Double π- and σ-hydrogen bonding in formic acid complexes with pyrrole and imidazole: an ab initio and density functional theory study

Ab initio [MP2(fu)/6-311++G^**] and DFT (B3LYP/6-311++G^**) calculations predict that the cyclic 1:1 complexes of formic acid with pyrrole or imidazole are stabilised by non-conventional double hydrogen σ- and π-bonds.