Synthesis and Relative Stability of a Series of Compounds of Type [Fe(II)(bztpen)X]⁺, Where bztpen = Pentadentate Ligand, N₅, and X^- = Monodentate Anion

Abstract

The structural and solution characterization of novel Fe(II) compounds of the general formula [Fe(bztpen)X]PF6 and [Fe(bztpen)CH3CN](PF6)2 is presented, where bztpen is the pentadentate ligand N-benzyl-N,N',N'-tris(2-methylpyridyl)ethylenediamine and X- is a monodentate ligand. All complexes were characterized in solution and in the solid state, employing the usual techniques and single-crystal X-ray diffraction. The results obtained are discussed in terms of the existing information for some previously reported analogous compounds to arrive at a rationalization regarding the influence of a variation in the coordination environment of all compounds and to evaluate their relative stability. The observed magnetic response in the solid state is paramagnetic in the entire temperature range for the Cl-, Br-, I-, OCN-, and SCN- derivatives, while the N(CN)2-, CH3CN, and CN- derivatives are diamagnetic. The diamagnetic character of these last two compounds is confirmed in acetonitrile solution, while a spin transition step is observed for the N(CN)2- derivative. Diffraction data for all compounds as hexafluorophosphates shows that the I-, Br-, and OCN- derivatives crystallize in the orthorhombic space group Pbca, while the CN-, SCN-, and CH3CN compounds crystallize in the triclinic space group P. Average bond lengths and the trigonal distortion parameter can be correlated to the observed magnetic susceptibility depending on the coordinated monodentate ligand. Solution measurements of electronic properties for the compounds follow the trend established by the spectrochemical series. The relative stability of the Fe(II) complexes can be established in terms of the percentage of dissociation from the voltammetry and conductivity results, which are consistent with those obtained spectrophotometrically, mainly, the larger stability for the CN- derivative and the lower for the I- derivative. The redox potential and percentage of dissociation values allow for the estimation of the relative stability constants for the Fe(II) and Fe(III) complexes.

Electronic Structure Modulation in an Exceptionally Stable Non‐Heme Nitrosyl Iron(II) Spin‐Crossover Complex

“…Synthesis of compound 1 : Samples of compound 1 essentially constituted of single crystals were obtained in a very good yield (≈90 %) by bubbling nitric oxide for 10 min through diluted solutions of [Fe(bztpen)CH 3 CN](PF 6 ) 2 (≈30 mg 0.037 mmol in 40 mL of MeOH). The final violet solution was kept under argon in repose and closed for three days to lead the precipitation of single crystals of appropriate size for single‐crystal X‐ray diffraction The crystals melt with decomposition at approximately 480 K. Elemental analysis calcd (%) for C 27 H 29 F 12 FeN 6 OP 2 : C 40.57, H 3.66, N 10.51; found: C 39.81, H 3.73, N 10.39.…”

Correlating Properties in Iron(III) Complexes: A DFT Description of Structure, Redox Potential and Spin Crossover Phenomena

“…Typically, these complexes display a [Fe III N 4 O 2 ] coordination environment, which can be achieved by the participation of ancillary ligands . Recently, we have studied the formation of [Fe II (bztpen)X] +/2+ complexes, where bztpen is the nitrogen pentadentate ligand N‐Benzyl‐N,N’,N’‐tris(2‐pyridylmethyl) ethylenediamine and X is an anion or solvent molecule (see Scheme a and 1b). The stability of these complexes in acetonitrile (CH 3 CN) solution towards oxidation follows the expected behavior considering the ligand field of the exogenous ligand X.…”

Iron(II) Complexes of Two Amine/Imine N5 Chelate Ligands Containing a 1,4‐Diazepane Core – To Crossover or Not To Crossover

“…2.2 Å indicates high-spin iron(II) in all cases at 150(1) K (Table 1). [15,16] The halide ligand X1 (X = Cl or Br) is trans to a tertiary amine N atom (N1) in all structures, although, at least for complexes of ligand 4b, a trans arrangement N10-Fe1-X1 would not appear precluded by structural constraints. Indeed, structural data to be published elsewhere show that ligand exchange [(chloride Ǟ triflate (OTf)] leads to a trans arrangement (N10-Fe1-OTf) in the triflatoiron(II) complex of ligand 4b.…”