Self-Assembly of Triple Helical and meso-Helical Cylindrical Arrays Tunable by Bis-Tripodal Coordination Converters

The synergistic interplay of coordination and hydrogen-bonding interactions leads to assembly of isomorphous compounds of the general formula [Ln(ntb)(2)](ClO4)(3) center dot (BDA4BPy)(3) center dot 2MeCN}(infinity) (Ln = La, Sm and Pr, ntb = tris(2-benzimidazoylmethyl)amine, and BDA4BPy = N-1,N-4-bis(pyridin-4-ylmethylene)-benzene-1,4-diamine), of which polymorphic crystals can be isolated in a different solvent system. In acetonitrile (MeCN) solution, the compounds crystallize as a red color (Ln = La, meso-1, Ln = Pr, meso-2), while in an acetonitrile-benzonitrile (MeCN-PhCN) mixture, yellow crystals are obtained (Ln = Pr, helical-2). The single-crystal X-ray diffraction analyses of these crystals reveal that the structures display similar cylindrical arrays containing polycompartmental cavities for guest inclusion. Occurrence of polymorphism is due to formation of helical and meso-helical arrays, giving rise to a way to tune the helicity through the solvent effects on the helix propensity of the bis-tripodal coordination converters.