AgI, CdII, and HgII complexes with 2,5-bis(pyridyl)pyrazine ligands: syntheses, spectral analyses, single crystal, and powder X-ray analyses

Vallat, Olivier ; Neels, Antonia ; Stoeckli-Evans, Helen

In: Journal of Chemical Crystallography, 2003, vol. 33, no. 1, p. 39-50

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    2,5-Bis(4-pyridyl)pyrazine (4-bppz) and 2,5-bis(3-pyridyl)pyrazine (3-bppz) have been synthesized and characterized spectroscopically and crystallographically. 4-bppz [unit cell: a = 7.319(1), b = 5.746(1), c = 12.756(2) Å, β = 93.16(1)° space group: P21/a] was characterized by X-ray single crystal diffraction methods while the structure of 3-bppz [unit cell: a = 10.9148(4), b = 4.5722(1), c = 11.4462(2) Å, β = 109.571(2)° space group: P21/c] was determined from laboratory X-ray powder diffraction data. In these compounds, the pyrazine ring contains two symmetrically attached pyridine substituents with the nitrogen atom in the para positions for 4-bppz and in the meta positions for 3-bppz. Both compounds possess Ci symmetry with the pyridine rings twisted by 17.7° (4-bppz) and 2.6° (3-bppz) with respect to the pyrazine ring. 4-bppz was used in the formation of coordination compounds with silver(I) and cadmium(II). The silver(I) complex [Ag(OAc)(4-bppz)] n (1) [unit cell: a = 8.472(1), b = 13.051(1), c = 19.063(2) Å, β = 109.96(1)° space group: P21/c] is characterized by the formation of a perfectly linear chain containing the silver ions bridged by the ligand molecule, the latter using its pyridine nitrogen donor atoms for coordination. A pair of chains is interconnected by silver-silver interactions, the silver coordination sphere being completed by acetate anions. A similar one-dimensional coordination polymer, [Cd(OAc)2(4-bppz)(MeOH)] n (2) [unit cell: a = 8.680(1), b = 10.035(1), c = 13.445(1) Å, α = 77.35(1), β = 71.17(1), γ = 80.14(1)° space group: $$P\bar 1$$ ], was obtained by the reaction of 4-bppz with Cd(OAc)2. Ligand 3-bppz forms an analogous cadmium(II) complex, [Cd(OAc)2(3-bppz)(MeOH)] n (3) [unit cell: a = 9.306(1), b = 9.733(1), c = 11.550(1) Å, α = 87.86(1), β = 76.73(1), γ = 85.91(1)° space group: $$P\bar 1$$ ], containing the molecules arranged in double zigzag chains. The reaction of 3-bppz with HgI2 leads surprisingly to a binuclear complex, [Hg2I4(3-bppz)2] (4) [unit cell: a = 17.555(1), b = 12.973(1), c = 16.195(1) Å, β = 115.32(1)° space group: C2/c]. Two ligand molecules are bridged by two mercury(II) ions forming a cyclic structure, the tetrahedral coordination sphere of the metal being completed by iodide anions