LAUSR

The work in this report describes the syntheses, crystal structures, dc/ac magnetic behaviour, and theoretical calculations (both ab initio CASSCF and DFT) of three defect dicubane/planar butterfly type tetradysprosium(III) compounds of compositions [DyIII4L4(μ3-OH)2(carboxylate)2(dmf)2] (carboxylate = formate (1), acetate (2), propionate (3)), where H2L = 2-(2-hydroxy-3-ethoxybenzylideneamino)phenol. In the butterfly type structures, two DyIII centres (Dyb) occupy the body positions while two other (Dyw) units occupy the wing positions. SHAPE analyses reveal that the coordination geometries of the Dyb and Dyw centres, both octacoordinated, are triangular dodecahedron (TDD) and square antiprism (SAPR), respectively. Variable-temperature magnetic susceptibility measurements give an indication of weak antiferromagnetic interactions and variable-field magnetization measurements reveal strong anisotropy in all the three compounds. The variable-temperature/frequency in-phase/out-of-phase AC susceptibility data reveal that all these three compounds are SMMs with two relaxation channels under zero dc field; slow relaxation (SR) and fast relaxation (FR) processes could be assigned to the SAPR (Dyw) and TDD (Dyb) metal centres, respectively. The simulated Ueff and τ0 values are: 49.0 cm-1 and 1.76 × 10-7 s for 1, 30.3 cm-1 and 1.51 × 10-8 s for 2 and 23.4 cm-1 and 9.64 × 10-7 s for 3. Furthermore, ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations reveal that the ground state of DyIII centres are axial in nature with a dominating contribution from mJ = |±15/2>. The magnetization relaxation occurs via the first excited KD resulting in the large computed blocking barrier of Dyw (SAPR) centres compared to that of the Dyb (TDD) centres which corroborates the experimental measurements. The exchange parameters obtained from DFT calculations are generally in line with those obtained from the fitting of χMT vs. T in POLY_ANISO calculations. Interesting structural and magneto-structural correlations have been found, which are the major outcomes of this investigation.