Synthesis, crystal structure, magnetic properties and DFT calculations of a mononuclear copper(II) complex: Relevance of halogen bonding for magnetic interaction

The synthesis, crystal structure, magnetic properties and DFT calculations of a new mononuclear copper(II) complex containing a pyrazole-based ligand are reported. In the crystal structure of the [CuCl2L2] complex (L = Ethyl 5-amino-1-(4-methoxyphenyl)-1H-pyrazole-4-carboxylate), a network of hydrogen bonds connects the molecular units in the crystal packing. The magnetic studies revealed predominant antiferromagnetic interactions among molecular units. Since there are multiple intermolecular contacts that can act as pathway for magnetic interactions, DFT calculations revealed the fundamental role of N-H center dot center dot center dot Cl short intermolecular contacts in magnetic behavior. Supported by DFT calculation, the magnetic data above 7.0 K was modeled as a regular Heisenberg chain (H = -2J Sigma(n-1)(i-1) (S) over right arrow (Ai)center dot(S) over right arrow (Ai+1)) resulting in a weak magnetic coupling constant (J) of -2.6 cm(-1). Below this temperature, an unusual magnetic behavior for mononuclear copper(II) complexes was observed: divergence between zero-field cooled (ZFC) and field cooled (FC) magnetic susceptibilities and magnetic hysteresis cycles at low temperatures attributed to spin canting along the chain.