Impact of 3d Metal Ions on the Magnetic Dynamics in Isostructural Tetranuclear Butterfly {Ni<sub>2</sub><sup>II</sup>Dy<sub>2</sub><sup>III</sup>} and {Co<sub>2</sub><sup>II</sup>Dy<sub>2</sub><sup>III</sup>} Complexes
Narayan Ch. Jana, Albert Escuer, Radovan Herchel, Joan Serra, Rakhi Nandy, Anangamohan Panja
Abstract
This paper describes the synthesis, structures, and magnetic properties of four isostructural butterfly-type heterometallic tetranuclear 3d-4f complexes, [Ni 2 Dy 2 (HL 1 ) 2 (μ 3 –OH) 2 (piv) 6 ]·2CH 3 CN ( 1 ), [Ni 2 Dy 2 (HL 2 ) 2 (μ 3 –OH) 2 (piv) 6 ]·2CH 3 CN ( 2 ), [Co 2 Dy 2 (HL 1 ) 2 (μ 3 –OH) 2 (piv) 6 ]·2H 2 O ( 3 ), and [Co 2 Dy 2 (HL 2 ) 2 (μ 3 –OH) 2 (piv) 6 ]·2CH 3 CN ( 4 ), derived from two closely related Schiff base ligands H 2 L 1 and H 2 L 2 in the presence of pivalate (piv) ions. X-ray crystallographic studies of 1 – 4 revealed that all of the complexes are constructed with a type-II butterfly core in which Dy III ions are located at body positions, while the 3d metal ions (Ni II and Co II ) occupy the wingtip positions. It is noteworthy that all reported systems containing Ni II and Co II have been isolated as type-I butterfly structures, with only one report each on the Ni 2 II Dy 2 III and Co 2 II Dy 2 III type-II butterfly core systems, which have been both structurally and magnetically characterized. Direct current magnetic susceptibility measurements performed on 1 – 4 revealed that the susceptibility response is dominated by the depopulation of Stark sublevels of the Dy III ions and the ZFS of the Co II cations in the case of 3 and 4 and the weak intramolecular superexchange interactions have been calculated by means of CASSCF and CASSCF/NEVPT2 calculations. Dynamic magnetic studies revealed that only Co II analogues ( 3 and 4 ) display single-molecule magnet behaviors in which the additional anisotropy of the Co II centers is responsible for the occurrence of the out-of-phase response in contrast to 1 and 2 with poorly anisotropic Ni II cations.