Carboxyl-Bonded Low-Spin Iron(III). Chemistry of a Family of Coordination Type cis-FeN4O2

Selective cyanide sensing using a Fe(III) complex of pyridoxal-beta alanine Schiff base

Fluorogenic chemosensors using pyridoxal derivatized ligands as fluorophore is a rapidly growing field of research. Here we report a new Fe(III) complex, [Fe(HBala-pydx)(Bala-pydx)] (H₂Bala-pydx is the Schiff base of pyridoxal with beta-alanine), which can serve as a sensitive and selective turn-on fluorescent sensor for the detection of cyanide(CN^-) in micromolar concentrations (L.O.D. is 1.134 µM), via the ligand displacement approach, in aqueous-acetonitrile medium. The Fe(III) complex is adequately characterized by analytical and spectroscopic methods along with X-ray crystal structure determination.

Synthesis, Crystal Structure and Magnetic Properties of 1D Chain Complexes Based on Azo Carboxylate Oxime Ligand

Two carboxylate-bridged one-dimensional chain complexes, {[MnII(MeOH)2][FeIII(L)2]2}n (1) and {[MnII(DMF)2][MnIII(L)2]2·DMF}n (2) [H2L = ((2-carboxyphenyl)azo)-benzaldoxime], containing a low-spin [FeIII(L)2]− or [MnIII(L)2]− unit were synthesized. Magnetic measurements show that the adjacent high-spin MnII and low-spin MIII ions display weak antiferromagnetic coupling via the syn–anti carboxyl bridges, with J = −0.066(2) cm−1 for complex 1 and J = −0.274(2) cm−1 for complex 2.

A Redox-Induced Spin-State Cascade in a Mixed-Valent Fe3 (μ3 -O) Triangle

One-electron reduction of a pyrazolate-bridged triangular Fe₃ (μ₃ -O) core induces a cascade wherein all three metal centers switch from high-spin Fe³⁺ to low-spin Fe^2.66+ . This hypothesis is supported by spectroscopic data (¹ H-NMR, UV-vis-NIR, infra-red, ⁵⁷ Fe-Mössbauer, EPR), X-ray crystallographic characterization of the cluster in both oxidation states and also density functional theory. The reduction induces substantial contraction in all bond lengths around the metal centers, along with diagnostic shifts in the spectroscopic parameters. This is, to the best of our knowledge, the first example of a one-electron redox event causing concerted change in multiple iron centers.

Regiospecific Oximato Coordination at the Oxygen Site: Ligand Design and Low-Spin Mn(II) and Fe(II/III) Species

The (pyridylazo)oxime ligand (C(5)H(4)N)N=NC(=NOH)C(6)H(4)R(p), HRL (R = H, Me), has been synthesized with the objective of promoting the very rare mononuclear oximato-O coordination. The synthesis involves hydrazone nitrosation. HRL reacts with M(ClO(4))(2).6H(2)O, affording [M(RL)(2)] (M = Mn, Fe), and X-ray structure determinations have indeed revealed the presence of the desired oximato-O coordination mode in the distorted octahedral MN(4)O(2) sphere characterized by a 2-fold axis of symmetry relating the two tridentate ligands, all chelate rings being five-membered. The M-N and M-O distances are relatively short (1.84-1.99 Å), consistent with spin-pairing (M = Mn, S = (1)/(2); M = Fe, S = 0). The M-N bond length trend, Mn(II) > Fe(II), is in accord with the larger radius of the low-spin Mn(II) atom. The M-O length order is, however, Mn(II) < Fe(II). This reversal occurs because of the rigidity of the ligand skeleton. Significant M-azo back-bonding is present (N=N length approximately 1.30 Å). [Mn(RL)(2)] displays hyperfine-split axial EPR spectra (g( parallel) approximately 1.98, g( perpendicular) approximately 2.06, A( parallel) approximately 170 G, A( perpendicular) approximately 65 G) in frozen solution as well as in polycrystalline [Fe(RL)(2)] lattices. The quasireversible Fe(III)/Fe(II) couple of [Fe(RL)(2)] has E(1/2) approximately 0.7 V. The oxidized complex [Fe(RL)(2)]PF(6) has been electrosynthesized. It is low-spin (S = (1)/(2)) and displays axial EPR spectra (g( parallel) approximately 1.98, g( perpendicular) approximately 2.14) in frozen solution. The Mn(II) --> Mn(III) oxidation ( approximately 1.0 V) in [Mn(RL)(2)] is irreversible. Crystal data for [Mn(HL)(2)].CH(2)Cl(2): crystal system monoclinic, space group I2/a, a = 14.142(7) Å, b = 10.721(7) Å, c = 16.933(10) Å, beta = 93.01(4) degrees, Z = 4. Crystal data for [Fe(HL)(2)].CH(2)Cl(2): crystal system monoclinic, space group I2/a, a = 14.254(6) Å, b = 10.742(6) Å, c = 16.719(8) Å, beta = 92.35(4) degrees, Z = 4.