The sol–gel method is employed for producing high surface area silica nanoparticles from a cheap precursor, that is water glass (sodium silicate). To design the experiments systematically, the response surface method (RSM) combined with the central composite design (CCD) approach is used. Four major factors including the concentration of sodium silicate solution, solution pH, reaction temperature and reaction time are identified as the major controlling parameters and the particle surface area is considered as the response or the output parameter. A total of 31 experiments are designated by the CCD. The experiments are conducted at a centre point chosen based on experience and at its vicinity to investigate how the response changes as the factors change. Nanoparticles with a surface area as high as 630 m2/g and a particle size as low as 8 nm are produced at the optimum parameters of sodium silicate concentration of 1.5 × 10−4 g/L, pH of 4, a reaction temperature of 25°C and a reaction time of 1.5 h. A regression analysis is performed on the experimental data and a correlation is obtained that may be used to predict the particle surface area and investigate the effect of varying the factors on the response. Within the range of parameters studied here, it is found that the solution pH and then the process temperature have a profound effect on the surface area and concentration and reaction time have a moderate effect. An increase of the solution pH from 4 to higher values results in a rapid drop in the particle surface area.

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The title polymeric compound {(C3H12N2)[Cu(C7H3NO4)2]·3H2O}n or {(pnH2)[Cu(py-2,3-dc)2]·3H2O}n (pn is propane-1,3-diamine and py-2,3-dcH2 is pyridine-2,3-dicarboxylic acid), was synthesized by reaction of copper(II) chloride dihydrate with a proton-transfer compound, propane-1,3-diammonium pyridine-2,3-dicarboxyl­ate or (pnH2)(py-2,3-dc), in aqueous solution. The anion is a six-coordinate complex (site symmetry ), with a distorted octa­hedral geometry around CuII, consisting of two bidentate pyridine-2,3-dicarboxyl­ate groups and two O atoms of bridging ligands from (py-2,3-dc)2− fragments, which are located in trans positions. The (pnH2)2+ cation is disordered over two sites by the center of inversion. Inter­molecular hydrogen bonds, π–π [centroid–centroid distances of 3.539 (3) Å] and C—O⋯π stacking inter­actions [O⋯Cg = 3.240 (5) Å; Cg is the center of the pyridine ring], connect the various components into a supra­molecular structure.

The title polymeric compound, [Cd(C7H3NO4)(H2O)3]n or [Cd(py-2,3-dc)(H2O)3]n, where py-2,3-dcH2 is pyridine-2,3-dicarboxylic acid, was obtained by the reaction of cadmium(II) nitrate hexa­hydrate with (pipzH2)(py-2,3-dc) as a proton-transfer compound in aqueous solution (pipz is piperazine). The mol­ecular structure shows that only the anionic fragment of the starting proton-transfer compound is present in the complex, while the (pipzH2)2+ dication has been lost. Each (py-2,3-dc)2− ligand bridges two CdII atoms in two different coordination modes, i.e. one end acts as a monodentate and the other end as a bidentate ligand. The three remaining coordination sites on the metal center are occupied by water mol­ecules. The geometric arrangement of the six donor atoms around the CdII atom is distorted octa­hedral. In the crystal structure, O—H⋯O and C—H⋯O hydrogen bonds play an important role in stabilizing the supra­molecular structure.

Novel metal organic frameworks including {(pipzH 2 )[Mn(py-2,3-dc) 2 ]·7.75H 2 O} n , 1, {(pipzH 2 )[Zn(py-2,3-dc) 2 ]·4H 2 O} n , 2, [Cd(py-2,3-dc)(H 2 O) 3 ] n , 3 and {(pipzH 2 )[Hg 4 Cl 10 ]} n , 4, in which pipz is piperazine and py-2,3-dcH 2 is pyridine-2,3-dicarboxylic acid were synthesized applying a proton transfer ion pair i.e. (pipzH 2 )(py-2,3-dcH) 2 and corresponding metallic salts and studied by IR, 1 H NMR, 13 C NMR spectroscopy and single crystal X-ray diffractometry. The space group of compounds 1 and 4 are P2 1 /c and C2/c of monoclinic system, respectively. The crystal dimensions are a = 20.108(2) Å, b = 19.910(2) Å, c = 12.997(1) Å, ȕ = 94.354(2)Û for 1 and a = 15.940(1) Å, b = 11.2690(9) Å, c = 11.1307(9) Å, ȕ = 90.685(2)Û for 4. The crystal structures of 2 and 3 have been reported previously. However, their solution studies are discussed here. The compounds had all polymeric structures. Although Zn II , Cd II and Hg II were elements of the same group, their behavior against the ion pair was essentially different. Various supramolecular interactions mainly hydrogen bonds of the type O-H···O, N-H···O, C-H···O, N-H···Cl and C-H···Cl were observed in the structures. There was an unusual and huge water cluster in the structure of compound 1. The solution states of compounds 1-4 were studied and reported. The protonation constants of pipz and py-2,3-dc, the py-2,3-dc/pipz proton transfer equilibrium constants and stoichiometry and stability of the system with Mn 2+ , Zn 2+ , Cd 2+ and Hg 2+ ions in aqueous solution were investigated by potentiometric pH titrations.