Cu(i) and Zn(ii) complexes of 7-azaindole-containing scorpionates: Structures, luminescence and fluxionality

Abstract

A new scorpionate borate ligand K[HB(7-azain)₃] (1, 7-azain = 7-azaindolyl) has been obtained from the reaction of KBH₄ with excess 7-azaindole. The scorpionate ligand 1 was found to be able to form complexes with Zn^II and Cu^I ions. Complex 2 with the formula [BH(7-azain)₃](ZnCl) has been obtained from the reaction of ZnCl₂ with 1. Complex 3 with the formula [BH(7-azain)₃][Cu(PPh₃)] has been obtained from the reaction of [Cu(PPh₃)₂(CH₃CN)₂][BF₄] with 1. The crystal structures of 1–3 have been determined by single-crystal X-ray diffraction analyses which revealed that 1 has a dimeric structure linked together by two K⁺ ions, 2 has a symmetric tripodal structure with all three 7-azaindolyl groups being coordinated to the Zn^II center, and 3 has an asymmetric structure with two of the 7-azaindolyl groups being coordinated to the Cu^I center and the third 7-azaindolyl group uncoordinated. Variable temperature ¹H NMR experiments established that 3 is highly dynamic in solution involving a rapid exchange between the coordinated and the non-coordinated 7-azaindolyl groups. All three compounds display blue emission in the solid state at ambient temperature. However, in solution at ambient temperature, compounds 1 and 2 display bright blue emission while compound 3 has no emission at all. At 77 K, solutions of all three compounds display blue-green phosphorescent emission with a long decay lifetime (> 2 ms).