Ag(I)···π-Influenced, Anion-Controlled Structural Variation in Coordination Networks of E-3-Pyridylvinyl Benzoxazole: Sunlight-Driven Regioselective Photodimerization in the Solid State

Abstract

The coordination chemistry of the flexible N-donor ligand E-3-pyridylvinyl benzoxazole (3-PVBO) with various silver salts has been investigated for the first time. Four novel coordination compounds of silver(I), namely, {[Ag₂(3-PVBO)](BF₄)} (1), {[Ag(3-PVBO)](CF₃SO₃)}_∞¹ (2), {[Ag(3-PVBO)(CF₃CO₂)]}_∞¹ (3), and {[Ag₂(3-PVBO)](SbF₆)}_∞¹ (4), have been synthesized and structurally characterized. 3-PVBO adopts two different configurations, i.e., syn- and anti-, and offers structural variation in the series with different anions. In both 1 and 2, it adopts syn-configuration, and thus, 16-membered metallacycles are formed. In 3, with the trifluoroacetate anion, it adopts anti-configuration, and thus, a zigzag 1D coordination polymeric network is formed. However, in 4 with the SbF₆^– anion, despite it adopting the syn-configuration, instead of a metallacycle, a 1D coordination polymeric network is observed. More interestingly, 3-PVBO ligands were found to stack parallel in 3 and 4, suitable for the photodimerization reaction in the solid state. 3 exhibited photodimerization in the head-to-tail fashion, leading to the formation of the coordination polymer, {[Ag(rctt-HT-PBOCB)(CF₃CO₂)]}_∞² (5), where PBOCB = 1,3-bis(benzoxazole)-2,4-bis(3′-pyridyl) cyclobutane. However, 4 underwent photodimerization in the head-to-head fashion. Thus, varying the anions achieved a regioselective synthesis of functional cyclobutane derivatives. No argentophilic but Ag(I)···π interaction was observed in this series.