The synthesis, structural analysis and spectroscopic characterisation of
three new 7-azaindole ligands is reported, alongside a novel 7-azaindole
derived coordination polymer, with the aim of identifying new bridging
ligands containing inner-sphere hydrogen bond donor functionality.
Structural characterisation shows that the 7-azaindole hydrogen bond donor
ability is significantly stronger in the hydrazone and imine species 1 and 2
compared to the amine 3, with the opposite trend evident in their hydrogen
bond acceptor character. These findings are mirrored by the fluorescence
spectroscopy results which show bimodal emission, characteristic of multiple
emissive species related by proton transfer, is only evident in the amine
species and not the more acidic imines. The polymeric copper(II) complex of
the hydrazone ligand 1 shows the anticipated inner-sphere hydrogen bonding
with a similar donor strength to that observed in the free ligand, which
leads to deformation in the remainder of the coordination sphere. These
results show the untapped versatility of the 7-azaindole functional group as
a building block for ligands in coordination polymers and other multinuclear
assemblies, with the potential for both stabilisation through hydrogen
bonding and interesting photophysical properties.