Synthesis and Reactivity of the Methoxozirconium Pentatungstate (ⁿBu₄N)₆[{(μ-MeO)ZrW₅O₁₈}₂]:  Insights into Proton-Transfer Reactions, Solution Dynamics, and Assembly of {ZrW₅O₁₈}^2- Building Blocks

Abstract

The methoxo-bridged, dimeric, ZrIV-substituted Lindqvist-type polyoxometalate (POM) (nBu4N)6[{(mu-MeO)ZrW5O18}2], (TBA)61, has been synthesized by stoichiometric hydrolysis of Zr(OnPr)4, [{Zr(OiPr)3(mu-OnPr)(iPrOH)}2], or [{Zr(OiPr)4(iPrOH)}2] and [{WO(OMe)4}2] in the presence of (nBu4N)2WO4, providing access to the systematic nonaqueous chemistry of ZrW5 POMs for the first time and an efficient route to 17O-enriched samples for 17O NMR studies. 1H NMR provided no evidence for dissociation of 1 in solution, although exchange with MeOH was shown to be slow by an EXSY study. Reactions with HX at elevated temperatures gave a range of anions [{XZrW5O18}n]3n- (X = OH, 3; OPh, 4; OC6H4Me-4, 5; OC6H4(CHO)-2, 6; acac, 7; OAc, 8), where n = 2 for 3 and n = 1 for 4-8, while 1H and 17O NMR studies of hydrolysis of 1 revealed the formation of an intermediate [(mu-MeO)(mu-HO)(ZrW5O18)2]6-. Electrospray ionization mass spectrometry of 1 and 3 illustrated the robust nature of the ZrW5O18 framework, and X-ray crystal structure determinations showed that steric interactions between ligands X and the ZrW5O18 surface are important. The coordination number of Zr is restricted to six in aryloxides 4 and 5, while seven-coordination is achieved in the chelate complexes 6-8. Given the inert nature of the methoxo bridges in 1, protonation of ZrOW sites is proposed as a possible step in reactions with HX. The diphenylphosphinate ligand in [(Ph2PO2)ZrW5O18]3- was found to be labile and upon attempted recrystallization the aggregate [(mu3-HO)2(ZrW5O18)3H]7- 9 was formed, which was found to be protonated at ZrOZr and ZrOW sites. This work demonstrates the flexibility of the {ZrW5O18}2- core as a molecular platform for modeling catalysis by tungstated zirconia surfaces.

A Quantum Chemical Study of the Structure, Bonding Characteristics and Nonlinear Optical Properties of Aryloxido and Salicylaldehydo Derivatives of [XW5O18]3– (X = Zr or Ti)

“…The optimized partial geometrical parameters are listed in Table 1, which also includes experimental data. [21,22] Clearly, the important structural parameters are well-reproduced by the theoretical calculations. This suggests that our adopted method and basis sets are reliable for the systems studied.…”

“…[28,29] The geometries of all systems were optimized and the initial geometric data were obtained from the crystal data. [21,22] The local density approximation (LDA) characterized by the Vosko-WilkNusair (VWN) [30] parametrization for correlation was used. The generalized-gradient approximation (GGA) was employed in the geometry optimizations by using the Beck [30,31] and Perdew [32] exchange-correlation (XC) functional.…”

“…Errington and co-workers [21] recently reported the successful synthesis of a series of aryloxido and salicylaldehydo [ZrW 5 3-have been synthesized. [22] The POM structures in these newly synthesized complexes are group 4 metal-substituted Lindqvist-type polytungstate anions [XW 5 O 18 ] 3-(X = Zr or Ti).…”

Extending the Lindqvist Family to Late 3d Transition Metals: A Rational Entry to CoW5 Hexametalate Chemistry

“…[6] The alkoxido group in these anions can be systematically replaced by a wide variety of other ligands in straightforward exchange reactions with protic reagents. [7] This reactivity also enabled us to attach TiW 5 hexametalates to derivatised silicon surfaces in the first demonstration of covalent surface immobilisation of POMs. [8] Scheme 1 illustrates this methodology and indicates how it has been extended to group 5 analogues by adjusting the reaction stoichiometry.…”

Quantum Chemical Design for Enhanced Second‐Order NLO Response of Terpyridine‐Substituted Hexamolybdates

“…Firstly, they offer a wide range of metals with different coordination states and various organic groups which possess large π-conjugated systems. [27][28][29] Secondly, many of these compounds are known to possess intense low-lying electronic transitions. [22] Last but not least, POMs have been found to be extremely flexible building blocks as the non-centrosymmetric molecular structures can be achieved easily for such compounds.…”