Layered Inorganic–Organic 3,5-Dimethylpyrazole-4-Sulfonate Films for Protection of Copper Surfaces against Corrosion

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, and CdL 2 (H 2 O) 3 •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 NH 4 L are stable up to 285 and 90 °C, respectively, whereas the anhydrous metal compounds decompose above 200−230 °C. The pK a values of 3,5-dimethylpyrazole-4-sulfonic acid (HL) and pyrazole-4-sulfonic acid were determined by 1 H NMR titrations with H 2 SO 4 . Copper corrosion experiments indicate that 3,5-dimethylpyrazole-4sulfonic 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.

Isostructural behaviour in ammonium and potassium salt forms of sulfonated azo dyes

“…The absorption correction was multi-scan for NH 4 1 (CrysAlis PRO; Rigaku OD, 2019) and K1 (SADABS; Bruker, 2012) the structure of sulfonated azo pigments has been to study systematically the structures of similarly functionalized, but easier to manipulate, dyes and then to cross-check any structure-to-property relationships identified against those pigment structures that are known (Kennedy et al, 2004(Kennedy et al, , 2009(Kennedy et al, , 2012. Ammonium salt forms of sulfonated azo colourants are sometimes used in preference to alkali-metal salts, either in the finished product or as an intermediate prior to laking (Christie & Mackay, 2008;Al Isawi et al, 2021;Gonzalez & Miksovska, 2014). Despite this, only two structures of ammonium salts of sulfonated azo colourants appear to have been determined, namely, those of diammonium Orange G tetrahydrate and of the nitrile-substituted [NH 4 ][O 3 S(C 6 H 4 )-NN(C 6 H 4 )NHCH 2 CH 2 CN]•H 2 O (Ojala et al, 1994;Astbury et al, 2013).…”