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The molecular-based magnetic materials Cs(2)Mn(||)[V(||)(CN)(6)] (1) and (Et(4)N)(0.5)Mn(l.25)- [V(CN)(5)].2H(2)O (2) (where Et is ethyl) were prepared by the addition of manganese(II) triflate to aqueous solutions of the hexacyanovanadate(II) ion at 0 degrees C. Whereas 1 crystallizes in a face-centered cubic lattice, 2 crystallizes in a noncubic space group. The cesium salt (1) has features characteristic of a three-dimensional ferrimagnet with a Néel transition at 125 kelvin. The tetraethylammonium salt (2) also behaves as a three-dimensional ferrimagnet with a Néel temperature of 230 kelvin; only two other molecular magnets have higher magnetic ordering temperatures. Saturation magnetization measurements indicate that in both compounds the V(II) and high-spin Mn(II) centers are antiferromagnetically coupled. Both 1 and 2 exhibit hysteresis loops characteristic of soft magnets below their magnetic phase-transition temperatures. The high magnetic ordering temperatures of these cyano-bridged solids confirm that the incorporation of early transition elements into the lattice promotes stronger magnetic coupling by enhancing the backbonding into the cyanide pi* orbitals.

Selective thermal emission in a useful range of energies from a material operating at high temperatures is required for effective solar thermophotovoltaic energy conversion. Three-dimensional metallic photonic crystals can exhibit spectral emissivity that is modified compared with the emissivity of unstructured metals, resulting in an emission spectrum useful for solar thermophotovoltaics. However, retention of the three-dimensional mesostructure at high temperatures remains a significant challenge. Here we utilize self-assembled templates to fabricate high-quality tungsten photonic crystals that demonstrate unprecedented thermal stability up to at least 1,400°C and modified thermal emission at solar thermophotovoltaic operating temperatures. We also obtain comparable thermal and optical results using a photonic crystal comprising a previously unstudied material, hafnium diboride, suggesting that refractory metallic ceramic materials are viable candidates for photonic crystal-based solar thermophotovoltaic devices and should be more extensively studied.

This paper describes a method for growing thin polymer films from the surface of a silicon wafer bearing a native oxide (Si/SiO 2 ) by ring-opening metathesis polymerization (ROMP). 1,2 We have prepared norbornenederived polymer films with a wide range of thicknesses (up to 1 µm) and with a control over the chemical composition of the film perpendicular to the surface. Recently, surface-initiated polymerization has become an area of great interest, and several groups have developed approaches to grow thin polymer films on silicon and gold using cationic, anionic, and radical methods. 3 However, these methods often require rigorous reaction conditions and/or an input of thermal energy and have limited abilities to produce films of controlled thickness and chemical composition. Notably, Weck et al. recently reported the use of ROMP in a surface-initiated polymerization. 1b In their work, the polymerization was allowed to occur only at defects within a self-assembled monolayer (SAM) and yielded an extremely small amount of a polymeric material on the surface. Characterizations of the polymerization process and the resulting polymer were not possible. In this paper, we present the use of surface-initiated ROMP as a strategy for offering a high degree of control over a surface polymerization process that occurs at room temperature and demonstrate its use in the facile formation of patterned polymer films on silicon when used with the technique of microcontact printing (µCP).Scheme 1 outlines our three-step procedure: (i) the formation of a self-assembled monolayer (SAM) on silicon that presents norbornenyl groups; (ii) the attachment of a ruthenium catalyst [(Cy 3 P) 2 Cl 2 RudCHPh, Cy ) cyclohexyl] (1) to the surface using the norbornenyl groups; (iii) the polymerization of added monomers to generate the film. 4 In the first step, a SAM of 5-(bicycloheptenyl)trichlorosilane (2) was formed on a Si/SiO 2 surface by immersing a UV-ozone cleaned substrate in a toluene solution of 2 (60 mM) for 6-12 h. The presence of the resulting 0.6 nm thick film of 2 was confirmed by attenuated total reflection (ATR) IR spectroscopy (see the Supporting Information) and ellipsometry. We then attached an immobilized derivative of catalyst 1 to this norbornenyl surface by dipping the substrate into a CH 2 -Cl 2 solution of 1 (17 mM) for 30 min. Subsequent exposure of the substrate to norbornene-based monomers such as 5-(bicycloheptenyl)triethoxysilane (3) or exo-N-methyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide (4) (0.01-0.4 M) in CH 2 Cl 2 produced a polymeric film on the surface. Typical polymerization times were 30 min, and the substrate was washed extensively with CH 2 Cl 2 between each step. We characterized the resulting films by transmission IR spectroscopy, ellipsometry, optical microscopy, scanning electron microscopy, and atomic force microscopy (AFM).Parts a and b of Figure 1 show transmission IR spectra of films of poly-3 and poly-4 on silicon, respectively, prepared by the procedure in Scheme 1. In Figure 1a, the str...