A 2D coordination polymer assembled from a nickel(II) tetraazamacrocyclic cation and 4,4'-(dimethylsilanediyl)diphthalate(3-) linker.

The preformed nickel(II) complex of the 14-membered macrocyclic ligand 1,4,8,11-tetraazacyclotetradecane (cyclam, L), when treated with 4,4'-(dimethylsilanediyl)diphthalic acid (HA) in a DMF/HO mixture (4:1 v/v) under heating, leads to [Ni(L)](HA)·3DMF (I·DMF). Redissolution of this compound in a DMF/HO/MeOH mixture (4:1:30 v/v/v) with mild acidification under gentle heating results in the formation of a similar compound but containing water and methanol molecules of crystallization, [Ni(L)](HA)·5HO·2MeOH (II·HO). At lower temperature and concentration of reactants and longer reaction time, single crystals of composition {[{Ni(L)}(HA)]·4CHOH} (II·MeOH) were isolated. Single-crystal X-ray diffraction analysis of this compound, which, according to PXRD is isostructural with II·HO but different from I·DMF, revealed its two-dimensional (2D) polymeric structure, i.e. poly[[bis{μ-4-[(4-carboxy-3-carboxylatophenyl)dimethylsilyl]benzene-1,2-dicarboxylato-κO:O:O}tris(1,4,8,11-tetraazacyclotetradecane-κN)trinickel(II)] methanol tetrasolvate], {[Ni(CHOSi)(CHN)]·4CHOH}. It is built up of the monoprotonated tricarboxylate HA ligand coordinated in a monodentate manner in the axial positions of two crystallographically independent Ni cations, one of which is located on a crystallographic inversion centre. Both metal ions adopt a slightly tetragonally elongated trans-NO octahedral geometry. The compound has a lamellar structure with polymeric layers oriented parallel to the (10-2) plane, which are in turn linked via hydrogen bonds involving protonated carboxylic acid groups of the ligand. Bulk compounds I·DMF and II·HO were characterized by FT-IR and diffuse reflectance spectroscopy and thermogravimetry, which provide evidence of their structural differences.