Conjunction of Chirality and Slow Magnetic Relaxation in the Supramolecular Network Constructed of Crossed Cyano-Bridged Co^II–W^V Molecular Chains

Abstract

The addition of chiral 2,2'-(2,6-pyridinediyl)bis(4-isopropyl-2-oxazoline) (iPr-Pybox) to a self-assembled Co(II)–[W(V)(CN)(8)] magnetic system gives two enantiomorphic cyano-bridged chains, {[Co(II)((S,S)-iPr-Pybox)(MeOH)](3)[W(V)(CN)(8)](2)·5.5MeOH·0.5H(2)O}(n) (1-SS) and {[Co(II)((R,R)-iPr-Pybox) (MeOH)](3)[W(V)(CN)(8)](2)·5.5MeOH·0.5H(2)O}(n) (1-RR). Both compounds crystallize with a structure containing a unique crossed arrangement of one-dimensional chains that form a microporous supramolecular network with large channels (14.9 Å × 15.1 Å × 15.3 Å) filled with methanol. The investigated materials exhibited optical chirality, as confirmed by natural circular dichroism and UV-vis absorption spectra. 1-(SS) and 1-(RR) are paramagnets with cyano-mediated Co(II)-W(V) magnetic couplings that lead to a specific spin arrangement with half of the W(V) ions coupled ferromagnetically with their Co(II) neighbors and the other half coupled antiferromagnetically. Significant magnetic anisotropy with the easy axis along the [101] direction was confirmed by single-crystal magnetic studies and can be explained by the single-ion anisotropy of elongated octahedral Co(II) sites. Below 3 K, the frequency-dependent χ(M)"(T) signal indicated slow magnetic relaxation characteristic of single-chain magnets.

Optical Activity and Dehydration-Driven Switching of Magnetic Properties in Enantiopure Cyanido-Bridged CoII3WV2 Trigonal Bipyramids

“…Such different nature of magnetic interactions was previously suggested for other cyanido-mediated Co II −W V magnetic systems, consisting also of three slightly different octahedral Co sites. 5 However, the fitted parameters J 1 and J 3 are larger than those found for similar cyanide-bridged W−Co com- pounds. 68,69 We suggest that the relatively large values of J 1 and J 3 could appear because of the large ZFS on Co sites.…”

“…65,66 The magnetization of 1 measured as a function of the external magnetic field at 2 K does not saturate to 50 kOe, reaching a value of 8.0 μ B , but tends roughly in an asymptotic manner limit of 8.5 μ B , which is expected for ferromagnetic alignment of Co II and W V magnetic moments within the {Co II 3 W V 2 } units ( Figure 6b). 5,33,67 There is no detectable signal in the out-of-phase magnetic susceptibility above 1.8 K precluding the SMM behavior of 1.…”

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…Consequently, hexa-coordinated high-spin Co II complexes appear to be promising building units for constructing nano-magnets. Therefore, octahedral high-spin Co II complexes are employed extensively to provide strong magnetic anisotropy even if it is not necessarily Ising-type [2,163,220,[262][263][264][265][266][267][268][269]. A well-known example is the first SCM reported by Sessoli et al, which is a chain based on hexacoordinated high-spin [Co II (hfac) 2 (O) 2 ] units linked by organic radicals [270].…”

Neutral Low-Dimensional Assemblies of a Mn(III) Schiff Base Complex and Octacyanotungstate(V): Synthesis, Characterization, and Magnetic Properties

“…Indeed, at low temperatures the relaxation dynamics of SCMs are typically described by the finite-length model [11]. Cyano-bridged metal assemblies have provided a large number of compounds with SMM [31][32][33][34][35][36][37][38] and SCM behaviors [39][40][41][42][43][44][45][46][47][48]. The larger part of these materials comprise 3d metal ions as the core magnetic units.…”