Pentacoordinate cobalt(II) complexes with neutral tripodal N-donor ligands: Zero-field splitting for a distorted trigonal bipyramidal geometry

Abstract A series of pentacoordinate Co(II) complexes of the composition [Co(bpdmpz)Cl]ClO 4 ( 1 ), [Co(bpdmpz)Cl]PF 6 ( 2 ), [Co(bdmpzp)Cl]ClO 4 ·H 2 O ( 3 ), [Co(bdmpzp)Cl]PF 6 ( 4 ), [Co(tdmpza)Cl]ClO 4 (5) and [Co(tdmpza)Cl]PF 6 (6) (bpdmpz = bis[(2- pyridylmethyl )-( di (3,5- dimethyl -1 H - pyrazolyl ) methyl )]amine, bdmpzp = bis[( di (3,5- dimethyl -1 H - pyrazolyl ) methyl ))-(2- pyridylmethyl )]amine and tdmpza = tris[ di (3,5- dimethyl -1 H - pyrazolyl ) methyl )]amine) was prepared and thoroughly characterized. Single-crystal X-ray analyses of complexes 1 – 5 revealed that they possess very close molecular structures with a distorted trigonal bipyramidal geometry. The static DC magnetic experiments revealed the ZFS parameters pointing out small magnetic anisotropy (with the | D | values lying in a relative narrow range of 4.4–5.7 cm −1 ) and rhombicity (with the E / D parameters in the range of 0–0.26). The dynamic magnetic data revealed that AC susceptibility is temperature and frequency-dependent for 1 , 2 and 3 , and thus, these compounds belong to a group of field-induced pentacoordinate Co(II) single-molecule magnets (SMMs). The evaluation of magnetic data was also supported by the CASSCF/NEVPT2 calculations.