Optical Activity and Dehydration-Driven Switching of Magnetic Properties in Enantiopure Cyanido-Bridged Co^II₃W^V₂ Trigonal Bipyramids

Abstract

The unique enantiopure {[Λ-Co(II)((R)-mpm)2]3[W(V)(CN)8]2}·9H2O [(R)-1] and {[Δ-Co(II)((S)-mpm)2]3[W(V)(CN)8]2}·9H2O [(S)-1], where mpm = α-methylpyridinemethanol, magnetic spongelike materials, crystallizing in the chiral P21 space group, are constructed of cyanido-bridged {Co3W2} trigonal bipyramids with three cis-[Co(II)(mpm)2(μ-NC)2] moieties in equatorial sites and two [W(V)(CN)8](3-) units in apical positions. The arrangement of {Co3W2} clusters in the crystal lattice is controlled by interactions with crystallization H2O molecules, resulting in two independent hydrogen-bonding systems: the first weaving along open channels in the a direction (weakly bonded H2O) and the second closed in the cages formed by the surrounding [W(CN)8](3-) and mpm fragments (strongly bonded H2O). The strong optical activity of (R)- and (S)-1 together with continuous chirality measure (CCM) analysis confirms the chirality transfer from enantiopure (R)- and (S)-mpm to [Co(mpm)2(μ-NC)2] units, a cyanido-bridged skeleton, and to the whole crystal lattice. Magnetic properties confronted with ab initio calculations prove the ferromagnetic couplings within Co(II)-NC-W(V) linkages inside {Co3W2} molecules, accompanied by weak antiferromagnetic intermolecular interactions. The reversible removal of weakly bonded H2O above 50 °C induces the structural phase transition 1 ⇄ 1deh and strongly affects the magnetic characteristics. The observed changes can be interpreted in terms of the combined effects of the decreasing strength of ferromagnetic Co(II)-W(V) coupling and the increasing role of antiferromagnetic intermolecular correlation, both connected with dehydration-induced structural modifications in the clusters' core and supramolecular network of 1.

Tuning of High Spin Ground State and Slow Magnetic Relaxation within Trimetallic Cyanide‐Bridged {NiIIxCoII9−x[WV(CN)8]6} and {MnIIxCoII9−x[WV(CN)8]6} Clusters

“…Upon cooling from room temperature, all curves increase slowly down to 100 K and then much more abruptly to reach a rather sharp maximum of 75–95 cm 3 ⋅K mol −1 located between 8–12 K. With larger amounts of Ni in the sample, the sharp increase begins at slightly higher temperatures. This indicates the domination of ferromagnetic (F) interactions in all clusters, in agreement with the literature data for 15‐nuclear clusters and other related cyanide‐bridged systems . The values of the χT product read at T= 8 K ( H dc =1 kOe) are slightly smaller than the values of Curie constants, C , expected for the congeners in the series, calculated using the relevant spin in the ground state S gr and the effective Landé factors g eff (Figure a bottom and Table S6) The values of S gr were estimated by the sum of total spin of all W, Co and Ni centres along the backbone, assuming the ferromagnetic W−Co and W−Ni interactions, whereas the effective values of g eff factors were approximated by weighting the sum of g Ni =2.2, g W =2 and g Co =4.33, according to the number of the relevant centres in a given solid‐solution.…”

Tuning of Charge Transfer Assisted Phase Transition and Slow Magnetic Relaxation Functionalities in {Fe9–xCox[W(CN)8]6} (x = 0–9) Molecular Solid Solution

“…10 K. For 6 – 8 the χT signals increase monotonically, and show that the maximum increases with growing x . The appearance of the maximum is reminiscent of the ferromagnetic interaction HS Co II –W V observed in {Co 9 W 6 } clusters, , and other polynuclear Co II -[W V (CN) 8 ] 3– assemblies. , The overall gradual rise of the χT ( T ) signals at low temperatures is confirmed by isothermal M ( H ) curves measured at 1.8 K (Figure S11). They could be divided into two sets: those for the 5 – 9 solids start to saturate at lower values of the magnetic field, and reach higher values of magnetization compared to those of 0 – 4 .…”

In Situ Ligand Transformation for Two-Step Spin Crossover in FeII[MIV(CN)8]4– (M = Mo, Nb) Cyanido-Bridged Frameworks

“…45−47 These large cyanide metal complexes are useful in construction of functional moleculebased materials, 47−50 especially molecular magnets combining magnetic phenomena (spin ordering, slow magnetic relaxation, etc.) with extra functionalities, including luminescence, 51,52 optical activity, 53,54 second harmonic generation, 55 and proton conductivity. 56 [M(CN) 8 ]-based heterometallic frameworks have been fruitfully used for synthesis of molecule-based switches, exploring magnetic sponge-like behavior, thermo-or photoswitchable charge-transfer phase transitions, and photoinduced spin switching of [Mo/W(CN) 8 ] 4− ions.…”

“…Octacyanidometallates [M IV/V (CN) 8 ] 4–/3– (M = Mo, W, Re, Nb) are promising prerequisites for SCO materials because they offer up to eight cyanide bridges, resulting in a diversity of coordination topologies. − These large cyanide metal complexes are useful in construction of functional molecule-based materials, − especially molecular magnets combining magnetic phenomena (spin ordering, slow magnetic relaxation, etc.) with extra functionalities, including luminescence, , optical activity, , second harmonic generation, and proton conductivity . [M­(CN) 8 ]-based heterometallic frameworks have been fruitfully used for synthesis of molecule-based switches, exploring magnetic sponge-like behavior, thermo- or photoswitchable charge-transfer phase transitions, and photoinduced spin switching of [Mo/W­(CN) 8 ] 4– ions. − The [M­(CN) 8 ] n − building blocks have been also employed in the preparation of SCO materials based on Fe II . ,− The best results were found for the relatively rare, paramagnetic [Nb IV (CN) 8 ] 4– ion, which together with Fe II produced a series of tetragonal 3-D coordination networks, {[Fe II (L) 4 ] 2 [Nb IV (CN) 8 ]}· n (solvent) (L = pyridine derivatives or pyrazole). − They enabled the unique discoveries of a light-induced SCO magnet, pressure-induced SCO-based photomagnetism, and the 90° photoswitching of second harmonic light in a chiral SCO photomagnet .…”