كرار عبد علي سعيد العميد

A mononuclear AuI-NHC complex was synthesized in good yield via the reaction of KAuCl4 with an imidazolium-linked cyclophane salt in the presence of a mild base. The new complex was fully characterized by 1H and 13C NMR spectroscopy and mass spectrometry. The 1H NMR studies, supported by DFT analysis, show how the mononuclear AuI-NHC complex dimerizes to its corresponding dinuclear AuI-NHC analogue slowly in solution (DMSO or CH3CN). The thermodynamic properties show a distinctive preference for dinuclear Au formation over that of the monomer. We have also discussed the unconventional structural contrast between the experimental and computational geometrical analysis of the dinuclear AuI-NHC complex.

Synthesis, spectroscopic characterizations and single crystal X-ray structure of a new dinuclear Copper(II) complex of the form [Cu2L(µ-O-OAc)(OAc)2](PF6) are reported. The molecular structure of the complex indicates that acetate ions coordinate to metals in different types, as a unidentate ligand, as a chelating ligand and in arrangement involving chelation and bridging. The metal centers in this complex are five coordinated with two different geometries (trigonal bipyramid and square pyramidal). Magnetic measurements show the presence of a strong Cu–Cu antiferromagnetic interaction. Moreover, density functional theory (DFT) calculations were performed to deeper analysis of the structure and vibrational properties of the synthesized complex. An interesting result is failure of DFT and second order Møller-Plesset perturbation (MP2) methods for prediction of antiferromagnetic coupling in the synthesized complex which introduces its as a new challenging material for future computational chemistry investigations

In this study, we report the synthesis of a series of new gold compounds in different solvation media. First, gold(I) thiosemicarbazone (TSC) [Au–(TSC)2]Cl was synthesized by reacting [Au(SMe2)]Cl with a thiosemicarbazone ligand in acetonitrile. Then, we successfully managed to replace one of the monodentate thiosemicarbazone ligands with Cl to prepare the TSC–AuCl complex by the reaction of KAuCl4 with thiosemicarbazone in acetonitrile. In a different strategy, the reaction of KAuCl4 with thiosemicarbazone in methanol formed a [TSC–AuCl]AuCl2 complex of tridentate (NNS) thiosemicarbazone. All complexes were fully characterized by X-ray diffraction, 1H and 13C NMR spectroscopy, and mass spectrometry. The 1H and 13C NMR spectra of the [Au–(TSC)2]Cl in DMSO-d6 solution showed two sets of signals, suggesting the presence of two complexes formed from (E)- and (Z)-TSC, respectively. X-ray studies showed only one complex from (Z)-TSC, and the (Z)-TSC ligands provide an exactly linear coordination arrangement around the Au(I) centres. X-ray crystallography showed [TSC–AuCl]+ cations in the AuCl2 salts to have a square pyramidal geometry. Complexes of TSC–AuCl and [TSC–AuCl]AuCl2 had limited stability, decomposing rapidly in solution, while the [Au–(TSC)2]Cl complex was stable in solution.

Predictive and mechanistically driven access to polynuclear oxo clusters and related materials remains a grand challenge of inorganic chemistry. We here introduce a novel strategy for synthetic control over highly sought-after transition metal {M4O4} cubanes. They attract interest as molecular water oxidation catalysts that combine features of both heterogeneous oxide catalysts and nature’s cuboidal {CaMn4O5} center of photosystem II. For the first time, we demonstrate the outstanding structure-directing effect of straightforward inorganic counteranions in solution on the self-assembly of oxo clusters. We introduce a selective counteranion toolbox for the controlled assembly of di(2-pyridyl) ketone (dpk) with M(OAc)2 (M = Co, Ni) precursors into different cubane types. Perchlorate anions provide selective access to type 2 cubanes with the characteristic {H2O-M2(OR)2-OH2} edge-site, such as [Co4(dpy-C{OH}O)4(OAc)2(H2O)2](ClO4)2. Type 1 cubanes with separated polar faces [Co4(dpy-C{OH}O)4(L2)4]n+ (L2 = OAc, Cl, or OAc and H2O) can be tuned with a wide range of other counteranions. The combination of these counteranion sets with Ni(OAc)2 as precursor selectively produces type 2 Co/Ni-mixed or {Ni4O4} cubanes. Systematic mechanistic experiments in combination with computational studies provide strong evidence for type 2 cubane formation through reaction of the key dimeric building block [M2(dpy-C{OH}O)2(H2O)4]2+ with monomers, such as [Co(dpy-C{OH}O)(OAc)(H2O)3]. Furthermore, both experiments and DFT calculations support an energetically favorable type 1 cubane formation pathway via direct head-to-head combination of two [Co2(dpy-C{OH}O)2(OAc)2(H2O)2] dimers. Finally, the visible-light-driven water oxidation activity of type 1 and 2 cubanes with tuned ligand environments was assessed. We pave the way to efficient design concepts in coordination chemistry through ionic control over cluster assembly pathways. Our comprehensive strategy demonstrates how retrosynthetic analyses can be implemented with readily available assembly directing counteranions to provide rapid access to tuned molecular materials.

One‐electron reduction of a pyrazolate‐bridged triangular Fe3(μ3‐O) core induces a cascade wherein all three metal centers switch from high‐spin Fe3+ to low‐spin Fe2.66+. This hypothesis is supported by spectroscopic data (1H‐NMR, UV‐vis‐NIR, infra‐red, 57Fe‐Mössbauer, EPR), X‐ray crystallographic characterization of the cluster in both oxidation states and also density functional theory. The reduction induces substantial contraction in all bond lengths around the metal centers, along with diagnostic shifts in the spectroscopic parameters. This is, to the best of our knowledge, the first example of a one‐electron redox event causing concerted change in multiple iron centers.

The reaction of mixtures of Fe(O2CMe)2·2H2O and Ni(O2CMe)2·4H2O of various compositions with di-2-pyridyl ketone (py2CO, dpk) in MeCN under an inert atmosphere afforded a family of hetero-metallic enneanuclear clusters with general formula [Fe9−xNix(μ4-OH)2(O2CMe)8(py2CO2)4] (2, x = 1.00; 3: x = 6.02; 4, x = 7.46; 5, x = 7.81). Clusters 2–5 are isomorphous to the homo-metallic [Fe9] cluster (1) previously reported by some of us, and also isostructural to the known homo-metallic [Ni9] cluster. All four clusters contain a central MII ion in an unusual 8-coordinate site and eight peripheral MII ions in distorted octahedral environments. The distribution of FeII and NiII ions over these two distinct coordination sites in 2–5 can be established through a combination of X-ray fluorescence and Mössbauer spectroscopies, which show that FeII preferentially occupies the unique 8-coordinate metal site while NiII accumulates in the octahedral holes. Density functional theory indicates that the distribution of ions across the two sites arises not from any intrinsic preference of the FeII ions for the 8-coordinate sites, but rather because of the large ligand field stabilization energy available to NiII in octahedral coordination.

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