Theoretical Studies of Some Polymeric-Cu(II)-Pyrimidine-Carboxylate Ligands: Crystal Parameters and J Exchange Coupling

Polymeric pyrimidines containing copper(II) complexes are well known in different formulations. They exhibit a variety of magnetic interactions. It seems that the two nitrogen atoms of the pyrimidine ring are oriented favourably to form coordinate bonds with an infinite 1D chain. In the presence of other ligands, 2D layers are also possible. For example, the simple dinitrato polymer shows ferromagnetic coupling between the copper(II) centers, a 2D infinite layered structure with bridging pyrimidine ligands and J = + 0.62 cm [1]. The complex polymer [Cu2(oxen)(pym)2]n(ClO4)2n, where oxen and pym are the N,N’-(2-aminoethyl)oxamide dianion and pyrimidine respectively, was synthesized and characterized by magnetic measurements [2]. This compound consists of layers of a two-dimensional network arrayed along the a axis. Within the layer, trans-oxamido-bridged copper(II) dimers connected by pyrimidine in an asymmetric fashion spread out over the bc plane to form 2D infinite networks. The magnetic study of the compound showed a strong antiferromagnetic exchange interaction with J = -582 cm. The copper(II) atoms are separated by about 5.2 Å. Another complex, Cu(NO3)2(H2O)2(pym)2 showed antiferromagnetic interactions at extremely low temperatures [3]. In this compound the pyrimidine bridges the copper ions to form one-dimensional coordination chains. Formation of coordination polymers allows the appearance of the magnetic interactions. The details of the coordination of the bridging organic moieties should also play an important role in the magnetic properties. Magnetic measurements show that it is a good Theoretical Studies of Some Polymeric-Cu(II)-Pyrimidine-Carboxylate