CoII single-ion magnet and its multi-dimensional aggregations: Influence of the structural rigidity on magnetic relaxation process

Two CoII-based complexes, {[Co(dps)2(N3)2]∙H2O}n (1) and [Co(dps)2(N3)2]n (2), show a 1D chain and a 3D network, respectively. The central CoII ions in the complexes have the same coordination environment with the [Co(dps)4(N3)2] unit. Although the differences in crystal parameters are nearly negligible, their magnetic properties are very different. AC susceptibility data show that 1 behaves as a typical field-induced single-ion magnet (SIM) with the out-of-phase (χM'') signals, while 2 shows ac signals of χM'' without peaks even under applied dc filed within our measurement window. Far-IR magneto-spectra (FIRMS) show strong spin-phonon couplings at 0 T in 2, likely making the magnetic relaxation in 2 fast, while the couplings are negligible in 1. Small spin-phonon coupling in 1 likely leads to slower magnetic relaxation, making 1 a SIM. The difference in the properties is due to the structural rigidity of 2 in its 3D network, leading to stronger spin-phonon coupling. Combined high-field EPR (HF-EPR) and FIRMS studies give spin-Hamiltonian parameters, including D = 64.0(9) cm-1, |E| = 15.7(2) cm-1 for 1 and D = 80.0(2) cm-1, |E| = 19.0(1) cm-1 for 2.