Síntese e caracterização de derivados do anidrido piromelítico.

In the present study isomers of 4,6-bis (aminocarbonyl) isophthalic acid (1), and 2,5-bis (aminocarbonyl) terephthalic acid (2) were obtained through reaction of anhydrous ammonia and pyromellitic anhydride in solution of dimethyl ketone at room temperature. The mixture (PMNH2) was characterized by physical methods. Quantum-chemical calculations were carried out for comparison with experimental results and for conformational analysis. Ab initio calculations up to the B3LYP/6-311G__+ level were used to simulate the gas-phase geometry of the conformers: eight conformations of 1, six of 2 and one of the 1,2,4,5 benzenetetracarboxylato (BTEC). Intramolecular O􀀀H_ _ _ O, N􀀀H_ _ _O and O􀀀H_ _ _N hydrogen bonds were observed and correlated to molecular stability. Crystalline samples grow in water solution of PMNH2, Cu2+, Zn2+ and Co2+ ions and were analysed by means of X-ray single-crystals diffraction. Hydrolysis of the amide groups leads to formation of the salts: triaquacopper(II) 1,2,4,5 benzenetetracarboxylato dihydrate (C10H20O18Cu2; C2=c; a = 12:116(2)A, b = 18:091(4)A, c = 9:5910(19)A and b = 112:90(3)o; z = 4); diaquazinc(II) 1,2,4,5 benzenetetracarboxylato (C5H5O6Zn; P21=n; a = 5:246(1) A, b = 16:320(3) A, c = 8:114(2) A and b = 97:95(1)o; z = 4) and diaquacobalt( II) 1,2,4,5 benzenotetracarboxylato trihydrate (C20H24O25Co3; P21=n; a = 9:521(2) A, b = 11:075(2) A, c = 14:020(3) A and b = 104:13(2)o; z = 4). The water molecules have an important role in the crystal structures, specially in the hydrogen bonding interactions and metal coordination. The former can be classified in mean and weak hydrogen bonds, since the d(H _ _ _ O) and D(O_ _ _ O) geometrical parameters are in the range 1:691(4)􀀀2:574(5)A for the shorter, and 2:424(3)􀀀3:099(3)A for the longer hydrogen bonds, respectively. The ionic sites are penta-coordinated (for Cu2+ and Zn2+ transition metals) and hexa-coordinated (Co2+) by oxygen atoms from water and from carboxylate groups. In the crystal structure the Co2+ cations are separated by 3:553(1)A. The distorted trigonal bipyramid coordination geometry of the Zn2+ is unusual for BTEC compounds, and to date not reported in the scientific literature.