Deoxygenation of Polynuclear Metal−Oxo Anions:  Synthesis, Structure, and Reactivity of the Condensed Polyoxoanion [(C₄H₉)₄N]₄(NbW₅O₁₈)₂O

Abstract

The deoxygenation of the mixed-metal polyoxoanion [(C(4)H(9))(4)N](3)NbW(5)O(19) with benzoyl chloride in dichloromethane forms quantitatively the condensed polyoxanion [(C(4)H(9))(4)N](4)(NbW(5)O(18))(2)O, in which two polyoxoanion fragments are linked together by a Nb-O-Nb oxo bridge. The product is characterized by a strong IR band at 692 cm(-)(1) assigned to a Nb-O-Nb stretch and a broad single (93)Nb NMR resonance at 975 ppm. Partial hydrolysis of [(C(4)H(9))(4)N](4)(NbW(5)O(18))(2)O to NbW(5)O(19)O(3)(-) in wet acetonitrile was observed by IR and (17)O NMR spectroscopy. The reaction of [(C(4)H(9))(4)N](4)(NbW(5)O(18))(2)O with a variety of alcohols and phenol forms alkoxide-derivatized polyoxoanions [(C(4)H(9))(4)N](2)Nb(OR)W(5)O(18) (R = methyl, ethyl, isopropyl, cholesteryl, phenyl). The similarity of the IR spectra of these deriviatives suggests that functionalization occurs at the terminal NbO oxygen. A crystallographic study of [(C(4)H(9))(4)N](4)(NbW(5)O(18))(2)O revealed a crystallographically imposed linear Nb-O-Nb oxo bridge (Nb-O(bridge) = 1.887(3) Å) and a structure in which the terminal tungsten-oxo bonds on the adjoining polyoxoanion fragments are eclipsed. Crystal data: orthorhombic, Cmca; Z = 4, a = 15.817(2) Å, b = 17.870(2) Å, c = 35.058(2) Å; V = 9928.0(10) Å(3); R = 5.52%.

Langmuir and Langmuir-Blodgett Films of Organic Dye-Inorganic Nanosheet Hybrids

“…Lu et al [5] unambiguously showed that the stretching mode of the terminating Nb-O bond in a polyoxoanion NbW 3 second highest antisymmetric modes reaches 1.39, being unacceptably larger than 956/791 (the present experimental data). In addition, it is not obvious whether introduction of double bonds decreases this energy ratio.…”

“…The former and the latter are respectively assignable to the antisymmetric stretching modes of the outer and central NbO bonds in the O-Nb-O-Nb-O-Nb-O chain (Fig. 5) [5,6]. This Nb 3 O 4 chain is the spine of the three interconnected NbO 6 octahedrons, which is the basic structural unit of CNO nanosheets [2].…”

Synthesis and Characterization of New Organosilyl Derivatives of Polyoxometalates (nBu4N)2[NbW5O19SiRR′2] (R = R′ = Et, iPr, OtBu, Ph;R = tBu and R′ = Me) – X‐ray Crystal Structure of (nBu4N)2[NbW5O19SiPh3]

“…[17,18] Moreover, the oxygen-niobium bond in NbW 5 O 19 is known to be labile with respect to 17 O exchange. [8,19] Although the terminal ONb oxygen atoms are not the most basic among the oxygen atoms bound to Nb atoms both the lability and steric interaction allow reactions with electrophilic species to occur selectively at this oxygen site. [8] Actually in the case of the substituted Keggin anion PW 11 NbO 40 the reaction of Me 3 SiSO 3 CF 3 leads directly to the trimethylsilyl derivatives PW 11 O 39 -NbOSiMe 3 .…”

“…[8,19] Although the terminal ONb oxygen atoms are not the most basic among the oxygen atoms bound to Nb atoms both the lability and steric interaction allow reactions with electrophilic species to occur selectively at this oxygen site. [8] Actually in the case of the substituted Keggin anion PW 11 NbO 40 the reaction of Me 3 SiSO 3 CF 3 leads directly to the trimethylsilyl derivatives PW 11 O 39 -NbOSiMe 3 . [20] In our case the reaction of R 3 SiSO 3 CF 3 (R = Me, Et) and tBuMe 2 6-instead of the monomer Klemperer described the clean synthesis of terminal alkoxide and organosilyl-Lindqvist derivatives.…”

“…While monosubstituted niobotungstates are relatively poorly reactive, [7] dimeric species with connecting Nb-ONb bridge(s) are excellent starting materials for the preparation of organic and organometallic derivatized polyoxoanions. [8][9][10][11] Herein, we report the preparation and char-reactive site in (nBu 4 N) 3 [NbW 5 O 19 ]. This is supported by Xray crystallographic analysis of (nBu 4 N) 2 In addition the reaction of these anions with respect to hydrolysis has been investigated.…”