Structure and Magnetic Properties of a Non-Heme Diiron Complex Singly Bridged by a Hydroxo Group

Abstract

The synthesis of the first singly bridged non-heme diiron complex with a mu-hydroxo bridging ligand, [{(salten)Fe}2(OH)][B(C6H5)4].(CH3CN)x.(H2O)y (1) [H2salten = 4-azaheptane-1,7-bis(salicylideneiminate)], is reported. The complex has been characterized with X-ray crystallography, FTIR, magnetic susceptibility measurements, and Mössbauer spectroscopy. The data have been compared with the results of DFT calculations on both 1 and a model with an unsupported mu-oxo bridge (2) to verify the formulation of the complex as a mu-hydroxo-bridged species. The X-ray structure [Fe-O(H) = 1.997(1) A and Fe-O(H)-Fe = 159 degrees ] is consistent with the DFT-optimized geometry of 1 [Fe-O(H) = 2.02 A and Fe-O(H)-Fe = 151 degrees ]; the Fe-O(H) distance in 1 is about 0.2 A longer than the Fe-O separations in the optimized geometry of 2 (1.84 A) and in the crystallographic structures of diiron(III) compounds with unsupported mu-oxo bridges (1.77-1.81 A). The formulation of 1 as a hydroxo-bridged compound is also supported by the presence of an O-H stretch band in the FTIR spectrum of the complex. The magnetic susceptibility measurements of 1 reveal antiferromagnetic exchange (J = 42 cm(-1) and H(ex) = JS(1).S(2)). Nearly the same J value is obtained by analyzing the temperature dependence of the Mössbauer spectra (J = 43 cm(-1); other parameters: delta = 0.49 mm s(-1), DeltaE(Q) = -0.97 mm s(-1), and eta = 0.45 at 4.2 K). The experimental J values and Mössbauer parameters agree very well with those obtained from DFT calculations for the mu-hydroxo-bridged compound (J = 46 cm(-1), delta = 0.48 mm s(-1), DeltaE(Q) = -1.09 mm s(-1), and eta = 0.35). The exchange coupling constant in 1 is distinctly different from the value J approximately 200 cm(-1) calculated for the optimized mu-oxo-bridged species, 2. The increased exchange-coupling in 2 arises primarily from a decrease in the Fe-O bond length.

Synthesis and Crystal Structures of μ‐Oxido‐ and μ‐Hydroxido‐Bridged Dinuclear Iron(III) Complexes with an N2O Donor Ligand – A Theoretical Study on the Influence of Weak Forces on the Fe–O–Fe Bridging Angle

“…The highest energy bands (255, 231 nm for 1a; 260, 233 nm for 1b; 256 and 234 nm for 2) are attributed to πǞπ* transitions of the ligand, but contributions from less intense oxido-to-Fe CT are also expected in this region. [12] …”

“…Conversely, the hydroxido bridge is relatively unusual. [12] A fundamental structural component of the chemistry of these functional Fe III complexes is the variable Fe-O-Fe bridging angle, which is usually in the range 139-180°. However, in the majority of complexes where other bridging ligands are [ .…”

Fe2 and Fe4 Clusters Encapsulated in Vacant Polyoxotungstates: Hydrothermal Synthesis, Magnetic and Electrochemical Properties, and DFT Calculations

“…Focusing on iron systems, it has been shown that for supported [38] and unsupported [39] oxo bridged compounds the FeÀO distance is the main parameter which governs the strength of the magnetic interaction. In complex 1, the Fe-(m-OA C H T U N G T R E N N U N G (POM)) distances are long (1.915(11) and 2.106(11) ) compared to those classically found in dinuclear m-O bridged Fe III complexes, which justifies the low J value determined for this compound.…”

New Insights into the Ring‐Opening Polymerization of β‐Butyrolactone Catalyzed by Chromium(III) Salphen Complexes

“…[16] In contrast, freshly prepared Cr-1 c exhibits av ery weakb and at ñ = 3590cm À1 that can be assigned to the OH stretcho ft he coordinated water molecule. An older batch of Cr-1 c is characterized by al ower chloride content according to EDXa nalysisa nd exhibits incompletes olubility in THF ( Figure S6), which suggests that the slow loss of HCl with the formation of m-hydroxo-bridged specieso ccurs during storage.…”

“…This behavior is far from ideal living polymerization and suggests www.chemcatchem.org the existence of different catalytic sites that feature asignificant variation in activity,s ometimes even reflectedi nabimodality of PHB samples (see gel-permeationc hromatogram (GPC) in Figure S14). Furthermore, the gross polymerization rate decreaseso nly marginally upon monomer consumption, and this holds true up to high conversions (experiments [13][14][15][16]. This might be because the rate-determining step is independent of the monomer concentration in first approximation,a lthough other explanations can also be given.…”