Cu(I) and Zn(II) complexes of 7-azaindole-containing scorpionates: structures, luminescence and fluxionality

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 . The crystal structures of 1-3 have been determined by single-crystal X-ray diffraction analyses which revealed that 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).