Heptanuclear [FeIII6CrIII]3+ Complexes Experimentally Studied by Means of Magnetometry, X-ray Diffraction, XAS, XMCD and Spin-Polarized Electron Spectroscopy in Cross-Comparison with [MnIII6CrIII]3+ Single-Molecule Magnets

Dohmeier N, Helmstedt A, Müller N, et al. Heptanuclear [FeIII6CrIII]3+ Complexes Experimentally Studied by Means of Magnetometry, X-ray Diffraction, XAS, XMCD and Spin-Polarized Electron Spectroscopy in Cross-Comparison with [MnIII6CrIII]3+ Single-Molecule Magnets. Magnochemistry. 2016;2(1): 5

The first trinuclear manganese triplesalen complex: Synthesis, structural, and magnetic characterization of [(talen(NO2)){Mn-III(DMSO)(2)}(3)](ClO4)(3)

Glaser T, Heidemeier M, Froehlich R. The first trinuclear manganese triplesalen complex: Synthesis, structural, and magnetic characterization of [(talen(NO2)){Mn-III(DMSO)(2)}(3)](ClO4)(3). COMPTES RENDUS CHIMIE. 2007;10(1-2):71-78.The reaction of the nitro-substituted triplesalen ligand H(6)talen(NO2) with Mn(ClO4)(2)center dot 6H(2)O in CH3CN in the presence of Et3N and DMSO results in the formation of [(talen(NO2)){Mn-III(DMSO)(2)}(3)](ClO4)(3) (1) which has been characterized by elemental analysis, FTIR, UV-vis-NIR, ESI-MS, single-crystal X-ray diffraction, and magnetic measurements. The triplesalen ligand (talen(NO2))(6-) provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. The coordination environment of each Mn-III ion is completed by two O-bonded DMSO molecules. The folding of the triplesaten ligand results in an overall dish-like geometry for the trication in 1. The magnetic characterization has been performed by temperature dependent magnetic susceptibility measurements and variable temperature-variable field (VTVH) magnetization data in order to determine both the exchange couplings J between the S-i = 2 ion and the local zero-field splittings D-i. Simulations to the appropriate spin-Hamiltonian using a full-matrix diagonalization approach provided a weak antiferromagnetic interaction J = -0.30 +/- 0.05 cm(-1) but a strong magnetic anisotropy expressed by D = -4.0 +/- 0.4 cm(-1). The potential applications of 1 and forthcoming members of this new family of trinuclear manganese triplesalen complexes in molecule-based magnetism and homogenous catalysis are discussed

Spin-polarization in 1,3,5-trihydroxybenzene-bridged first-row transition metal complexes

Glaser T, Theil H, Heidemeier M. Spin-polarization in 1,3,5-trihydroxybenzene-bridged first-row transition metal complexes. COMPTES RENDUS CHIMIE. 2008;11(10):1121-1136.The late Olivier Kahn formulated a research objective for molecular magnetism: 'The normal trend for the molecular state is the pairing of electrons [...] with a cancellation of the electron spins. The design of a molecule-based magnet requires that this trend be successfully opposed.' One strategy for enforcing ferromagnetic interactions is the spin-polarization mechanism. While this mechanism is almost always working in organic chemistry, the application to transition metal complexes is not straight-forward. We have established a structurally related series of trinuclear complexes bridged by modified 1,3,5-trihydroxybenzene (phloroglucinol) ligands. The trinuclear Cu-II complexes all exhibit weak, but ferromagnetic interactions. The trinuclear V-IV complex exhibits even smaller ferromagnetic interactions, while a trinuclear Mn complex exhibits anti ferromagnetic interactions. The correlation between structural and magnetic parameters in the series of Cu complexes gives experimental insight into the spin-polarization mechanism. The crucial parameter for an efficient spin-polarization mechanism through the bridging benzene unit seems to be the amount of spin density in the p(z)(pi) orbitals of the phenolic oxygen atoms. This spin density crucially depends on the remaining coordination sites and on the ligand folding at the central Cu-phenolate bond. The spin transfer from the metal to the phenolate oxygen atom occurs by two different mechanisms, namely spin-polarization and spin-delocalization, which can provide opposing contributions. The main conclusion of this study is that for a more efficient spin-polarization through the central benzene ring the spin density in the phenolate O p(z)(pi) orbital must be maximized, which can mainly be achieved by increasing the covalency of the metal-phenolate bond. To cite this article: T Glaser et al., C R. Chimie 11 (2008). (C) 2008 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

Synthesis and structural characterization of a monofunctionalized phloroglucin-derivative: A precursor for heterotrinuclear meta-phenylene bridged complexes

Glaser T, Heidemeier M, Krickemeyer E, Bögge H. Synthesis and structural characterization of a monofunctionalized phloroglucin-derivative: A precursor for heterotrinuclear meta-phenylene bridged complexes. ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES. 2006;61(6):753-757.As part of our synthetic efforts for new triplesalen derivatives, we reacted 2,4,6-triacetyl-1,3,5-trihydroxybenzene (1) with excess Cu(ClO4)(2) center dot 6H(2)O, imidazole, and ethylenediamine. However, not the triple ketimine derivative was formed but the mononuclear Cull complex [LCuII(ImH)jClO(4) center dot 0.5EtOH center dot 0.5H(2)O (HL = 6-(1-(2-aminoethylimino)ethyl)-2,4-diacetyl-1,3,5-trihydroxybenzene) with only one ketimine function. This complex forms a one-dimensional coordination polymer in the solid state through the apical binding of a keto-oxygen atom of one cation to the Cu-II ion of a neighboring cation. Magnetic measurements reveal the presence of weak antiferromagnetic intra-chain interactions

Structural influences on the exchange coupling and zero-field splitting in the single-molecule magnet [(Mn6MnIII)-Mn-III](3+)

Höke V, Heidemeier M, Krickemeyer E, et al. Structural influences on the exchange coupling and zero-field splitting in the single-molecule magnet [(Mn6MnIII)-Mn-III](3+). Dalton Transactions. 2012;41(41):12942-12959.A comprehensive synthetic, structural, mass spectrometrical, FT-IR and UV/Vis spectroscopic, electrochemical, and magnetic study on [(Mn6MnIII)-Mn-III](3+) (= [{(talen(t-Bu2)) Mn-3(III)}(2){Mn-III(CN)(6)}](3+)) is presented. The high stability of [(Mn6MnIII)-Mn-III](3+) in solution allows the preparation of different salts and solvates: [(Mn6MnIII)-Mn-III](BPh4)(3)center dot 3MeOH center dot 3MeCN center dot 3Et(2)O (1), [(Mn6MnIII)-Mn-III(MeOH)(4)](BPh4)(3)center dot 5MeOH (2), [(Mn6MnIII)-Mn-III(MeOH)(6)](BF4)(3)center dot 9MeOH (3), [(Mn6MnIII)-Mn-III(MeOH)(6)](PF6)(2)(OAc)center dot 11MeOH (4), and [(Mn6MnIII)-Mn-III(MeOH)(6)](lactate)(3)center dot 5MeOH center dot 10H(2)O (5). The molecular structure of [(Mn6MnIII)-Mn-III](3+) is closely related to the already published [Mn(6)(III)Mc](3+) complexes (M-c = Cr-III, Fe-III, Co-III). ESI mass spectra exhibit the signal of the [{(talen(t-Bu2))Mn-3(III)}(2){Mn-III(CN)(6)}](3+) trication. FT-IR spectra show the characteristic bands of the triplesalen ligand in [Mn(6)(III)Mc](3+) and the symmetric nu(C N) vibration of the [Mn-III(CN)(6)](3-) unit at 2135 cm(-1). UV/Vis spectra are dominated by intense transitions of the trinuclear Mn-3(III) triplesalen subunits above 20 000 cm(-1). The electrochemical studies establish the occurrence of ligand-centered oxidations at approximate to 1.0 V vs. Fc(+)/Fc, an oxidation of the central Mn-III at 0.78 V, and a series of reductions of the terminal Mn-III ions between -0.6 and -1.2 V. AC magnetic measurements indicate single-molecule magnet (SMM) behavior for all compounds. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting with full consideration of the relative orientation of the D-tensors, and Zeeman interaction, taking into account the diamagnetic nature of the central Mn-III at low temperatures as inferred from a previous ab initio study. The spin-Hamiltonian simulations indicate Mn-III-Mn-III interactions in the -0.37 to -0.70 cm(-1) range within the trinuclear triplesalen subunits and in the -0.02 to + 0.23 cm(-1) range across the central Mn-III ion, while D-Mn = -3.1 to -5.0 cm(-1). The differences in the exchange parameters and the relaxation behavior of the [(Mn6MnIII)-Mn-III](3+) compounds are rationalized in terms of subtle variations in the molecular structures, especially regarding the distortion of the central [Mn-III(CN)(6)](3-) core and the ligand folding. In comparison with the other [(Mn6Mc)-M-III](3+) compounds, this allows us to establish some general magnetostructural correlations for this class of complexes

From triplesalen to triplesalacen: Synthesis spectroscopic, redox, and magnetic properties of the trinuclear Cu-3(II) triplesalacen complex

Walleck S, Theil H, Heidemeier M, et al. From triplesalen to triplesalacen: Synthesis spectroscopic, redox, and magnetic properties of the trinuclear Cu-3(II) triplesalacen complex. Inorganica Chimica Acta. 2010;363(15):4287-4294.The tris(tetradentate) triplesalacen ligand H(6)talacen and its trinuclear copper complex, namely [(talacen) Cu-3(II)], were synthesized and its molecular and electronic structure determined. The ligand is prepared by the triple condensation of 2,4,6-trisacetyl-1,3,5-trihydroxybenzene (1) and excess acacen half-unit (2). The molecular structure of [(talacen)Cu-3(II)] exhibits a strong ligand folding around the central Cu-II-phenolate bonds. This ligand folding is stronger than that observed in the trinuclear copper triplesalen complexes. The electronic absorption spectrum exhibits a prominent intense band at 32 400 cm (1) and d-d transitions around 19 000 cm (1). These spectral features are related to the ligand folding, which opens an O-Ph(p(z))-Cu-II (d(x2-y2)) bonding pathway. Electrochemical studies provide an irreversible oxidation at a relatively low potential of 0.17 V versus Fc(+)/Fc, which is assigned to a ligand-centered oxidation of the central phloroglucinol backbone. A ferromagnetic coupling of J = 1.20 cm (1) (H = Sigma(i<j) - 2J(ij)S(i)S(j)) is established in agreement with the spin-polarization mechanism. A critical analysis of the bond distances of the central phloroglucinol unit provides evidence that not only the usual phenolate-imine but also the keto-enamide mesomeric form contribute to the resonance hybrid. This might explain the relatively weak ferromagnetic coupling. (C) 2010 Elsevier B. V. All rights reserved

Exchange Interactions and Zero-Field Splittings in C-3-Symmetric (Mn6FeIII)-Fe-III: Using Molecular Recognition for the Construction of a Series of High Spin Complexes Based on the Triplesalen Ligand

Glaser T, Heidemeier M, Krickemeyer E, et al. Exchange Interactions and Zero-Field Splittings in C-3-Symmetric (Mn6FeIII)-Fe-III: Using Molecular Recognition for the Construction of a Series of High Spin Complexes Based on the Triplesalen Ligand. Inorganic Chemistry. 2009;48(2):607-620.The reaction of the tris(tetradentate) triplesalen ligand H(6)talen(t-Bu2), which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with Mn-II salts under aerobic conditions affords, in situ, the trinuclear Mn-III triplesalen complexes [(talen(2)(t-Bu)){Mn-III(solv)(n)}(3)](3+). These can be used as molecular building blocks in the reaction with [Fe(CN)(6)](3-) as a hexaconnector to form the heptanuclear complex [{(talen(2)(t-Bu)){Mn-III(solv)(n)}(3)}(2){Fe-III(CN)(6)}](3+) ([(Mn6FeIII)-Fe-III](3+)). The regular ligand folding observed in the trinuclear triplesalen complexes preorganizes the three metal ions for the reaction of three facially coordinated nitrogen atoms of a hexacyanometallate and provides a driving force for the formation of the heptanuclear complexes [(M6Mc)-M-t](n+) (M-t, terminal metal ion of the triplesalen building block; Me, central metal ion of the hexacyanometallate) by molecular recognition, as has already been demonstrated for the single-molecule magnet [(Mn6CrIII)-Cr-III](3+)center dot [{(talen(2)(t-Bu))(Mn-III(MeOH))(3)}(2){Fe-III(CN)(6)}][Fe-III(CN)(6)] (1) was characterized by single-crystal X-ray diffraction, FTIR, ESI- and MALDI-TOF-MS, Mossbauer spectroscopy, and magnetic measurements. The molecular structure of [(Mn6FeIII)-Fe-III](3+) is overall identical to that of [(Mn6CrIII)-Cr-III](3+) but exhibits a different ligand folding of the Mn-III salen subunits with a helical distortion. The Mossbauer spectra demonstrate a stronger distortion from octahedral symmetry for the central [Fe(CN)(6)](3-) in comparison to the ionic [Fe(CN)(6)](3-). At low temperatures in zero magnetic fields, the Mossbauer spectra show magnetic splittings indicative of slow relaxation of the magnetization on the Mossbauer time scale. Variable-temperature-variable-field and yen versus T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian, consisting of isotropic exchange, zero-field splitting, and Zeeman interaction taking into account the relative orientation of the D tensors. Satisfactory reproduction of the experimental data has been obtained for parameters sets J(Mn-Mn) = -(0.85 +/- 0.15) cm(-1), J(Fe-Mn) = +(0.70 +/- 0.30) cm(-1), and D-Mn = -(3.0 +/- 0.7) cm(-1). Comparing these values to those of [Mn Cr-III(6)III](3+) provides insight into why [(Mn6FeIII)-Fe-III](3+) is not a single-molecule magnet

Environmental Influence on the Single-Molecule Magnet Behavior of [(Mn6CrIII)-Cr-III](3+): Molecular Symmetry versus Solid-State Effects

Höke V, Heidemeier M, Krickemeyer E, et al. Environmental Influence on the Single-Molecule Magnet Behavior of [(Mn6CrIII)-Cr-III](3+): Molecular Symmetry versus Solid-State Effects. Inorganic Chemistry. 2012;51(20):10929-10954.The structural, spectroscopic, and magnetic properties of a series of [(Mn6CrIII)-Cr-III](3+) (= [{(talen(t-Bu2))-Mn-3(III)}(2){Cr-III(CN)(6)}](3+)) compounds have been investigated by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and electronic absorption spectroscopy, elemental analysis, electro spray ionization-mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), cyclic voltammetry, AC and DC magnetic measurements, as well as theoretical analysis. The crystal structures obtained with [Cr-III(CN)(6)](3-) as a counterion exhibit (quasi-)one-dimensional (1D) chains formed by hydrogen-bonded (1) or covalently linked (2) trications and trianions. The rod-shaped anion lactate enforces a rod packing of the [(Mn6CrIII)-Cr-III](3+) complexes in the highly symmetric space group R (3) over bar (3) with a collinear arrangement of the molecular S-6 axes. Incorporation of the spherical anion BPh4- leads to less-symmetric crystal structures (4-6) with noncollinear orientations of the [(Mn6CrIII)-Cr-III](3+) complexes, as evidenced by the angle between the approximate molecular C-3 axes taking no specific values in the range of 2 degrees-69 degrees. AC magnetic measurements on freshly isolated crystals (1a and 3a-6a), air-dried crystals (3b-6b), and vacuum-dried powder samples (3c-6c) indicate single-molecule magnet (SMM) behavior for all samples with U-eff values up to 28 K. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting, and Zeeman interaction, taking into account the relative orientation of the D-tensors. Simulations for 3a-6a and 3c-6c indicate a weak antiferromagnetic exchange between the Mn-III ions in the trinuclear subunits (J(Mn-Mn) = -0.70 to -0.85 cm(-1), (H) over cap (ex) = -2 Sigma(i(j),(S) over cap (j)) that is overcome by the stronger antiferromagnetic interaction via the Cr-C N-Mn pathway (J(Cr-Mn) = -3.00 to -5.00 cm(-1)), leading to an overall ferrimagnetic coupling scheme with an S-t = 21/2 spin ground state. The differences in U-eff, J(Mn-Mn), and J(Cr-Mn) for the investigated samples are rationalized in terms of subtle variations in the molecular and crystal structures. In particular, a magnetostructural correlation between the Mn-N-C N bond length and the J(Cr-Mn) exchange coupling is inferred from the magnetic measurements and corroborated by DFT calculations. The results of this detailed study on [(Mn6CrIII)-Cr-III](3+) allow the formulation of some key recipes for a rational improvement of the SMM behavior

Environmental Influence on the Single-Molecule Magnet Behavior of [(Mn6CrIII)-Cr-III](3+): Molecular Symmetry versus Solid-State Effects

Höke V, Heidemeier M, Krickemeyer E, et al. Environmental Influence on the Single-Molecule Magnet Behavior of [(Mn6CrIII)-Cr-III](3+): Molecular Symmetry versus Solid-State Effects. Inorganic Chemistry. 2012;51(20):10929-10954.The structural, spectroscopic, and magnetic properties of a series of [(Mn6CrIII)-Cr-III](3+) (= [{(talen(t-Bu2))-Mn-3(III)}(2){Cr-III(CN)(6)}](3+)) compounds have been investigated by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and electronic absorption spectroscopy, elemental analysis, electro spray ionization-mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), cyclic voltammetry, AC and DC magnetic measurements, as well as theoretical analysis. The crystal structures obtained with [Cr-III(CN)(6)](3-) as a counterion exhibit (quasi-)one-dimensional (1D) chains formed by hydrogen-bonded (1) or covalently linked (2) trications and trianions. The rod-shaped anion lactate enforces a rod packing of the [(Mn6CrIII)-Cr-III](3+) complexes in the highly symmetric space group R (3) over bar (3) with a collinear arrangement of the molecular S-6 axes. Incorporation of the spherical anion BPh4- leads to less-symmetric crystal structures (4-6) with noncollinear orientations of the [(Mn6CrIII)-Cr-III](3+) complexes, as evidenced by the angle between the approximate molecular C-3 axes taking no specific values in the range of 2 degrees-69 degrees. AC magnetic measurements on freshly isolated crystals (1a and 3a-6a), air-dried crystals (3b-6b), and vacuum-dried powder samples (3c-6c) indicate single-molecule magnet (SMM) behavior for all samples with U-eff values up to 28 K. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting, and Zeeman interaction, taking into account the relative orientation of the D-tensors. Simulations for 3a-6a and 3c-6c indicate a weak antiferromagnetic exchange between the Mn-III ions in the trinuclear subunits (J(Mn-Mn) = -0.70 to -0.85 cm(-1), (H) over cap (ex) = -2 Sigma(i(j),(S) over cap (j)) that is overcome by the stronger antiferromagnetic interaction via the Cr-C N-Mn pathway (J(Cr-Mn) = -3.00 to -5.00 cm(-1)), leading to an overall ferrimagnetic coupling scheme with an S-t = 21/2 spin ground state. The differences in U-eff, J(Mn-Mn), and J(Cr-Mn) for the investigated samples are rationalized in terms of subtle variations in the molecular and crystal structures. In particular, a magnetostructural correlation between the Mn-N-C N bond length and the J(Cr-Mn) exchange coupling is inferred from the magnetic measurements and corroborated by DFT calculations. The results of this detailed study on [(Mn6CrIII)-Cr-III](3+) allow the formulation of some key recipes for a rational improvement of the SMM behavior