Protonierung einer linearen, Oxo‐verbrückten Dieisen‐Einheit ohne Rehybridisierung des verbrückenden Sauerstoffatoms: Struktur des (μ‐Hydroxy)bis(tetraphenyl‐porphyrinato)eisen(III)‐Kations

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.

Section: Resultsmentioning

confidence: 96%

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

Krishnamurthy

Sarjeant

Goldberg

et al. 2005

“…It is also important to compare the structural and geometrical parameters of the diiron(III)‐μ‐hydroxo bisporphyrins reported here with two other hydroxo‐bridged porphyrinic cores [{Fe III (OEP)} 2 (OH)] + and [{Fe III (TPP)} 2 (OH)] + reported in the literature 3a,b. The Fe‐O(H)‐Fe angle is significantly decreased to 146.2(2)° in [{Fe III (OEP)} 2 (OH)]ClO 4 compared with the corresponding Fe‐O‐Fe angles of 172.2(2)° (triclinic) and 176.2(2)° (monoclinic) observed in [Fe III (OEP)] 2 O 3a.…”

Section: Resultsmentioning

confidence: 99%

“…The Fe‐O(H)‐Fe angle is significantly decreased to 146.2(2)° in [{Fe III (OEP)} 2 (OH)]ClO 4 compared with the corresponding Fe‐O‐Fe angles of 172.2(2)° (triclinic) and 176.2(2)° (monoclinic) observed in [Fe III (OEP)] 2 O 3a. For the TPP complex, however, the Fe‐O(H)‐Fe angles are only slightly decreased to 173.6(5)° and 169.2(1)° in [{Fe III (TPP)} 2 (OH)] + with [CB 11 H 6 Cl 6 ] − and [B(C 6 F 5 ) 4 ] − counterions, respectively, compared to the corresponding Fe‐O‐Fe angle of 176.1(2)° observed in [Fe III (TPP)] 2 O 3b…”

Section: Resultsmentioning

confidence: 99%

“…It was considered of interest to compare the spin states of the μ‐hydroxo bisporphyrins reported here with those of other unsupported diiron(III) porphyrins with a single hydroxo bridge reported in the literature. For [{Fe III (TPP)} 2 (OH)] + , the pyrrole protons gave rise to a single peak at δ =−42 or +28 ppm in the 1 H NMR spectra when the counter anions were [CB 11 H 6 Cl 6 ] − and [B(C 6 F 5 ) 4 ] − , respectively 3b,d. Mössbauer spectra of the solids showed only one quadrupole‐split doublet, suggesting two equivalent Fe III centers with admixed iron spins in both of the complexes.…”

Section: Resultsmentioning

confidence: 99%

“…Evans et al. reported two almost linear hydroxo‐bridged diiron complexes with the core structure [{Fe III (TPP)} 2 (OH)] + (TPP=tetraphenylporphyrin) (the two complexes differed in their counter anions), prepared by protonation of the corresponding μ‐oxo‐diiron complex [{Fe III (TPP)} 2 O] 3b. A hydroxo‐bridged iron dimer of an N‐confused porphyrin with Na bridging the outer N atoms was reported by Hung et al 3c.…”

Section: Introductionmentioning

confidence: 83%

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Effect of Heme–Heme Interactions and Modulation of Metal Spins by Counter Anions in a Series of Diiron(III)‐μ‐hydroxo Bisporphyrins: Unusual Stabilization of Two Different Spins in a Single Molecular Framework

Ghosh

Bhowmik

Sil

et al. 2013

A new family of five ethene-bridged diiron(III)-μ-hydroxo bisporphyrins with the same core structure but different counter anions, represented by the general formula [Fe2 (bisporphyrin)]OH·X (X=counter anion), is reported herein. In these complexes, two different spin states of Fe are stabilized in a single molecular framework. Protonation of the oxo-bridged dimer 1 by strong Brønsted acids such as HI, HBF4, HPF6, HSbF6 , and HClO4 produces the μ-hydroxo complexes with I5(-)(2), BF4(-)(3), PF6(-)(4), SbF6(-)(5), and ClO4(-)(6) as counter anions, respectively. The X-ray structures of 2 and 6 have been determined, which provide a rare opportunity to investigate structural changes upon protonation. Spectroscopic characterization has revealed that the two iron(III) centers in 2 are nonequivalent with nearly high and admixed-intermediate spins in both the solid state and solution. Moreover, the two different Fe(III) centers of 3-5 are best described as having admixed-high and admixed-intermediate spins with variable contributions of S=5/2 and 3/2 for each state in the solid, but two different admixed-intermediate spins in solution. In contrast, the two Fe(III) centers in 6 are equivalent and are assigned as having high and intermediate spin states in the solid and solution, respectively. The X-ray structures reveal that the Fe-O bond length increases on going from the μ-oxo to the μ-hydroxo complexes, and the Fe-O(H)-Fe unit becomes more bent, with the dihedral angle decreasing from 150.9(2)° in 1 to 142.3(3)° and 143.85(2)° in 2 and 6, respectively. Variable-temperature magnetic data have been subjected to a least-squares fitting using the expressions derived from the spin Hamiltonians H=-2JS1·S2 -μ·B+D[S(2)(z) - 1/3S(S + 1)] (for 2, 3, 4, and 5) and H=-2JS1·S2 (for 6). The results show that strong antiferromagnetic coupling between the two Fe(III) centers in 1 is attenuated to nearly zero (-2.4 cm(-1)) in 2, whereas the values are -46, -32.6, -33.5, and -34 cm(-1) for 3, 4, 5, and 6, respectively.

Protonation of an Oxo‐Bridged Diiron Unit Gives Two Different Iron Centers: Synthesis and Structure of a New Class of Diiron(III)‐μ‐hydroxo Bisporphyrins and the Control of Spin States by Using Counterions

Bhowmik

Ghosh

Layek

et al. 2012

Reported herein is a hitherto unknown family of diiron(III)-μ-hydroxo bisporphyrins in which two different spin states of Fe are stabilized in a single molecular framework, although both cores have identical molecular structures. Protonation of the oxo-bridged dimer (2) by using strong Brønsted acids, such as HI, HBF(4), and HClO(4), produce red μ-hydroxo complexes with I(3)(-) (3), BF(4)(-) (4), and ClO(4)(-) (5) counterions, respectively. The X-ray structure of the molecule reveals that the Fe-O bond length increases on going from the μ-oxo to the hydroxo complex, whereas the Fe-O(H)-Fe unit becomes more bent, which results in the smallest known Fe-O(H)-Fe angles of 142.5(2) and 141.2(1)° for 3 and 5, respectively. In contrast, the Fe-O(H)-Fe angle remains unaltered in 4 from the corresponding μ-oxo complex. The close approach of two rings in a molecule results in unequal core deformations in 3 and 4, whereas the cores are deformed almost equally but to a lesser extent in 5. Although 3 was found to have nearly high-spin and admixed intermediate Fe spin states in cores I and II, respectively, two admixed intermediate spin states were observed in 4. Even though the cores have identical chemical structures, crucial bond parameters, such as the Fe-N(p), Fe-O, and Fe⋅⋅⋅Ct(p) bond lengths and the ring deformations, are all different between the two Fe(III) centers in 3 and 4, which leads to an eventual stabilization of two different spin states of Fe in each molecule. In contrast, the two Fe centers in 5 are equivalent and assigned to high and intermediate spin states in the solid and solution states, respectively. The spin states are thus found to be dependent on the counterions and can also be reversibly interconverted. Upon protonation, the strong antiferromagnetic coupling in the μ-oxo dimer (J, -126.6 cm(-1)) is attenuated to almost zero in the μ-hydroxo complex with the I(3)(-) counterion, whereas the values of J are -36 and -42 cm(-1), respectively, for complexes with BF(4)(-) and ClO(4)(-) counterions.