Search for: All records

Three amidine-based ligands were used in the crystal design of a series of mononuclear Zn(II) complexes. Interaction of zinc chloride, ZnCl2, with N-2-pyridylimidoyl-2-pyridylamidine (Py2ImAm) resulted in complexes [Zn(Py2ImAm)2] (1) and [ZnCl2(Py2ImAm)] (2). In [Zn(Py2ImAm)2] (1, monoclinic, P21/c), the metal ion was coordinated with the bidentate pocket of the anionic form of Py2ImAm, while in [ZnCl2(Py2ImAm)] (2, monoclinic, P21/n), the tridentate coordination to a neutral Py2ImAm was completed by two chloride anions. This structural variation was achieved by a pH-controlling strategy using the weak base triethylamine (TEA). Otherwise, three ionic complexes were obtained with 2-amidinopyridine (PyAm) and Zinc(II), [ZnCl(PyAm)2]Cl (3, triclinic, P-1), [ZnCl(PyAm)2]2[ZnCl4]·C2H5OH (4, monoclinic, P21/n), and [ZnCl(PyAm)2]2Cl·CH3OH (5, triclinic, P-1). They comprised the same [ZnCl(PyAm)2]+ monocation with a butterfly-like shape provided by the bidentate chelate coordination of two PyAm neutral entities and a chloride ligand. In a similar butterfly shape, ionic complex [ZnCl(PmAm)2]2[ZnCl4] (6, monoclinic, C2/c) comprised the mononuclear [ZnCl(PmAm)2]+ cations with two bidentate chelate-coordinated 2-amidinopyrimidine (PmAm) as neutral ligands. The Zn(II) pentacoordinated arrangement in 3–6 was variable, from square pyramidal to trigonal bipyramidal. The reported compounds’ synthetic protocols, crystal structures and photoluminescence properties are discussed. 

To increase the number of potential materials for application as MRI contrast agents, several Cu(II) complexes were synthesized. Cu(II) complexes were chosen because they are less expensive in comparison with the presently used Gd(III), Mn(II) and other agents. Pyridine-2-carboximidamide (1), pyrimidine-2-carboximidamide (2) and pyrazole-2-carboximidamide (3) in the form of different salts along with CuCl2 and NaCl or CuBr2 and NaBr were used to obtain four Cu(II) complexes: dichloro-pyrimidine-2-carboximidamide copper(II) (4), dibromo-pyrimidine-2-carboximidamide copper(II) (5), dichloro-pirazole-2-carboximidamide copper(II) (6), and dibromo-pirazole-2-carboximidamide copper(II) (7). X-ray diffraction analysis revealed that molecular complexes 4–7 contain square planar coordinated Cu(II) atoms and their structures are very similar, as well as their packing in crystals, which allows us to consider them isomorphs. The same synthetic approach to complex preparation where NaCl or NaBr was not used brought us to the formation of dimeric complexes μ-chloro{chloro(pyridine-2-carboximidamide)copper(II)} (8) and μ-chloro{chloro(pyrimidine-2-carboximidamide)copper(II)} (9). In the dimeric complexes, two fragments which were the same as in monomeric complexes 4–7 are held together by bridging Cu-Cl bonds making the coordination of Cu equal to 5 (square pyramid). In dimeric complexes, axial Cu-Cl bonds are 2.7360 and 2.854 Å. These values are Cu-Cl bonds on the edge of existence according to statistical data from CSD. Synthesized complexes were characterized by IR spectroscopy, TGA, PXRD, EPR, and quantum chemical calculations. The higher thermal stability of monomer pyrimidine-based complexes with Cl and Br substituents makes them more prospective for further studies.