Rhenium(I) based irregular pentagonal-shaped metallacavitands

Neutral ditopic flexible N-donor ligands (L-n = bis(4-(naphtho[2,3-d]imidazol-1-ylmethyl)phenyl)methane, L-1 bis(4-(benzimidazol-1-ylmethyl)phenyl)methane, L-2 or bis(4-(2-nonylbenzimidazol-1-ylmethyl)phenyl)methane, L-3) possessing a bis(4-methylphenyl)methane spacer with two imidazolyl donor units were designed and synthesized. The ligands were utilized to develop metallacavitands analogous to irregular pentagonal-shaped metallacavitands with larger cavities. The metallacavitands 1-4 were assembled from Re-2(CO)(10), a rigid bis-chelating donor (1,4-dihydroxy-9,10-anthraquinone or chloranilic acid) and L(n)via a solvothermal approach. The ligands and the metallacavitands were characterized by analytical and spectroscopic methods. The molecular structures of 1 and 4 were further confirmed by single crystal X-ray diffraction analysis which revealed that a toluene molecule resides in the hydrophobic cavity. L-n and 1-4 are emissive in DMSO at room temperature. The internal cavity of the metallacavitand acts as a host for aromatic guest molecules. The host-guest interaction properties of 1 with anthracene, naphthalene, nitrobenzene, 2-nitrotoluene, 4-nitrotoluene and 2,4-dinitrotoluene were studied by an emission spectroscopic method.