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 (Tp py ) ligand are prepared and examined. Crystallographic results of those Tp py Fe(II) complexes exhibit several new types of binding modes resulting in a mononuclear or dinuclear species formation. Mononuclear complex [Tp py FeCl]( 1 ) has a distorted square pyramidal Fe(II) center with one arm (pyrazolyl-pyridyl) dangling outside of coordination sphere; this is newly finding in Tp py Fe(II) chemistry. Complex [(Tp py ) 2 Fe(OH 2 )]( 2 ) has shown unique coordination behaviour and hydrogen bonding interactions with dangling pyrazolyl-pyridyl arms of Tp py ligands which might shorten the Fe-OH 2 bond length and stabilize the coordination modes. In contrast, complex [Tp py Fe(μ-OMe)] 2 ( 3 ) shows an unique methoxy bridging centrosymmetric dinuclear structure which is isolated from the reaction of KTp py with FeSO 4 ·7H 2 O 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 [Tp py Fe(BF 4 )]( 4 ) and [Tp py Fe(N 3 )]( 5 ) which was confirmed by crystallography. The podand Tp py ligand and nature of exogenous ligand elucidate the systematic modification and coordination modes in ferrous complexes.