Silver Complexes of Azobenzene and Derivatives

Abstract

Thirty four silver(I) complexes of azobenzene and derivatives have been synthesised, only two of which have been previously published. The azobenzene derivatives used are 2-bromo, 3-bromo, 4-bromo, 3,4’-dibromo, 2,4’-dibromo, 3-nitro, 4-dimethylamino, 4-methoxy, 2,6-dimethyl-4’-chloro, 2,6,2’,6’-tetramethyl and 2,2’-ethyleneazobenzene. 2,2’- and 4,4’-azobispyridine were also used along with diphenyltriazine. Six different silver(I) salts were used to make the complexes; they are tetrafluoroborate, hexafluorophosphate, perchlorate, nitrate, triflate and trifluoroacetate. All of the complexes were analysed using X-ray crystallography. In the complexes with azobenzene the anion was the most crucial factor in determining the resulting structure, as five different molecular topologies were seen with each change of anion. The 2-bromoazobenzene containing complexes continue this trend giving similar topologies to the azobenzene containing complexes. Once we come to the 3-bromo and 4-bromoazobenzene, we get a different molecular topology for the hexafluorophosphate containing complexes when compared to the original azobenzene containing complex, but we see a very similar structure for the perchlorate containing complexes. This would suggest that the coordinating anions give more predictable structures than the non-coordinating anions. The trend continues with both the 3,4’-dibromo and 2,4’-dibromoazobenzene complexes with triflate being structurally similar to the previous triflate containing complexes. The trend is reinforced further with 3-nitro and 4-methoxyazobenzene showing similar structures to the previously discussed complexes. The complex containing 4-dimethylaminoazobenzene can be disregarded, as the ligand has become protonated and therefore is unlike all the previously described results. When we come to the sterically hindered ligands 2,6-dimethyl-4’-chloroazobenzene the first three complexes show the same molecular topology of a silver atom bound to two ligands with a coordinating anion, however once we come to a tridentate coordinating anion triflate a 1-D metallopolymer is observed. This breaks the trend, as the structures are similar regardless of the change in anion. A similar effect is seen in 2,6,2’,6’-tetramethylazobenzene with both structures standing alone as no complexes with a similar molecular topology were observed. This effect is again noted in the complexes containing 2,2’-ethyleneazobenzene. The complexes all form a similar structure regardless of the anion used. As expected the 2,2’- and 4,4’-azobispyridine along with diphenyltriazine do not follow the trend observed earlier with the non-sterically hindered ligands as they can coordinate through additional nitrogen atoms in the aromatic ring or in the case of diphenyltriazine an additional nitrogen atom in the triazine group.