Magnetic anisotropy of [Mo(CN)7]4- anions and fragments of cyano-bridged magnetic networks

Quantum chemistry calculations of CASSCF/CASPT2 level together with ligand field analysis are used for the investigation of magnetic anisotropy of [Mo(CN)7]4- complexes. We have considered three types of heptacyano environments: two ideal geometries, a pentagonal bipyramid and a capped trigonal prism, and the heptacyanomolybdate fragment of the cyano-bridged magnetic network K2[Mn(H2O)2]3[Mo(CN)7]2.6H2O. At all geometries the first excited Kramers doublet is found remarkably close to the ground one due to a small orbital energy gap in the ligand field spectrum, which ranges between a maximal value in the capped trigonal prism (800 cm(-1)) and zero in the pentagonal bipyramid. The small value of this gap explains (i) the axial form of the g tensor and (ii) the strong magnetic anisotropy even in strongly distorted complexes. Comparison with available experimental data for the g tensor of the mononuclear precursors reveals good agreement with the present calculations for the capped trigonal prismatic complex and a significant discrepancy for the pentagonal bipyramidal one. The calculations for the heptacyanomolybdate fragment of K2[Mn(H2O)2]3[Mo(CN)7]2.6H2O give g(perpendicular)/g(parallel) approximately 0.5 and the orientation of the local anisotropy axis close to the symmetry axis of an idealized pentagonal bipyramid. These findings are expected to be important for the understanding of the magnetism of anisotropic Mo(III)-Mn(II) cyano-bridged networks based on the [Mo(CN)7]4- building block.     

Tetrahedral Fulleroids

Fulleroids are cubic convex polyhedra with faces of size 5 or greater. They are suitable models of carbon molecules. In this paper sufficient and necessary conditions for existence of fulleroids of tetrahedral symmetry types and with pentagonal and n-gonal faces only depending on number n are presented. Either infinite series of examples are found to prove existence or nonexistence is proved using symmetry invariants.     

Polyhedral structures with an odd number of vertices: nine-coordinate metal compounds

The stereochemistry of nine-coordinate transition-metal and rare-earth compounds has been studied by means of continuous shape measures (CShM) and related tools. Several reference nine-vertex polyhedra have been defined and their minimal distortion interconversion paths established. A theoretical shape map is presented in which the structures can be placed according to their distances in CShM space to the capped square antiprism and the tricapped trigonal prism, which are the most common polyhedra in nine-coordinate compounds. The structures of almost 2000 metal coordination spheres in molecular and extended solid-state compounds have been analyzed. Clear stereochemical trends can be established for subsets of these compounds grouped according to the nature of their ligands, which include families of compounds spread along the interconversion paths between the capped square antiprism and the capped cube, or between the tricapped trigonal prism and the tridiminished icosahedron.     

The role of neutral coligands on the stabilization of mono-Tp(i)Pr2 U(III) complexes

The reaction of [UI(3)(THF)(4)] with 1 equiv of KTp()i(Pr)()2 in toluene in the presence of several neutral coligands allowed the synthesis of a novel family of mono-Tp()i(Pr)()2 complexes, [UI(2)Tp()i(Pr)()2(L)(x)()] [L = OPPh(3), x = 1 (3); L = C(5)H(5)N, x = 2 (4); L = Hpz()t(Bu,Me), x = 2 (5); and L = bipy, x = 1 (6)]. The adduct with THF, [UI(2)Tp()i(Pr)()2(THF)(2)(-)(3)] (1), could also be isolated by reacting [UI(3)(THF)(4)] with 1 equiv of KTp()i(Pr)()2 in tetrahydrofuran. However, complex 1 is not a good starting material to enter into the mono-Tp()i(Pr)()2 U(III) complexes as it decomposes in solution, leading to mixtures of U(III) species coordinated with Hpz()i(Pr)()2. The solid-state structures of 3, 4, and 6 were determined by single-crystal X-ray diffraction and revealed that this family of mono-Tp()i(Pr)()2 complexes can be six- (3) or seven-coordinated (4 and 6), depending on the nature of the neutral coligand. Complex 3 displays distorted octahedral coordination geometry, while 4 and 6 display distorted pentagonal bipyramid and capped octahedral geometries, respectively. Complexes 3 and 6 are static in solution, and the patterns of the (1)H NMR spectra are consistent with the C(s)() symmetry found in the solid state. The other complexes (1, 4, and 5) are fluxional, but the dynamic processes involved can be slowed by decreasing the temperature.     

Catenated polymeric molecular patterns in structures of two calcium(II) complexes with pyridine-2,3-dicarboxylate (quinolinic) and water ligands

The structure of triclinic catena-tetraquo(μ-pyridine-2,3-dicarboxylato-N,O; O′)calcium(II) is composed of two symmetry independent Ca(II) ions and two independent ligand molecules. Each Ca(II) is coordinated by a N,O-bonding moiety of a ligand, four water oxygens, and a carboxylate oxygen donated by an adjacent bridging ligand. The resulting molecular ribbons are propagating in the [010] crystal direction. Both Ca(II) ions are eight coordinate forming a capped pentagonal bipyramidal with strongly distorted pentagonal equatorial planes. Hydrogen bonds between carboxylate oxygens and coordinated waters are responsible for the stability of the structure. The orthorhombic structure of catena-trisaquo[(μ-2, 3-dicarboxypyridin-1-ium-O,O′; O′′) (H pyridine-2,3-dicarboxylato-N,O)]calcium(II) is composed of molecular ribbons in which the bridging of Ca(II) ions occurs through a ligand using one bidentate carboxylate. The other carboxylate of this ligand donates only one O atom to Ca(II), the second remaining inactive. A proton is attached to the hetero-nitrogen. Each Ca(II) is also chelated by a N,O-bonding moiety of a second ligand, which does not bridge and its second carboxylate remains protonated. Three water oxygen atoms complete the coordination around the Ca(II) ion to eight. The resulting coordination polyhedron is a capped pentagonal bipyramid with a strongly distorted equatorial plane. Hydrogen bonds in which coordinated waters act as donors are responsible for the stability of the structure.     

The isocloso capped pentagonal bipyramid versus the closo bisdisphenoid in hypoelectronic eight-vertex metallaboranes having 16 skeletal electrons

The lowest energy structures for all of the eight-vertex [M]CB₆H₇ {[M] = CpFe, CpRu. Co(CO)₂, Rh(CO)₂, (Me₃P)₂Fe(H), (Me₃P)₂Ru(H)}, [M]C₂B₅H₇ {[M] = CpMn, CpRe, Cr(CO)₃, Mo(CO)₃}, and [M]₂C₂B₄H₆ ([M] = CpFe, CpRu) systems having 16 skeletal electrons were found by density functional theory to be capped pentagonal bipyramids providing a degree 6 vertex for a metal atom. Thus the capped pentagonal bipyramid plays a similar role for eight-vertex metallaboranes with 16 skeletal electrons as the isocloso deltahedra play in 9- and 10-vertex metallaboranes with 18 and 20 skeletal electrons, respectively. Furthermore, in all of these metallaborane systems the closo bisdisphenoidal structures were always found to be higher energy structures than their capped pentagonal bipyramidal isomers. For the bimetallic systems Cp₂M₂C₂B₄H₆ (M = Fe, Ru) even higher energy hexagonal bipyramid structures with degree 6 vertices for both metal atoms were also found.     

Air-Stable Hexagonal Bipyramidal Dysprosium(III) Single-Ion Magnets with Nearly Perfect D6h Local Symmetry

Eight-coordinated Dy^III centres with D_6h symmetry are expected to act as high-performance single-molecule magnets (SMMs) due to the simultaneous fulfilment of magnetic axiality and a high coordination number (a requisite for air stability). But the experimental realization is challenging due to the requirement of six coordinating atoms in the equatorial plane of the hexagonal bipyramid; this is usually too crowded for the central Dy^III ion. Here a hexaaza macrocyclic Schiff base ligand and finetuned axial alkoxide/phenol-type ligands are used to show that a family of hexagonal bipyramidal Dy^III complexes can be isolated. Among them, three complexes possess nearly perfect D_6h local symmetry. The highest effective magnetic reversal barrier is found at 1338(3) K and an open hysteresis temperature of 6 K at the field sweeping rate of 1.2 mT s⁻¹; this represents a new record for D_6h SMMs.     

Structure and stability of binary transition-metal clusters (NbCo)n (n < or = 5): a relativistic density-functional study

Equilibrium geometries and electronic properties of binary transition-metal clusters, (NbCo)n (n < or = 5), have been investigated by means of the relativistic density-functional approach. The metal-metal bonding and stability aspects of these clusters have been analyzed on the basis of calculations. Present results show that these clusters exhibit rich structural varieties on the potential-energy surfaces. The most stable structures have a compact conformation in relatively high symmetry, in which the Nb atoms prefer to form an inner core and Co atoms are capped to the facets of the core. Such building features in clustering of the Nb/Co system are related to the order of bond strength: Nb-Nb>Nb-Co>Co-Co. As the binary cluster size increases, the Nb-Co bond may become stronger than the Nb-Nb bond in the inner niobium core, which results in a remarkable increment of the Nb-Nb bond length. Amongst these binary transition-metal clusters, the singlet (NbCo)4 in T(d) symmetry has a striking high stability due to the presence of the spherical aromaticity and electronic shell closure. The size dependence of the bond length and stability of the cluster has been explored.     

A new type of hexaosmium boride cluster, H3Os6(CO)16B, that does not conform to electron counting rules

A new type of hexaosmium boride cluster, H3Os6(CO)16B, was produced in the thermolysis of H3Os3(CO)9(BCO). This complex is an 86 valence electron cluster, but the Os6 framework does not possess one of the geometries previously observed for Os6 clusters that have 86 valence electrons. [HOs6(CO)18]- and [Os6(CO)18]2- have octahedral frameworks while that of H2Os6(CO)18 is a face-capped square pyramid. The Os6 framework of H3Os6(CO)16B can be viewed as being derived from a pentagonal bipyramid that is missing one equatorial vertex. It contains an interior boron atom. Alternatively, it can be viewed like the 84 valence cluster Os6(CO)18 as either a bicapped tetrahedron, with a boron atom residing on the edge of the tetrahedron that is common to the capped faces, or a face-capped trigonal bipyramid, with the boron atom on an equatorial edge of the bipyramid that is also an edge of the capped face. H3Os6(CO)16B was characterized by 1H, and 11B, 13C NMR, IR, and mass spectroscopies and single-crystal X-ray diffraction analysis. The molecular structure was determined from two separate crystals. The analysis of each crystal yielded virtually identical structures, but their volumes differed by 36 A3 due to differences in packing in the unit cell. Data for crystal I of H3Os6(CO)16B: monoclinic P2(1/n), a = 9.954(2) A, b = 15.780(4) A, c = 16.448(3) A, beta = 91.07(1) degrees, Z = 4. Data for crystal II of H3Os6(CO)16B: monoclinic P2(1/n), a = 9.927(2) A, beta = 16.623(2) A, b = 16.0233(10) A, beta = 97.78(1) degrees, Z = 4.     

Density functional theory study of nine-atom germanium clusters: effect of electron count on cluster geometry

Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge(9)(z) clusters (z = -6, -4, -3, -2, 0, +2, and +4) starting from three different initial configurations. Double-zeta quality LANL2DZ basis functions extended by adding one set of polarization (d) and one set of diffuse (p) functions were used. The global minimum for Ge(9)(2)(-) is the tricapped trigonal prism expected by Wade's rules for a 2n + 2 skeletal electron structure. An elongated tricapped trigonal prism is the global minimum for Ge(9)(4)(-) similar to the experimentally found structure for the isoelectronic Bi(9)(5+). However, the capped square antiprism predicted by Wade's rules for a 2n + 4 skeletal electron structure is only 0.21 kcal/mol above this global minimum indicating that these two nine-vertex polyhedra have very similar energies in this system. Tricapped trigonal prismatic structures are found for both singlet and triplet Ge(9)(6)(-), with the latter being lower in energy by 3.66 kcal/mol and far less distorted. The global minimum for the hypoelectronic Ge(9) is a bicapped pentagonal bipyramid. However, a second structure for Ge(9) only 4.54 kcal/mol above this global minimum is the C(2)(v)() flattened tricapped trigonal prism structure found experimentally for the isoelectronic Tl(9)(9)(-). For the even more hypoelectronic Ge(9)(2+), the lowest energy structure consists of an octahedron fused to two trigonal bipyramids. For Ge(9)(4+), the global minimum is an oblate (squashed) pentagonal bipyramid with two pendant Ge vertices.     

Structure and properties of lanthanide catalysts: the crystal and molecular structure of SmBr3·4iPr(OH)

The crystal of the title compound is monoclinic (space group C2/c), with a = 22,067(17), b = 10.111 (10), c = 16.886(11) Å,=142.95(5)°, and Z = 4. Its structure is based on the packing of SmBr₃·4iPr(OH) (iPr = isopropyl) molecules. The metal atom is coordinated by three Br ions and by the oxygen atoms of the four iPr(OH) ligands. The coordination polyhedron is a distorted pentagonal bipyramid of C2 symmetry, with Sm and one of the Br atoms lying on the twofold axis of crystallographic symmetry. Polymerization experiments are reported showing that the activity of the catalytic system based on the title complex is much lower than that shown by systems based on similar Nd complexes. A possible rationalization of this fact is given in terms of the oxidation capacity of the rare-earth ions.     

Shape and spin state in four-coordinate transition-metal complexes: the case of the d(6) configuration

Generalized polyhedral interconversion coordinates are defined within the framework of Avnir's continuous shape measures. The application of such interconversion coordinates to the study of the potential energy surfaces that define the stereochemical choice in four-coordinate transition metal complexes with different spin states is presented, and the correlation between potential energy curves and distribution of experimental structures along the tetrahedron to square interconversion path is shown for the case of the d(6) transition-metal complexes.     

Stable Tin (n = 2-15) clusters and their geometries: DFT calculations

We present a detailed structural analysis for small Tin (n = 2-15) clusters based on ab initio quantum mechanical calculations of their binding energies, frontier orbital gaps, and second energy derivatives. Local density approximation calculations revealed that while the smaller clusters (n < or = 8) prefer hexagonal atomic arrays with bulklike crystal symmetry, the bigger clusters prefer pentagonal atomic arrays. From the stability criteria of the magic number clusters we could identify three magic number clusters Ti7, Ti13, and Ti15. While the most stable configuration of Ti7 is a decahedral bipyramid induced by tetrahedral atomic arrays, the most stable configuration of Ti13 is an icosahedron. The other stable cluster Ti15 takes a closed-shell icosahedron-like configuration with both pentagonal and hexagonal symmetries. The stability of the Tin clusters strongly depends on their geometries and charge states. The HOMO-LUMO gap of the Tin clusters approaches its bulk value for n > 8. While there is not much difference between the HOMO and LUMO isosurface charge distributions for the Ti7 and Ti13 clusters in their most stable configurations, they are very different in the case of Ti15. Such a distinct charge distribution in Ti15 indicates its singular chemical selectivity over the other two magic number clusters.     

立体化学刚性的七配位环戊二烯基三(二苄基二硫代氨基甲酸)钛、锆、铪配合物的合成和性质

二烷基二硫代氨基甲酸基作为良好的双齿配体较易与过渡金属生成高配位的配合物,含有环戊二烯基的高配位钛、锆、铪配合物的研究相继出现,这类七配位、18-电子构型的配合物是立体化学刚性,具有独特的光谱性质和结构行为。选择钛、锆和铪二茂二氯化物与三当量的二苄基二硫代氨基甲酸钠反应合成了五种未见报道的七配位配合物,讨论了产物的光谱性质和配位结构。     

Structures of tin cluster cations Sn3(+) to Sn15(+)

We employ a combination of ion mobility measurements and an unbiased systematic structure search with density functional theory methods to study structure and energetics of gas phase tin cluster cations, Sn(n)(+), in the range of n = 3-15. For Sn(13)(+) we also carry out trapped ion electron diffraction measurements to ascertain the results obtained by the other procedures. The structures for the smaller systems are most easily described by idealized point group symmetries, although they are all Jahn-Teller distorted: D(3h) (trigonal bipyramid), D(4h) (octahedron), D(5h) (pentagonal bipyramid) for n = 5, 6, and 7. For the larger systems we find capped D(5h) for Sn(8)(+) and Sn(9)(+), D(3h) (tricapped trigonal prism) and D(4d) (bicapped squared antiprism) plus adatoms for n = 10, 11, 14, and 15. A centered icosahedron with a peripheral atom removed is the dominant motif in Sn(12)(+). For Sn(13)(+) the calculations predict a family of virtually isoenergetic isomers, an icosahedron and slightly distorted icosahedra, which are about 0.25 eV below two C(1) structures. The experiments indicate the presence of two structures, one from the I(h) family and a prolate C(1) isomer based on fused deltahedral moieties.     

ChemInform Abstract: Investigation of a Naked Ag7 Cluster: Configurations and Spectral Characteristics.

DFT calculations show that the most stable Ag₇ cluster is a pentagonal bipyramid, whereas synthesized Ag₇ clusters are planar due to interactions with ligands as revealed by Raman and UV/VIS spectroscopy.     

Bis(p‐nitrobenzoxasulfamato) Complexes of Cadmium(II) and Mercury(II) ‐ Synthesis,Spectra, and X‐Ray Crystal Structures

The reaction of sodium benzoxasulfamate (nbs) with cadmium(II) and mercury(II) sulfate in aqueous solution yield the novel complexes [Cd(nbs)₂(H₂O)₄] (1) and [Hg(nbs)₂(H₂O)₃] ( 2 ), respectively. The complexes were characterized by elemental analyses, IR spectroscopy and X‐ray crystallography. Complex 1 is monomeric and has an octahedral arrangement in which the N‐donor nbs ligands occupy the axial positions, while the water oxygen atoms form the equatorial plane. Complex 2 is polymeric and shows a pentagonal bipyramidal arrangement achieved by the bridging of the HgN₂O₃ units through the weak interaction of the O atoms of the nitro group. The nbs ligands also occupy the axial positions of the pentagonal bipyramid, whereas three water and two nitro oxygen atoms constitute the pentagonal plane. The crystal structure packing in both crystals is achieved by the intermolecular hydrogen bonds involving water hydrogen atoms, nitro and sulfonyl oxygen atoms.     

Isomers in the chemistry of iron coordination compounds

The coordination chemistry of iron covers a wide field, as shown by a survey covering the crystallographic and structural data of almost one thousand and three hundred coordination complexes. About 6.7% of these complexes exist as isomers and are summarized in this review. Included are distortion (96.6%) and cis — trans (3.4%) isomers. These are discussed in terms of the coordination about the iron atom, bond length and interbond angles. Distortion isomers, differing only by degree of distortion in Fe-L, Fe-L-Fe and L-Fe-L parameters, are the most common. Iron is found in the oxidation states zero, +2 and +3 of which +3 is most common. The stereochemistry around iron centers are tetrahedral, five — coordinated (mostly trigonal — bipyramid) and six — coordinated. The most common ligands have O and N donor sites.