Investigation on the coordination behaviors of tris(2-pyridyl)pyrazolyl borates iron(II) complexes

Abstract

A series of Fe(II) complexes bearing hydrotris[3-(2-pyridyl)-pyrazolyl]borate (Tppy) ligand are prepared and examined. Crystallographic results of those TppyFe(II) complexes exhibit several new types of binding modes resulting in a mononuclear or dinuclear species formation. Mononuclear complex [TppyFeCl](1) has a distorted square pyramidal Fe(II) center with one arm (pyrazolyl-pyridyl) dangling outside of coordination sphere; this is newly finding in TppyFe(II) chemistry. Complex [(Tppy)2Fe(OH2)](2) has shown unique coordination behaviour and hydrogen bonding interactions with dangling pyrazolyl-pyridyl arms of Tppy ligands which might shorten the Fe-OH2 bond length and stabilize the coordination modes. In contrast, complex [TppyFe(μ-OMe)]2(3) shows an unique methoxy bridging centrosymmetric dinuclear structure which is isolated from the reaction of KTppy with FeSO4·7H2O after re-crystallization process in methanol. The complex 3 also could isolate independently from the reaction of complex 1 with sodium methoxide. To further investigate the coordination modes on mononuclear complex 1, exogenous anionic substituents used to form [TppyFe(BF4)](4) and [TppyFe(N3)](5) which was confirmed by crystallography. The podand Tppy ligand and nature of exogenous ligand elucidate the systematic modification and coordination modes in ferrous complexes.