Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

Abstract

The mixed N3S(thiolate) ligand 1-[bis[2-(pyridin-2-yl)ethyl]amino]-2-methylpropane-2-thiol (Py2SH) was used in the synthesis of four iron(II) complexes: [(Py2S)FeCl] (1), [(Py2S)FeBr] (2), [(Py2S)4Fe5II(mu-OH)2](BF4)4 (3), and [(Py2S)2Fe2II(mu-OH)]BF4 (4). The X-ray structures of 1 and 2 revealed monomeric iron(II)-alkylthiolate complexes with distorted trigonal-bipyramidal geometries. The paramagnetic 1H NMR spectra of 1 and 2 display resonances from delta = -25 ppm to +100 ppm, consistent with a high-spin iron(II) ion (S = 2). Spectral assignments were made on the basis of chemical shift information and T1 measurements and show the monomeric structures are intact in solution. To provide entry into hydroxide-containing complexes, a novel synthetic method was developed involving strict aprotic conditions and limiting amounts of H2O. Reaction of Py2SH with NaH and Fe(BF4)2.6 H2O under aprotic conditions led to the isolation of the pentanuclear, mu-OH complex 3, which has a novel dimer-of-dimers type structure connected by a central iron atom. Conductivity data on 3 show this structure is retained in CH2Cl2. Rational modification of the ligand-to-metal ratio allows control over the nuclearity of the product, yielding the dinuclear complex 4. The X-ray structure of 4 reveals an unprecedented face-sharing, biooctahedral complex with an [S2O] bridging arrangement. The magnetic properties of 3 and 4 in the range 1.9-300 K were successfully modeled. Dinuclear 4 is antiferromagnetically coupled [J = -18.8(2) cm(-1)]. Pentanuclear 3 exhibits ferrimagnetic behavior, with a high-spin ground state of S(T) = 6, and was best modeled with three different exchange parameters [J = -15.3(2), J' = -24.7(3), and J'' = -5.36(7) cm(-1)]. DFT calculations provided good support for the interpretation of the magnetic properties.

Sulfide oxidation by O2: Synthesis, structure and reactivity of novel sulfide-incorporated Fe(II) bis(imino)pyridine complexes

“…Bond distances for complexes 1 and 2 are consistent with high-spin ferrous centers [71] and are in good agreement with similar bis(imino)pyridine compounds reported in the literature [65, 70, 72]. A comparison of bond lengths from cations 1 and 2 with closely related compounds in the literature are summarized in Table 2.…”

Secondary Coordination Sphere Influence on the Reactivity of Nonheme Iron(II) Complexes: An Experimental and DFT Approach

“…The Fe-N py distances for 3 (2.165(1)–2.379(1); 2.172(1)–2.442(1) Å) are indicative of high-spin (hs) Fe II -N py bond lengths. 2 The paramagnetically shifted 1 H NMR spectrum (from 151 to −7 ppm) as well as a magnetic moment measurement by Evan’s method in CD 3 CN (exptl μ eff = 5.2; calcd (spin-only, S = 2) μ eff = 4.9) confirmed that 3 is hs-Fe II . Thus the addition of phenyl substituents to the N4Py scaffold causes a spin state change from low-spin (ls) Fe II for [Fe II (N4Py)(CH 3 CN)] 2+ to hs-Fe II for 3 .…”

Geometric Preferences in Iron(II) and Zinc(II) Model Complexes of Peptide Deformylase

“…10 The IR data for 1 in the solid state (KBr) exhibits a strong peak at 1630 cm −1 assigned to the asymmetric stretch of the monodentate formate ligand. A similar peak is found in the IR spectrum of 1 in CH 3 CN at 1625 cm −1 .…”

“…11 The 1 H NMR spectrum of 1 in CD 3 CN exhibits reasonably sharp, paramagnetically shifted peaks over the range +78 to −25 ppm, which is characteristic of a high-spin Fe II complex, and the pattern of peaks is similar to that observed for the complexes (Py 2 S)Fe II X (X = Br, Cl). 10 The IR data for 1 in the solid state (KBr) exhibits a strong peak at 1630 cm −1 assigned to the asymmetric stretch of the monodentate formate ligand. A similar peak is found in the IR spectrum of 1 in CH 3 CN at 1625 cm −1 .…”

“…The N(amine)-Fe II distance of 2.366(4) Å is long, but is quite close to the related complexes (Py 2 S)Fe II X (X = Br, N(amine)-Fe II = 2.387(1) Å; X = Cl (2.352(2) Å). 10 There is no obvious reason for the elongation of this bond in these complexes, and theoretical calculations show that another isomer of 1 with a more conventional Fe II -N(amine) distance should be accessible (vide infra). Interestingly, the formate ligand is clearly monodentate with Fe-O(2) = 4.12 Å, and is in fact bound in an anti disposition.…”