The triplesalen ligand system based on three salen-like coordination environments bridged by a common phloroglucinol ring has been designed and successfully applied for the rational synthesis of single-molecule magnets from two trinuclear triplesalen complexes and one hexacyanometallate by supramolecular recognition. In order to optimize this system with respect to magnetic anisotropy, the triplesalophen ligand system has been identified, which should allow for the synthesis of nonanuclear complexes composed of two trinuclear triple-salophen complexes and three connecting units. Herein, the convergent synthesis of the triplesalophen ligand system is described, which differs fom the divergent strategy for the triplesalen ligand system. The molecular and elecrtronic structures of the triplesalophen ligands H(6)baron(R) (R = Me, Cl, Br) have been established by single-crystal X-ray diffraction, NMR, FTIR, and UV-vis spectroscopies. These complementary methods allowed the assignment of the central compartment not to be in the O-protonated tautomer but in the N-protonated tautomer with the prevalence of a keto-enamine resonance description, which resembles a heteroradialene. Furthermore, the comparison with the mononucleating unsymmetrical salophen reference ligand H(2)carl(Cl) and with compounds from the literature provides unique signatures for the appearance of the heteroradialene motif not only in NMR spectra and structural parameters but also in IR and UV-vis spectra. These signatures form the basis for the interpretation and understanding of the electronic structures of transition metal complexes with the triplesalophen ligand system.

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The coordination chemistry of the triplesalophen ligands H 6 baron R (R = Me, Cl, Br) with Cu II and Ni II has been studied. The triplesalophen ligand system is an extension of the triplesalen ligand system and is composed of a bridging phloroglucinol ring with three meta-phenylene salophen coordination compartments. The completely sp 2 hybridized backbone of the triplesalophen ligands should favor a more planar molecular structure of the trinuclear complexes in comparison to the triplesalen complexes. Reaction of the ligands with the metal acetates in n-butanol/CHCl 3 provided the complexes [(baron Me )Ni 3 ]a, [(baron Cl )Ni 3 ]a, [(baron Br )-Ni 3 ]a, [(baron Me )Cu 3 ], [(baron Cl )Cu 3 ], and [(baron Br )Cu 3 ]. For the Ni II complexes, recrystallization from pyridine or performing the reaction in pyridine provided the compounds [(baron Me )Ni 3 ]b and [(baron Cl )Ni 3 ]b, whereas for the bromo derivative the complex [(baron Br ){Ni(py) 2 } 2 Ni] with one fourcoordinate and two six-coordinate Ni II ions have been obtained. In contrast, for the Cu II complexes, two [(baron R ){Cu(py)} 2 Cu] (R = Me, Cl, Br) units dimerize via [a] Lehrstuhl für Anorganische Chemie I, 5934bridging of a coordinated phenolate. The structural analysis reveals a strong tendency for π stacking of the trinuclear complexes resulting in a planarization of the complexes. The trinuclear triplesalophen complexes exhibit the four signatures of heteroradialene formation, which were extracted from single-crystal X-ray diffraction, NMR, FTIR, and UV/ Vis spectroscopy. Analysis of these experimental data with regard to the respective data of the free ligands H 6 baron R (R = Me, Cl, Br) and the mononuclear analogue H 2 carl Cl and its complexes [(carl Cl )Ni] and [(carl Cl )Cu] clearly demonstrates that the heteroradialene resonance structure, which has been established as the dominant resonance structure for the free ligands, still has a strong but smaller contribution in the trinuclear triplesalophen complexes. The magnetic properties demonstrate weak intramolecular ferromagnetic interactions mediated by the triplesalophen ligands in the trinuclear Cu II 3 complexes, which are experimentally difficult to determine due to intermolecular antiferromagnetic interactions of the same order of magnitude. molecular structures of the trinuclear Ni II 3 complexes [2] and the trinuclear Cu II 3 complexes [11] of the tert-butyl ligand H 6 talen tBu 2 exhibit a strong ligand folding along the central O-N vectors, resulting in overall bowl-shaped molecular structures. This ligand folding preorganizes the axial coordination sites of the metal salen subunits for the complementary binding of a hexacyanometallate. In combination with a strong tendency of two [(talen tBu 2 )M t 3 ] m+ complexes to dimerize due to van der Waals interaction of the tertbutyl phenyl groups, [12] a high driving force results for the formation of heptanuclear complexes [M t 6 M c ] n+ (= [{(talen tBu 2 )M t 3 } 2 {M c (CN) 6 }] n+ ) by the supramolecular assembly of two [(talen tBu ...

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The ligands (L(t-Bu(2)))(2-), (L(Me(2)))(2-), and (L(Cl(2)))(2-) have been employed for the synthesis of the dinuclear Fe(III) complexes [L(t-Bu(2))Fe(μ-O)FeL(t-Bu(2))], [L(Me(2))Fe(μ-O)FeL(Me(2))], and [L(Cl(2))Fe(μ-O)FeL(Cl(2))]. The strongly electron-donating groups (tert-amines and phenolates) were chosen to increase the electron density at the coordinated ferric ions and thus to facilitate the oxidation of the complexes, with the possibility of fine-tuning the electronic structures by variation of the remote substituents. Molecular structures established in the solid (by single-crystal X-ray diffraction) and in solution (by X-ray absorption spectroscopy) show that the Fe ions are five-coordinate in a square-pyramidal coordination environment with the ligand adopting a trans-conformation. Spectroscopic and magnetic characterization establishes the highly covalent nature of the Fe(III)-O(oxo) and Fe(III)-O(Ph) bonds. The variations in the donor capabilities of the phenolates (due to changes in the remote substituents) are compensated for by a flexible electron donation of the Fe(III)-O(oxo) bonding. Spectroelectrochemical characterization demonstrates that [L(t-Bu(2))Fe(μ-O)FeL(t-Bu(2))] can be oxidized reversibly at +0.27 and +0.44 V versus Fc(+)/Fc, whereas [L(Me(2))Fe(μ-O)FeL(Me(2))] and [L(Cl(2))Fe(μ-O)FeL(Cl(2))] exhibit irreversible oxidations at +0.29 and +0.87 V versus Fc(+)/Fc, respectively. UV-vis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), and Mössbauer spectroscopy show that the successive oxidations of [L(t-Bu(2))Fe(μ-O)FeL(t-Bu(2))] are ligand-centered leading to the monophenoxyl radical complex [(•)L(t-Bu(2))Fe(III)(μ-O)Fe(III)L(t-Bu(2))](+) (with the oxidation primarily localized on one-half of the molecule) and the diphenoxyl radical complex [(•)L(t-Bu(2))Fe(III)(μ-O)Fe(III•)L(t-Bu(2))](2+). Both products are unstable in solution and decay by cleavage of an Fe(III)-O(oxo) bond. The two-electron oxidized species is more stable because of two equally strong Fe(III)-O(oxo) bonds, whereas in the singly oxidized species the Fe(III)-O(oxo) bond of the non-oxidized half is weakened. The decay of the monocation results in the formation of [L(t-Bu(2))Fe(III)](+) and [L(t-Bu(2))Fe(IV)=O], while the decay of the dication yields [(•)L(t-Bu(2))Fe(III)](2+) and [L(t-Bu(2))Fe(IV)=O]. Follow-up reactions of the oxidized fragments with the counteranion of the oxidant, [SbCl(6)](-), leads to the formation of [Fe(III)Cl(4)](-).