Not So Similar: Different Ways of Nb(V) and Ta(V) Catecholate Complexation

Abstract

The reactions between catechol (H2cat) and niobium(V) or tantalum(V) precursors in basic aqueous solutions lead to the formation of catecholate complexes of different natures. The following complexes were isolated and characterized by single-crystal X-ray diffraction (SCXRD): (1) (NH4)3[NbO(cat)3]∙4H2O; (2) K2[Nb(cat)3(Hcat)]·2H2cat·2H2O; (3) Cs3[NbO(cat)3]·H2O; (4) (NH4)4[Ta2O(cat)6]·3H2O; (5) Cs2[Ta(cat)3(Hcat)]·H2cat; (6) Cs4[Ta2O(cat)6]·7H2O. The isolated crystalline products were characterized by elemental analysis, X-ray powder diffraction (XRPD), FTIR, and TGA. The structural features of these complexes, such as {Ta2O} unit geometry, Cs-π interactions, and crystal packing effects, are discussed.

Bulky olefin epoxidation under mild conditions over Mo-based oxide catalysts

“…MoO 2 nanoparticles may be susceptible to partial oxidation of interfacial Mo( iv ) sites, 95–97 and small variations in the molybdenum valence may affect the physical properties. 83 Accordingly, differences in redox properties and coordination features of Ta and Nb sites (discussed in the literature for different coordination compounds of these metals 94,98 ) may have implications on the stability of immobilized MoO 2 .…”

Toward Redox- and Photoredox-Based Niobium/Tantalum Separations

“…35−38 Consequently, subtle variations in their coordination chemistry, electrochemical potential, and photochemical behaviors are observed. Evidence for such differences is found in their coordination patterns, for example, their oxo, fluoro, and imido complexes, 2,39 their electrochemical behaviors in oxo-and BINOLate-complexes, 34,40 differences in metal−ligand covalency in amidophenolate-and catecholate-type complexes, 41,42 and their distinct photochemical properties in imido chloride complexes. 43 Therefore, such distinctions can lay the groundwork for the differentiation of these two elements through redox-driven and photoredox-mediated methods.…”

“…Despite the pronounced similarities in coordination chemistry between Nb V and Ta V ions, which can be attributed to the lanthanide contraction, distinct energetic differences are present in the metals’ frontier orbitals that may offer means for realizing separations. , Niobium’s fifth ionization energy is 1165 kcal mol –1 , while tantalum’s is slightly lower (1113 kcal mol –1 ), indicating a thermodynamically more accessible oxidation of tantalum from the +4 to +5 oxidation state. − This energy difference arises from the properties of the frontier orbitals of niobium and tantalum free ions: niobium’s 4d orbitals are marginally smaller and energetically lower compared to tantalum’s 5d orbitals. − Consequently, subtle variations in their coordination chemistry, electrochemical potential, and photochemical behaviors are observed. Evidence for such differences is found in their coordination patterns, for example, their oxo, fluoro, and imido complexes, , their electrochemical behaviors in oxo- and BINOLate-complexes, , differences in metal–ligand covalency in amidophenolate- and catecholate-type complexes, , and their distinct photochemical properties in imido chloride complexes . Therefore, such distinctions can lay the groundwork for the differentiation of these two elements through redox-driven and photoredox-mediated methods.…”

Isolation of a Dodecanuclear Polyoxo Cluster {Nb12O21} Showing a Rare Case of Five‐fold Coordinated Niobium(V) Centers with a Square Pyramidal Geometry

“…[46] This interaction generates through the BHMP ligand, a tetranuclear species [(BHMP){Nb 2 O-(OEt) 5 } 2 ], without any additional μ-oxo groups linking the niobium atoms. Such an association of niobium carboxylate from the alkoxide route is also illustrated in a mixed bismuthniobium moiety, [47] which has been synthesized using salicylic acid (2- [48] To date, the largest poly-oxo cluster in niobium carboxylate chemistry has been identified from a solvothermal reaction of niobium ethoxide with pivalic acid in acetonitrile. It led to the formation of an hexadecaniobate cluster [Nb 16 O 28 (OEt) 12 (piv) 12 ].…”