Bis‐Sulfonyl O,C,O‐Chelated Metallylenes (Ge,Sn) as Adjustable Ligands for Iron and Tungsten Complexes

The synthesis and characterization of an E₂CE₂ bis‐sulfonyl aryl pincer ligand and its efficiency for the stabilization of compounds containing low‐valent Group 14 elements (Ge and Sn) are reported. Complexation reaction of these metallylenes with iron or tungsten complexes resulted in the modulation of the oxygen atoms of the sulfonyl groups implicated in the stabilization of the Group 14 elements, demonstrating the original adjustable character of the bis‐sulfonyl O₂S‐C‐SO₂ aryl pincer.     

Exploring Group 14 Structures: 1D to 2D to 3D

Various one‐, two‐ and three‐dimensional Group 14 (C, Si, Ge, Sn, and Pb) element structures at P=1 atm are studied in this work. As expected, coordination number (CN)—not an unambiguous concept for extended structures—plays an important part in the stability of structures. Carbon not only favors four‐coordination, but also is quite happy with π‐bonding, allowing three‐ and even two‐coordination to compete. Highly coordinated (CN>4) discrete carbon molecules are rare; that “saturation of valence” is reflected in the instability of C extended structures with CN>4. Si and Ge are quite similar to each other in their preferences. They are less biased in their coordination than C, allowing (as their molecular structures do) CN=5 and 6, but tending towards four‐coordination. Sn and Pb 3D structures are very flexible in their bonding, so that in these elements four‐ to twelve‐coordinate structures are close in energy. This lack of discrimination among ordered structures also points to an approach to the liquid state, consistent with the low melting point of Sn and Pb. The Group 14 liquid structures we simulate in molecular dynamics calculations show the expected, effective, first coordination number increase from 5.1 for Si to 10.4 for Pb. A special point of interest emerging from our study is the instability of potential multilayer graphene structures down Group 14. Only for C will these be stable; for all the other Group 14 elements pristine, unprotected, bi‐ and multilayer graphenes should collapse, forming “vertical” bonds as short as the in‐plane ones.     

Molecular Double‐Bond Covalent Radii for Elements Li–E112

The previous systems of triple‐bond and single‐bond self‐consistent, additive covalent radii, R(AB)=r(A)+ r(B), are completed with a fit for σ²π² double‐bonds.The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same, self‐consistent fit. Many of the calculated primary data came from E?CH₂ and H? E?CH₂ models. Homonuclear LE?EL, formaldehyde‐type Group 14–Group 16 and open‐shell, X ³ Σ Group‐16 dimer data are included. The standard deviation for the 316 included data points is 3 pm.     

The Stability of the Oxidation State +4 in Group 14 Compounds from Carbon to Element 114

The stability of the oxidation state +4 decreases from silicon to element 114, as shown by relativistic and nonrelativistic calculations on the hydrides, fluorides, and chlorides of the Group 14 elements (the energies of the decomposition reaction (1) are given in the plot). Thus it is unlikely that superheavy element 114, which may have stable isotopes due to its magic numbers of protons and neutrons, can be studied by atom-at-a-time chemistry in the oxidation state +4.     

Semiconducting Group 15 Monolayers: A Broad Range of Band Gaps and High Carrier Mobilities

Optoelectronic applications require materials both responsive to objective photons and able to transfer carriers, so new two‐dimensional (2D) semiconductors with appropriate band gaps and high mobilities are highly desired. A broad range of band gaps and high mobilities of a 2D semiconductor family, composed of monolayer of Group 15 elements (phosphorene, arsenene, antimonene, bismuthene) is presented. The calculated binding energies and phonon band dispersions of 2D Group 15 allotropes exhibit thermodynamic stability. The energy band gaps of 2D semiconducting Group 15 monolayers cover a wide range from 0.36 to 2.62 eV, which are crucial for broadband photoresponse. Significantly, phosphorene, arsenene, and bismuthene possess carrier mobilities as high as several thousand cm² V^?1 s^?1. Combining such broad band gaps and superior carrier mobilities, 2D Group 15 monolayers are promising candidates for nanoelectronics and optoelectronics.     

High-pressure structural trends of Group 15 elements: simple packed structures versus complex host-guest arrangements

The Group 15 elements P, As, Sb, and Bi all have layered structures consisting of six-membered rings under ambient conditions and attain the body-centered cubic (bcc) structure at the highest pressures applied. In the intermediate pressure region, however, phosphorus and its heavier congeners behave profoundly differently. In this region P first attains the open packed simple cubic (sc) structure for a wide range of pressures and then transforms into the rarely observed simple hexagonal (sh) structure. For the heavier congeners complex, incommensurately modulated host-guest structures emerge as intermediate pressure structures. We investigated the high-pressure behavior of P and As by ab initio density functional calculations in which pseudopotentials and a plane wave basis set were employed. The incommensurately modulated high-pressure structure of As was approximated by a supercell. Our calculations reproduced the experimentally established pressure stability ranges of the sc and sh structures for P and the host-guest structure for As very well. We found that the sc and especially the sh structure are decisively stabilized by the admixture of d states in the occupied levels of the electronic structure. This admixture releases s-s antibonding states above the Fermi level (s-d mixing). With pressure, s-d mixing increases rapidly for P, whereas it remains at a low level for As. As a consequence, the band energy contribution to the total energy determines the structural stability for P in the intermediate pressure region, giving rise to simple packed structures. On the other hand, in the intermediate pressure region of the heavier Group 15 elements, a delicate interplay between the electrostatic Madelung energy and the band energy leads to the formation of complex structures.     

内蒙古中部渣尔泰山群微量元素地球化学特征

通过对内蒙古中部渣尔泰山群各层位岩石采样,对该山群中共43个微量元素（含稀土元素）与地壳丰度进行了对比分析,总结了该山群微量元素的地球化学特征。研究表明,该山群富集W、Re、Cu、Pb、Co等元素,而In、V、Cr、Ni等元素亏损较严重;微量元素在板岩和云母石英片岩中相对含量较高,在灰岩中相对贫化;此外,该山群稀土元素地球化学特征表现为轻稀土富集,重稀土亏损;具有明显的Eu的负异常,Ce的弱正异常。     

Geometry prediction of hafnocenes by quantum chemical methods

The performance of quantum chemical methods for geometry prediction of hafnocenes was evaluated. HF, B3LYP and MP2 in combination with nonrelativistic (MHF) and relativistic (MWB and LANL2DZ) basis sets for hafnium together with standard basis sets 3-21G*, 6-31G* and 6-311G** for other elements were applied. Five basic structural parameters of the optimized structures of the hafnocenes were compared with experimental crystal structures obtained from the Cambridge structural database. Altogether 80 hafnocenes were included in the analysis. The results show that relativistic corrections are necessary for Hf atom. However, even the Hartree–Fock (HF) method, when combined with relativistic pseudopotentials, reproduces the experimental crystal structures with significant accuracy. The good performance of the HF method can be understood to originate from the absence of significant near-degeneracy correlations for hafnium. On average, the B3LYP and MP2 methods provide structural parameters somewhat closer to the experimental ones.     

Trace elements in size-fractionated coal ash from two Polish power plants

Concentration of 38 elements in size-fractionated brwon and hard coal ash from two Polish power plants have been measured by instrumental neutron activation analysis (INAA). Based on the enrichment factors calculated relative to iron and average crustal rock composition, the elements are grouped into three classes: Group I elements show little or no enrichment in the small fraction; Group II elements increase their enrichment with decreasing particle size; the behaviour of Group III elements is intermediate between those of elements in Groups I and II.     

Aromaticity in Group 14 homologues of the cyclopropenylium cation

The nature of the bonding and the aromaticity of the heavy Group 14 homologues of cyclopropenylium cations E₃H₃⁺ and E₂H₂E′H⁺ (E, E′=C–Pb) have been investigated systematically at the BP86/TZ2P DFT level by using several methods. Aromatic stabilization energies (ASE) were evaluated from the values obtained from energy decomposition analysis (EDA) of charged acyclic reference molecules. The EDA‐ASE results compare well with the extra cyclic resonance energy (ECRE) values given by the block localized wavefunction (BLW) method. Although all compounds investigated are Hückel 4n+2 π electron species, their ASEs indicate that the inclusion of Group 14 elements heavier than carbon reduces the aromaticity; the parent C₃H₃⁺ ion and Si₂H₂CH⁺ are the most aromatic, and Pb₃H₃⁺ is the least so. The higher energies for the cyclopropenium analogues reported in 1995 employed an isodesmic scheme, and are reinterpreted by using the BLW method. The decrease in the strength of both the π cyclic conjugation and the aromaticity in the order C?Si>Ge>Sn>Pb agrees reasonably well with the trends given by the refined nucleus‐independent chemical shift NICS(0)_πzz index.     

Atom‐Precise Organometallic Zinc Clusters

The bottom‐up synthesis of organometallic zinc clusters is described. The cation {[Zn₁₀](Cp*)₆Me}⁺ ( 1 ) is obtained by reacting [Zn₂Cp*₂] with [FeCp₂][BAr₄^F] in the presence of ZnMe₂. In the presence of suitable ligands, the high reactivity of 1 enables the controlled abstraction of single Zn units, providing access to the lower‐nuclearity clusters {[Zn₉](Cp*)₆} ( 2 ) and {[Zn₈](Cp*)₅(^tBuNC)₃}⁺ ( 3 ). According to DFT calculations, 1 and 2 can be described as closed‐shell species that are electron‐deficient in terms of the Wade–Mingos rules because the apical ZnCp* units that constitute the cluster cage do not have three, but only one, frontier orbitals available for cluster bonding. Zinc behaves flexibly in building the skeletal metal–metal bonds, sometimes providing one major frontier orbital (like Group 11 metals) and sometimes providing three frontier orbitals (like Group 13 elements).     

Molecular Single‐Bond Covalent Radii for Elements 1–118

A self‐consistent system of additive covalent radii, R(AB)=r(A) + r(B), is set up for the entire periodic table, Groups 1–18, Z=1–118. The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same fit. Both E–E, E–H, and E–CH₃ data are incorporated for most elements, E. Many E–E′ data inside the same group are included. For the late main groups, the system is close to that of Pauling. For other elements it is close to the methyl‐based one of Suresh and Koga [J. Phys. Chem. A 2001 , 105, 5940] and its predecessors. For the diatomic alkalis MM′ and halides XX′, separate fits give a very high accuracy. These primary data are then absorbed with the rest. The most notable exclusion are the transition‐metal halides and chalcogenides which are regarded as partial multiple bonds. Other anomalies include H₂ and F₂. The standard deviation for the 410 included data points is 2.8 pm.     

A Cationic Phosphapyramidane

Pyramidanes C[C₄R₄] constitute a novel class of highly strained and reactive polyhedral clusters that attracted a great deal of attention of both theoreticians and experimentalists. Although well‐studied from the theoretical viewpoint, pyramidanes were synthetically inaccessible, and only very recently their very first isolable representatives have been described. In this Communication, we report on the synthesis and structural studies of the cationic pyramidane with the Group 15 element at the apex, namely, phosphapyramidane, an isoelectronic analogue of the neutral pyramidanes of the Group 14 elements.     

Homoleptic Lanthanide Complexes of Chelating Phosphanamides—An Experimental and Theoretical Study

Four chelating ligands are present in the first phosphanamide complexes of Group 3 metals and the lanthanides (see structure shown). However, these ligands coordinate to form a distorted molecular structure. The compounds were characterized by single-crystal X-ray structure analysis and quantum-mechanical investigations with density functional theory and MP2 methods.     

Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3− (A=As,Sb, Bi) Complexes

Heteronuclear transition‐metal–main‐group‐element carbonyl complexes of AsFe(CO)₃^?, SbFe(CO)₃^?, and BiFe(CO)₃^? were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass‐selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C_3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)₃^?. Chemical bonding analyses on the whole series of AFe(CO)₃^? (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp–p) type of transition‐metal–main‐group‐element multiple bonding. The σ‐type three‐orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)₃^? (A=As, Sb, Bi) complexes.     

Static and Frequency‐Dependent Dipole–Dipole Polarizabilities of All Closed‐Shell Atoms up to Radium: A Four‐Component Relativistic DFT Study

We test the performance of four‐component relativistic density functional theory by calculating the static and frequency‐dependent electric dipole–dipole polarizabilities of all (ground‐state) closed‐shell atoms up to Ra. We consider 12 nonrelativistic functionals, including three asymptotically shape‐corrected functionals, by using two smooth interpolation schemes introduced by the Baerends group: the gradient‐regulated asymptotic connection (GRAC) procedure and the statistical averaging of (model) orbital potentials (SAOP). Basis sets of doubly augmented triple‐zeta quality are used. The results are compared to experimental data or to accurate ab initio results. The reference static electric dipole polarizability of palladium has been obtained by finite‐field calculations using the coupled‐cluster singles, doubles, and perturbative triples method within this work. The best overall performance is obtained using hybrid functionals and their GRAC shape‐corrected versions. The performance of SAOP is among the best for nonhybrid functionals for Group 18 atoms but its precision degrades when considering the full set of atoms. In general, we find that conclusions based on results obtained for the rare‐gas atoms are not necessarily representative of the complete set of atoms. GRAC cannot be used with effective core potentials since the asymptotic correction is switched on in the core region.     

Dimers of Nineteen‐Electron Sandwich Compounds: Crystal and Electronic Structures,and Comparison of Reducing Strengths

The dimers of some Group 8 metal cyclopentadienyl/arene complexes and Group 9 metallocenes can be handled in air, yet are strongly reducing, making them useful n‐dopants in organic electronics. In this work, the X‐ray molecular structures are shown to resemble those of Group 8 metal cyclopentadienyl/pentadienyl or Group 9 metal cyclopentadienyl/diene model compounds. Compared to those of the model compounds, the DFT HOMOs of the dimers are significantly destabilized by interactions between the metal and the central C?C σ‐bonding orbital, accounting for the facile oxidation of the dimers. The lengths of these C?C bonds (X‐ray or DFT) do not correlate with DFT dissociation energies, the latter depending strongly on the monomer stabilities. Ru and Ir monomers are more reducing than their Fe and Rh analogues, but the corresponding dimers also exhibit much higher dissociation energies, so the estimated monomer cation/neutral dimer potentials are, with the exception of that of [RhCp₂]₂, rather similar (?1.97 to ?2.15 V vs. FeCp₂^+/0 in THF). The consequences of the variations in bond strength and redox potentials for the reactivity of the dimers are discussed.     

tBuP(NH2)2--a reactive synthon for the synthesis of molecular imidophosphinates of group 13 metals

Reactions of tBuP(NH(2))(2) with Group 13 trialkyls MR(3) (M=Al, Ga, In; R=Me, tBu) were investigated in detail. According to variable-temperature (VT) NMR investigations, the reaction proceeds stepwise with the initial formation of aminophosphane adducts, which subsequently react to give iminophosphorane adducts and finally the heterocyclic metallonitridophosphinates. BP86/TZVPP (DFT) calculations were performed to verify this reaction pathway, to elucidate the influence of the central Group 13 element on the stability of the reaction intermediates and the heterocycles, as well as to assess the thermodynamics of their formation. The relative stability of free and complexed aminophosphane RP(NH(2))(2) and iminophosphorane R(H(2)N)(H)P=NH (adducts) with P(III) and P(V) centers was studied in more detail with DFT and MP2 methods. In addition, the influence of the substituent R was investigated by variation of R from H to Me, tBu, F, and NH(2). In general, the aminophosphane form was found to be favored for the free ligand, however, upon complexation with MR(3) (M=Al, Ga; R=alkyl) both forms are almost equal in energy.     

Halides of the Heavier Group 14 Homologues Germanium,Tin, and Lead—A Journey through Unusual Compounds and Oxidation States

Classical halides of the heavier Group 14 homologues germanium, tin, and lead are common precursors for the synthesis of exciting compounds, such as polyhedral clusters. To get access to larger metalloid cluster compounds of Group 14, the disproportionation reaction of metastable monohalide solutions, accessible through a preparative co-condensation reaction, proved to be quite successful. As the identity of the subvalent halides within the metastable solutions were yet unknown the reaction course from a monohalide precursor to a metalloid cluster was mostly unidentified. This might change now, as a first subhalide cluster [Ge₁₄Br₈(Et₃P)₄] could be characterized, being the first trapped intermediate of the disproportionation reaction of Group 14 subhalides. All these aspects are included within this Minireview, together with a short historical overview, dealing with the development of the preparative co-condensation technique out of the matrix isolation technique, being the essential first step of the synthesis of metastable monohalide solutions of the heavier Group 14 elements Ge and Sn.