A flame retardant-hardener for epoxy resins: Synthesis, structural, and DFT studies of the [Cu(H₂NC₂H₄NH₂)₂ (H₂O)Cl]Cl complex

Authors: BORYS MYKHALICHKO, HELEN LAVRENYUK, OLEG MYKHALICHKO

Abstract: The aqua-bis(ethylenediamine)-chloro-copper(II) chloride complex, [Cu(en)₂ (H₂O)(Cl)]Cl (1), was synthesized by direct interaction of CuCl₂×2H₂O with pepa (pepa is a polyethylenepolyamine containing ethylenediamine (en)). The crystalline complex 1 was characterized by IR spectra and structurally studied. Crystals of this complex consist of the [Cu(en)₂(H₂O)(Cl)] ⁺ discrete cations, whose Cu²⁺ ion is chelated by two en molecules. The Cu(II) coordination polyhedron has the shape of an elongated square bipyramid, in which four nitrogen atoms of the -NH₂ groups of en molecules form the base of this bipyramid, and the oxygen atom of the water molecule and Cl^- are in its apical positions. Three-dimensional framework 1 is formed due to hydrogen bonds O-H...Cl and N-H...Cl. The Cu(II)-(H₂NC₂H₄NH₂) chelation was studied by DFT using the 6-31G* basis set. The calculated electron-stereochemical parameters are in good agreement with the ability of complex 1 to simultaneously be a flame retardant and a curing agent of epoxy resins.

Keywords: Copper(II) chelate complexes, synthesis, X-ray crystal structure determination, IR spectroscopy, DFT calculation

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