Substitution of the laser borane anti-B18H22 with pyridine: a structural and photophysical study of some unusually structured macropolyhedral boron hydrides.

Reaction of anti-B18H221 with pyridine in neutral solvents gives sparingly soluble B16H18-3',8'-Py23a as the major product (ca. 53%) and B18H20-6',9'-Py22 (ca. 15%) as the minor product, with small quantities of B18H20-8'-Py 4 (ca. 1%) also being formed. The three new compounds 2, 3a and 4 are characterized by single-crystal X-ray diffraction analyses and by multinuclear multiple-resonance NMR spectroscopy. Compound 2 is of ten-vertex nido:ten-vertex arachno two-atoms-in-common architecture, long postulated for a species with borons-only cluster constitution, but previously elusive. Compound 3a is of unprecedented ten-vertex nido:eight-vertex arachno two-atoms-in-common architecture. The single-crystal X-ray diffraction analysis for the picoline derivative B16H18(NC5H4Me)23b, similarly obtained, is also presented. B18H20Py 4 is also previously unreported but is of known ten-vertex nido:ten-vertex nido two-atoms-in-common architecture of anti configuration, but now with the pyridine ligand positioned differently to other reported examples of B18H20L compounds. Factors behind the remarkably low solubility of 3a and 3b are elucidated in terms of electrostatic potential (ESP) calculations, polarity, and van der Waals complementarities. In view of contemporary developing high interest in the fluorescent properties of macropolyhedral boron-containing species, a detailed assessment of the photophysical characteristics of 3a and 4 is also presented. In contrast to the thermochromic fluorescence of 2 (from 620 nm brick-red at room temperature to 585 nm yellow at 8 K, quantum yield 0.15), compound 3a is only weakly phosphorescent in the yellow region (590 nm, quantum yield 0.01), whereas compound 4 exhibits no luminescence. The far more photoactive nature of compound 2 is associated with S1 excited-state minima structures that differ from each other only by the relative rotational positions of the pyridine substituents on its disubstituted ten-vertex {arachno-B10Py2}-subcluster. The wavelength and relative intensity of fluorescence from these structures depends on the rotational positions of the pyridine ligands, which in turn are influenced by temperature and/or rotational inhibition in the solid-state.

Duplex-selective ruthenium-based DNA intercalators.

We report the design and synthesis of small molecules that exhibit enhanced luminescence in the presence of duplex rather than single-stranded DNA. The local environment presented by a well-known [Ru(dipyrido[3,2-a:2',3'-c]phenazine)L2 ](2+) -based DNA intercalator was modified by functionalizing the bipyridine ligands with esters and carboxylic acids. By systematically varying the number and charge of the pendant groups, it was determined that decreasing the electrostatic interaction between the intercalator and the anionic DNA backbone reduced single-strand interactions and translated to better duplex specificity. In studying this class of complexes, a single Ru(II) complex emerged that selectively luminesces in the presence of duplex DNA with little to no background from interacting with single-stranded DNA. This complex shows promise as a new dye capable of selectively staining double- versus single-stranded DNA in gel electrophoresis, which cannot be done with conventional SYBR dyes.

The contrarotational fluxionality of [3,3-(PMe2Ph)2-closo-3,1,2-PtC2B9H11] and related species.

DFT calculations allied with experimental crystallographic and NMR results elucidate the energetics and the geometrical and (11)B nuclear shielding changes in the contrarotational fluxionality of [3,3-(PMe2Ph)2-closo-3,1,2-PtC2B9H11] and confirm the identities of two stable rotational conformers. There is a relatively unhindered contrarotation of the {Pt(PR3)2} and nido-shaped carbons-together {C2B9H11} entities about an axis that contains the platinum atom, with a transition from trihapto to tetrahapto to pentahapto metal-to-cluster interaction as the rotation progresses from 0° to 90°, and a reversal as it progresses in turn through to 180°, and thence through a similar cycle through to 360° for a complete rotation. The overall energy minimum is the trihapto conformation, but there is also an island of stability for the tetrahapto conformation at slightly higher energy, corresponding to experimental observation of these two configurations. The highest-energy pentahapto mode constitutes a transition state, and its energy defines the activation energy for the complete contrarotation, which is matched by activation energies derived from NMR spectroscopy. The shallow minima and small energy differences suggest that ready cluster flexibility will be expected about the minima, again in accord with subtle rotamer angle differences seen in experimental results. Nuclear magnetic shielding criteria suggest significant changes in intracluster bonding as the rotation progresses. The trihapto bonding geometry and the corresponding electronic structure are favoured over quite a substantial arc (some 40°) of the rotation, before rapid changes ensue, and then, after progression through the tetrahapto conformation, the electronics and the bonding geometry then again remain similar within the pentahapto mode for a further 40° or so of the rotational arc about this transition state.

Stabilization of a highly porous metal-organic framework utilizing a carborane-based linker.

The first tritopic carborane-based linker, H3BCA (C15B24O6H30), based on closo-1,10-C2B8H10, has been synthesized and incorporated into a metal-organic framework (MOF), NU-700 (Cu3(BCA)2). In contrast to the analogous MOF-143, NU-700 can be activated with retention of porosity, yielding a BET surface area of 1870 m(2) g(-1).

Zwitterionic weak-link approach complexes based on anionic icosahedral monocarbaboranes.

The anionic hemilabile phosphinothioether ligand, [1-(Ph2PCH2CH2S)-closo-1-CB11H11 ](-), which is functionalized with an anionic icosahedral monocarbaborane anion, was synthesized in three steps from [HNMe3][closo-CB11H12]. The ligand was used to synthesize a family of zwitterionic Weak-Link Approach (WLA) complexes that contain platinum(II), palladium(II), and rhodium(I). These complexes were characterized using multinuclear NMR spectroscopy, high-resolution mass spectrometry, and single-crystal X-ray diffraction analyses. Although the C-bound [closo-CB11H11](-) anion behaves as an electron-withdrawing moiety, hemilabile phosphinothioether ligands that are based on this unit are strongly chelating, as determined via the measurement of the chloride association constant. The chelating strength is comparable to that of hemilabile ligands that are functionalized with the very electron-rich B-bound closo-1,7-C2B10H11 moiety, thus demonstrating the use of charge to influence ligand coordination strength. The anionic Rh(I) WLA complex that is synthesized using this ligand can act as the noncoordinating anion of a regular cationic Rh(I) WLA complex. Thus, an unprecedented type of salt, in which the anion and cation are mutually isostructural and isoelectronic WLA complexes, has been synthesized and characterized crystallographically.

An exceptionally high boron content supramolecular cuboctahedron.

A boron-rich supramolecular cuboctahedron containing an impressive 240 boron atoms has been synthesized via coordination-driven assembly. The cuboctahedron, which is composed of Cu(2+) paddle-wheel nodes and carborane-isophthalic acids, was obtained simply and in high purity. The ability to precisely characterize the nanostructure via X-ray diffraction makes it unique among boron-rich nanostructures.

General strategy for the synthesis of rigid weak-link approach platinum(II) complexes: tweezers, triple-layer complexes, and macrocycles.

Air-stable, heteroligated platinum(II) weak-link approach (WLA) tweezer and triple-layer complexes that possess P,X-Aryl hemilabile ligands (P^ = Ph2PCH2CH2-, X = chalcoethers or amines) have been synthesized via the halide-induced ligand rearrangement (HILR) reaction, using a one-pot, partial chloride-abstraction method. The approach is general and works with a variety of phosphine-based hemilabile ligands; when a P,S-Ph ligand is used as the relatively strongly chelating ligand, heteroligated complexes are formed cleanly when an ether- (P,O-Ph), amine- (P,N-Ph2), or fluorinated thioether-based (P,S-C6F4H) hemilabile ligand is used as the weakly chelating counterpart. The HILR reaction has also been used to synthesize bisplatinum(II) macrocycles free of oligomeric material without having to resort to the high-dilution conditions typical for macrocycle synthesis. This approach is complementary to the traditional WLA to the synthesis of macrocyclic complexes which typically proceeds via fully closed, chloride-free intermediates. The structures of the complexes may be toggled between semiopen (with only one chelating ligand) and fully closed (with both ligands chelating) via the abstraction and addition of chloride.

Crystal-packing trends for a series of 6,9,12,15,18-pentaaryl-1-hydro[60]fullerenes.

The relationship between the size of the substituents of aryl groups in a series of fifteen 6,9,12,15,18-pentaaryl-1-hydro[60]fullerenes and the solid-state structures and packing motifs of these compounds has been analyzed. Pentaarylfullerenes have a characteristic "badminton shuttlecock" shape that causes several derivatives to crystallize into columnar stacks. However, many pentaarylfullerenes form non-stacked structures with, for example, dimeric, layered, diamondoid, or feather-in-cavity relationships between molecules. Computational modeling gave a qualitative estimate of the best shape match between the ball and socket surfaces of each pentaarylfullerene. The best match was for pentaarylfullerenes with large, spherically shaped para-substituents on the aryl groups. The series of pentaarylfullerenes was characterized by single-crystal X-ray diffraction. A total of 34 crystal structures were obtained as various solvates and were categorized by their packing motifs.

Unfairly forgotten member of the iodocarborane family: synthesis and structural characterization of 8-iodo-1,2-dicarba-closo-dodecaborane, its precursors, and derivatives.

8-Iodo-1,2-dicarba-closo-dodecaborane (7) was prepared in three steps starting from decaborane-14 with 20% overall yield. In the presence of nucleophiles, compound 7 undergoes selective removal of the boron vertex in the position para to the iodine substituent to form the anionic nido-carborane 1-iodo-7,8-dicarba-nido-undecaborate. Capping of the corresponding dicarbollide dianion with BI(3) led to formation of the new carborane, 3,10-diiodo-1,2-dicarba-closo-dodecaborane (15). The same dicarbollide dianion reacts with cobalt and nickel acetylacetonates in anhydrous tetrahydrofuran to form the corresponding bis(dicarbollide) complexes with excellent yields. All compounds were characterized by multinuclear NMR and high-resolution mass spectroscopy. Structures of 2-iododecaborane (2), 8-iodo-1,2-dicarba-closo-dodecaborane (7), 1-ethoxycarbonyl-8-iodo-1,2-dicarba-closo-dodecaborane (10), cesium 1-iodo-7,8-dicarba-nido-undecaborate (13), 3,10-diiodo-1,2-dicarba-closo-dodecaborane (15), and cesium 3,3'-commo-(10-iodo-1,2-dicarba-3-cobalta-closo-dodecaborane)-(10'-iodo-1',2'-dicarba-3'-cobalta-closo-dodecaborane) (16) were established by X-ray analysis of single crystals.

A coordination chemistry dichotomy for icosahedral carborane-based ligands.

Although the majority of ligands in modern chemistry take advantage of carbon-based substituent effects to tune the sterics and electronics of coordinating moieties, we describe here how icosahedral carboranes-boron-rich clusters-can influence metal-ligand interactions. Using a series of phosphine-thioether chelating ligands featuring meta- or ortho-carboranes grafted on the sulfur atom, we were able to tune the lability of the platinum-sulfur interaction of platinum(II)-thioether complexes. Experimental observations, supported by computational work, show that icosahedral carboranes can act either as strong electron-withdrawing ligands or electron-donating moieties (similar to aryl- or alkyl-based groups, respectively), depending on which atom of the carborane cage is attached to the thioether moiety. These and similar results with carborane-selenol derivatives suggest that, in contrast to carbon-based ligands, icosahedral carboranes exhibit a significant dichotomy in their coordination chemistry, and can be used as a versatile class of electronically tunable building blocks for various ligand platforms.

Complexes of gold(I), silver(I), and copper(I) with pentaaryl[60]fullerides.

Gold(I), silver(I), and copper(I) phosphine complexes of 6,9,12,15,18-pentaaryl[60]fullerides 1a and 1b, namely, [(4-MeC(6)H(4))(5)C(60)]Au(PPh(3)) (2a), [(4-t-BuC(6)H(4))(5)C(60)]Au(PPh(3)) (2b), [(4-MeC(6)H(4))(5)C(60)]Ag(PCy(3)) (3a), [(4-t-BuC(6)H(4))(5)C(60)]Ag(PPh(3)) (3b), [(4-t-BuC(6)H(4))(5)C(60)]Ag(PCy(3)) (3c), [(4-MeC(6)H(4))(5)C(60)]Cu(PPh(3)) (4a), and [(4-t-BuC(6)H(4))(5)C(60)]Cu(PPh(3)) (4b), have been synthesized and characterized spectroscopically. All complexes except for 3c were also characterized by single-crystal X-ray diffraction. Several coordination modes between the cyclopentadienyl ring embedded in the fullerene and the metal centers are observed, ranging from η(1) with a slight distortion toward η(3) in the case of gold(I), to η(2)/η(3) for silver(I), and η(5) for copper(I). Silver complexes 3a and 3b are rare examples of crystallographically characterized Ag(I) cyclopentadienyls whose preparation was possible thanks to the steric shielding provided by fullerides 1a and 1b, which stabilizes these complexes. Silver complexes 3a and 3b both display unexpected coordination of the cyclopentadienyl portion of the fulleride anion with Ag(I). DFT calculations on the model systems (H(5)C(60))M(PH(3)) and CpMPH(3) (M = Au, Ag, or Cu) were carried out to probe the geometries and electronic structures of these metal complexes.

Stabilization of acyclic phosphazides using the ortho-closo-dicarbadodecaboranyl residue.

The reactions of triphenylphosphine with the azido-ortho-closo-dicarbadodecaboranes 1-N(3)-2-R-closo-1,2-C(2)B(10)H(10) [R = Me (1a), Ph (1b)] produce the stable and isolatable carboranyl phosphazides 1-(N(3)PPh(3))-2-R-closo-1,2-C(2)B(10)H(10) [R = Me (2a), Ph (2b)] in good yields. Single crystal X-ray diffraction analysis revealed that, in the solid state, phosphazide 2a adopts an unusual s-cis conformation, whereas 2b adopts an s-trans conformation.

Gold(I) triphenylphosphine complexes incorporating pentaarylfulleride ligands.

Two gold(I) complexes, (Ph(3)P)Au[C(60)(4-MeC(6)H(4))(5)] (1) and (Ph(3)P)Au[C(60)(4-t-BuC(6)H(4))(5)] (2), were prepared in excellent yield and characterized by single-crystal X-ray diffraction. Complex 1, grown from two solvent systems, has different coordination modes of the fullerene-embedded Cp ring to the (PPh(3))Au fragment. For 1.(ODCB)(2), the cyclopentadienyl ring coordinates to the (Ph(3)P)Au fragment in an eta(1) fashion distorted toward eta(3) geometry, while in 1.(CHCl(3))(2)(CS(2)), crystal packing forces produce enough distortion to give near eta(2) coordination.

Toward unidirectional rotary motion in nickelacarboranes: characterization of diastereomeric nickel bis(dicarbollide) complexes derived from the [nido-7-CH3-7,8-C2B9H11]- anion.

Two diastereomeric pairs of nickel bis(C-monomethyldicarbollide) complexes, derived from the racemic [nido-7-CH(3)-7,8-C(2)B(9)H(11)](-) anion, have been synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. Neutral (dd/ll) [1(2),1'(2')-Me(2)-closo-3,1,2-Ni(IV)C(2)B(9)H(10)-{3:3'}-closo-3',1',2'-Ni(IV)C(2)B(9)H(10)] 1 and (meso) [1,2'-Me(2)-closo-3,1,2-Ni(IV)C(2)B(9)H(10)-{3:3'}-closo-3',1',2'-Ni(IV)C(2)B(9)H(10)] 2 adopt typical cisoid conformations in the solid state. The temperature-dependent (11)B and (1)H NMR spectra of 2 indicate that the energy barrier to the interconversion of racemic rotational isomers is 66.5 +/- 2 kJ/mol. In the solid state, the [NMe(4)](+) salts of the (dd/ll) [1(2),1'(2')-Me(2)-closo-3,1,2-Ni(III)C(2)B(9)H(10)-{3:3'}-closo-3',1',2'-Ni(III)C(2)B(9)H(10)](-) anion NMe(4) x 3 and the (meso) [1,2'-Me(2)-closo-3,1,2-Ni(III)C(2)B(9)H(10)-{3:3'}-closo-3',1',2'-Ni(III)C(2)B(9)H(10)](-) anion NMe(4) x 4 adopt gauche and transoid configurations, respectively, with transoid methyl substituents in both cases.

Self-assembling fullerenes for improved bulk-heterojunction photovoltaic devices.

The fullerene adducts 1a and 1b, whose molecular shapes either promote or hinder the formation of 1-D stacks, have been examined for their potential to form 1-D wire-like domains in bulk-heterojunction organic solar cells. The photovoltaic efficiency of solar cells based on blends of the stacking fullerene 1a with regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) is greatly enhanced compared to nonstacking model fullerene 1b.

Frail older patient care by interdisciplinary teams: a primer for generalists.

Frail older patients-unlike younger persons in the health care system or even well elders-require complex care. Most frail older patients have multiple chronic illnesses. Optimum care cannot be achieved by following the paradigm of ongoing traditional health care, which emphasizes disease and cure. Because no one health care professional can possibly have all of the specialized skills required to implement such a model of health care delivery, interdisciplinary team care has evolved. This paper describes the roles of the participating team members in the context of interdisciplinary care for frail older adults. In addition, the challenges that occur when Geriatric Interdisciplinary (ID) Teams involved in providing care to frail older patients are identified and discussed.