Exploration of a Variety of Copper Molybdate Coordination Hybrids Based on a Flexible Bis(1,2,4-triazole) Ligand: A Look through the Composition-Space Diagram

Abstract

We investigated the coordination ability of the bis(1,2,4-triazolyl) module, tr₂pr = 1,3-bis(1,2,4-triazol-4-yl)propane, toward the engineering of solid-state structures of copper polyoxomolybdates utilizing a composition space diagram approach. Different binding modes of the ligand including [N-N]-bridging and N-terminal coordination and the existence of favorable conformation forms (anti/anti, gauche/anti, and gauche/gauche) resulted in varieties of mixed metal Cu^I/Mo^VI and Cu^II/Mo^VI coordination polymers prepared under hydrothermal conditions. The composition space analysis employed was aimed at both the development of new coordination solids and their crystallization fields through systematic changes of the reagent ratios [copper(II) and molybdenum(VI) oxide precursors and the tr₂pr ligand]. Nine coordination compounds were synthesized and structurally characterized. The diverse coordination architectures of the compounds are composed of cationic fragments such as [Cu^II₃(μ₂-OH)₂(μ₂-tr)₂]⁴⁺, [Cu^II₃(μ₂-tr)₆]⁶⁺, [Cu^II₂(μ₂-tr)₃]⁴⁺, etc., connected to polymeric arrays by anionic species (molybdate MoO₄^2-, isomeric α-, δ-, and β-octamolybdates {Mo₈O₂₆}^4- or {Mo₈O₂₈H₂}^6-). The inorganic copper(I,II)/molybdenum(VI) oxide matrix itself forms discrete or low-dimensional subtopological motifs (0D, 1D, or 2D), while the organic spacers interconnect them into higher-dimensional networks. The 3D coordination hybrids show moderate thermal stability up to 230-250 °C, while for the 2D compounds, the stability of the framework is distinctly lower (∼190 °C). The magnetic properties of the most representative samples were investigated. The magnetic interactions were rationalized in terms of analyzing the planes of the magnetic orbitals.