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.

A Cu−carborane-based metal−organic framework (MOF), NU-135, which contains a quasi-spherical para-carborane moiety, has been synthesized and characterized. NU-135 exhibits a pore volume of 1.02 cm 3 /g and a gravimetric BET surface area of ca. 2600 m 2 /g, and thus represents the first highly porous carborane-based MOF. As a consequence of the unique geometry of the carborane unit, NU-135 has a very high volumetric BET surface area of ca. 1900 m 2 /cm 3. CH 4 , CO 2 , and H 2 adsorption isotherms were measured over a broad range of pressures and temperatures and are in good agreement with computational predictions. The methane storage capacity of NU-135 at 35 bar and 298 K is ca. 187 v STP /v. At 298 K, the pressure required to achieve a methane storage density comparable to that of a compressed natural gas (CNG) tank pressurized to 212 bar, which is a typical storage pressure, is only 65 bar. The methane working capacity (5−65 bar) is 170 v STP /v. The volumetric hydrogen storage capacity at 55 bar and 77 K is 49 g/L. These properties are comparable to those of current record holders in the area of methane and hydrogen storage. This initial example lays the groundwork for carborane-based materials with high surface areas. ■ INTRODUCTION Nanoporous materials such as metal−organic frameworks (MOFs) with tailorable pore volumes, high internal surface areas, 1,2 and chemical diversity form an important emerging class of materials that are potentially useful in a wide range of applications including ion exchange, 3 catalysis, 4,5 gas separation , 6−8 sensing, 9 and storage. 10−12 In particular, MOFs have attracted great interest for onboard hydrogen and methane storage in vehicles, which is a long-standing goal for those interested in energy independence and the protection of the environment. Over the past decade, significant progress has been made toward building new classes of MOFs with desired material characteristics. This has been achieved via, for example, the tailoring of pore geometry, volume, surface area, and density, and by the incorporation of unsaturated metal centers. 13,14 Control over these parameters is crucial for realizing materials with high gas uptake capacity. Polyhedral boranes and heteroboranes are a unique class of cluster compounds with properties and geometries that are not accessible with carbon-based systems. 15 Among the polyhedral boranes, the family of isomeric icosahedral dicarbaboranes (closo-C 2 B 10 H 12) 15 and their metallo-derivatives 16 have received much attention because of their varied chemistry, 17 redox properties, 18 thermal stability, and their potential for applications in the areas of medicine 19 and materials chemistry. 15 Recently we reported a series of MOFs that are derived from closo-1,12-C 2 B 10 H 12 (para-carborane). The carborane-based MOFs displayed exceptional thermal stability and large CO 2 /CH 4 and CO 2 /N 2 adsorption selectiv-ities. 7,8,20−22 However, the pore volumes and internal surface areas of these carborane-based MOFs were relatively small, thus...

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[2,3-a:3',2'-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 RuII 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 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).