Synthesis and structures of five-coordinate bis-o-iminobenzosemiquinone complexes M(ISQ-R)2X (X = Cl, Br, I, or SCN; M = CoIII, FeIII, or MnIII)

Abstract

New five coordinate complexes Co(ISQ Pr i ) 2 Cl, Co(ISQ Me) 2 Cl, Co(ISQ Me) 2 I, Co(ISQ Me) 2 (SCN), Mn(ISQ Pr i ) 2 Cl, and Fe(ISQ Me) 2 Br (ISQ Pr i and ISQ Me are the 4,6 di tert butyl N (2,6 diisopropylphenyl) and 4,6 di tert butyl N (2,6 dimethylphenyl) o iminobenzosemiquinone radical anions, respectively) were synthesized. The complexes were characterized by UV Vis and IR spectroscopy and magnetochemistry. The molecular struc tures of the Fe(ISQ Me) 2 Br and Mn(ISQ Pr i ) 2 Cl complexes were established by X ray diffrac tion. The singlet ground state (S = 0) of the cobalt complexes is caused by antiferromagnetic coupling between the unpaired electrons of the radical ligands (S = 1/2) through the fully occupied atomic orbitals of low spin cobalt(III) (d 6 , S = 0). The effective magnetic moments of the complexes at 10 К are 0.18 µ B for Co(ISQ Pr i ) 2 Cl and 0.16 µ B for Co(ISQ Me) 2 I. The ground state of the manganese complex is triplet (S = 1). Two unpaired electrons of the o iminobenzosemiquinone ligands are strongly antiferromagnetically coupled with two of four unpaired electrons of high spin manganese(III) (d 4 , S = 2).Abundant data on o semiquinone complexes have been accumulated. 1,2 Studies of metal complexes with o imino benzoquinone ligands (analogs of o benzoquinones) are of considerable interest because o iminobenzoquinones have distinguishing features due to which such studies extend the range of related compounds and add to our knowledge of this class of complexes.Unlike o quinones, o iminoquinones are asymmetric, and the presence of the nitrogen atom allows one to in vestigate the spin density distribution in the chelate ring. The use of o iminosemiquinone as a spin labeled ligand in metal complexes helps in solving structural dynamic problems 3 and makes it possible to determine the spatial arrangement of ligands containing magnetic nuclei with respect to the plane of the o iminosemiquinone plane. 4 At the same time, o iminosemiquinones, like o semi quinones, serve as magnetic centers. From this stand point, investigation of spin couplings between ligands and/or between ligands and metals are of interest.The steric hindrance of the metal centers in com plexes can be varied over a wide range by introducing various substituents at the nitrogen atom. For example, o iminobenzoquinones containing the unsubstituted phe nyl substituent at the nitrogen atom form tris ligand tran sition metal complexes, which are very similar to o semi quinone derivatives. 5-7

Structural Changes in Five‐Coordinate Bromido‐bis(o‐iminobenzo‐semiquinonato)iron(III) Complex: Spin‐Crossover or Ligand‐Metal Antiferromagnetic Interactions?

“…The values of Fe−N, Fe−O, and Fe−Br bond distances obtained from EXAFS data at various temperatures are in good agreement with the data of XRD analysis for ( Me imSQ) 2 FeBr [44,45] . Although the distances from XRD were obtained only at three temperatures of 100, 240, and 293 K, an increase in the Fe−O distances in the coordination center from 1.9009(19), 1.9052(19) Å (100 K) to 1.944(2), 1.948(2) Å (293 K) and Fe−N distances from 1.940(2), 1.940(2) Å (100 K) to 1.993(3), 2.003(3) Å (293 K), respectively.…”

“…The values of FeÀ N, FeÀ O, and FeÀ Br bond distances obtained from EXAFS data at various temperatures are in good agreement with the data of XRD analysis for ( Me imSQ) 2 FeBr. [44,45] Although the distances from XRD were obtained only at three temperatures of 100, 240, and 293 K, an increase in the FeÀ O distances in the coordination center from 1.9009 (19) (Figure 6 open circles). The values of FeÀ Br obtained from XRD of the distances of 2.3816(6) Å (100 K) and 2.3755(7) Å (293 K) also confirm our conclusion, obtained from the EXAFS analysis, that they remain constant over the entire temperature range.…”

“…The experimental data were simulated using the theoretical photoelectron mean free path λ(k), amplitude F i (k) and phase functions Ψ i (k) (formula 1) calculated using the program FEFF7 [52] and the crystallographic structure for ( Me imSQ) 2 FeBr. [45] (1)…”

“…The structural parameters, including interatomic distances (R i ), coordination numbers (N i ) and the distance mean‐square deviations from thermal motion and static disorder of the absorbing and scattering atoms, also known as Debye‐Waller factors (σ 2 ), were found by the non‐linear fit of theoretical spectra to experimental ones. The experimental data were simulated using the theoretical photoelectron mean free path λ(k), amplitude F i (k) and phase functions Ψ i (k) (formula 1) calculated using the program FEFF7 [52] and the crystallographic structure for ( Me imSQ) 2 FeBr [45] …”

New Germanium Complexes Containing Ligands Based on 4,6‐Di‐tert‐butyl‐N‐(2,6‐diisopropylphenyl)‐o‐iminobenzoquinone in Different Redox States

“…The Cl(1) ··· H(2) distance is 2.59(3) Å, which is significantly less than the sum of the van der Waals radii (2.97 Å) 9. The heteroatom‐to‐germanium‐to‐heteroatom angles reveal the difference, which is unusual for five‐coordinate complexes of the ML 2 X type (L is an o ‐iminobenzoquinonato‐based ligand): the value of the angle O(1)–Ge(1)–O(2) [148.92(6)°] is less than that for N(1)–Ge(1)–N(2) [160.53(7)°], while in transition‐metal complexes M(ISQ) 2 Hal (M = Co, Fe, Mn) a decrease in the N–M–N angle relative to O–M–O is usual 10f…”