Supramolecular host-guest systems of luminescent Zn(II) complexes with benzene, nitrobenzene, and ethanol: Selectivity of guest inclusion and solid-state fluorescence modulation studies

The luminescent Zn(II) complex [Zn(phen)(aba)(2)] (B) {phen = 1,10-phenanthroline, aba = 4-(dimethylamino)benzoate} crystallizes as [Zn(phen)(aba)(2)(H2O)] (B1) from moist solvents. Compound B shows high selectivity toward benzene in the presence of other organic guests in solution as well as in the vapor phase forming {[Zn(phen)(aba)(2)(H2O)]center dot 1/2C(6)H(6)}(n) (1). Compound 1 assumes a channel structure where benzene molecules are trapped in alternate channels via various supramolecular interactions. Compound B1, on the other hand, does not show any selectivity toward guest inclusion and readily assembles as {[Zn(phen)(aba)(2)(H2O)]center dot 2C(6)H(5)NO(2)}(n) (2) in the presence of nitrobenzene or as {[Zn(phen)(aba)(2)(H2O)]center dot 2C(2)H(5)OH}(n) (3) in the presence of ethanol. In 2, nitrobenzene molecules form zigzag tapes via C-H center dot center dot center dot O and C-H center dot center dot center dot pi interactions inside the channels, while the structure of 3 looks like a two-dimensional network with voids occupied by tetrameric ethanol clusters. The three structures exhibit significantly red-shifted emission in the solid state with respect to the parent complex. In the case of 1, the desorption and resorption of benzene are thermally reversible as monitored by X-ray powder diffraction.