Combination of hydrogen and coordination bonding for the construction of one-dimensional networks based on a 7-azaindole appended dipyrrin

Abstract

A new ligand (L) incorporating a dipyrrin unit acting as a strong chelate under basic conditions and a 7-azaindole group offering a self-complementary hydrogen bonding site has been designed and synthesized. Both hetero- and homoleptic complexes have been prepared and their organization in the solid state investigated by single-crystal X-ray diffraction. As in the case of the dipyrromethane precursor, the heteroleptic copper complex (acac)CuL forms a H-bonded dimer featuring the well-known R₂²(8) hydrogen bonding motif between two 7-azaindole groups. Interestingly, in the case of the (salen)CoL complex offering a competing H-bond acceptor site, the dihapto mode of H-bonding is disrupted. However, the robustness of the formation of the R₂²(8) motif is demonstrated in a series of homoleptic complexes of the ML₂ type (M = Zn(II), Cu(II), Ni(II)). In spite of the different coordination sphere around the divalent metal ions, the self-complementary R₂²(8) hydrogen bonding motif is observed in all three cases leading to 1D chains.