Ring currents in wholly inorganic heteropoly blue complexes.  Evaluation by a modification of Evans' susceptibility method

Kozik, Mariusz; Casan-Pastor, Nieves; Hammer, Charles F.; Baker, Louis C. W.

doi:10.1021/ja00231a019

Cited by 90 publications

(48 citation statements)

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“…Kozik et al (35) and Casan-Pastor (36) attributed enhanced diamagnetic susceptibilities of two-electron reduced heteropolytungstate blues to ring currents. Our general observation that chemical shifts of central 31 of the intense optical absorption band and decreased shielding of the phos phorus nucleus.…”

Section: Ring-current Effectsmentioning

confidence: 99%

Intramolecular Electron Transfer and Electron Delocalization in Molybdophosphate Heteropoly Anions

Barrows

Pope

1989

Electron Transfer in Biology and the Solid State

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The electronic structures of mixed-valence heteropoly 12-molybdo phosphate anions (heteropoly blues) were investigated by electronic absorption spectroscopy and by 17 O and 31 P NMR spectroscopy in aqueous and acetonitrile solutions. The one-, two-, and four-electron reduced forms of a-PMo12O403-(aI, aII, and aIV), are shown to retain, on the NMR time scale, the tetrahedral symmetry of the ox idized Keggin structure. These anions are class II mixed-valence spe cies, with the additional electrons weakly trapped on molybdenum centers. The particularly stable four-electron reduced species β-Η χΡΜo12O40(7-x)-(βIV) is derived from the C3v isomer of the Keggin structure. This anion is shown, on the basis of its intense narrow optical absorption band, 17 O NMR, and anomalous 31 P chemical shift, to contain delocalized valences (class III). Upon deprotonation, βIV reverts to a class II species with "normal" spectroscopic properties.

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Section: Ring-current Effectsmentioning

confidence: 99%

Intramolecular Electron Transfer and Electron Delocalization in Molybdophosphate Heteropoly Anions

Barrows

Pope

1989

Electron Transfer in Biology and the Solid State

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“…Subsequently, the added ''blue'' electrons couple with the first via multipath antiferromagnetic interactions (see Antiferromagnetism), and the delocalization of the blue electron pairs generates enhanced diamagnetism (see Diamagnetism) as a consequence of ring currents within the heteropolyanions. 20 The molybdate blues especially have long been used for colorimetric determination of trace levels of elements that readily form Keggin anions, e.g., phosphate and silicate. Heteropoly ''browns'' are more highly reduced tungstates, generated by spontaneous intraionic disproportionation of the blues under acidic conditions.…”

Section: Redox Behaviormentioning

confidence: 99%

PolyoxometalatesUpdate based on the original article by Michael T. Pope,Encyclopedia of Inorganic Chemistry© 2005, John Wiley & Sons, Ltd.

Pope¹,

Kortz²

2012

Encyclopedia of Inorganic and Bioinorganic Chemistry

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The class of complexes known as polyoxometalates (POMs) is predominantly populated by polyoxoanions of high‐valent (d 0 , d 1 ) transition metals of groups 5 and 6 that typically incorporate some 5‐50 metal centers in structures of high symmetry. In most cases, the metal atoms occupy {MO 6 } octahedra that share vertices and edges. However, recent reports of POMs that incorporate square‐planar {Pd II O 4 } and hexagonal‐bipyramidal {U VI O 2 (η 2 − O 2 ) 2 (OH) 2 } building blocks indicate that further expansion of the field is in progress. The descriptive chemistry of many polyoxomolybdates and polyoxotungstates dates from the last third of the nineteenth century but it was not until the mid‐twentieth century that structural principles and the aqueous equilibria controlling the formation of POMs from monomeric oxoanions began to be recognized and quantified. That additional heteroatoms (metallic or nonmetallic) can be incorporated into the structures of, especially, polymolybdates and tungstates accounts for the enormous and rapidly developing variety of structures and possible applications of POMs. Four general types of POM structure, based on the mode of incorporation of the heteroatom(s), are described and it is shown how these can lead to hybrid organo‐POM complexes and to functionalization of POMs. Certain POM structures are reducible to mixed‐valence “heteropoly blue” versions, and those incorporating domains of paramagnetic heteroatoms can exhibit single‐molecule magnetic properties. The possibility that Mo VI and W VI can occupy a seven‐coordinate {O = M(O 6 )} polyhedron in POMs was first observed in [Mo 36 O 112 (H 2 O) 8 ] 8− {Mo 36 }; subsequent work has led to the development of other macrosized POMs including rings {Mo 154 }, hollow icosahedral “Keplerates” {Mo 60 W 72 }, and the “blue hedgehog” {Mo 368 }. Aqueous and aqueous‐organic solutions of such macro‐POMs spontaneously form hollow spherical vesicular structures (“blackberries”) with diameters typically 90 nm, with inter‐POM separations of 1 nm, depending upon the dielectric constant of the solvent. The various properties of POMs (such as large size, high molecular weight, solubility in polar and nonpolar solvents, electron and proton transfer and storage capacity, high thermal stability) have sparked applications in several fields, most notably in catalysis, both heterogeneous and homogeneous. Other applications include their use as electron‐dense staining and imaging agents, and their antiviral and antitumoral activity. Unconventional POMs are mainly represented by polyoxopalladates(II) and polyperoxodioxouranates(VI), which are also isolated from aqueous media. Unlike the early transition‐metal‐based POMs, the palladate structures are terminated by heteroatom groups and may also contain an internal heteroatom. The class of polyperoxodioxouranates(VI) isolated from more alkaline media frequently have fullerene‐like structures based on hexagonal bipyramidal bipyramids linked by η 2 ‐peroxo groups and hydroxo, oxalato, diphosphato, or diphosphonato bridges.

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“…This prevents complete spin pairing in [V 6 B 20 O 50 H 8 ] 8− , thereby leading to a paramagnetic species in contrast to the diamagnetic benzene. The implied the possibility of interactions between transition metals separated by oxygen bridges in polyoxometalate structures relates to the 1988 experimental observation by Baker and co-workers of ring currents in wholly inorganic heteropolyoxometalate blue structures using a modification of Evans’ susceptibility method [4]. …”

Section: Introductionmentioning

confidence: 99%

Analogies between Vanadoborates and Planar Aromatic Hydrocarbons: A High-Spin Analogue of Aromaticity

King

2017

Materials

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The vanadium-vanadium interactions in the polygonal aggregates of d1 vanadium(IV) atoms, with a total of 4k + 2 vanadium electrons (k an integer) imbedded in an electronically inactive borate matrix in certain vanadoborate structures are analogous to the ring carbon-carbon interactions in diamagnetic planar cyclic hydrocarbons. They thus represent a high-spin analogue of aromaticity. Thus, the vanadoborate anion [V6B20O50H8]8− with six V(IV) electrons (i.e., 4k + 2 for k = 1) contains a macrohexagon of d1 V(IV) atoms with four unpaired electrons. This high-spin system is related to the low-spin aromaticity in the diamagnetic benzene having six π electrons. Similarly, the vanadoborate anion [V10B28O74H8]16− with ten V(IV) electrons (i.e., 4k + 2 for k = 2) contains a macrodecagon of d1 V(IV) atoms with eight unpaired electrons. Again, this high-spin system is related to the aromaticity in the diamagnetic 1,6-methanol[10]annulene, having ten π electrons.

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Ring currents in wholly inorganic heteropoly blue complexes. Evaluation by a modification of Evans' susceptibility method

Cited by 90 publications

References 1 publication

Intramolecular Electron Transfer and Electron Delocalization in Molybdophosphate Heteropoly Anions

Intramolecular Electron Transfer and Electron Delocalization in Molybdophosphate Heteropoly Anions

PolyoxometalatesUpdate based on the original article by Michael T. Pope,Encyclopedia of Inorganic Chemistry© 2005, John Wiley & Sons, Ltd.

Analogies between Vanadoborates and Planar Aromatic Hydrocarbons: A High-Spin Analogue of Aromaticity

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