Abstract
Adduct of mononuclear and dinuclear citrate zinc complex [Zn(Hcit)(phen)(H(2)O)][Zn(2)(Hcit)(phen)(2)(H(2)O)(3)]·13.5H(2)O (1) and its aggregate [Zn(3)(Hcit)(2)(phen)(4)](n)·14nH(2)O (2) (H(4)cit = citric acid, phen = 1,10-phenanthroline) were synthesized in weak acidic solutions. The former was obtained from the reaction of zinc nitrate, citric acid and phenanthroline in a molar ratio of 3 : 2 : 3, while a slightly excess of phenanthroline results in the formation of the polymeric product 2 in a molar ratio of 3 : 2 : 4. Transformation of 1 to 2 was finished by the reaction of 1 with an equimolar of phenanthroline in 72% yield. Reverse conversion of 2 to 1 is obtained in 77% yield, showing an equilibrium between 1 and 2. Neutral compound 1 consists of one monomeric anionic unit [Zn(Hcit)(phen)(H(2)O)](-) and one dimeric cationic unit [Zn(2)(Hcit)(phen)(2)(H(2)O)(3)](+) that connect each other by strong hydrogen bonds [O6⋯O4w 2.636(2); O7⋯O3w 2.630(3) Å]. In 2, the citrate ligand links each trinuclear unit [Zn(3)(Hcit)(2)(phen)(4)] to generate an infinite 1D chain that extents into a 3D supramolecular structure by intra- and inter-molecular hydrogen bonds. Moreover, 1 and 2 exhibit strong fluorescence at room temperature.