Crystal Structure, Vibrational Spectroscopic Characterization, and Bond Valence Sum (BVS) Analysis of a Copper(II)-H2EDTA-Based Coordination Polymer [Cu(H2EDTA)]n·H2O

Abstract

A new copper (II) coordination compound, [Cu (H₂EDTA)]·H₂O, was synthesized via slow evaporation from a mixed aqueous-DMF medium under controlled pH conditions. Single-crystal X-ray diffraction analysis revealed a six-coordinate copper (II) center surrounded by four oxygen and two nitrogen donor atoms from a partially deprotonated H₂EDTA ligand, forming a distorted octahedral geometry. The crystallographic results confirmed the chelation of both carboxylate oxygen and amine nitrogen atoms to the Cu (II) ion.

Fourier-transform infrared (FT-IR) and Raman spectroscopic studies supported the coordination mode by identifying characteristic asymmetric and symmetric stretching vibrations of coordinated carboxylate groups. The observed Δν (ν_asym-ν_sym) values indicate predominantly bidentate coordination of the carboxylate moieties. Metal-ligand vibrations in the low-frequency region further confirmed Cu-O and Cu-N bond formation.

 Bond Valence Sum (BVS) analysis yielded a value of 2.07, consistent with the +2 oxidation state of copper and supporting the structural data obtained from single-crystal analysis. Minor deviation from the ideal value reflects slight geometric distortion within the coordination sphere. Thermal behavior examined by TG-DTA demonstrated the presence of lattice water molecules and indicated stepwise decomposition of the coordinated framework.

The combined crystallographic and spectroscopic investigations provide a comprehensive understanding of the coordination environment and bonding characteristics of the Cu(II)- H₂EDTA system, contributing to the structural chemistry of EDTA-based copper complexes.