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We have developed a family of dinuclear complexes using 2,7-disubstituted 1,8-naphthalenediol ligands that bind by molecular recognition to two neighboring phosphate diesters of the DNA backbone with the dinuclear Cu II and Ni II complexes exhibiting a severe cytotoxicity for human cancer cells. To increase the binding affinity, we intended to synthesize the corresponding dinuclear Fe III complex. Surprisingly, we obtained a tetranuclear Fe III perylene-based complex instead of the expected dinuclear Fe III naphthalene-based complex. In order to establish a rational and reproducible synthesis, we carefully analyzed this reaction. This revealed a multistep oxidative cascade reaction including the pre-coordination of Fe II ions in the N 3 -binding pockets, the Lewis-acid assisted MOM-deprotection of the pre-ligand by the pre-oriented Fe II ions, two oxidative aromatic C-C coupling reactions, oxidation of the perylene-based backbone and of Fe II to Fe III . The careful analysis of bond lengths, HOMA indices (harmonic oscillation model of aromaticity), FTIR and UV-Vis-NIR spectra supported by DFT calculations reveals the presence of an aromatic 18-electron oxidized perylenequinone ligand backbone. In summary, a multistep cascade reaction involving in total a 10-electron oxidation has been established for the straight-forward synthesis of an unprecedented perylenequinone-based ligand system., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

The first confacial pentaoctahedron comprised of transition metal ions namely Zn II Fe III A Fe III B Fe III A Zn II has been synthesized by using a dinucleating nonadentate ligand. The face-sharing bridging mode enforces short Zn II ⋅⋅⋅Fe III A and Fe III A ⋅⋅⋅Fe III B distances of 2.83 and 2.72 Å, respectively. Ab-initio CASSCF/NEVPT2 calculations provide significant negative zero-field splittings for Fe III A and Fe III B with |D A |>|D B | with the main component along the C 3 axis. Hence, a spin-Hamiltonian comprised of anisotropic exchange, zero-field, and Zeeman term was employed. This allowed by following the boundary conditions from the theoretical results the simulation in a theory-guided parameter determination with J xy =+0.37, J z =-0.32, D A =-1.21, E A =-0.24, D B =-0.35, and E B =-0.01 cm -1 supported by simulations of high-field magnetic Mössbauer spectra recorded at 2 K. The weak but ferromagnetic Fe III A Fe III B interaction arises from the small bridging angle of 84.8° being at the switch from anti- to ferromagnetic for the face-sharing bridging mode., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The additive-free tetrazine/enol ether click reaction was performed in ultra-high vacuum (UHV) with an enol ether group covalently linked to a silicon surface: Dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate molecules were coupled to the enol ether group of a functionalized cyclooctyne which was adsorbed on the silicon (001) surface via the strained triple bond of cyclooctyne. The reaction was observed at a substrate temperature of 380 K by means of X-ray photoelectron spectroscopy (XPS). A moderate energy barrier was deduced for this click reaction in vacuum by means of density functional theory based calculations, in good agreement with the experimental results. This UHV-compatible click reaction thus opens a new, flexible route for synthesizing covalently bound organic architectures., (© 2021 The Authors. Published by Wiley-VCH GmbH.)

The anisotropy barrier of polynuclear single-molecule magnets is expected to be higher with less tunneling the better stabilized the spin ground state is so that less M S mixing in the ground state and with excited spin states occur. We have realized this experimentally in two structurally related heptanuclear SMMs: the triplesalen-based [Mn III 6 Cr III ] 3+ and the triplesalalen-based *[Mn III 6 Cr III talalen t Bu 2 was designed. Here, we present the building block [(talalen t Bu 2 )Mn 3+ . The ligand system triplesalen was developed to enforce ferromagnetic interactions by the spin-polarization mechanism. However, we found weak antiferromagnetic couplings, that we assigned to an inefficient spin-polarization by a heteroradialene formation. To prevent this heteroradialene formation, the triplesalalen ligand H 6 and its application for the assembly of [{(talalen t Bu 2 )Mn III 3 ] 3+ and its application for the assembly of [{(talalen t Bu 2 )Mn III 3 } 2 {Cr III (CN) 6 ). Both the trinuclear and heptanuclear complexes are SMMs. The comparison to the related triplesalen complex [(feld t Bu 2 )Mn 3+ (=*[Mn III 6 Cr III interactions in the (talalen t Bu 2 ) 3+ ). Both the trinuclear and heptanuclear complexes are SMMs. The comparison to the related triplesalen complex [(feld t Bu 2 )Mn III 3 ] 3+ proves the absence of heteroradialene character and the enforcement of ferromagnetic Mn III -Mn III interactions in the (talalen t Bu 2 ) 6- complexes. This results in an increase of the barrier for spin reversal U eff from 25 K in the triplesalen-based [Mn III 6 Cr III ] 3+ SMMs to 37 K in the triplesalalen-based *[Mn III 6 Cr III ] 3+ SMM proving the success of our concept. Based on this study, the next step in the rational improvement of our SMMs is discussed., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Extended phloroglucinol ligands and complexes are best described as nonaromatic heteroradialenes. Herein, the electronic structures of extended thiophloroglucinol ligands and their Ni(II) 3 complexes are evaluated by comparison to their phloroglucinol analogs by means of NMR, FTIR, UV/Vis, and structural parameters. To provide a full set of compounds for this comparison of S versus O substitution, a new triplesalen ligand, its Ni(II) 3 complex, and a new thiophloroglucinol were synthesized. (1) H and (15) N NMR chemical shifts and coupling constants prove that the thiophloroglucinol ligands exist as the N-protonated and not the O-protonated tautomer. (13) C and (15) N NMR chemical shifts and structural parameters further demonstrated that the extended thiophloroglucinol ligands must be described with a predominant thione-enamine (heteroradialene) character despite the participation of a CS double bond. In the Ni(II) 3 complexes, this heteroradialene character is reduced but still predominant., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The present study refers to a variety of reduced metal-oxide core-shell hybrids, which are unique with regard to their electronic structure, their geometry, and their formation. They contain spherical {Mo72Fe30} Keplerate-type shells encapsulating Keggin-type polyoxomolybdates based on very weak interactions. Studies on the encapsulation of molybdosilicate as well as on the earlier reported molybdophosphate, coupled with the use of several physical methods for the characterization led to unprecedented results (see title). Upon standing in air at room temperature, acidified aqueous solutions obtained by dissolving sodium molybdate, iron(II) chloride, acetic acid, and molybdosilicic acid led to the precipitation of monoclinic greenish crystals (1). A rhombohedral variant (2) has also been observed. Upon drying at room temperature, compound 3 with a layer structure was obtained from 1 in a solid-state reaction based on cross-linking of the shells. The compounds 1, 2, and 3 have been characterized by a combination of methods including single-crystal X-ray crystallography, magnetic studies, as well as IR, Mössbauer, (resonance) Raman, and electronic absorption spectroscopy. In connection with detailed studies of the guest-free two-electron-reduced {Mo72Fe30}-type Keplerate (4) and of the previously reported molybdophosphate-based hybrids (including 31P NMR spectroscopy results), it is unambiguously proved that 1, 2, and 3 contain non-reduced Keggin ion cores and reduced {Mo72Fe30}-type shells. The results are discussed in terms of redox considerations (the shell as well as the core can be reduced) including those related to the reduction of "molybdates" by FeII being of interdisciplinary including catalytic interest (the MoVI/MoV and FeIII/FeII couples have very close redox potentials!), while also referring to the special formation of the hybrids based on chemical Darwinism.

The chiral triplesalen ligand H(6)chand provides three chiral salen ligand compartments in a meta-phenylene arrangement by a phloroglucinol backbone. The two diastereomeric versions H(6)chand(RR) and H(6)chand(rac) have been used to synthesize the enantiomerically pure chiral complex [(FeCl)(3)(chand(RR))] (3(RR)) and the racemic complex [(FeCl)(3)(chand(rac))] (3(rac)). The molecular structure of the free ligand H(6)chand(rac) exhibits at the terminal donor sides the O-protonated phenol-imine tautomer and at the central donor sides the N-protonated keto-enamine tautomer. The trinuclear complexes are comprised of five-coordinate square-pyramidal Fe(III) ions with a chloride at the axial positions. The crystal structure of 3(rac) exhibits collinear chiral channels of approximately 11 A in diameter making up 33.6 % of the volume of the crystals, whereas the crystal structure of 3(RR) exhibits voids of 560 A(3). Mössbauer spectroscopy demonstrates the presence of Fe(III) high-spin ions. UV/Vis spectroscopy is in accordance with a large delocalized system in the central backbone evidenced by strong low-energy shifts of the imine pi-pi* transitions relative to that of the terminal units. Magnetic measurements reveal weak intramolecular exchange interactions but strong magnetic anisotropies of the Fe(III) ions. Complexes 3(rac) and 3(RR) are good catalysts for the sulfoxidation of sulfides providing very good yields and high selectivities with 3(RR) being enantioselective. A comparison of 3(RR) and [FeCl(salen')] provides higher yields and selectivities but lower enantiomeric excess values (ee values) for 3(RR) relative to [FeCl(salen')]. The low ee values of 3(RR) appeared to be connected to a strong ligand folding in 3(RR), opening access to the catalytically active high-valent Fe-O species. The higher selectivity is assigned to a cooperative stabilization of the catalytically active high-valent Fe-O species through the phloroglucinol backbone in the trinuclear complexes.

The 16-Fe(III)-containing 48-tungsto-8-phosphate [P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)](20-) (1) has been synthesised and characterised by IR and ESR spectroscopy, TGA, elemental analyses, electrochemistry and susceptibility measurements. Single-crystal X-ray analyses were carried out on Li(4)K(16)[P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)]66 H(2)O2 KCl (LiK-1, orthorhombic space group Pnnm, a=36.3777(9) A, b=13.9708(3) A, c=26.9140(7) A, and Z=2) and on the corresponding mixed sodium-potassium salt Na(9)K(11)[P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)].100 H(2)O (NaK-1, monoclinic space group C2/c, a=46.552(4) A, b=20.8239(18) A, c=27.826(2) A, beta=97.141(2) degrees and Z=4). Polyanion 1 contains--in the form of a cyclic arrangement--the unprecedented {Fe(16)(OH)(28)(H(2)O)(4)}(20+) nanocluster, with 16 edge- and corner-sharing FeO(6) octahedra, grafted on the inner surface of the crown-shaped [H(7)P(8)W(48)O(184)](33-) (P(8)W(48)) precursor. The synthesis of 1 was accomplished by reaction of different iron species containing Fe(II) (in presence of O(2)) or Fe(III) ions with the P(8)W(48) anion in aqueous, acidic medium (pH approximately 4), which can be regarded as an assembly process under confined geometries. One fascinating aspect is the possibility to model the uptake and release of iron in ferritin. The electrochemical study of 1, which is stable from pH 1 through 7, offers an interesting example of a highly iron-rich cluster. The reduction wave associated with the Fe(III) centres could not be split in distinct steps independent of the potential scan rate from 2 to 1000 mV s(-1); this is in full agreement with the structure showing that all 16 iron centres are equivalent. Polyanion 1 proved to be efficient for the electrocatalytic reduction of NO(x), including nitrate. Magnetic and variable frequency EPR measurements on 1 suggest that the Fe(III) ions are strongly antiferromagnetically coupled and that the ground state is tentatively spin S=2.

A series of trinuclear Cu(II) complexes with the tris(tetradentate) triplesalen ligands H(6)talen, H(6)talen(tBu(2) ), and H(6)talen(NO(2) ), namely [(talen)Cu(II) (3)] (1), [(talen(tBu(2) ))Cu(II) (3)] (2), and [(talen(NO(2) ))Cu(II) (3)] (3), were synthesized and their molecular and electronic structures determined. These triplesalen ligands provide three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. The structure of [(talen)Cu(II) (3)] (1) was communicated recently. The structure of the tert-butyl derivative [(talen(tBu(2) ))Cu(II) (3)] (2) was established in three different solvates. The molecular structures of these trinuclear complexes show notable differences, the most important of which is the degree of ligand folding around the central Cu(II)-phenolate bonds. This folding is symmetric with regard to the central phloroglucinol backbone in two structures, where it gives rise to bowl-shaped overall geometries. For one solvate two trinuclear triplesalen complexes form a supramolecular disk-like arrangement, hosting two dichloromethane molecules like two pearls in an oyster. The FTIR spectra of these complexes indicate the higher effective nuclear charge of Cu(II) in comparison to the trinuclear Ni(II) complexes by the lower C--O and higher C=N stretching frequencies. The UV/Vis/NIR spectra of 1-3 reflect the stronger ligand folding in the tert-butyl complex 2 by an intense phenolate-to-Cu(II) LMCT. This absorption is absent in 1 and is obscured by the nitro chromophore in 3. The more planar molecular structures cause orthogonality of the Cu(II) d(x(2)-y(2) ) orbital and the phenolate O p(z) orbital, which leads to small LMCT dipole strengths. Whereas 1 and 3 exhibit only irreversible oxidations, 2 exhibits a reversible one-electron oxidation at +0.26 V, a reversible two-electron oxidation at +0.59 V, and a reversible one-electron oxidation at +0.81 V versus Fc(+)/Fc. The one-electron oxidized form 2(+) is strongly stabilized with respect to reference mononuclear salen-like Cu complexes. Chemical one-electron oxidation of 2 to 2(+) allows the determination of its UV/Vis/NIR spectrum, which indicates a ligand-centered oxidation that can be assigned to the central phloroglucinol unit by analogy with the trinuclear Ni triplesalen series. Delocalization of this oxidation over three Cu(II)-phenolate subunits causes the observed energetic stabilization of 2(+). Temperature-dependent magnetic susceptibility measurements reveal ferromagnetic couplings for all three trinuclear Cu(II) triplesalen complexes. The trend of the coupling constants can be rationalized by two opposing effects: 1) electron-withdrawing terminal substituents stabilize the central Cu(II)-phenolate bond, which results in a stronger coupling, and 2) ligand folding around the central Cu(II)-phenolate bond opens a bonding pathway between the magnetic Cu(II) d(x(2)-y(2) ) orbital and the phenolate O p(z) orbital, which results in a stronger coupling. Density functional calculations indicate that both spin-polarization and spin-delocalization are operative and that slight geometric variations alter their relative magnitudes.

The 2(3),9(10),16(17),23(24)-tetrasubstituted metalphthalocyanines 1-7 (M = In, Ni, Zn) were synthesized, as mixtures of four different structural isomers, from the corresponding 4-alkoxy-1,2-dicyanobenzenes and the appropriate metal salts. Separation of the four structural isomers was successfully achieved on a C30 alkyl phase by high-performance liquid chromatography (HPLC). The determination of the point groups of the structural isomers was carried out for 1 and 3, the composition of the structural isomers of 4-7 was accomplished by comparing their retention times and UV/Vis spectra with the data of 1 and 3. For the phthalocyanines 8-10 and the naphthalocyanines 11 and 12 only the C4h and D2h isomers could be separated.

Only the second octahedral, paramagnetic copper(III) complex (S=1) has now been synthesized and characterized. Six thiolato bridging ligands in the heterotrinuclear species [LCo III Cu III Co III L](ClO 4 ) 3 ⋅2 Me 2 CO (L=1,4,7-tris(4-tert-butyl-2-sulfidobenzyl)-1,4,7-triazacyclononane) stabilize this rare electron configuration. A section of the structure of the reduced form (Cu II , S=½) is shown. XAS, EXAFS, and EPR spectroscopy prove unambiguously that the one-electron oxidation to the copper(III) is metal- rather than ligand-centered., (© 1999 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

The relative orientation of the two magnetic orbitals, the Cu II d x 2-y 2 orbital and the half-occupied π orbital of the tyrosyl radical, is the key to answering the question in the title. The arrangement shown (Cu II -O-C bond angle of about 130° and a dihedral angle of about 90° between the x,y plane of the Cu II polyhedron and the tyrosyl ring plane) leads to an overlap of the orbitals, which results in a singlet ground state., (© 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)