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

The unique enantiopure {[Λ-CoII(­(R)-mpm)2]3[WV(CN)8]2}·9H2O [(R)-1] and {[Δ-CoII((S)-mpm)2]3[WV(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-[CoII(mpm)2(μ-NC)2] moieties in equatorial sites and two [WV(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 CoII–NC–WV 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 CoII–WV 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.