A high-spin square-planar Fe(ii) complex stabilized by a trianionic pincer-type ligand and conclusive evidence for retention of geometry and spin state in solution

Abstract

Extensive spectroscopic evaluation of a novel ONO3– trianionic pincer Fe(ii) complex indicates the rare square-planar geometry and S = 2 spin state are retained in solution.

The [Fe{(SePPh2)2N}2] Complex Revisited: X‐ray Crystallography, Magnetometry, High‐Frequency EPR, and Mössbauer Studies Reveal Its Tetrahedral FeIISe4 Coordination Sphere

“…It is of interest that square planar Fe II O 4 sites have been found in solid‐state structures, including the rare mineral gillespite (BaFe II Si 4 O 10 ) and a catalytically active Fe II zeolite site converting methane to methanol . On the other hand, only a handful of molecular Fe II systems contain square planar FeO 4 [44b], or FeO 2 NCl coordination spheres, and these are qualified as highly unusual. [47c] The above systems have been shown to contain high spin, S = 2, sites, exhibiting unique Mössbauer spectroscopic signatures (vide infra).…”

“…High spin, S = 2, square‐planar Fe II sites are rather rare (vide supra). Among this family of Fe II systems, those that have been studied by Mössbauer spectroscopy[44b], , [50a], exhibit quadrupole doublets with remarkably low |Δ E Q | values (<< 1.0 mm s –1 ). This trend, which has also been observed for S = 2, trigonal planar Fe II sites with thiolate ligands, may be qualitatively understood on the basis of the symmetry of the square planar ligand environment.…”

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…However, the most interesting cases involved Re IV metal ions with octahedral geometry in a series of complexes (Fig. 27), which can be categorized as: (i) hexahalorhenates(IV) [119,[139][140][141][142][143][144][145][146] (79), and I (80)) [139], (ii) pentahalorhenates(IV) with one labile coordination site [147,148] such as (NH 2 Me 2 )[Re IV X 5 (DMF)] (where X = Cl (81) and Br (82)) [147], (iii) tetrahalorhenates(IV) with cis-blocking chelating organic ligands [110,[149][150][151][152][153][154][155][156] such as (NBu 4 ) 2 [Re(ox)X 4 ] (where ox = oxalate, X = Cl (83) and Br (84) For a hexa-coordinated 3d 3 ion with ideal O h geometry, significantly high first-order SOC and thus large magnetic anisotropy will be obtained from the triply degenerate ground state (involving d xy , d xz , and d yz orbitals) if Jahn-Teller distortion, which inevitably breaks the degeneracy and minimizes the SOC, is not present. In octahedral complexes, Jahn-Teller distortion splits the lowest lying triply degenerate d orbitals, thereby leading to two sets of orbitals, i.e., d xy and (d xz , d yz ), irrespective of whether the nature of the distortion is compression (where the energy order is d xy < (d xz , d yz )) or elongation (where the energy order is d xy > (d xz , d yz )).…”

“…SP complexes are generally stabilized by anionic ligands with one or more following characteristics: (i) strong -donor ligands in order to destabilize the sterically stable tetrahedral geometry, (ii) weak -donating ligands to minimize the anti-bonding character of the dx²-y² orbital [18], (iii)sterically demanding ligands [75,76]. Magnetic anisotropy was investigated for several square-planar complexes [77][78][79][80]. For instance, large and positive D was demonstrated for two Co III (d 6 ) complexes with square-planar geometry [81], [Co III (C 6 X 5 ) 4 ] -(52 for X = F, as shown in Fig.…”

“…The counter-cation in these complexes is a paramagnetic Fe III center, but its bulkiness prevents the propagation of intermolecular magnetic superexchange interactions. Detailed magnetic investigations obtained g factors = 1.82, 1.85, and 1.83, and the absolute axial ZFS parameters were |D| = 16.0, 14.5, and 12.0 cm -1 for the Cl (78), Br (79), and I (80) analogues, respectively [139]. The D parameters for (AsPh 4 ) 2 [Re IV Cl 6 ] 2-and (NBu 4 ) 2 [Re IV Cl 6 ] 2-were positive with magnitudes of 13 and 9 cm -1 , respectively [156].…”