31 research outputs found
An Iron(II) Spin Crossover Complex with a Maleonitrile Schiff base-like Ligand and Scan Rate-dependent Hysteresis above Room Temperature
The Elemental Multifariousness of the DefectâPyrochlore Crystal Structure and Application in Photocatalytic Hydrogen Generation
Sterically Encumbered Coordination Sites : Iron(II) Complexes of JĂ€ger-type ligands with a Terphenyl Backbone
Design of a flexible but robust setup for temperature-dependent electrochemistry down to cryogenic temperatures
Running in the Family : Molecular Factors controlling Spin Crossover of Iron(II) Complexes with Schiffâbase like Ligands
Running in the Family : Molecular Factors controlling Spin Crossover of Iron(II) Complexes with Schiffâbase like Ligands
Tailoring of spin state energetics of transition metal complexes and even the correct prediction of the resulting spin state is still a challenging task, both for the experimentalist and the theoretician. Apart from the complexity in the solid state imposed by packing effects, molecular factors of the spin state ordering are required to be identified and quantified on equal rights. In this work we experimentally record the spin states and SCO energies within an eight-member substitution-series of N4O2 ligated iron(II) complexes both in the solid state (SQUID magnetometry and single-crystal X-ray crystallography) and in solution (VT-NMR). The experimental survey is complemented
by exhaustive theoretical modelling of the molecular and electronic structure of the open-chain N4O2 family and its macrocyclic N6 congeners through density-functional theory methods. Ligand topology is identified as the leading factor defining ground-state multiplicity of the corresponding iron(II) complexes. Invariably the low-spin state is sterically trapped in the macrocycles, whereas subtle substitution effects allow for a molecular fine tuning of the spin state in the open-chain ligands. Factorization of computed relative SCO energies holds promise for directed design of future SCO systems
Direct Base-Assisted CâH Cyclonickelation of 6-Phenyl-2,2'-bipyridine
The organonickel complexes [Ni(Phbpy)X] (X = Br, OAc, CN) were obtained for the first time in a direct base-assisted arene C(sp2)-H cyclometalation reaction from the rather unreactive precursor materials NiX2 and HPhbpy (6-phenyl-2,2'-bipyridine) or from the versatile precursor [Ni(HPhbpy)Br2]2. Different from previously necessary CâBr oxidative addition at Ni(0), an extended scan of reaction conditions allowed quantitative access to the title compound from Ni(II) on synthetically useful timescales through base-assisted CâH activation in nonpolar media at elevated temperature. Optimisation of the reaction conditions (various bases, solvents, methods) identified 1:2 mixtures of acetate and carbonate as unrivalled synergetic base pairs in the optimum protocol that holds promise as a readily usable and easily tuneable access to a wide range of direct nickelation products. While for the base-assisted CâH metalation of the noble metals Ru, Ir, Rh, or Pd, this acetate/carbonate method has been established for a few years, our study represents the leap into the world of the base metals of the 3d series
OâO Bond Formation and Liberation of Dioxygen Mediated by N5âCoordinate NonâHeme Iron(IV) Complexes
Formation of the OâO bond is considered the critical step in oxidative water cleavage to produce dioxygen. Highâvalent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the OâO bond in solution, from nonâheme, N5âcoordinate oxoiron(IV) species. Oxygen evolution from oxoiron(IV) is instantaneous once metaâchloroperbenzoic acid is administered in excess. Oxygenâisotope labeling reveals two sources of dioxygen, pointing to mechanistic branching between HAT (hydrogen atom transfer)âinitiated freeâradical pathways of the peroxides, which are typical of catalaseâlike reactivity, and ironâborne OâO coupling, which is unprecedented for nonâheme/peroxide systems. Interpretation in terms of [FeIV(O)] and [FeV(O)] being the resting and active principles of the OâO coupling, respectively, concurs with fundamental mechanistic ideas of (electroâ) chemical OâO coupling in water oxidation catalysis (WOC), indicating that central mechanistic motifs of WOC can be mimicked in a catalase/peroxidase setting.DFG, 12489635, SFB 658: Elementarprozesse in molekularen Schaltern auf OberflĂ€chenTU Berlin, Open-Access-Mittel - 201
Quenched Lewis Acidity : Studies on the Medium Dependent Fluorescence of Zinc(II) Complexes
Three new zinc(II) coordination units [Zn(1â3)] based on planarâdirecting tetradentate Schiff baseâlike ligands H(2)(1â3) were synthesized. Their solidâstate structures were investigated by single crystal Xâray diffraction, showing the tendency to overcome the squareâplanar coordination sphere by axial ligation. Affinity in solution towards axial ligation has been tested by extended spectroscopic studies, both in the absorption and emission mode. The electronic spectrum of the pyridine complex [Zn(1)(py)] has been characterized by MCâPDFT to validate the results of extended TDâDFT studies. Green emission of nonâemissive solutions of [Zn(1â3)] in chloroform could be switched on in the presence of potent Lewisâbases. While interpretation in terms of an equilibrium of stacked/nonâfluorescent and destacked/fluorescent species is in line with precedents from literature, the sensitivity of [Zn(1â3)] was greatly reduced. Results of a computationâbased structure search allow to trace the hidden Lewis acidity of [Zn(1â3)] to a new stacking motif, resulting in a strongly enhanced stability of the dimers