Stepwise Assembly of an Electroactive Framework from a Co6 S8 Superatomic Metalloligand and Cuprous Iodide Building Units.

Invited for the cover of this issue is Christopher Bejger and co-workers at UNC Charlotte, Columbia University, and Donghua University. The image depicts a pair of star clusters in the constellation Perseus as the structure of two metal clusters in the reported framework. Read the full text of the article at 10.1002/chem.20201215.

Stepwise Assembly of an Electroactive Framework from a Co6 S8 Superatomic Metalloligand and Cuprous Iodide Building Units.

The design of metal-organic frameworks (MOFs) that incorporate more than one metal cluster constituent is a challenging task. Conventional one-pot reaction protocols require judicious selection of ligand and metal ion precursors, yet remain unpredictable. Stable, preformed nanoclusters, with ligand shells that can undergo additional coordination-driven reactions, provide a platform for assembling multi-cluster solids with precision. Herein, a discrete Co6 S8 (PTA)6 (PTA=1,3,5-triaza-7-phosphaadamantane) superatomic-metalloligand is assembled into a three-dimensional (3D) coordination polymer comprising Cu4 I4 secondary building units (SBUs). The resulting heterobimetallic framework (1) contains two distinct cluster constituents and bifunctional PTA linkers. Solid-state diffuse reflectance studies reveal that 1 is an optical semiconductor with a band-gap of 1.59 eV. Framework-modified electrodes exhibit reversible redox behavior in the solid state arising from the Co6 S8 superatoms, which remain intact during framework synthesis.

Desymmetrized hexasubstituted [3]radialene anions as aqueous organic catholytes for redox flow batteries.

Negatively substituted trimethylenecyclopropane dianions, a subclass of hexasubstituted [3]radialenes, are candidates for use as active species in redox flow batteries (RFBs) due to their stability in water, reversible electrochemistry, and tailorable synthesis. Hexacyano[3]radialene disodium is investigated as a pH 7 aqueous organic catholyte. The dianion and radical anion are stable in air and aqueous solutions at neutral pH. Systematic introduction of asymmetry via step-wise synthesis leads to enhanced solubility and higher capacity retention during galvanostatic cycling. An aqueous flow cell comprising a diester-tetracyano[3]radialene catholyte, sulfonated-methyl viologen as the anolyte, and a cation exchange membrane provides an operating Vcell = 0.9 V, 99.609% coulombic efficiency, and minimum capacity fade over 50 cycles.

Ball and Socket Assembly of Binary Superatomic Solids Containing Trinuclear Nickel Cluster Cations and Fulleride Anions.

The superlattice structures of hierarchical cluster solids are dictated by short-range interactions between constituent building blocks. Here we show that shape complementary sites, as well as halogen and chalcogen bonding between exposed capping ligands and fullerides, govern the packing arrangement of the resulting binary solids. Four new superatomic solids, [Ni3(µ3-I)2(µ2-dppm)3+](C60•-) (1·C60), [Ni3(µ3-I)2(µ2-dppm)3+](C70-)2 (1·C70), [Ni3(µ3-Te)2(µ2-dppm)3+](C60•-) (2·C60), and [Ni3(µ3-Te)2(µ2-dppm)3](C70-)2 (2·C70), (dppm = Ph2PCH2PPh2) were prepared and crystallized from solution. All four compounds were characterized by single crystal X-ray diffraction, IR spectroscopy, and SQUID magnetometry. Charge transfer between the molecular clusters is confirmed via optical spectroscopy and structural data. Compounds 1·C60 and 2·C60 are paramagnetic and 100 times more conductive than the constituent cluster precursors. The obtained solids exhibit close contacts, indicative of halogen/chalcogen bonds, between the fulleride anions and the nickel cluster capping ligands (I/Te) in the solid-state.