Silver(I) nitrate complexes of three tetra-kis-thio-ether-substituted pyrazine ligands: metal-organic chain, network...

The reaction of the ligand 2,3,5,6-tetra-kis-[(methyl-sulfanyl)-meth-yl]pyrazine (L1) with silver(I) nitrate led to {[Ag(C₁₂H₂₀N₂S₄)](NO₃)} , (I), catena-poly[[silver(I)-μ-2,3,5,6-tetra-kis-[(methyl-sulfan-yl)meth-yl]pyrazine] nitrate], a compound with a metal-organic chain structure. The asymmetric unit is composed of two half ligands, located about inversion centres, with one ligand coordinating to the silver atoms in a bis-tridentate manner and the other in a bis-bidentate manner. The charge on the metal atom is compensated for by a free nitrate anion. Hence, the silver atom has a fivefold S₃N₂ coordination sphere. The reaction of the ligand 2,3,5,6-tetra-kis-[(phenyl-sulfanyl)-meth-yl]pyrazine (L2) with silver(I) nitrate, led to [Ag₂(NO₃)₂(C₃₂H₂₈N₂S₄)] , (II), poly[di-μ-nitrato-bis-{μ-2,3,5,6-tetra-kis-[(phenyl-sulfan-yl)meth-yl]pyrazine}disilver], a compound with a metal-organic network structure. The asymmetric unit is composed of half a ligand, located about an inversion centre, that coordinates to the silver atoms in a bis-tridentate manner. The nitrate anion coordinates to the silver atom in a bidentate/monodentate manner, bridging the silver atoms, which therefore have a sixfold S₂NO₃ coordination sphere. The reaction of the ligand 2,3,5,6-tetra-kis-[(pyridin-2-yl-sulfanyl)-meth-yl]pyrazine (L3) with silver(I) nitrate led to [Ag₃(NO₃)₃(C₂₈H₂₄N₆S₄)] , (III), poly[trinitrato{μ₆-2,3,5,6-tetra-kis[(pyri-din-2-ylsulfan-yl)meth-yl]pyrazine}-trisilver(I)], a compound with a metal-organic framework structure. The asymmetric unit is composed of half a ligand, located about an inversion centre, that coordinates to the silver atoms in a bis-tridentate manner. One pyridine N atom bridges the monomeric units, so forming a chain structure. Two nitrate O atoms also coordinate to this silver atom, hence it has a sixfold S₂N₂O₂ coordination sphere. The chains are linked via a second silver atom, located on a twofold rotation axis, coordinated by the second pyridine N atom. A second nitrate anion, also lying about the twofold rotation axis, coordinates to this silver atom via an Ag-O bond, hence this second silver atom has a threefold N₂O coordination sphere. In the crystal of (I), the nitrate anion plays an essential role in forming C-H⋯O hydrogen bonds that link the metal-organic chains to form a three-dimensional supra-molecular structure. In the crystal of (II), the metal-organic networks (lying parallel to the bc plane) stack up the a-axis direction but there are no significant inter-molecular inter-actions present between the layers. In the crystal of (III), there are a number of C-H⋯O hydrogen bonds present within the metal-organic framework. The role of the nitrate anion in the formation of the coordination polymers is also examined.