTOBER 24,1988 Selbin J. Oxovanadium(IV) complexes. Coord. Chem. Rev. 1:293-314, 1966. [Department of Chemisuy, Louisiana State University, Baton Rouge, LAI This paper reviews the flurry of interest sur2~ persists in almost all reactions with ligands, rounding the oxovanadium(IV) species, VO , permitted observations not possible with comin particular the 70 or so papers published since plexes of atom-ions. 1 my more comprehensive review. Complexes The most obvious new variable available of V02+ and their examination by X-ray dif- with an oxometal species was the infrared fraction, infrared spectroscopy, thermodynam- stretching frequency of the metal.oxygen 2 1 ic (stability) studies, electron spin resonance bond. This frequency (940-1,020 cm- ) instudies, and electronic spectral studies, and at- deed turned out to be sensitive not only to the tempts at theoretical models, are 8 critically re- nature and strength of the equatorial ligands— viewed and updated. [The SCP indicates that V02+ complexes are nearly always square this paper has been cited in over 260 publica- pyramidal with axial oxygen and with occasional transaxial ligands, but in a few cases are tions.1 distorted tngonal bipyramidal—but even more 23 2~ sensitive to axial ligands. ’ Thus the VO could serve to generate a ligand series based upon the strengthening or weakening of the Joel Selbin V-0 bond, and the equatorial ligands could serve to enhance either the “softness” or the Department of Chemistry “hardness” of the central metal species. The Louisiana State University presence of a single d electron generated not Baton Rouge, LA 70803-1804 only experimental studies of electronic spectra and the electron spin resonance (ESR) spectra but several attempts at theoretical treatment June 30, 1988 of the molecule-ion system. Increasing numbers of single crystal X-ray diffraction studies began to rt~veala very short V-O bond length (1.55-1.76A), but one that was not too sensiIn 1959, when I first became interested in tive to the other ligands. complexes of oxocations, the most extensively ThèI~iquentcitation olihis paper undoubtstudied such species 2~ was the dioxouranium(VI) edly arose from its critical nature and its timeor uranyl ion, UO .My first PhD student, liness in the mid-1960s. There was rapidly inLarry Holmes, and2I began a brief collabora- creasing interest in the preparation of new tion with Sean P. McGlynn, a molecular spec- transition-metal complexes and their study by troscopist at Louisiana State University, on a electronic and ESR spectral techniques and in study of the variation of the symmetric and the growing correlation of such data with preantisymmetric stretching vibrations of the dictive models, such as ligand field and moUO with different ligands. We established lecular orbital theories. Adding to its continued 2~ series that exhibited striking similari- frequent citation no doubt is the absence of a ligand ties to the well-known spectrochemical ligand any more recent general review of V02+. series that had generally been generated from Later work by many others with V02+, unoptical spectral data. It occurred to me then diminished in quantity, has largely been more that by studying complexes of molecule-ions, of the same type, simply with new complexes, in particular oxocations, we would have more until the bioinorganic connections and biohandles on the complexes for studying metal- chemical use of V02+ began to be made. Alligand interactions than there are on com- though no more recent general reviews of plexes of atom-ions. V02+ have appeared since my review, there I believed then—and still believe—that per- have been valuable summaries of selected haps the best, simplest, and most stable and areas of research, such as the 2~inorganic and persistent such molecule-cation is VO~,oxo- biochemical aspects of VO electron4 paravanadium(IV) or vanadyl. Thisspecies has the magnetic resonance spin probes. The added feature of being a “single electron” (d’ roughly 250 references in2~this latter review beyond closed shells) electronic system; that chapter suggest that VO researchis alive proved to be a mixed blessing. The very strong. and well and occurring in new and exciting perhaps triply bonded, oxygen, which readily areas. I. 2. 3. 4. SelbIn J. The chemistry of oxovanadium(IV). Chezn. Rev. 65:153-75, 1965. (Cited 385 times.) Selbin J, Holmes L H & McGIynn S P. Vanadyl complexes. Chein. lad—London 1961:746-7. (Cited 25 times.) Selbbi J & Holmes LII. complexes of oxovanadium(IV). I. litorg. Nuci. Chem. 24:1111-9, 1962. (Cited 70 times.) Chiateen N D. Vanadyl(IV) EPR spin probes. Inorganic and biochemical aspects. (Berliner L J & Reuben I, eds.) Biological magneticresonanen. New York: Plenum Press. 1981. Vol. 3. p. ~3-t 19. (Uncited.) ©1988by1Sl® CURRENT CONTENTS® 18 /1 / // 1:~/~ / (~_~