Supramolecular coordination cages and polymers bear exceptional advantages over their organic counterparts. They are available in one-pot reactions and in high yields and display physical properties ...that are generally inaccessible with organic species. Moreover, their weak, reversible, noncovalent bonding interactions facilitate error checking and self-correction. This review emphasizes the achievements in supramolecular coordination container as well as polymer chemistry initiated by serendipity and their materialization based on rational design. The recognition of similarities in the synthesis of different supramolecular assemblies allows prediction of potential structures in related cases. The combination of detailed symmetry considerations with the basic rules of coordination chemistry has only recently allowed for the design of rational strategies for the construction of a variety of nanosized spherical containers, bowls, 1D-, 2D-, and 3D-coordination polymers with specified size and shape.
Reaction of cobalt(II) chloride hexahydrate with N‐substituted diethanolamines H2L2–4 (3) in the presence of LiH in anhydrous THF leads under anaerobic conditions to the formation of three ...isostructural tetranuclear cobalt(II) complexes CoII4(Cl)4(HL2–4)4 (4) with a Co4(μ3‐O)44+ cubane core. According to X‐ray structural analyses, the complexes 4 a,c crystallize in the tetragonal space group I41/a, whereas for complex 4 b the tetragonal space group P$\bar 4$ was found. In the solid state the orientation of the cubane cores and the formation of a 3D framework were controlled by the ligand substituents of the cobalt(II) cubanes 4. This also allowed detailed magnetic investigations on single crystals. The analysis of the SQUID magnetic susceptibility data for 4 a gave intramolecular ferromagnetic couplings of the cobalt(II) ions (J1≈20.4 K, J2≈7.6 K), resulting in an S=6 ground‐state multiplet. The anisotropy was found to be of the easy‐axis type (D=−1.55 K) with a resulting anisotropy barrier of Δ≈55.8 K. Two‐dimensional electron‐gas (2DEG) Hall magnetization measurements revealed that complex 4 a is a single‐molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep‐rate dependencies below a blocking temperature of about 4.4 K. The hysteresis loops collapse at zero field owing to fast quantum tunneling of the magnetization (QTM). The structural and electronic properties of cobalt(II) cubane 4 a, deposited on a highly oriented pyrolytic graphite (HOPG) surface, were investigated by means of STM and current imaging tunneling spectroscopy (CITS) at RT and standard atmospheric pressure. In CITS measurements the rather large contrast found at the expected locations of the metal centers of the molecules indicated the presence of a strongly localized LUMO.
Inversion of magnetoanisotropy: The novel tetranuclear CoII cubane CoII4(Cl)4(HL2)4 shown in the figure (R=nBu) was synthesized from N‐substituted diethanolamine H2L2, LiH, and CoII ions (D>0 K). It exhibits an easy‐axis type of single‐molecule magnet behavior with an energy barrier of Δ≈55.8 K (D=−1.55 K), which is comparable to that of {Mn12}, and a blocking temperature of 4.4 K, but the hysteresis loops are collapsed owing to fast zero‐field relaxation.
A Crystalline Iron Terminal Methylidene Aghazada, Sadig; Munz, Dominik; Heinemann, Frank W ...
Journal of the American Chemical Society,
10/2021, Letnik:
143, Številka:
41
Journal Article
Recenzirano
Iron methylidene species are alleged intermediates in the Fischer–Tropsch process and in olefin cyclopropanation, yet iron methylidene complexes with unambiguously established molecular and ...electronic structures remain elusive. In this study, we characterize an iron terminal methylidene complex by single-crystal X-ray diffractometry (scXRD), CHN combustion elemental analysis, 1H/13C/31P/1H–13C NMR, and zero-field 57Fe Mössbauer spectroscopy and study its reactivity. A series of closely related complexes in different oxidation states were synthesized, isolated and characterized in order to validate the electronic structure of the title methylidene complex. The computational analysis substantiates the proposed Fischer-type electronic description while emphasizing high FeCH2 bond covalency, considerable double bond order, and thus, substantial alkylidene character.
Dihydrogen evolution was observed in a two‐step protonation reaction starting from a Ni0 precursor with a tripodal N‐heterocyclic carbene (NHC) ligand. Upon the first protonation, a NiII monohydride ...complex was formed, which was isolated and fully characterized. Subsequent protonation yields H2 via a transient intermediate (INT) and an isolable NiII acetonitrile complex. The latter can be reduced to regenerate its Ni0 precursor. The mechanism of H2 formation was investigated by using a deuterated acid and scrutinized by 1H NMR spectroscopy and gas chromatography. Remarkably, the second protonation forms a rare nickel dihydrogen complex, which was detected and identified in solution and characterized by 1H NMR spectroscopy. DFT‐based computational analyses were employed to propose a reaction profile and a molecular structure of the Ni−H2 complex. Thus, a dihydrogen‐evolving, closed‐synthetic cycle is reported with a rare Ni−H2 species as a key intermediate.
Nickel complexes with a N‐heterocyclic carbene ligand (TIMENiPr) have been synthesized and characterized. Starting from the Ni0 precursor, a NiII hydride is synthesized that reacts with protons to form a rare Ni−H2 intermediate, which was studied by NMR spectroscopy and DFT calculations. Further reduction closes the synthetic cycle.
We revisit the star-shaped iron-based single-molecule magnet FeIII{FeIII(L)2}3 (2) (exact chemical formula C30H66Fe4N6O12, H2L = N-methyldiethanolamine) in order to clarify some open questions ...concerning the exact electronic and magnetic properties arising from earlier studies on this specific compound. Namely, we address the internal magnetic structure by applying X-ray magnetic circular dichroism to the Fe L2,3 edges and carefully investigate radiation photochemistry. We observe an Fe3+ to Fe2+ photoreduction process, taking place under soft X-ray radiation.
The low‐temperature (<−35 °C) reduction of the trivalent uranium monoarene complex {(Ad,MeArO)3mes}U (1), with potassium spheres in the presence of a slight excess of 2.2.2‐cryptand, affords the ...quantitative conversion of 1 into the uranium(II) monoarene complex K(2.2.2‐crypt)((Ad,MeArO)3mes)U (1‐K). The molecular and electronic structure of 1‐K was established experimentally by single‐crystal X‐ray diffraction, variable‐temperature 1H NMR and X‐band EPR spectroscopy, solution‐state and solid‐state magnetism studies, and optical absorption spectroscopy. The electronic structure of the complex was further investigated by DFT calculations. The complete body of evidence confirms that 1‐K is a uranium(II) monoarene complex with a 5f 4 electronic configuration supported by δ backbonding and that the nearly reversible, room‐temperature reduction observed for 1 at −2.495 V vs. Fc/Fc+ is principally metal‐centered.
U2 rocks: The molecular and electronic structure of a uranium(II) monoarene complex with a 5f 4 electronic configuration supported by δ backbonding was established experimentally by single‐crystal X‐ray diffraction, variable‐temperature 1H NMR and X‐band EPR spectroscopy, solution‐state and solid‐state magnetism studies, and optical absorption spectroscopy. The electronic structure of the complex was further investigated by DFT calculations.
Herein, we report the isolation and a reactivity study of the first example of an elusive palladium(II) terminal imido complex. This scaffold is an alleged key intermediate for various catalytic ...processes, including the amination of C−H bonds. We demonstrate facile nitrene transfer with H−H, C−H, N−H, and O−H bonds and elucidate its role in catalysis. The high reactivity is due to the population of the antibonding highest occupied molecular orbital (HOMO), which results in unique charge separation within the closed‐shell imido functionality. Hence, N atom transfer is not necessarily associated with the high valency of the metal (PdIII, PdIV) or the open‐shell character of a nitrene as commonly inferred.
Elusive palladium terminal imido complexes with an antibonding HOMO are isolable and catalytically activate C−H, H−H, N−H, and O−H bonds.
Scanning transmission X-ray microspectroscopy (STXM) and L-edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopy have been applied to study the valence states of metal ions in various ...Fe- and Mn-containing single-molecule magnet materials, in particular the ligand-stabilized metal complexes NaFe
(so-called “ferric wheel”), Fe
(so-called “ferric star”) and Mn
(so-called “manganese wheel”).We compare dose-dependent L-edge absorption spectra with the results of theoretical studies of the involved metal ions to conclude on the change in oxidation state upon increasing the X-ray dose. It is found that even low-intensity irradiation induces the reduction of the weakly interacting metal ions, and that the soft X-ray-induced photoreduction is less pronounced in microcrystalline films.
