Two Acentric Mononuclear Molecular Complexes with Unusual Magnetic and Ferroelectric Properties

Two acentric, i.e., noncentrosymmetric, mononuclear complexes, Co­(5-ATZ)4Cl2, 1, and Cu­(5-ATZ)4Cl2, 2, where 5-ATZ is the monodentate 5-amino-1-H-tetrazole ligand, have been prepared and characterized. Both complexes crystallize in the tetragonal system with the P4nc space group, a member of the polar noncentrosymmetric 4mm class, and thus both 1 and 2 can exhibit ferroelectric and nonlinear optical properties. Magnetic studies indicate that 1 is a paramagnetic high-spin cobalt­(II) complex with a rather extensive spin–orbit coupling, modeled as a zero-field splitting parameter, D, of ±91(3) cm–1 and with very weak long-range antiferromagnetic exchange interactions. Direct current (dc) and ac magnetic studies indicate that 2 is a paramagnetic copper­(II) complex that exhibits weak ferromagnetic exchange interactions below 15 K. Both 1 and 2 exhibit ferroelectric hysteresis loops at room temperature with remanent polarizations of 0.015 μC/cm2 and coercive electric fields of 5.5 and 5.7 kV/cm, respectively.