Syntheses and Structure Investigations of 3d Transition Metal Complexes with a Flexible N4O2-Donor Hexadentate Schiff-Base Ligand

Abstract

The syntheses and structure investigations of four new 3d transition metal complexes (1–4) with a flexible N4O2-donor hexadentate Schiff-base ligand are described; three complexes (1, 2, and 4) of FeIII, CoIII, and CuII metal ions have been investigated by UV-vis, FT-IR, high-resolution mass spectrometry (HR-MS), and scanning electron microscopy–electron dispersive spectroscopy, as well as single crystal X-ray diffraction. The X-ray structure of NiII complex 3 is also reported. The molecular structures of the complexes (1–3) demonstrate distorted octahedral coordination geometry, each exhibiting 1 : 1 (M : L) ratios and the CuII complex 4 shows a trinuclear structure with a CuII : L ratio of 3 : 2 in the solid state, which has been proven by X-ray diffraction. On the other hand, a mononuclear species of the CuII complex is formed in solution, which has been identified by electrospray ionization HR-MS.

Crystallographic Detection of the Spin State in FeIII Complexes

“…These complexes all facilitate strong intermolecular hydrogen bonding and other close contacts, likely helping stabilize the spin doublet ground state. The bond lengths of these complexes are all consistent with those expected for spin doublet Fe III . − …”

“…Complexes with additional −CH 2 – groups in the alkylene linkers, such as [Fe III (R-sal 2 333)]­X, have also recently been shown to support both the HS and LS states, although switching between the two has not yet been observed . A handful of complexes of the [Fe III (R-sal 2 323)]­X form has been reported in the literature, − and in each case, the complexes supported the LS state. Hayami et al.…”

High-Temperature Spin Crossover in FeIII N4O2 Complexes Incorporating an [R-sal2323] Backbone

“…Herein, we extend the work on our previously reported [Fe III (NEt 2 -sal 2 323)]ClO 4 (1•ClO 4 ) compound 38 to explore the magnetic susceptibility of this family of compounds at higher temperatures. Two ligand substituents were selected for comparison, possessing a σ-electron donating (NEt 2 ) or withdrawing (Br) substituent respectively on the sal 2 323 phenyl ring, which were subsequently crystallized with both The possible electronic effects of the ligand substituents, the effect of counterions, as well as any changes in the intermolecular interactions or crystal packing that these alterations had on the nature of SCO in these compounds is explored and compared to previous literature.…”

Investigation of the High-Temperature Spin-Transition of a Mononuclear Iron(II) Complex Using X-ray Photoelectron Spectroscopy

“…Ligands with this degree of flexibility can produce many interesting coordination arrangements under different conditions, and the ability to manipulate metallo-supramolecular structure in these compounds allows their physical properties to be altered. Conformational flexibility can also be an important factor in the design of ligands that facilitate intermolecular interactions in their consequent coordination compounds. ,− The temperature-dependent spin-transition of 1 was explored using the Quantum Design Versalab Measurement System with a vibrating sample magnetometer (VSM) attachment, and further evidence was provided by variable temperature (VT) single crystal X-ray diffraction and variable temperature X-ray photoelectron spectroscopy (VT-XPS) experiments. These experiments all demonstrated excellent correlation of the SCO behavior.…”