Weaving Nanoscale Cloth through Electrostatic Templating

Here we disclose a simple route to nanoscopic 2D woven structures reminiscent of the methods used to produce macroscopic textiles. We find that the same principles used in macroscopic weaving can be applied on the nanoscale to create two-dimensional molecular cloth from polymeric strands, a molecular thread. The molecular thread is composed of Co6Se8(PEt3)4L2 superatoms that are bridged with L = benzene bis-1,4-isonitrile to form polymer strands. As the superatoms that make up the polymer chain are electrochemically oxidized, they are electrostatically templated by a nanoscale anion, the tetragonal Lindqvist polyoxometalate Mo6O192–. The tetragonal symmetry of the dianionic template creates a nanoscale version of the box weave. The crossing points in the weave feature π-stacking of the bridging linker. By examining the steps in the weaving process with single crystal X-ray diffraction, we find that the degree of polymerization at the crossing points is crucial in the cloth formation. 2D nanoscale cloth will provide access to a new generation of smart, multifunctional materials, coatings, and surfaces

Quantum dots coordinated with conjugated organic ligands: new nanomaterials with novel photophysics

CdSe quantum dots functionalized with oligo-(phenylene vinylene) (OPV) ligands (CdSe-OPV nanostructures) represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Single-molecule spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures

Relation between magnetic and structural anisotropy in the Ni23Se12(PEt3)13 cluster compound

We have measured the magnetic properties of the cluster compound Ni23Se12(PEt3)13, where PEt3 is triethyl phosphine, by dc magnetization (1.5–300 K) and ac susceptibility (0.280–4 K). We observe a small, almost temperature-independent, magnetic moment of only ~2μB/cluster indicating the presence of two unpaired spins in the cluster. Despite the large shape anisotropy of the molecule, we find no preferred magnetic axis. We interpret this as the result of delocalization of the valence electrons due to covalent Ni-Se bonding.

Electron correlations in transition metal-telluride cluster compounds

We report the magnetic properties of a new class of materials: Ni9Te6n+ and Co6Te8n+ with n = 0, 1, 2. These cluster compounds, which can be charged by chemical means from neutral to 2 +, provide a unique and novel way to change the Fermi level. For most charge states, we observe quenching of the spin and orbital moments at low temperatures, accompanied by a large value for the temperature-independent susceptibility of the ground state. The magnitude and universality of these results among different charge states can be explained neither by local moments in a finite size system nor by the molecular orbital approximation. The generic presence of low-energy magnetic excitations in these compounds indicates that these systems exhibit strong electron correlations and form mesoscopic analogues of the mixed valence/heavy fermion compounds.

Cr6Te8(PEt3)6 and a Molecule-Based Synthesis of Cr3Te4

The molecular cluster compound Cr6Te8(PEt3)6 (1) is formed by the reaction of TePEt3 with either (Et3P)2Cr(allyl)2 or Cr(2,4-dimethylpentadienyl)2. This compound can be converted to the extended inorganic solid state compound Cr3Te4 by simple thermolysis. We have determined the structure of the title compound crystallographically (monoclinic; a = 13.076(5) Å, b = 21.194(7) Å, c = 23.694(7) Å, β = 105.21(5)°, V = 6276(10) Å3, Z = 4). The molecule is formed by a Cr6 octahedron, a Te8 cube, and a (PEt3)6 octahedron, all of which are concentric. We compare and contrast the structure and properties of the cluster with those of related solid-state compounds.

Effect of Diverse Ligands on the Course of a Molecules-to-Solids Process and Properties of Its Intermediates

We have been studying chemical processes that use discrete molecular reagents to form extended solid inorganic materials. The goals of this program have been to determine how best to design and implement these molecular precursor reactions and to discover what chemical intermediates lie on the molecules-to-solids paths. In this manuscript we report studies of the reactions of the low-valent iron complex Fe(C8H8)2 with low-valent tellurium compounds of the form TePR3 (R = various hydrocarbon groups) that lead ultimately to the exclusively inorganic extended solid compounds FexTey. We have found four Fe/Te cluster types that are chemical intermediates in this process: Fe4Te4(PEt3)4, 1; Fe4Te4(PiPr3)4, 2; Fe6Te8(PMe3)6, 3; (dmpe)2FeTe2, 4; (depe)2FeTe2, 5; Fe4Te6(dmpe)4, 6. (Here iPr = CHMe2, dmpe = Me2PCH2CH2PMe2, and depe = Et2PCH2CH2PEt2.) The different clusters form when different supporting phosphine ligands are employed. We report the syntheses, structures, and properties of these intermediates and the comparisons and contrasts between these molecular intermediates and the extended solid products. We note that when larger ligands are used smaller clusters are formed. We also note what features of the molecular structures lead to ferromagnetic versus antiferromagnetic coupling of the distinct Fe centers. We have determined the structures of the following materials crystallographically: 2 (C36H84Fe4Te4P4; tetragonal, P421c; a = 14.0469(7) Å, c = 13.5418(9) Å; Z = 2); 3 (C18H54Fe6Te8P6; trigonal, R3; a = 11.859(2) Å, c = 26.994(5) Å; Z = 3); dmpe·2Te (C6H16Te2P2; monoclinic, P21/c; a = 6.0890(4) Å, b = 10.7934(7) Å, c = 9.8200(5) Å, β = 104.63(7)°; Z = 2); 5 (C20H48FeTe2P4; orthorhombic, Pbnn; a = 10.997(3) Å, b = 14.157(3) Å, c = 18.345(4) Å; Z = 4); 6 (C24H64Fe4Te6P8; orthorhombic, Abaa; a = 12.056(3) Å, b = 17.725(5) Å, c = 21.403(8) Å; Z = 4).

Electron Correlations on a Mesoscopic Scale: Magnetic Properties of Transition Metal Telluride Cluster Compounds

We report the magnetic properties of a new class of materials: Ni9Te6n+ and Co6Te8n+ with n=0,1,2. These cluster compounds, which can be charged by chemical means from neutral to 2+, provide a unique and novel way to change the Fermi level. For most charge states we observe quenching of the spin and orbital moments at low temperatures, accompanied by a large value for the temperature independent susceptibility of the ground state. The generic presence of low-energy magnetic excitations in these compounds indicates that these systems exhibit strong electron correlations and form mesoscopic analogs of the mixed-valence–heavy-fermion compounds.