A flame retardant-hardener for epoxy resins: Synthesis, structural, and DFT studies ofthe $[Cu(H_2NC_2H_4NH_2)_2(H_2O)Cl]Cl$ complex

Abstract

The aqua-bis(ethylenediamine)-chloro-copper(II) chloride complex, $[Cu(en)_2 (H_2 O)(Cl)]Cl$ (1), was synthesized by direct interaction of $CuCl_2 ×2H_2 O$ 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 $[Cu(en)_2 (H_2 O)(Cl)]^{+}$ discrete cations, whose $Cu^{2+}$ 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 $–NH_2$ 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 $Cu(II)–(H_2 NC_2 H4 NH_2 )$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.