CdX2 Coordination Polymers with 2-Chloropyrazine and 2-Methylpyrazine: Similar Ligands - Similar Structures - Different Reactivity.

Several coordination compounds, based on Cd halides and 2-methylpyrazine (Mepyz) or 2-chloropyrazine (Clpyz) as N-donor coligands, are synthesized and their crystal structures determined by either single-crystal or X-ray powder diffraction (XRPD). In [CdX2(2-Clpyz)2]n (X = Cl: 1-Cl-Clpyz; X = Br: 1-Br-Clpyz; and X = I: 1-I-Clpyz) and [CdX2(2-Mepyz)2]n (X = Cl: 1-Cl-Mepyz; X = Br: 1-Br-Mepyz; and X = I: 1-I-Mepyz), the Cd cations are octahedrally coordinated by two N-donor ligands and are linked into chains by the halide anions that share common edges. In the ligand-deficient compounds [CdX2(2-methylpyrazine)] n (X = Cl: 2-Cl-Mepyz; X = Br: 2-Br-Mepyz; and X = I: 2-I-Mepyz), similar CdX2 chains, which are connected into layers by the N-donor ligands, are observed. Thermal analysis of all 1-Mepyz compounds shows a transformation into 2-Mepyz, which is not observed for the 2-chloropyrazine compounds. On further heating, compounds of composition [(CdX2)2(2-Mepyz)]n (X = Cl: 3-Cl-Mepyz; X = Br: 3-Br-Mepyz) and [(CdI2)3(2-Mepyz)2] (4-I-Mepyz) are observed. A discrete complex, with the composition CdI2(2-Mepyz)2 monohydrate (1-I-Mepyz-H2O), and a hydrate with the composition [(CdI2)(2-Mepyz)]·1.5H2O (2-IMepyz-H2O) with an unknown structure, were also synthesized. Both lose the water molecules upon heating. Luminescence measurements show blue to orange emissions in the range of ca. 22530-16276 cm-1, depending on the halide or pyrazine substituent, as well as the metal halide/ligand ratio. [ABSTRACT FROM AUTHOR]