Unveiling the catalytic potency of copper-integrated [P6Mo18O73]n−-based complexes: structural basis and enhanced performance in selective oxidation of aromatic alcohol

Abstract

The catalytic performance of materials is intrinsically governed by their structural characteristics, where subtle variations can profoundly impact reactivity. This structure–activity relationship is particularly pronounced in complex systems like polyoxometalate (POM)-based functional complexes, where even subtle differences in their structural configurations can lead to remarkable variations in catalytic activity. Herein, we synthesized two [P₆Mo₁₈O₇₃]ⁿ⁻ ({P₆Mo₁₈})-based complexes that share similar polyoxometalate cores but exhibit distinct coordination environments: (HL)₆(Cu^IL₂)₈[Cu^II(H₂O)₂(Sr⊂P₆Mo^V₂Mo^VI₁₆O₇₃)₂]·35H₂O (1) features both [Cu^IL₂] coordination units and a Cu^II(H₂O)₂ unit along with six protonated ligands (L = benzimidazole), whereas (HL)₃₄[Na^I(H₂O)₂(HSr⊂P₆Mo^V₄Mo^VI₁₄O₇₃)₂]₂·3L·28H₂O (2) only contains Na^I(H₂O)₂ and thirty four protonated ligands with a different coordination geometry. Structural analysis revealed that complex 1 features unsaturated Cu^I/II coordinated sites, which conferred remarkable catalytic superiority over 2 in the selective oxidation of benzyl alcohol (BA) to benzoic acid (BZA). Under optimal conditions, catalyst 1 demonstrated exceptional performance (99.5% conversion and 98.4% selectivity), retaining ∼99% efficiency even at 5 mmol scale. Systematic comparisons establish clear structure–activity relationships, providing fundamental insights for designing high-performance POM catalysts.