Single-molecule magnets (SMMs) are molecular nano-objects expected to be used in the information storage techniques in the future, as well as to find applications in quantum computing and molecular spintronics.[1] The SMM properties are controlled by the large-spin ground state (S T ) and uni-axial anisotropy (D) [2] of these complexes, creating an energy barrier (D) between AE m(S T ) states. Below a blocking temperature, SMMs behave as tiny magnets, exhibiting slow relaxation of their magnetization. The energy barrier implied in this process is required to be as large as possible to maximize the blocking temperatures and the relaxation time. Numerous synthetic approaches have been developed to reach this goal, among them the insertion of anisotropic high-spin lanthanide ions [1b] into mono-and polynuclear 4f metal complexes, [3,4] but also in variety of heterometallic 3d-4f systems. [5, 6] To date, the record for the barrier to magnetization relaxation for a 3d-4f complex, 74 K, has been held by a high-nuclearity complex with an {Mn 21 Dy} core.[5]Here we report the first examples of a new family of heterometallic lanthanide-manganeseA C H T U N G T R E N N U N G (III) SMMs with an {Mn III 6 O 3 Ln 2 } core (1 and 2; Ln= La and Tb respectively); these complexes were synthesized by means of a facile twostep self-assembly process (Scheme 1) and they display remarkably high SMM energy barriers, reaching 103 K for 2.As summarized in Scheme 1, stoichiometric amounts of MnCl 2 ·4 H 2 O and the salicylaldoxime ligand (Scheme 2) in methanol were mixed with tetraethylammonium hydroxide before adding two equivalents of solid lanthanide nitrate (1:. After 12 h of stirring, concentration on rotary evaporator and filtration, the resulting black solution was layered by diethyl ether. Single crystals suitable for X-ray diffraction are obtained after 1-2 weeks (see the Supporting Information, Figure S1-S3, Tables S1-S4).Complexes 1 and 2 show analogous molecular structures that only differ by the involved Ln ions in the central het- (Figure 1 a,b) It should be mentioned that a similar core has been described in a related class of complexes reported recently by Rigaux et al.[5b] Each Mn center has an axially distorted octahedral coordination sphere confirming its + III oxidation state (Table S3 in the Supporting Information). The Jahn-Teller axes (O9-Mn1-O22, O4-Mn2-O21, O24-Mn3-O5, O6-Mn4-O23, O7-Mn5-O26, O8-Mn6-O25) are not collinear and are distributed in a rotary fashion around the central Ln···Ln axis, that is, around the pseudo-C 3 axis of the near D 3d symmetry of the complexes (Figure 1 c).It is worth noting that the deviation from ideal D 3d symmetry is not only due to slightly different positions of the organic groups and the different terminal ligands, but is also
A series of model dinuclear manganese(IV) complexes of the general formula [(H 3 COH)(L′)Mn IV (μ-L) 2 Mn IV (L′)(HOCH 3 )] is presented. These compounds feature capping 4,6,10-trihydroxo-3,5,7-trimethyl-1,4,6,10-tetraazaadamantane ligands derived from a polydentate oxime compound (L′). The bridging ligands L include azide (1), methoxide (2), and oxalate (3) anions. The magnetic properties and high-field (HF) EPR spectra of 1−3 were studied in detail and revealed varying weak antiferromagnetic coupling and modest zero-field splitting (ZFS) of the local quartet spin sites. Our HF EPR studies provide insight into the dimer ZFS, including determination of the corresponding parameters by giant spin approach for methoxido-bridged complex 2. Furthermore, the physicochemical properties of 1−3 were studied using IR, UV−vis, and electrochemical (cyclic voltammetry) methods. Theoretical exchange coupling constants were obtained using broken-symmetry (BS) density functional theory (DFT). Computational estimates of the local quartet ground spins state ZFSs of 1−3 were obtained using coupled-perturbed (CP) DFT and complete active space self-consistent field (CASSCF) calculations with n-electron valence state perturbation theory (NEVPT2) corrections. We found that the CP DFT calculations which used the B3LYP functional and models derived experimental structures performed best in reproducing both the magnitude and the sign of the experimental D values. Moreover, our computational investigation of 1−3 suggests that we observe metals sites which have an increased +3 character and are supported by redox noninnocent 4,6,10-trihydroxo-3,5,7-trimethyl-1,4,6,10-tetraazaadamantane ligands. The latter conclusion is further corroborated by the observation that the free ligand can be readily oxidized to yield a NO-based radical.
Depending on the temperature, the twofold deprotonation of 1,1′‐methylenebis(3‐methylimidazole‐2‐thione) (1) and the subsequent reaction with 2 equiv. of trimethylsilyl chloride (TMSCl) gives two different bis‐TMS‐functionalized isomers, namely, 1,1′‐methylenebis(3‐methyl‐4‐trimethylsilylimidazole‐2‐thione) (2) and 1,1′‐methylenebis(3‐methyl‐5‐trimethylsilylimidazole‐2‐thione) (3). The cyclic dimethylsilyl‐bridged derivative 1,1′‐methylene‐5,5′‐dimethylsilylenebis(3‐methylimidazole‐2‐thione) (4) can also be obtained, corroborating the 5/5′ addition under certain conditions. All compounds have been examined by multinuclear 1D and 2D NMR experiments (1–4) together with single‐crystal X‐ray diffraction (3 and 4). Additionally, the dilithiated species 5 was synthesized by reacting 1 with 2 equiv. of nBuLi at ambient temperature in solution (THF). 1H and 7Li pulsed field‐gradient spin‐echo (PGSE) NMR, 7Li–1H heteronuclear Overhauser spectroscopy (HOESY), gradient heteronuclear multiple quantum correlation (gHMQC) and gradient heteronuclear multiple bond correlation (gHMBC) experiments showed that 5 exists as a monomeric contact ion pair (CIP) in THF solution. On the contrary, the X‐ray diffraction analysis of 5 revealed a polymeric chain, which can be described as [{5(thf)2}2]∞. Quantum chemical DFT and MP2 calculations were also conducted to determine the energies required for the deprotonation of 1. These results explain the regioselective deprotonation of 1 by CIP formation depending on the temperature and fully support the results of the synthetic and spectroscopic experiments.
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