| Abstract |
A series of 11 compounds, including alkali (Li, Na, K, Rb, Cs) and alkaline-earth (Mg, Ca, Sr, Ba) coordination polymers, transition- metal ( Cu, Cd) complexes, and the ammonium salt of 3,5-dimethylpyrazole-4-sulfonic acid (HL), were synthesized. Single crystals of HL center dot H2O, LiL(H2O), NaL-(H2O), RbL, CsL, CaL2(H2O), SrL2(H2O), BaL2(H2O), CuL2(H2O)(3)center dot 2.3H(2)O center dot 0.5(acetone), and CdL2(H2O)(3)center dot 2H(2)O were obtained from aqueous solutions either by evaporation or acetone vapor diffusion. Characterization by single-crystal X-ray diffraction reveals that the coordination compounds of L- (except Cu) possess alternating inorganic-organic layered structures, in which L- engages in extensive charge-assisted networks of H-bonding and aromatic interactions as well as metal coordination through the pyrazole N atom and/or the sulfonate O atom. A topological analysis and classification of underlying metal-organic or hydrogen-bonded networks uncover a number of distinct topological nets (3,5L2, hcb, 6,6L1, 3,5C1, 3,8L28, hex, and pcu). A thermogravimetric analysis shows that HL and NH4L are stable up to 285 and 90 degrees C, respectively, whereas the anhydrous metal compounds decompose above 200-230 degrees C. The pK(a) values of 3,5-dimethylpyrazole-4-sulfonic acid (HL) and pyrazole-4-sulfonic acid were determined by H-1 NMR titrations with H2SO4. Copper corrosion experiments indicate that 3,5-dimethylpyrazole-4-sulfonic acid (HL) is a better anticorrosion agent than the parent pyrazole-4-sulfonic acid at pH 4, whereas the coordination polymers of L- offer weaker corrosion protection in comparison to the corresponding pyrazole-4-sulfonate complexes. The latter result is corroborated by the less compact and less robust thin films formed by metal-L compounds, as indicated by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) measurements, and the weaker acidity of HL, which allows for easier protonation of the conjugate base L- in metal-L compounds. |
