On the Preparation of Coordination Polymers by Controlled Thermal Decomposition:  Synthesis, Crystal Structures, and Thermal Properties of Zinc Halide Pyrazine Coordination Compounds

Abstract

The five zinc(II) halide pyrazine coordination compounds poly-bis(mu2-pyrazine)-dichloro-zinc(II) (I), poly-(mu2-pyrazine-N,N')-dichloro-zinc(II) (II), poly-bis(mu2-pyrazine-N,N')-dibromo-zinc(II) (III), catena-(mu2-pyrazine-N,N')-dibromo-zinc(II) (IV), and catena-(mu-pyrazine)-diiodo-zinc(II) (V) were prepared by the reaction of ZnX2 (X = Cl, Br, I) with pyrazine in acetonitrile. In the crystal structure of compound I, the zinc atoms are coordinated by two chlorine atoms and two pyrazine ligands within distorted tetrahedra. The zinc atoms are linked by the N-donor ligands into layers. The crystal structure of compound III is very similar to that of compound I. The structure of compound III was originally reported in space group Ccca with similar a and b axes, but it was proved that the correct space group is I4/mmm. Ligand-poor compound V is isotypic to compound IV, in which ZnX2 units (X = Br, I) are connected by the pyrazine ligands into chains. It was originally reported in the noncentrosymmetric space group P2(1), but we found that the correct space group is P2(1)/m. If ligand-rich 1:2 compounds I and III are heated in a thermobalance, different mass steps are observed. We have proven that in the first step, ligand-poor compounds II and IV are formed in quantitative yields. On further heating, a second mass step occurs that leads to the formation of two new compounds of composition (ZnCl2)2(pyrazine) (VI) and (ZnBr2)2(pyrazine) (VII). However, the mass step is not well-resolved. and the new compounds are not phase-pure after the thermal event. If ligand-poor 1:1 compound V is investigated by thermogravimetry, a not-well-resolved single mass step is observed in which new ligand-poor 2:1 compound (ZnI2)2(pyrazine) (VIII) is formed. On further heating, all 2:1 compounds lose their remaining ligands and transform into the pure zinc(II) halides.

(Di-2-pyridyl sulfide-κ2N,N′)diiodidozinc(II)

“…Recently, we are interested in the synthesis, structures and thermal properties of coordination polymers based on zinc (II) halides and N-donor ligands (Bhosekar et al, 2007). We have found for example that most of the ligand rich compounds can be transformed into ligand deficient compounds on heating.…”

“…For related literature, see: Anderson & Steel (1998); Bhosekar et al (2007); Kondo et al (1995); Nicolò et al (1996); Teles et al (1999); Tresoldi et al (1991Tresoldi et al ( , 1992.…”

Halide-bridged polymers of divalent metals with donor ligands – structures and properties

“…Pyrazine represents an obvious equivalent to 4,4 -bipy and acts in the same way in [Zn(-Cl) 2 (-pyz)] 2 ∞ . This solid crystallizes in space group Cmmm [145] and may alternatively be obtained via controlled thermal decomposition [146]. In contrast, the corresponding [M(-X) 2 (-pyz)] 2 ∞ derivatives for M = Cu, X = Cl [147], M = Cu, X = Br [148] and M = Hg, X = Cl [149] are all isomorphous and adopt the subgroup C2/m, with lattice parameters rather similar to the Zn(II) compound.…”

Crystal structures and photoluminescence of the Zn(II) and Cd(II) complexes of N-methylpyrazinium obtained by a less hazardous approach

“…The bond length of Zn-N is 2.157(3) Å, and Zn-I bond distances vary from 2.5538(5) to 2.5844(5) Å. These bond lengths are slightly longer than zinc-pyrazine complexes, such as [ZnI 2 (pyrazine)] n with Zn-N and Zn-I bond lengths of 2.082(4) Å and 2.519(1) Å, respectively [21]. The bond angles of I-Zn-I and N-Zn-I, ranging between 100.56 (8)°and 119.60(2)° (Table S1), are in rough agreement with those found in metal complexes with tetra-coordinated zinc(II) atoms [22].…”