Chirality- and Threefold-Symmetry-Directed Assembly of Homochiral Octupolar Metal−Organoboron Frameworks

Homochiral octupolar metal−organoboron frameworks with the general formula [M2L(OH)(MeOH)]·3H2O [M = Co (1), Mn (2), Ni (3), Cu (4), Zn (5), Cd (6)] have been constructed from racemic C3-symmetric tris(4-benzoic acid)tridurylborane and the divalent metal ions. Compounds 1−6 are isostructural and crystallize in the chiral cubic space group F432, and they adopt an eightfold-interpenetrating (10,3)-a network formed by linking bimetal building blocks with three bidentate carboxylate groups of bridging Λ-L ligands. Bulk crystals of each of the six compounds are not a racemic mixture, and their optical activity and enantiomeric nature were demonstrated by solid-state circular dichroism spectra. Consistent with their polar structures, the colorless compounds 5 and 6 exhibit powder second harmonic generation intensities 3−4 times higher than that of potassium dihydrogen phosphate, making them, to the best of our knowledge, the first two examples of NLO-active, homochiral octupolar metal−organic solids.