Guest driven self-assembly of a rectangular box from methylaquacobaloxime and 4,4′-biphenyldiboronic acid

We described the guest-induced synthesis of a rectangular host derived from methylaquacobaloxime CH3Co(dmgH)2H2O and 4,4′-biphenyldiboronic acid containing 4,4′-bipyridine (bipy) molecule as guest. The assembly, monitored by a time dependent 1H NMR experiment, showed that the guest thermodynamically drives the organization of the host. The structural characterization of the complex evidenced a centrosymmetric rectangular box having two biphenyldiboronate units and a central 4,4′-bipyridine spacer connecting the cobaloxime units (1). The spacers have coplanar rings, being negligible the tilt angle around the central C–C bond. The molecular structure of 1 and of the dinuclear complex [CH3Co(dmgH)2]2(bipy) indicates close comparable intermetallic distance for the rigid bipy bridge and a coplanar arrangement of the cobaloxime moieties that facilitates the formation of the molecular box. The other tested ditopic ligands L (α,α′-diamino-p-xylene and 1,6-diaminohexane) used in this study allowed only a partial assembly. These derivatives and the related dinuclear complexes [CH3Co(dmgH)2]2(L), which were synthesized with the aim to obtain further insights about the formation of the molecular boxes, were also characterized by X-ray structural analysis. The structures of [CH3Co(dmgH)2]2(L), beside the expected flexibility of L, indicate not facing cobaloxime moieties. CV measurements suggest the formation of dinuclear non organometallic Co(II) and Co(I) species after the first reduction for all the dinuclear compounds that are stable in solution. For 1 no electronic coupling is shown, in spite of coplanar conformation of the 4,4′-bipyridine rings.