Double Magnetic Relaxation and Magnetocaloric Effect in the {Mn₉[W(CN)₈]₆(4,4'-dpds)₄} Cluster-Based Network

Cyanide-bridged {Mn^II₉[W^V(CN)₈]₆} clusters with the ground state spin S_SG = 39/2 were connected by a 4,4'-dipyridyl disulfide (4,4'-dpds) linker into 2-D double-connected coordination layers of the I⁰O² type, {Mn^II₉(4,4'-dpds)₄(MeOH)₁₆[W^V(CN)₈]₆}·12MeOH (1). The intercluster contacts are controlled by the bridging Mn^II-(4,4'-dpds)-Mn^II coordination modes and direct hydrogen bonds W-CN···HO_MeOH-Mn in three crystallographic directions, with the vertex-to-vertex contact unprecedented in {Mn₉W₆}-based networks dominating over the typical edge-to-edge contacts. The resulting 3D supramolecular network of high-spin clusters was subjected to a thorough magnetic characterization in context of two critical issues. First, the intracluster W^V-CN-Mn^II exchange coupling and intercluster interaction were successfully modeled through the combination of dc measurements, Quantum Monte Carlo simulations, and mean-field calculations, yielding a reasonable J_ap = -8.0 cm^-1, J_eq = -19.2 cm^-1 (related to apical and equatorial CN bridges, depending on the angle they form with the S₄ axis of dodecahedral [W(CN)₈]^3- units, respectively), and zJ' = 0.014 cm^-1 with the average g_W = g_Mn = 2.0 parameter set. Continuing this approach, we simulated the magnetocaloric effect (MCE) and compared it to the experimental result of ΔS^max = 7.31 J kg^-1 K^-1 for fields >5.0 T. Second, two relaxation processes were induced by a relatively weak magnetic field, H_dc = 500 Oe, at an H_ac field frequency range of up to 10 kHz, which are related to dipole-dipole interactions between high-spin (39/2) moieties. The observed relaxation times significantly differ from each other, the slow process with τ_slow at tenths of a second being temperature independent and the faster process being 3-5 orders of magnitude faster with the effective energy barrier Δ_eff = 17.6 K. These dynamic properties are surprising, since the compound is made up of isotropic high-spin molecules.