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

Cyanide-bridged {MnII9[WV(CN)8]6} clusters with the ground state spin SSG = 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, {MnII9(4,4′-dpds)4(MeOH)16[WV(CN)8]6}·12MeOH (1). The intercluster contacts are controlled by the bridging MnII–(4,4′-dpds)–MnII coordination modes and direct hydrogen bonds W–CN···HOMeOH–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 WV–CN–MnII 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 Jap = −8.0 cm–1, Jeq = −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 gW = gMn = 2.0 parameter set. Continuing this approach, we simulated the magnetocaloric effect (MCE) and compared it to the experimental result of ΔSmax = 7.31 J kg–1 K–1 for fields >5.0 T. Second, two relaxation processes were induced by a relatively weak magnetic field, Hdc = 500 Oe, at an Hac 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 τslow at tenths of a second being temperature independent and the faster process being 3–5 orders of magnitude faster with the effective energy barrier Δeff = 17.6 K. These dynamic properties are surprising, since the compound is made up of isotropic high-spin molecules.

Hali tarjima qilinmagan