Polyhedral Expansion Research Articles

Polyhedral expansion of closo-hexaboranes

Polyhedral expansion of closo-hexaboranes

Borane-Mediated Polyhedral Expansion to Access Metal-Free Neutral and Cationic Derivatives of closo-Heptaboranes.

Boranes with closed polyhedral structures feature peculiar bonding and structural characteristics, rendering them widely applicable in diverse research areas ranging from basic functionalization reactions to applications such as medicine, nanomaterials, molecular electronics, and neutron capture therapy. Among the closed borane family, the neutral and cationic heptaborane B7 clusters have been missing in contemporary boron cluster chemistry to date. Herein, we report a polyhedral expansion protocol to construct a neutral derivative of closo-heptaborane (B7) from closo-hexaborane (B6) mediated by borane. Conversion of the neutral derivative of closo-heptaborane to a cationic derivative is also demonstrated. X-ray crystallographic and spectroscopic analyses with the aid of quantum chemical calculations reveal that both neutral and cationic derivatives of closo-heptaborane exhibit a pentagonal-bipyramidal geometry and involve the delocalized σ skeletal electrons, leading to three-dimensional aromaticity. Moreover, the B7 core of the former undergoes a complexation reaction with silver tetrafluoroborate, representing the first experimental demonstration of the nucleophilic nature of the closo-heptaborane.

Synthesis of sandwich metallaboranes [M(B11H11)2]3– (M = Cu, Ag) via polyhedral expansion of the closo-undecaborate anion [B11H11]2–

Reactions of the undecahydro-closo-undecaborate anion [B11H11]2– with copper(I) and silver(I) complexes [(Ph3P)3MX] (M = Cu, X = Cl; M = Ag, X = NO3) were found to result in the polyhedral expansion with the formation of the corresponding metallaboranes (Bu4N)3[commo-M(B11H11)2] rather than the M–H–B complexes typical of borane ligands. The crystal structure of complex (Bu4N)3[Ag(B11H11)2] was determined by single-crystal X-ray diffraction. Hirschfeld surface analysis and DFT calculations for both metallaboranes [M(B11H11)2]3– (M = Cu, Ag) were carried out.

Strategic Tuning of Photophysical Response in the Polyhedral Framework of the Garnet Structure toward White Light-Emitting Devices with Enhanced Color Rendering.

Designing a single-phase phosphor with high quantum efficiency and full spectrum emission is inevitable for today's scientific world. Herein, an optimal strategy for realizing white emission in a single component matrix is envisaged based on the structure-property-design-device policy. Cationic substitution corresponding to polyhedral expansion and contraction in A2A'B2V3O12 confirms the existence of strong and intricate linkage in the garnet structure. The dodecahedral expansion causes compression of VO4 tetrahedra and a blue shift. The direct correlation of V-O bond distance with red shift validates the distortion of the VO4 tetrahedra. The interdependence of photophysical properties via cationic substitution and subsequent correlation of the V-O bond distance with emission bands enabled the tailoring of phosphor-CaSrNaMg2V3O12 with a high quantum efficiency of 52% and excellent thermal stability of 0.39 eV. Bright warm white light-emitting diode (WLED) devices are fabricated based on Eu3+ and Sm3+-activators. A high quantum efficiency-74% is obtained for the designed Eu3+ phosphor. CIE coordinates near the achromatic point (0.329, 0.366), low CCT-5623 K, and high color rendering index (CRI)-87 are obtained for the single-phase WLED device. This work puts forth a new direction for designing and engineering promising WLEDs with enhanced color rendering based on single-phase phosphors with full spectrum emission.

Selective Voronoi tessellation as a method to design anisotropic and biomimetic implants

The geometry of a metallic scaffold is important for the success of bone implants, where the introduction of porosity can reduce stress shielding effects and allow for bone tissue integration. In this work, porous scaffolds were designed to closely mimic the natural structure of trabecular bone using selective Voronoi tessellation with preferential seeding. A workflow to generate these structures is introduced, where voided regions of seeds in the starting volume create preferential texture during polyhedral expansion, resulting in modified strut orientation in the implant. Anisotropy was digitally characterized by mean-intercept length and star volume distribution measurements to determine similarity to trabecular orientation. This work demonstrates that selective Voronoi tessellation is an effective method to generate biomimetic porous scaffolds with increased anisotropy and tunable strut architecture in three dimensions as a suitable alternative to patient-derived bone geometries.

Synthesis and Characterization of 14-Vertex Carboranes

Twelve new 14-vertex closo-carboranes, including CAd (carbon atoms adjacent), CAp (carbon atoms apart), and cage B-substituted species, were synthesized and structurally characterized via either a [13 + 1] or a [12 + 2] polyhedral expansion protocol. Treatment of various 13-vertex nido-carborane dianionic salts with HBBr2 gave the corresponding 14-vertex carboranes. Mono-B-substituted 14-vertex carboranes 1-R-2,3-(CH2)3-2,3-C2B12H11 (R = Ph, Cl, Br, I) were prepared from the reaction of nido-[8,9-(CH2)3-2,3-C2B11H11]2– with the dihaloborane reagents RBX2. CAd 14-vertex closo-carboranes were also synthesized by treatment of 12-vertex arachno-carborane tetraanionic salts with HBBr2 reagent. These new 14-vertex closo-carboranes were fully characterized by 1H, 13C, and 11B NMR spectroscopy as well as high-resolution mass spectrometry. Their structures were further confirmed by single-crystal X-ray analyses.

The synthesis and characterisation of homo- and heterobimetallic 1,14,2,9- and 1,14,2,10-M2C2B1014-vertex metallacarboranes

A high-yielding synthesis of the 13-vertex cobaltacarborane 4-Cp-4,1,12-closo-CoC(2)B(10)H(12) is described and this compound used to prepare the known 14-vertex species 1,14-Cp(2)-1,14,2,10-closo-Co(2)C(2)B(10)H(12) (II) and 1-(p-cymene)-14-Cp-1,14,2,10-closo-RuCoC(2)B(10)H(12) (IV), the latter by a new route. The related species 1,14-Cp(2)-2,10-Me(2)-1,14,2,10-closo-Co(2)C(2)B(10)H(10) (1) and 1,14-(η-C(9)H(7))(2)-1,14,2,10-closo-Co(2)C(2)B(10)H(12) (2) are also reported. Polyhedral expansion of 4,1,8-CoC(2)B(10) compounds affords a different isomer of the 14-vertex bimetallacarboranes, 1,14,2,9-Co(2)C(2)B(10), and three examples, 1,14-Cp(2)-1,14,2,9-closo-Co(2)C(2)B(10)H(12) (3), 1,14-Cp(2)-2,9-Me(2)-1,14,2,9-closo-Co(2)C(2)B(10)H(10) (4) and 1,14-(η-C(9)H(7))(2)-1,14,2,9-closo-Co(2)C(2)B(10)H(12) (5), are prepared and characterised. Patterns in (11)B NMR chemical shifts and in <δ(11)B>, the weighted average (11)B chemical shift, within and between related isomers of the 14-vertex compounds II and 1-5 are discussed. Compounds II, IV, 2, 4 and 5 were studied crystallographically, with cage C atom positions in these and related bicapped hexagonal antiprismatic 1,14,2,x-M(2)C(2)B(10) species analysed by the Vertex-to-Centroid Distance method.

Recent Progress in the Chemistry of Supercarboranes

The chemistry of boron clusters has been dominated by icosahedral carboranes for over half a century. Only in recent years has significant progress been made in the chemistry of supercarboranes (carboranes with more than 12 vertices). A number of CAd (carbon-atoms-adjacent) 13- and 14-vertex carboranes, and CAp (carbon-atoms-apart) 13-vertex carboranes as well as their corresponding 14- and 15-vertex metallacarboranes have been successfully prepared and structurally characterized. This breakthrough relied on the use of CAd nido-carborane dianions as starting materials. These supercarboranes can undergo single-electron reduction to give stable supercarborane radical monoanions with [2n+3] framework electrons, and electrophilic substitution reaction to afford hexasubstituted supercarboranes. They can react with nucleophiles to offer monocarba-closo-dodecaborate monoanions from cage-carbon extrusion reactions. Their unique chemical properties make the chemistry of supercarboranes distinct from that of their 12-vertex analogues. These studies open up new possibilities for the development of polyhedral clusters of extraordinary size. This focus review offers an overview of recent advances in this growing research field.

Fe–Cu octahedral carbide clusters, and the replacement of their labile halide ligands: Synthesis, solid state structure, substitution and electrochemical reactivity of [Fe 5C(CO) 14(CuBr)] 2−, [Fe 4C(CO) 12(CuCl) 2] 2−, [{Fe 4Cu 2C(CO) 12(μ-Cl)} 2] 2−, [Fe 5C(CO) 14(CuOC 4H 8)] − and [Fe 4C(CO) 12(CuNCMe) 2

The reactions between [Fe 6C(CO) 16] 2− and CuCl, in refluxing THF, yield [Fe 5C(CO) 14(CuCl)] 2− ( 1), [Fe 4C(CO) 12(CuCl) 2] 2− ( 2), or [{Fe 4Cu 2C(CO) 12(μ-Cl)} 2] 2− ( 3), depending on the Fe 6/CuCl ratio. The chloro ligands of these clusters can be displaced either spontaneously, or by metal-assisted substitution, to give the bromo derivative [Fe 5C(CO) 14(CuBr)] 2− ( 4) or the solvento complexes [Fe 5C(CO) 14(CuTHF)] − ( 5) and [Fe 4C(CO) 12(CuNCMe) 2] ( 6). The latter can be also obtained directly, by metal substitution from [Fe 6C(CO) 16] 2− and [Cu(NCMe) 4]BF 4, or by polyhedral expansion from [Fe 4C(CO) 12] 2−. All the clusters are octahedral, with the copper atoms in a pseudo-linear geometry, where one of the coordination positions is occupied by the interstitial carbide. The two copper atoms in the Fe 4Cu 2 clusters are always in cis geometry and, in the dimer [{Fe 4Cu 2C(CO) 12(μ-Cl)} 2] 2−, they are joined through chlorides. The role of the different metal centres in determining the redox activity of the heteronuclear Fe–Cu clusters 1, 2, 3, has been studied by electrochemical methods. In the bridged dimer 3, the two Fe 4Cu 2C cluster units resulted electronically not communicating.

The P21/m ↔ C2/m phase transition in amphiboles: new data on synthetic Na(NaMg)Mg5Si8O22F2 and the role of differential polyhedral expansion

The P21/m ↔ C2/m displacive phase transition has been studied on a synthetic amphibole with unit formula ANa0.90 B(Na0.92Mg1.08)C(Mg4.98V0.02)TSi8O22 O3F2. The evolution of the unit-cell parameters and of the intensities of a set of super-lattice reflections was monitored in the T range 100–944 K. Polynomial fitting of a 24 Landau potential to the evolution of the order parameter with T yielded a critical temperature (T c) of 395 ± 5 K (398 ± 6 when considering low-T saturation of the order parameter), and Landau coefficients compatible with second-order transition. The values of T c and the coefficients for the phase transition obtained in this work are compared to those previously obtained for synthetic ANa0.83 B(Na0.83Mg1.17)CMg5 TSi8O22 O3(OH)2 and to other data available in the literature. The substitution of OH by F at the O(3) site does not change the character of the transition, but decreases the T c by at least 132 K, showing that the size of the M(4) polyhedron is not the only significant factor, and that the size of the octahedra and/or their different thermal expansion also play a role. Single-crystal structure refinements done at 100, 160, 220, 280, 340, 406, 514, 621, 729, 836 and 944 K allowed monitoring the changes in the structure and in the shape of electron density, which occur approaching the transition and during further heating. Mean thermal expansion coefficients for the different polyhedra in the structure were calculated for the high-T C2/m phase, and are compared with those of other amphiboles with 5 Mg atoms per formula unit at the C-sites. The presence of F significantly affects both cation ordering within the A cavity and the thermal expansion along the b and c edges.

Symmetric and asymmetric 13-vertex bimetallacarboranes by polyhedral expansion

Symmetric 4,5,2,3-M(2)C(2)B(9) 13-vertex bimetallacarboranes of cobalt and ruthenium with 14 skeletal electron pairs are afforded by reduction and metallation of 3,1,2-MC(2)B(9) icosahedra; the symmetric species can be converted to their asymmetric 4,5,1,6-M(2)C(2)B(9) isomers by heat, but an easier route is by thermolysis of the reduced species before metallation.

Ligand-induced polyhedral opening in the mixed-metal cluster MeCCo2NiCp(CO)6 by 4,5-Bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd): X-ray structure of Co2NiCp(CO)4[μ2,η2,η1-C(Me)C=C(PPh2)C(O)CH2C(O)](μ2-PPh2)

The mixed-metal cluster MeCCo2NiCp(CO)6 (1) reacts with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in refluxing CH2Cl2 to afford the disubstituted cluster MeCCo2NiCp(CO)4(bpcd) (2), which exists as a 1:1 mixture of bridging and chelating bpcd isomers. VT 31P NMR spectroscopy confirms that the two bpcd isomers do not interconvert in solution over the temperature range of 182–298 K. Thermolysis of cluster 2 leads to bpcd/cluster activation and formation of the phosphido-bridged cluster Co2NiCp(CO)4[μ2,η2,η1-C(Me)C=C(PPh2)C(O)CH2C(O)](μ2-PPh2) (3). The ligand-induced polyhedral expansion that accompanies the formation of the title cluster was established by X-ray diffraction analysis. Co2NiCp(CO)4[μ2,η2,η1-C(Me)C=C(PPh2)C(O)CH2C(O)](μ2-PPh2) crystallizes in the triclinic space group P-1, a=9.679(2), b=11.691(2), c=16.653(3) A, α=85.849(3)°, β=85.456(4)°, γ=66.453(3)°, V=1720.3(6) A3, Z=2, D cacl=1.632 Mg/m3; R=0.0874, R w=0.1998 for 7053 observed reflections with I > 2σ(I).

Nitrosyl-cobalt monocarbollide complexes

The carborane anion [ closo-2-CB 10H 11] − undergoes a polyhedral expansion reaction with [Co(CO) 3(NO)] in tetrahydrofuran (THF) to afford [2-CO-2-NO- closo-2,1-CoCB 10H 11] −, isolated as the [N(PPh 3) 2] + salt 1a. An X-ray diffraction study confirmed that the NO group is linearly bonded to cobalt. The CO ligand in 1a is readily replaced by PPh 3 in the presence of Me 3NO, or by PEt 3 or CNBu t directly, to give the species [N(PPh 3) 2][2-L-2-NO- closo-2,1-CoCB 10H 11] [L=PPh 3 ( 1b), PEt 3 ( 1c), CNBu t ( 1d)]. Reactions of these anionic complexes with electrophilic reagents are exemplified by treatment of 1c with CF 3SO 3Me in CH 2Cl 2–THF to give the neutral, zwitterionic B-THF species [2-NO-2-PEt 3-7-O(CH 2) 4- closo-2,1-CoCB 10H 10] ( 3a), and by the reaction of 1b with [CuCl(PPh 3)] 4 and Tl[PF 6] in THF to give bimetallic [2,7,11-{Cu(PPh 3)}-7,11-(μ-H) 2-2-NO-2-PPh 3- closo-2,1-CoCB 10H 9] ( 4b). X-ray diffraction analysis of crystals of 4b confirmed the presence of a CoCu bond.

Direct electrophilic insertion into a twelve-vertex metallacarborane.

Polyhedral expansion of stable 12-vertex closo-ruthenacarborane [(η-C5Me5)Ru(C2B9H11)]− by direct insertion of [(η-C5R5)Ru]+ fragments takes place under very mild conditions (−78 °C). The resulting 13-vertex diruthenacarboranes (see picture) are very stable although they have two electrons less than required by Wade's rules.

Displacive Calcite and Grain Breakage in Sandstones

ABSTRACT Many calcrete profiles contain evidence of heterogeneous growth of displacive calcite which includes (1) cathode-luminescence-defined zones in crystals, indicating both linear unidirectional and polyhedral multidirectional growth vectors; (2) expanded micaceous grains; (3) broken quartz grains; and (4) the dispersal of clastic grains in a carbonate matrix. These features reflect the influence of the changing character of the growth environment consequent upon changes in the sediment itself. In the vadose zone of arid areas, rapid evaporation leads to supersaturation and thus crystallization. During drying, water withdraws from grain surfaces to capillary pores within micaceous grains and at grain-to-grain contacts. These form the primary sites for precipitation of calcite. Kinetic barriers to nucleation ensure that growth is initially restricted to a few stressed sites, and, since no other nucleation sites are available, continued growth of crystals is displacive. With the retention of greater volumes of pore water, there is a change from linear growth of a few faces to a polyhedral expansion of packed groups of crystals. The resulting dilation creates additional stresses within the sediment which are transmitted between grains and which, focussed by smaller areas of poi t contacts, break quartz grains. As permeability is reduced, larger volumes of saturated water are retained within the sediment. More nuclei form in pore throats, and subsequent growth promotes further expansion and dispersal of framework grains. This is primarily by growth of individual displacive crystals but may include the deposition of some micrite reflecting high nucleation and low growth rates. Later, oversized pores formed by expansion are filled by unstressed grains growing as a coarse cement. Continued post-burial diagenesis is reflected in neomorphism of displacive crystals, of micrite, and of cements, indicating a general trend towards chemical homogeneity and structural stability.

Metal carbide clusters synthesis systematics for heteronuclear species

Abstract The strategies in the synthesis of metal carbide cluster are examined and the full synthesis procedures for a number of heteronuclear metal carbide clusters are presented. Specific classes of carbide clusters prepared are octahedral Fe 5 MC(CO) x y- and Fe 4 M 2 C(CO) x y- clusters and square pyramidal Fe 4 MC(CO) x y- clusters. One synthesis strategy was polyhedral expansion based on [Fe 4 C(CO) 12 2- ] or [Fe 5 C(CO) 14 2- ] reactions with coordinately unsaturated metal complexes or labile complexes that readily yield coordinately unsaturated complexes. Selected oxidative degradations of these octahedral carbide clusters provided a synthesis step comprising elision of an iron center to yield square pyramidal Fe 4 MC(CO) x y- clusters.

Structures of metallocarboranes. 8. Crystal and molecular structure of the 11-vertex heterobimetallocarborane 1,8-di-.eta.-cyclopentadienyl-1-ferra-8-cobalta-2,3-dicarbaundecaborane(9), 1,8-(.eta.-C5H5)2-1-Fe-8-Co-2,3-C2B7H9

Abstract : Polyhedral metallocarboranes containing two different transition metal vertices can be prepared by use of either polyhedral expansion or polyhedral subrogation reactions on previously prepared metallocarboranes. To assess the effect of a one electron deficiency, the x-ray structural determination of (C5H5)2FeCoC2B7H9 was undertaken.

ChemInform Abstract: NIDO‐METALLOBORANES DERIVED FROM B10H10(2‐)

AbstractWasserfreies K2B10H10 reagiert mit cis‐Dichlorodiphosphin‐Pt(II)‐Komplexen in äthanolischem Chloroform zu den Komplexen (I) mit isomeren Äthoxy‐substituierten nido‐Metalloboranen.

ChemInform Abstract: NEW CHEMISTRY OF METALLOCARBORANES AND METALLOBORANES

Ten years after the discovery of metallocarboranes, this field of chemistry is still advancing at a rapid pace. While the polyhedral expansion of carboranes has proved to be a general method for the synthesis of metallocarboranes, polymetallic compounds may be synthesized by polyhedral expansion of monometallocarboranes, sometimes producing supraicosahedral complexes. The polyhedral contraction reaction, which produces lower metallocarborane compounds, may be used in conjunction with expansion techniques to regulate polyhedral size. Polyhedral subrogation allows the replacement of a polyhedral 81-fl vertex with a transition metal, and therefore complements the other two new synthetic tools. The synthesis of metallocarboranes by thermal metal transfer, while still in its early stages of development, may prove to be another valuable synthetic method. Recent studies on the chemistry of certain metallocarboranes have shown oxidative addition to a polyhedral {BH} vertex. In addition, specific catalytic hydrogen—deuterium exchange on boron hydrides, carboranes and metallocarboranes occurs with several transition metal complexes. A new rhodium metallocarborane has been shown to be an excellent catalyst for olefin hydrogenation, hydrogen—deuterium exchange on boron, olefin isomerization and hydrosilylation. 1. HISTORICAL PERSPECTIVE This year marks the tenth anniversary of the welding of two diverse areas of chemistry, those of the transition metals and of the boron hydrides, by the discovery of the first metallocarborane complex1. The rationale behind this combination of diverse specialities was developed from two major chemical advances: the synthesis2 and the molecular orbital description3 of ferrocene and the discovery4 of the degradation of icosahedral carboranes to produce anionic species. The realization that these carborane anions, when fully deprotonated to form C2B9HI dianions, should have orbitals of proper symmetry and energy to interact with transition metals, as was found with the cyclopentadienide ion, led to the synthesis of the carborane analogue of ferrocene, the bis(dicarbollyl)iron(II) dianion, [(l,2-C2B9H1 1)2Fe]2 *Contnbution No. 3321 from the Department of Chemistry, University of California, Los Angeles, California 90024.

Structures of metallocarboranes. V. Synthesis and crystal and molecular structure of the closo 20-electron bimetallocarborane 1,6-bis(.eta.-cyclopentadienyl)-1,6-diferra-2,3-dicarba-closo-decaborane(8), 1,6-(.eta.-C5H5)2-1,6,2,3-Fe2C2B6H8

Abstract : The polyhedral expansion of 4,5-C2B7H9 with ferrous chloride and sodium cyclopentadienide produced a new ferracarborane formulated as (C5H5)2-Fe2C2B6H8, which exists in paramagentic and diamagnetic forms. The crystal and molecular structure of the diamagnetic form has been determined by a three-dimensional x-ray diffraction study at - 160C. The compound crystallized in the monoclinic centrosymmetric space group P2(1)/n. The polyhedral geometry observed in this compound is a new 10-vertex species which is derived from a bicapped square antiprism. Structures of the title compound and of its cobalt analog are discussed in terms of the bonding theory of metallocarboranes.