Synthesis, structural, and thermal characterization of a new binuclear copper(II) chelate complex bearing an amine-hardener for epoxy resins

Abstract

A new di(μ-carbonato)bis[aqua(diethylenetriamine)copper(II)] hexahydrate complex, [{Cu(NH(C₂H₄NH₂)₂)(H₂O)(μ-CO₃)}₂]·6H₂O (1), was synthesized by direct interaction of malachite with diethylenetriamine (dien). The crystals of 1 were characterized by X-ray powder diffraction and IR spectra, as well as structurally characterized. Compound 1 consists of [{Cu(dien)(H₂O)(μ-CO₃)}₂] discrete units whose anions play the role of bridging ligands combining two Cu(II) chelate cores into a centrosymmetric dimer. The elongated octahedral environment of Cu²⁺ consists of three nitrogens of dien and an oxygen from at the base of the bipyramid; the two apical positions of such polyhedron are occupied by an oxygen from an adjacent and an O from H₂O. Combining the primary dimers into a framework is provided by O–H⋯O and N–H⋯O hydrogen bonds. The thermal behavior of 1 was investigated by differential thermal analysis. Thermal decomposition of 1 terminates at 400 °C, while the maximal combustion temperature of gaseous products is at 520 °C. Complex 1 may be an effective fire retardant and, at the same time, a curing agent for epoxy resins.

Keywords:

• Copper(II) chelate complexes
• synthesis
• X-ray crystal structure
• IR spectroscopy
• differential thermal analysis
• fire retardant-hardeners of epoxy resins