Unusually Strong Interactions Mediated by Both π—π Stacking and CH—π Interactions Present in the Dimer of Nickel(Ⅱ) Complex Coordinated with n-Butyl-Substituted Salen

摘要

It is becoming one of the major concerns of chemists to explore the applications of metal complexes as molecular devices. Among the materials under investigation, liquid crystalline complexes are one of the major targets. We reported that the crystalline nickel(Ⅱ) salen complexes with long alkyl side chains (dodecyl and hexyl) exhibit peculiar double-melting behavior. Upon heating, the crystal (K) changes first into the smectic E (S_E) liquid crystalline phase, then to the smectic A (S_A) phase, and finally to the isotropic liquid (IL) phase. Another striking feature of this double melting is that the second phase transition is accompanied by a shrinkage of layers by 5 A. We recently succeeded in solving the crystal structure of the dibutyl-substituted [Ni(salen)] complex {abbreviated [Ni(C4-salen)]} and found that, in the crystal, the complex molecules stack in the form of dimers with both π—π stacking and CH—π interactions. Such a structure is totally different from other dimer structures reported for the complexes of salen derivatives or analogous ligands. This is probably the first example of dimer formation mediated by both π-π stacking and CH-π interactions for such complexes. Further, this structural feature clarifies the mechanism of the "double-melting" phenomenon observed for the dodecyl- and hexyl-substituted analogues.