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 (H4A) in a DMF/H2O mixture (4:1 v/v) under heating, leads to [Ni(L)]3(HA)2·3DMF (I·DMF). Redissolution of this compound in a DMF/H2O/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)]3(HA)2·5H2O·2MeOH (II·H2O). At lower temperature and concentration of reactants and longer reaction time, single crystals of composition {[{Ni(L)}3(HA)2]·4CH3OH}n (II·MeOH) were isolated. Single-crystal X-ray diffraction analysis of this compound, which, according to PXRD is isostructural with II·H2O but different from I·DMF, revealed its two-dimensional (2D) polymeric structure, i.e. poly[[bis{μ3-4-[(4-carboxy-3-carboxylatophenyl)dimethylsilyl]benzene-1,2-dicarboxylato-κ3O1:O2:O3'}tris(1,4,8,11-tetraazacyclotetradecane-κ4N)trinickel(II)] methanol tetrasolvate], {[Ni3(C18H13O8Si)2(C10H24N4)3]·4CH3OH}n. It is built up of the monoprotonated tricarboxylate HA3- ligand coordinated in a monodentate manner in the axial positions of two crystallographically independent NiII cations, one of which is located on a crystallographic inversion centre. Both metal ions adopt a slightly tetragonally elongated trans-N4O2 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·H2O were characterized by FT-IR and diffuse reflectance spectroscopy and thermogravimetry, which provide evidence of their structural differences.
Keywords: 4,4′-(dimethylsilanediyl)diphthalic acid; IR spectroscopy; crystal structure; cyclam; nickel(II); reflection spectra; thermogravimetry; two-dimensional coordination polymer.