RESUMO
After exploring the potential energy surfaces of Mm CE2 p (E=S-Te, M=Li-Cs, m=2, 3 and p=m-2) and Mn CE3 q (E=S-Te, M=Li-Cs, n=1, 2, q=n-2) combinations, we introduce 38 new global minima containing a planar hypercoordinate carbon atom (24 with a planar tetracoordinate carbon and 14 with a planar pentacoordinate carbon). These exotic clusters result from the decoration of V-shaped CE2 2- and Y-shaped CE3 2- dianions, respectively, with alkali counterions. All these 38 systems fulfill the geometrical and electronic criteria to be considered as true planar hypercoordinate carbon systems. Chemical bonding analyses indicate that carbon is covalently bonded to chalcogens and ionically connected to alkali metals.
RESUMO
Postsynthetic installation of lanthanide cubanes into a metallosupramolecular framework via a single-crystal-to-single-crystal (SCSC) transformation is presented. Soaking single crystals of K6 [Rh4 Zn4 O(l-cys)12 ] (K6 [1]; l-H2 cys=l-cysteine) in a water/ethanol solution containing Ln(OAc)3 (Ln3+ =lanthanide ion) results in the exchange of K+ by Ln3+ with retention of the single crystallinity, producing Ln2 [1] (2Ln ) and Ln0.33 [Ln4 (OH)4 (OAc)3 (H2 O)7 ][1] (3Ln ) for early and late lanthanides, respectively. While the Ln3+ ions in 2Ln exist as disordered aqua species, those in 3Ln form ordered hydroxide-bridged cubane clusters that connect [1]6- anions in a 3D metal-organic framework through coordination bonds with carboxylate groups. This study shows the utility of an anionic metallosupramolecular framework with carboxylate groups for the creation of a series of metal cubanes that have great potential for various applications, such as magnetic materials and heterogeneous catalysts.
RESUMO
Embedding cubane [M4 (OH)4 ] (M=Ni, Co) clusters within the matrix of metal-organic frameworks (MOFs) is a strategy to develop materials with unprecedented synergistic properties. Herein, a new material type based on the pore-space partition of the cubic primitive minimal-surface net (MOF-14-type) has been realized. CTGU-15 made from the [Ni4 (OH)4 ] cluster not only has very high BET surface area (3537â m2 g-1 ), but also exhibits bi-microporous features with well-defined micropores at 0.86â nm and 1.51â nm. Furthermore, CTGU-15 is stable even under high pH (0.1 m KOH), making it well suited for methanol oxidation in basic medium. The optimal hybrid catalyst KB&CTGU-15 (1:2) made from ketjen black (KB) and CTGU-15 exhibits an outstanding performance with a high mass specific peak current of 527â mA mg-1 and excellent peak current density (29.8â mA cm-2 ) at low potential (0.6â V). The isostructural cobalt structure (CTGU-16) has also been synthesized, further expanding the application potential of this material type.
RESUMO
The structure, bonding, and stability of clusters with the empirical formula CE5- (E=Al-Tl) have been analyzed by means of high-level computations. The results indicate that, whereas aluminum and gallium clusters have C2v structures with a planar tetracoordinate carbon (ptC), their heavier homologues prefer three-dimensional C4v forms with a pentacoordinate carbon center over the ptC one. The reason for such a preference is a delicate balance between the interaction energy of the fifth E atom with CE4 and the distortion energy. Moreover, bonding analysis shows that the ptC systems can be better described as CE4- , with 17-valence electrons interacting with E. The ptC core in these systems exhibits double aromatic (both σ and π) behavior, but the σ contribution is dominating.
RESUMO
Cores for thought! A new [Mn4 O4 ]6+ "cubane" core complex (L6 Mn4 O4 ) with six facially bridging phosphinate chelate ligands (L- =(MePh)2 PO2- ) was synthesized. Photo-excitation releases molecular O2 by intramolecular coupling of two core oxygen atoms and selective rearrangement to a [Mn4 O2 ]6+ "butterfly" core ([L5 Mn4 O2 ]+ ; see scheme). Thus the Mn4 O4 cubane core exhibits unique reactivity in O2 evolution which may account for its presence in the photosynthetic enzyme.
RESUMO
Thermolysis of the dithiocarbamate complex 1 led to the formation of the thiocarbenoid complex 2 and two double cubanes: 3, which has an intercubane Cr-Cr bond and a dithiooxamide ligand in the µ-η2 ,η4 bonding mode, and 4, which contains two dithiocarbamate ligands in the µ-η1 ,η2 bonding mode.
RESUMO
Encapsulated in a protective [{Fe(pz)3 }4 ] outer layer, which provides the complex with structural stability, the octanuclear complex [Fe8 (µ4 -O)4 (µ-pz)12 Cl4 ] contains a Fe4 O4 core (see drawing) that withstands four consecutive reversible one-electron reductions. Iron-oxygen clusters are shown to possess redox properties which rival those of their better studied iron-sulfur analogues. pz=pyrazolate anion.