Interplay between H-bonding and interpenetration in an aqueous copper(ii)–aminoalcohol–pyromellitic acid system: self-assembly synthesis, structural features and catalysis

Abstract

Two new copper(II) coordination compounds, [Cu(H_1.5mdea)₂]₂(H₂pma) (1a) and [{Cu₂(μ-Hmdea)₂}₂(μ₄-pma)]_n·2nH₂O (1b), were self-assembled at different temperatures from the same multicomponent reaction system, comprising copper(II) nitrate, N-methyldiethanolamine (H₂mdea), pyromellitic acid (H₄pma), and potassium hydroxide. Products 1a and 1b were isolated as microcrystalline solids and fully characterized and their structures were established by single-crystal X-ray diffraction. Compound 1a features the bis-aminoalcohol(ate) monocopper(II) units and H₂pma²⁻ anions that are multiply interconnected by strong H-bonds into a firm 2D H-bonded layer. Compound 1b reveals the bis-aminoalcoholate dicopper(II) motifs that are interlinked by the μ₄-pma⁴⁻ spacers into a 3D + 3D interpenetrated metal–organic framework. From a topological perspective, both networks of 1a and 1b are uninodal and driven by similar 4-connected H₂pma²⁻ or pma⁴⁻ nodes, but result in distinct sql and dia topologies, respectively. Compound 1a was applied as an efficient catalyst for two model cycloalkane functionalization reactions: (1) oxidation by H₂O₂ to form cyclic alcohols and ketones and (2) hydrocarboxylation by CO/H₂O and S₂O₈²⁻ to form cycloalkanecarboxylic acids. The substrate scope, effects of various reaction parameters, selectivity and mechanistic features were also investigated.