Structural, spectroscopic, theoretical, and magnetic investigations of a novel cubane-like tetranuclear copper(II)-hydrazone complex.

This study details the synthesis of a novel ligand, (E)-5-chloro-N'-(2-hydroxy-3-methoxybenzylidene) thiophene-2-carbohydrazide ligand (for short, H2L), and its tetranuclear Cu(II) complex (Cu4L4), together with their X-ray crystal structures and the magnetic properties and EPR spectra of Cu4L4 within the 4-300 K temperature range. Furthermore, we report the spectroscopic characterization (FTIR and UV-Vis) of the compounds and perform a Hirshfeld analysis of their non-covalent interactions, along with certain quantum chemical calculations. H2L crystallizes in the monoclinic space group Cc with Z = 8 molecules per unit cell and the Cu4L4 complex crystallizes in the tetragonal space group P41/a with Z = 4. The complex is at a crystal site of S4 symmetry, conforming to a cubane-like Cu4O4 core. The main pathway for exchange interaction between neighboring copper ions in the core involves a relatively large overlap of the copper d(x2 - y2) electron ground state orbital with the sp2 lone-pair lobes of the bridging oxygen. Magnetic susceptibility in the 5-300 K range, mainly interpreted with the exchange Hamiltonian Ĥex = J(Ŝ1·Ŝ2 + Ŝ2·Ŝ3 + Ŝ3·Ŝ4 + Ŝ4·Ŝ1), confirms the expected relatively strong antiferromagnetic (AF) character of the complex (J = -61.5(1) cm-1). The powder room temperature Q-band EPR spectrum shows a very broad band (ΔBpp = 1980 Gauss) corresponding to a gyromagnetic g-factor of 2.13. The band intensity decreases sharply with temperature, as expected for a Cu(II) tetramer with a well isolated spin singlet (S = 0) ground state.