Second-sphere coordination of the tris(5,5′-diamino-2,2′-bipyridine)iron complex with arene-carboxylate ligands through N-H•••O hydrogen bonding

The tris(5,5'-diamino-2,2'-bipyridine)iron(II) complex [Fe(DABP)(3)](2+) can be engaged in hydrogen-bonding interactions from the amino groups to carboxylate-containing molecules as H-bond acceptors. This so-called second-sphere coordination of the metal complex is investigated here by using benzene-1,4-dicarboxylate (terephthalate, L-1), benzene-1,3-dicarboxylate (isophthalate, L-2), biphenyt-2,2'-dicarboxylate (L-3), and benzene-1,3,5-tricarboxylate (trimesate, L-4) anions for N-(HO)-O-... bonding. The second-sphere coordination of [Fe(DABP)(3)](2+) is further complemented by water molecules of crystallization in the isolated and structurally elucidated compounds of [Fe(DABP)(3)](L-1)(.)5H(2)O, [Fe(DABP)(3)](L-2)(.)8H(2)O, [Fe(DABP)(3)](L-1)(.)5H(2)O, and [Fe(DABP)(3)](3)(L-4)(2)(.)20H(2)O. The hydrogen-bonding between [Fe(DABP)(3)](2+) and the dicarboxylate anions (L-1-L-3) decreases from a three-dimensional supramolecular network (with V) to discrete units (with L 2 and V) with the increasing number of crystal water molecules. The tricarboxylate ligand L-4 is capable of capping the triangular face formed by the three amino groups in [Fe(DABP)(3)](2+). The solid-state structures of DABP(.)2H(2)O and 5,5'-bis(ethoxycarbonylamino)-2,2'-bipyridine (BEBP) are reported.