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

Abstract

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-κ3 O 1:O 2:O 3′}tris(1,4,8,11-tetraazacyclotetradecane-κ4 N)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\overline{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.