title: Coordination chemistry of chromium-Salen complexes studied by electrospray ionization mass spectrometry.
abstract: The gas-phase coordination behavior of the [Cr(III)(Salen)]PF(6) complex at the free axial positions has been studied in the presence of amines as ligands (propylamine and a series of diamines) under electrospray ionization conditions. The [Cr(III)(Salen)](+) complex formed stable five- and six-coordinated complex ions, [Cr(III)(Salen)(L)](+) and [Cr(III)(Salen)(L)(2)](+), respectively, where L = solvent molecule or amine. When diamines were used as ligands, abundant [Cr(III)(Salen)(L)](+) ions were observed in which two axial positions of the [Cr(III)(Salen)](+) species are occupied by the two amino groups of the diamine ligand. The relative abundances of ligated complex ions, fragment ions, and solvent adducts of fragment ions in the ESI mass spectra, were found to depend on the cone voltage used to record the spectrum. The ESI mass spectra of [Cr(III)(Salen)](+) in the presence of diamines as ligands, and experiments on ligand-pickup in the collision cell, clearly demonstrated that the [Cr(III)(Salen)(L)](+) complex ion is stable for 1,2-diaminoethane and 1,3-diaminopropane. The stability of [Cr(III)(Salen)(L)](+) ions gradually decreased from 1,4-diaminobutane to 1,6-diaminohexane, and then showed a slight increase for 1,7-diaminoheptane and 1,8-diaminooctane. The collision-induced dissociation spectra of [Cr(III)(Salen)(L)](+) ions support the above observations.
authors.affiliation: National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad - 500 007, India.
authors.forename: M Kiran
authors.initials: MK
authors.lastname: Kumar
authors.forename: S
authors.initials: S
authors.lastname: Prabhakar
authors.forename: M Ravi
authors.initials: MR
authors.lastname: Kumar
authors.forename: T Jagadeshwar
authors.initials: TJ
authors.lastname: Reddy
authors.forename: S
authors.initials: S
authors.lastname: Premsingh
authors.forename: S
authors.initials: S
authors.lastname: Rajagopal
authors.forename: M
authors.initials: M
authors.lastname: Vairamani