title: Metal-organic frameworks constructed from monomeric, dimeric and trimeric phenanthroline citrate zinc building units.
abstract: Adduct of mononuclear and dinuclear citrate zinc complex [Zn(Hcit)(phen)(H2O)][Zn2(Hcit)(phen)2(H2O)3]·13.5H2O (1) and its aggregate [Zn3(Hcit)2(phen)4]n·14nH2O (2) (H4cit = 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 product2in a molar ratio of 3 : 2 : 4. Transformation of1to2was finished by the reaction of1with an equimolar of phenanthroline in 72% yield. Reverse conversion of2to1is obtained in 77% yield, showing an equilibrium between1and2. Neutral compound1consists of one monomeric anionic unit [Zn(Hcit)(phen)(H2O)]-and one dimeric cationic unit [Zn2(Hcit)(phen)2(H2O)3]+that connect each other by strong hydrogen bonds [O6⋯O4w 2.636(2); O7⋯O3w 2.630(3) Å]. In2, the citrate ligand links each trinuclear unit [Zn3(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,1and2exhibit strong fluorescence at room temperature.
authors.affiliation: College of Chemistry and Chemical Engineering, State Key Laboratory of Physical Chemistry of Solid Surface, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, Xiamen University, Xiamen 361005, China.
authors.forename: Rong-Hua
authors.initials: RH
authors.lastname: Zhang
authors.forename: Wen-Sheng
authors.initials: WS
authors.lastname: Xia
authors.forename: Hong-Xin
authors.initials: HX
authors.lastname: Wang
authors.forename: Zhao-Hui
authors.initials: ZH
authors.lastname: Zhou
keywords: Citric acid; Crystal structure; Interconversion; Mixed ligands; Zinc