Synthesis and structural characterization of five-, six-, and seven-coordinate mononuclear manganese(II) complexes with N-tridentate ligands

A series of four mononuclear manganese (II) complexes with the N-tridentate neutral ligands 2,2′:6,2′′-terpyridine (terpy) and N,N-bis(2-pyridylmethyl)ethylamine (bpea) have been synthesized and crystallographically characterized. The complexes have five- to seven-coordinate manganese(II) ions depending on the additional ligands used. The [Mn(bpea)(Br)2] complex (1) has a five-coordinated manganese atom with a bipyramidal trigonal geometry, while [Mn(terpy)2](I)2 (2) is hexa-coordinated with a distorted octahedral geometry. Otherwise, the reactions of Mn(NO3)2 · 4H2O with terpy or bpea afforded novel seven-coordinate complexes [Mn(terpy)(NO3)2(H2O)] (3) and [Mn(bpea)(NO3)2] (4), respectively. 3 has a coordination polyhedron best described as a distorted pentagonal bipyramid geometry with one nitrate acting as a bidentate chelating ligand and the other nitrate as a monodentate one. 4 possesses a highly distorted polyhedron geometry with two bidentate chelating nitrate ligands. These complexes represent unusual examples of structurally characterized complexes with a coordination number seven for the Mn(II) ion and join a small family of nitrate complexes.