Synthesis, characterization and X-ray structures of the new dinucleating ligand 2,8-dimethyl-1,4,5,6,7,10,11,12-octahydroimidazo[4,5-h] imidazo[4,5-c][1,6]diazecine-5,11-diethanoic acid and its Cu(II) complex; an alternating chain of Cu(II) ions, coupled both intramolecularly and intermolecularly

Abstract

The design and synthesis of a new, rigid dinucleating ligand 2,8-dimethyl-1,4,5,6,7,10,11,12-octahydroimidazo[4,5-h] imidazo[4,5-c][1,6]diazecine-5,11-diethanoic acid (H2glymeim) is reported together with its molecular and crystal structure. The rigid ligand structure is confirmed by the structure and magnetic properties of its bis Cu(II) complex, [Cu2(C16H22N6O6)(H2O)4](ClO4)2(H2O)2, (Cu2glymeim). Crystals of free glymeim are composed of units of C16H22N6O4 and eight water molecules linked by a two dimensional network of hydrogen bonds. Six of them contribute to a one-dimensional network that links the organic molecules. The 1,6-diazecine ring shows a chair conformation, with expected angles and bond distance values. A stretched conformation of the glycine residue is observed in the free ligand. When this residue is coordinated, it produces significant stress over the diazecine ring caused by the closure of the glycine residue around the metal ion. The copper complex has a dinuclear structure with a square pyramidal environment around both metal ions. The apical position in the two pyramids point to opposite directions in the molecule and they are related by an inversion center. The pyramidal bases of both copper atoms are in the same plane. The intramolecular metal–metal distance in the complex is 7.445(3) Å. However, the shortest distance is of intermolecular nature, with a value of 5.378(2) Å. The crystal structure of the complex consists of a chain of dinuclear units, with an alternating chain arrangement. Low temperature magnetic susceptibility and EPR are in agreement with an antiferromagnetic dinuclear behavior in solution and like a linear chain uniformly spaced, with J=−8.54 cm−1 and α=1. The magnetic behavior of this compound can be explained as the result of an intramolecular magnetic exchange (long distance), and a superexchange path through the hydrogen bond network between adjacent dinuclear molecules.