Two novel 2-D homometallic cyano-bridged complexes: Synthesis,structures and fluorescent properties

Synthesis, structure and photoluminescent properties of two novel 2-D cyano-bridged complexes {[M₂(μ₂-L)(μ₂-CN)₂ (CN)₂] · H₂O}_n (M = Cd, Zn; L = 1,4-bis(pyridine-2-ylmethyl)piperazine) are presented. Both of them crystallize in the monoclinic space group of C2/c and possess a cyano-bridged 2-D brick wall-like layer structure. Both hydrogen bonds and π–π interactions play important roles in the stabilization of their solid state structure. The emission spectra of 1 and 2 in solid state show strong blue-light emission.     

Structural properties,electronic structures and optical properties of WB2 with different structures: A theoretical investigation

The structural, electronic and optical properties of six WB₂ diborides with hP3, hP6, hP12, oP6, hR9 and hR18 structures were systematically investigated using the first-principles calculation based on density functional theory. The optimized atomic coordinates and lattice parameters agree well with the corresponding experimental and theoretical results. All WB₂ are energetically stable, and hP6-WB₂ has the best phase stability and hP3-WB₂ shows the worst phase stability. The results of density of states and the charge density differences indicate that WB₂ have the strong W–B and B–B covalent bonds. The hardness was obtained from the Mulliken population. The predicted values of absorption coefficient α(ω) and reflectivity R(ω) reveal that the laser with a longer wavelength is recommended during the synthesis of WB₂ coatings on the substrate surface using the Nd-YAG laser. Finally, the anisotropy in optical properties for WB₂ was discussed via the polycrystalline and directional static dielectric constants ε₁(0) and static refractive indexes n(0).     

Synthesis,structures, and magnetic properties of tetranuclear nickel and cobalt complexes with 2-mercaptobenzoxazole

The synthesis and magnetic properties of two tetranuclear Ni complex Ni₄(L)₄(CH₃CN)₄(OCH₃)₄ 1 and Co complex Co₄(L)₄(CH₃CN)₄(OCH₃)₄ 2 (HL = 2-mercaptobenzoxazole) are reported. The X-ray structures reveal that 1 and 2 are isostructural with [Ni₄O₄] 1 and [Co₄O₄] 2 cubane-like cores. Analysis of the temperature dependent magnetic measurements data shows that both complexes are paramagnetic with weak antiferromagnetic coupling. One-J model and two-J model are both applied to fit the experimental magnetic data of 1 and the results indicate the exchange coupling between the type A Ni(II) ions affected by NCS three atoms bridge in 2-mercaptobenzoxazole ligand.     

Transition metal-carboryne complexes: synthesis, bonding, and reactivity

The construction and transformation of metal-carbon (M-C) bonds constitute the central themes of organometallic chemistry. Most of the work in this field has focused on traditional M-C bonds involving tetravalent carbon: relatively little attention has been paid to the chemistry of nontraditional metal-carbon (M-C(cage)) bonds, such as carborane cages, in which the carbon is hypervalent. We therefore initiated a research program to study the chemistry of these nontraditional M-C(cage) bonds, with a view toward developing synthetic methodologies for functional carborane derivatives. In this Account, we describe our results in constructing and elucidating the chemistry of transition metal-carboryne complexes. Our work has shown that the M-C(cage) bonds in transition metal-carboranyl complexes are generally inert toward electrophiles, and hence significantly different from traditional M-C bonds. This lack of reactivity can be ascribed to steric effects resulting from the carboranyl moiety. To overcome this steric problem and to activate the nontraditional M-C(cage) bonds, we prepared a series of group 4 and group 10 transition metal-carboryne complexes (where carboryne is 1,2-dehydro-o-carborane), because the formation of metallacyclopropane opens up the coordination sphere and creates ring strain, facilitating the reactions of M-C(cage) bonds with electrophiles. Structural and theoretical studies on metal-carboryne complexes suggest that the bonding interaction between the metal atom and the carboryne unit is best described as a resonance hybrid of the M-C σ and M-C π bonds, similar to that observed in metal-benzyne complexes. The nickel-carboryne complex (η(2)-C(2)B(10)H(10))Ni(PPh(3))(2) can (i) undergo regioselective [2 + 2 + 2] cycloaddition reactions with 2 equiv of alkyne to afford benzocarboranes, (ii) react with 1 equiv of alkene to generate alkenylcarborane coupling products, and (iii) also undergo a three-component [2 + 2 + 2] cyclotrimerization with 1 equiv of activated alkene and 1 equiv of alkyne to give dihydrobenzocarboranes. The reaction of carboryne with alkynes is also catalyzed by Ni species. Subsequently, a Pd/Ni co-catalyzed [2 + 2 + 2] cycloaddition reaction of 1,3-dehydro-o-carborane with 2 equiv of alkyne was developed, leading to the efficient formation of C,B-substituted benzocarboranes in a single process. In contrast, the zirconium-carboryne species, generated in situ from Cp(2)Zr(μ-Cl)(μ-C(2)B(10)H(10))Li(OEt(2))(2), reacts with only 1 equiv of alkyne or polar unsaturated organic substrates (such as carbodiimides, nitriles, and azides) to give monoinsertion metallacycles, even in the presence of excess substrates. The resultant five-membered zirconacyclopentenes, incorporating a carboranyl unit, are an important class of intermediates for the synthesis of a variety of functionalized carboranes. Transmetalation of zirconacyclopentenes with other metals, such as Ni and Cu, was also found to be a very useful tool for various chemical transformations. Studies of metal-carboryne complexes remain a relatively young research area, particularly in comparison to the rich literature of metal-benzyne complexes. Other transition metal-carborynes are expected to be prepared and structurally characterized as the field progresses, and the results detailed here will further that effort by providing easy access to a wide range of functionalized carborane derivatives.     

高Si掺杂RuO2材料的晶体结构、电子结构和导电性

通过密度泛函理论（density functional theory,DFT）的第一性原理,研究了高Si掺杂的（Ru_1-xSi_x）O₂（x=0、0.125、0.25、0.375、0.5）固溶体材料的晶体结构特征;对采用热分解制备的Si掺杂RuO₂的相分析,证实了通过合适的热分解工艺,可以实现高浓度Si的代位掺杂;能带结构研究显示,高Si掺杂RuO₂材料始终保持金属特性;态密度分析表明,Si可以提供少许Si-3p电子,但导电主体仍来自Ru-4d与O-2p电子;高Si掺杂（Ru_1-xSi_x）O₂的电导率随Si掺杂量的变化符合一阶指数衰减趋势。     

Theoretical analysis on the geometries and electronic structures of coplanar conjugated poly(azomethine)s

In this study, theoretical analysis on the geometries and electronic properties of various conjugated poly(azomethine)s is reported. The theoretical ground-state geometry and electronic structure of the studied poly(azomethine)s are optimized by the hybrid density functional theory (DFT) method treated in periodic boundary conditions at the B3LYP level of theory with 6-31G basis set. The geometry and electronic structure of poly(1,4-phenylenemethylidyneitrilo-1,4-phenylene-nitrilomethylidyne) (PPI) are compared with those of poly(p-phenylene vinylene) (PPV) or polyazine (PAZ). The theoretical results suggest the non-coplanar conformation of PPI but PPV and PAZ with a coplanar conformation. The electronic properties of PPI are in the intermediate between PPV and PAZ. The non-coplanar conformation of PPI could be released if the phenylene ring is replaced by the five-member ring of 3,4-ethylenedioxythiophene (PEEI), pyrrole (PYYI), thiophene (PTTI), furan (PFFI), or thiadiazole (PThThI). The theoretical E_g of PEEI, PYYI, PFFI, and PTTI are in the range of 1.11-1.67 eV, which is due to the coplanar configuration or donor-acceptor intrachain charge transfer. However, the large bond length alternation or lack of charge transfer characteristic makes the PThThI with a larger E_g of 2.47 eV than others. The trend on the IP or EA of the studied conjugated poly(azomethine)s are consistent with the electronic characteristic of the aromatic ring. The upper valence bandwidth of the studied five-member ring based poly(azomethine)s except PThThI is in the range of 562-613 meV, which is larger than that of PPI (247 meV) or PPV (373 meV). The results suggest that the electronic properties of conjugated poly(azomethine)s could be varied through various ring structure. The proposed new coplanar conjugated poly(zomethine)s can be potentially used as transparent conductors or thin film transistors.     

Ligand substitution in sandwich-type complexes of germanotungstates: Syntheses,crystal structures and magnetic properties

Two new sandwich-type germanotungstates K₂H₂{Zn(en)₂}{Zn(en)₂}₂{(GeW₉O₃₄)₂Zn₄(Hen)₂}·17H₂O (1) and K₂H₂{Ni(en)₂}{Ni(en)₂}₂{(GeW₉O₃₄)₂Ni₄(Hen)₂}·12H₂O (2) (en = ethylenediamine) have been hydrothermally synthesized. The polyanions of the two compounds are composed of a [Ge₂W₁₈M₄(Hen)₂O₆₈]^10? (M = Zn, Ni) group decorated by two [M(en)₂(H₂O)]²⁺ units. The luminescence of compound 1 exhibits an intense UV radiation emission maximum at λ ≈ 449 nm upon excitation of 372 nm. The magnetic investigation of compound 2 demonstrates the presence of ferromagnetic interactions between the Ni²⁺ ions of the Ni₄O₁₄(Hen)₂ clusters in 2.     

First-principles study on predicting the crystal structures,mechanical properties and electronic structures of HfCxN1-x

The crystal structures, mechanical properties and electronic structures of HfC_xN_1-x have been predicted by using evolutionary structure search followed by the first-principles calculations in this study. The crystal structures predicted indicate that there are 10 thermodynamic stable phases for HfC_xN_1-x, of which 8 are newly discovered crystal structures and 2 are already known. We investigated the mechanical properties, including the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and Vickers hardness, of all 10 stable phases, and further established the relationship between such properties and the ratio of nitrogen to carbon content. Besides, the Fermi energy level and electronic density of states of these 10 stable phases are calculated as well, and the results reveal the fundamental reason why the mechanical properties change with the ratio of nitrogen to carbon. The predictions of this study agree well with both the experimental data and the previous theoretical evaluations.     

Synthesis,structures and properties of Cu and Cd complexes with 1,10-phenanthroline

Three new Cu and Cd complexes, namely [Cu(phen)(isca)(EtOH)] (1),[Cu(phen)₂(HCOOH)] (2) and [Cd(phen)Cl₂](3) (phen = 1, 10-phenanthroline, isca = isophthalic acid) have been synthesized, which are characterized by elemental analysis, infrared spectrum and x-ray crystal diffraction. While strong hydrogen bonds play central roles in the formation of the 3D structure, the combined influence of the weak interactions such as C-H···O bonds, C-H···π and lone pair···π interactions are also evident in the structures. The preliminary investigation on the thermal and fluorescence property of the complexes are presented.     

Half metallicity in BC2)N nanoribbons: stability, electronic structures, and magnetism

Nanoribbons are suggested to be among the most promising candidates being considered as building blocks in future electronics. In this study, we use density functional calculations to examine the structures and electronic properties of BC(2)N nanoribbons with bare zigzag-shaped edges (zz-BC(2)NNRs). Four different types of atomistic edge configurations are considered, including ribbons terminated with two C edges, B and N edges, B an C edges, and C and N edges. We find the existence of half-metallicity in the ground state of the zz-BC(2)NNRs with two bare C edges and with bare C and N edges. The other two configurations of the zz-BC(2)NNRs can be either semiconducting or metallic, depending on the specific configuration. We also find that the stability of the zz-BC(2)NNRs are largely dependent on ribbon width. The zz-BC(2)NNRs become energetically more stable when the nanoribbon width exceeds 3.3 nm. It is interesting to find that half-metallic zz-BC(2)NNRs with a width of 0.7 nm are thermodynamically more stable than either metallic or semiconducting counterparts. Therefore, the possibility of synthesizing half-metallic zz-BC(2)NNRs exists.     

Microstructural,spectroscopic and mechanical properties of hot-pressed Er:SrF2 transparent ceramics

Raw SrF₂ powders were synthesized by the chemical precipitation method, and the mean particle size was 58.48 nm. Er:SrF₂ transparent ceramics were obtained by hot-pressed (HP) technique, and the effect of ErF₃ levels on the transparency, microstructure, luminescence spectroscopic and microhardness were studied. The ratio of emission intensities R (Red/Green) increased with the ErF₃ doping levels. The addition of ErF₃ was found effectively to reduce grain size and has a positive effect on improving the microhardness. The SrF₂ ceramic doped with 5 wt.% ErF₃ (2 mm thick) showed the best optical transparency, the transmittance at 500 nm and 1200 nm are 87.9 % and 89.5 %, respectively. The average grain size, Vickers hardness (Hv), and fracture toughness (K_IC) for the SrF₂ ceramic were 21.1 ± 4.5 μm, 1.73 ± 0.04 GPa, and 0.52 ± 0.08 MPa·m^1/2, respectively.     

Synthesis and electronic properties of double pincer-type cyclometalated iridium complexes

Double pincer-type cyclometalated iridium complexes were prepared based upon a few assumptions and their photophysical properties were examined.     

Mononuclear metal-o(2) complexes bearing macrocyclic N-tetramethylated cyclam ligands

Metalloenzymes activate dioxygen to carry out a variety of biological reactions, including the biotransformation of naturally occurring molecules, oxidative metabolism of xenobiotics, and oxidative phosphorylation. The dioxygen activation at the catalytic sites of the enzymes occurs through several steps, such as the binding of O(2) at a reduced metal center, the generation of metal-superoxo and -peroxo species, and the O-O bond cleavage of metal-hydroperoxo complexes to form high-valent metal-oxo oxidants. Because these mononuclear metal-dioxygen (M-O(2)) adducts are implicated as key intermediates in dioxygen activation reactions catalyzed by metalloenzymes, studies of the structural and spectroscopic properties and reactivities of synthetic biomimetic analogues of these species have aided our understanding of their biological chemistry. One particularly versatile class of biomimetic coordination complexes for studying dioxygen activation by metal complexes is M-O(2) complexes bearing the macrocyclic N-tetramethylated cyclam (TMC) ligand. This Account describes the synthesis, structural and spectroscopic characterization, and reactivity studies of M-O(2) complexes bearing tetraazamacrocyclic n-TMC ligands, where M ═ Cr, Mn, Fe, Co, and Ni and n = 12, 13, and 14, based on recent results from our laboratory. We have used various spectroscopic techniques, including resonance Raman and X-ray absorption spectroscopy, and density functional theory (DFT) calculations to characterize several novel metal-O(2) complexes. Notably, X-ray crystal structures had shown that these complexes are end-on metal-superoxo and side-on metal-peroxo species. The metal ions and the ring size of the macrocyclic TMC ligands control the geometric and electronic structures of the metal-O(2) complexes, resulting in the end-on metal-superoxo versus side-on metal-peroxo structures. Reactivity studies performed with the isolated metal-superoxo complexes reveal that they can conduct electrophilic reactions such as oxygen atom transfer and C-H bond activation of organic substrates. The metal-peroxo complexes are active oxidants in nucleophilic reactions, such as aldehyde deformylation. We also demonstrate a complete intermolecular O(2)-transfer from metal(III)-peroxo complexes to a Mn(II) complex. The results presented in this Account show the significance of metal ions and supporting ligands in tuning the geometric and electronic structures and reactivities of the metal-O(2) intermediates that are relevant in biology and in biomimetic reactions.     

An ac impedance spectroscopic study of Mg-doped LiCoO2 at different temperatures: electronic and ionic transport properties

An ac impedance spectroscopic study of LiMg_0.05Co_0.95O₂, prepared by sol-gel process, is presented. The results are interpreted on the basis of the equivalent circuit proposed for LiCoO₂ oxide that takes into account the ionic and electronic transport processes. The results demonstrate that the intercalation/deintercalation reaction occurs through two-steps processes involving an adatom mechanism that may be described in terms of partially desolvated lithium ions adsorbed/desorbed from the electrode surface and insertion/loss of an electron from the conduction band of the host followed by diffusion of Li⁺ to/from the lattice intercalation site. Mg doping of LiCoO₂ affects the electrochemical and electronic properties of the pristine oxide by facilitating the insulator-to-conductor transitions that are responsible of the phase transition in the undoped material.     

Four new cyclometalated phenylisoquinoline-based Ir(III) complexes: Syntheses,structures, properties and DFT calculations

Four new cyclometalated phenylisoquinoline-based iridium(III) complexes [Ir(C^∧N)₂(bipy)]PF₆ (5a–5d) (bipy = 2,2′-bipyridine) have been synthesized and fully characterized, where the C^∧N ligands are 1-(4-(trifluoromethyl)phenyl)isoquinoline, 4-(isoquinolin-1-yl)benzaldehyde, 4-(isoquinolin-1-yl)benzonitrile and 1-(3-fluoro-4-methylphenyl)isoquinoline, respectively. The crystal structures of 5a and 5c have been determined. The photophysical and electrochemical properties of these new complexes 5a–5d have been studied. All Ir(III) complexes exhibit orange phosphorescence in dichloromethane solution at room temperature with a maximum at 593–618 nm, quantum yield of 0.046–0.16. The frontier molecular orbital diagrams and the lowest-energy electronic transitions of 5a–5d have been calculated with density functional theory (DFT) and time-dependent DFT (TD-DFT).