Molecular Alloys: Syntheses and Structures of the Copper−Antimony Clusters [Cu17Sb8(dppm)6(Ph2PCHPPh2)] and [Cu20Sb10(PCy3)8]

Chemical Bonding and σ-Aromaticity in Charged Molecular Alloys: [Pd2As14]4- and [Au2Sb14]4- Clusters

We report a computational study on the structures and bonding of a charged molecular alloy D_2h [Pd₂As₁₄]⁴⁻ (1), as well as a model D_2h [Au₂Sb₁₄]⁴⁻ (2) cluster. Our effort makes use of an array of quantum chemistry tools: canonical molecular orbital analysis, adaptive natural density partitioning, natural bond orbital analysis, orbital composition analysis, and nucleus independent chemical shift calculations. Both clusters consist of two X₇ (X = As, Sb) cages, which are interconnected via a M₂ (M = Pd, Au) dumbbell, featuring two distorted square-planar MX₄ units. Excluding the Pd/As or Au/Sb lone-pairs, clusters 1 and 2 are 50- and 44-electron systems, respectively, of which 32 electrons are for two-center two-electron (2c-2e) As-As or Sb-Sb σ bonds and an additional 16 electrons in 1 for 2c-2e Pd-As σ bonds. No covalent Pd-Pd or Au-Au bond is present in the systems. Cluster 1 is shown to possess two globally delocalized σ electrons, whereas 2 has two σ sextets (each associated with an AuSb₄ fragment). Thus, 1 and 2 conform to the (4n + 2) Hückel rule, for n = 0 and 1, respectively, rendering them σ-aromaticity.

Lanthanide Clusters with Internal Ln: Fragmentation and the Formation of Dimers with Bridging Se2- and Se22- Ligands

Reactions of "LnI(x)(SePh)(3-x)" (Ln = Dy, Ho) with elemental S/Se give (THF)14Ln10S6(Se2)6I6. The compounds are composed of a Ln6S6 double cubane core, with two twisted "Ln2(SeSe)3" units condensed onto opposing rectangular sides of the Ln6S6 fragment. This deposition of Ln2Se6 totally encapsulates the two central Ln's with chalcogen atoms (four S and four Se atoms), excluding neutral THF donors or iodides from the two primary coordination spheres. Reactions of Ln(10) clusters with a stronger Lewis base result in fragmentation and, in the case of Ln = Er, the isolation of (py)6Er2(Se2)(S0.8Se0.2)I2, with two Ln(III) ions spanned by E2- and (EE)2- ligands. The related homochalcogen dimers (py)6Ln2(Se2)(Se)Br2 (Ln = Ho, Yb) were prepared to establish that such molecules could be prepared rationally, and to confirm the isolability of E2- ligands coordinated to only two sterically unconstrained Ln ions.