ABSTRACT
Five Pb(ii)-imidazolium carboxylate coordination assemblies with novel structural motifs were derived from the reaction between the corresponding flexible, semi flexible or rigid imidazolium carboxylic acid ligands and lead nitrate. The imidazolium linker present in these molecules likely plays a triple role such as the counter ion to balance the metal charge, the ligand being an integral part of the final product and the catalyst facilitating carbon-carbon bond formation reaction. These lead-imidazolium coordination assemblies exhibit, variable chemical and thermal stabilities, as well as catalytic activity. These newly prepared catalysts are highly active towards benzoin condensation reactions with good functional group tolerance.
ABSTRACT
Despite the popularity and versatility of transition-metalazolium carboxylate coordination polymers, there are very few examples of group 2 complexes supported by azolium carboxylate ligands in the literature, and there are none featuring luminescent calcium azolium carboxylates. New ionic calcium coordination networks, {[Ca2(L(1))2(H2O)4](Br)4·6H2O}∞ (1), {[(L(3))2Ca(H2O)2]2(Br)2}∞ (3), {[(L(4))2Ca(H2O)2]2(Br)2}∞ (4), and {[(L(5))2Ca3(Na)(H2O)9(Cl)](Br)6·2H2O}∞ (5) along with binuclear {[Ca2(L(2))2(H2O)9](Br)4·4H2O} (2), and trinuclear {[(L(6))2Ca3(H2O)9](Br)6} (6) were isolated from the reaction between the corresponding azolium carboxylates and calcium carbonate in aqueous solution. 16 were characterized by FT-IR, NMR, TGA, UV-vis, fluorescence and single crystal X-ray diffraction techniques. Interestingly, the first tetra-cationic binuclear calcium 2 was isolated using L(2)H2Br2 and hexa-cationic trinuclear calcium 6 was isolated using L(6)H3Br3. The 3D coordination polymers 1 and 4 were derived with the help of L(1)H2Br2 and L(4)H2Br2, respectively, through Br···H hydrogen bonding. The 3D MOF 3 with rhomboidal channels was constructed using L(3)H2Br2, where the channel size is about 4.8 × 2.9 nm. 5 was isolated as a rare 1D coordination polymer. The choice of azolium carboxylates in these solids not only changes the topology of the network but also affects the chemistry exhibited by the network. Calcium azolium carboxylate assemblies 14 and 6 exhibit interesting solid-state photoluminescence properties, driven by azolium carboxylate ligands. Variation of the bridging chromophore produced significant effects on the fluorescence properties. 14 and 6 represent the first examples of luminescent calcium azolium carboxylate complexes. As can be seen in the six metalorganic assemblies presented in this report, a combination of carboxylate groups and steric hindrance affects the topology and physical properties of the resultant solids.
ABSTRACT
The new copper dimer [LCu(DMF)]2(NO3)4(H2O)(DMF)2 (4), where L = [{1,1'-(CH2)2-C14H8)-3,3'-(CH2CO2)2}{(HCN)2CH}], and porous coordination polymers [{L2Cu(OH2)2}2Br2]x (5) and [{L2Zn(OH2)2}2Br2]x (6) have been isolated from reactions of luminescent imidazolium carboxylate ligand, LH2Br2 (3) and the corresponding metal precursors. The reaction between Cu(NO3)2·3H2O and LH2Br2 (3) in DMF at 100 °C yielded bluish green crystals of tetracationic discrete copper dimer 4, the structure of which contains a rare tetracationic [(DMF)Cu(ii)]2 dimer unit that is bridged by four carboxylates of two L in a "paddle-wheel" structure. When the reaction was carried out in the presence of a water-ethanol-methanol mixture, light green crystals of 5 were obtained. Molecule 5 comprises two-dimensional (2D) porous coordination polymeric sheets consisting of unique symmetrical dinuclear [(C(O)O)Cu(OH2)2(O(O)C)2]2 building blocks, which are connected by imidazolium anthracene spacers. The infinite 2D porous coordination polymeric sheets are further linked by significant intermolecular hydrogen-bonding interactions by bromide anions to form a three-dimensional supramolecular framework. Interestingly, the reaction between zinc dust and LH2Br2 (3) in H2O at room temperature gave similar structural features to those in 5, though they differ in terms of C-O bond distances and M-O-C angles. The solution-state UV-visible absorption spectra of 2-6 in water exhibits the comparable absorption pattern with decrease in the intensity of absorption from 5, 4, 3, 6 and 2, while the solid-state UV-visible absorption spectra of 2-6 are significantly different from the solution-state UV-visible absorption spectra. The considerable change in the fluorescent emission was observed upon complexation of 3 with corresponding metal precursors and the fluorescent emission was shifted towards the red region in the order of 2, 3, 6, 4 and 5 in water.
