Colin R. Willis

Enhanced Stability of Cu-BTC MOF via Perfluorohexane Plasma-Enhanced Chemical Vapor Deposition

Metal organic frameworks (MOFs) are a leading class of porous materials for a wide variety of applications, but many of them have been shown to be unstable toward water. Cu-BTC (1,3,5 benzenetricarboxylic acid, BTC) was treated with a plasma-enhanced chemical vapor deposition (PECVD) of perfluorohexane creating a hydrophobic form of Cu-BTC. It was found that the treated Cu-BTC could withstand high humidity and even submersion in water much better than unperturbed Cu-BTC. Through Monte Carlo simulations it was found that perfluorohexane sites itself in such a way within Cu-BTC as to prevent the formation of water clusters, hence preventing the decomposition of Cu-BTC by water. This PECVD of perfluorohexane could be exploited to widen the scope of practical applications of Cu-BTC and other MOFs.

Diels–Alder chemistry at furan ring functionalized solid surfaces

A substrate-independent method for Diels-Alder chemistry at solid surfaces is described for the first time.

Wetting Hierarchy in Oleophobic 3D Electrospun Nanofiber Networks.

Wetting behavior between electrospun nanofibrous networks and liquids is of critical importance in many applications including filtration and liquid-repellent textiles. The relationship between intrinsic nanofiber properties, including surface characteristics, and extrinsic nanofibrous network organization on resultant wetting characteristics of the nanofiber network is shown in this work. Novel 3D imaging exploiting focused ion beam (FIB) microscopy and cryo-scanning electron microscopy (cryo-SEM) highlights a wetting hierarchy that defines liquid interactions with the network. Specifically, small length scale partial wetting between individual electrospun nanofibers and low surface tension liquids, measured both using direct SEM visualization and a nano Wilhelmy balance approach, provides oleophobic surfaces due to the high porosity of electrospun nanofiber networks. These observations conform to a metastable Cassie-Baxter regime and are important in defining general rules for understanding the wetting behavior between fibrous solids and low surface tension liquids for omniphobic functionality.

Syntheses and crystal structures of Cu(II) and Zn(II) complexes of 2,2′-dipyridyl(N-propenyl)amine

Abstract Reaction between copper(II)- and zinc(II)-nitrates and 2,2′-dipyridyl(N-propenyl)amine (Prdpa) affords 1:1 complexes M(Prdpa)(NO3)2 (M=Cu, 1; M=Zn, 5) for both metal ions and a 1:2 adduct M(Prdpa)2(NO3)2 (2) for copper only. In ethanol 1 dissociates to form 2 and copper nitrate. X-ray diffraction studies on 1, 2 and 5, and on the 2,2′-dipyridylamine (Hdpa) analogue of 1, Cu(Hdpa)(NO3)2 (4), are reported. The metal centres exhibit square pyramidal (1) or distorted octahedral (2, 4, 5) primary coordination spheres. Bridging nitrate groups linking Cu atoms in 1 and 4 result in CuONOCu chains, which in the case of 4 are extensively cross-linked by N−H⋯ONO2 H-bonding into 3D-arrays. Intermolecular C−H⋯ONO2 interactions are apparent in the solid-state structure of 2. The structural effects of replacing the NH atom on Hdpa by a propenyl group in 6-coordinate Cu(II) complexes are assessed.

Synthesis of model organosiloxanes containing perfluoroether side-chains

A series of organotrisiloxanes [(Me3SiO)2MeSi(CH2)nO(CH2)mRf], (n = 3, m = 1, Rf = CF3; n = 3, m = 2, Rf = C4F9, C6F13, C8F17, C10F21, C7F15; n = 5, m = 1, Rf = CF3; n = 10, m = 0, Rf = C3HF6; n = 10, m = 1, Rf = CF3) have been prepared by the [Pt(cyclooctadiene)Cl2] catalysed hydrosilylation reaction between heptamethyltrisiloxane and CH2CH(CH2)n−2O(CH2)mRf. Yields are dependent upon the alkene chain length and degree of branching of the Rf group. Isomeric products [(Me3SiO)2MeSi(CH2)3OCH2CF3] and [(Me3SiO)2MeSiCH(Me)CH2OCH2CF3] were detected in reactions involving CH2CHCH2OCH2CF3 only.

The influence of humidity on the protective performance of a membrane based on poly(vinyl alcohol)

A solid-state NMR study has been used to rationalize the way humidity affects the barrier properties of a polyvinyl alcohol-based membrane. Polymer blends composed of polyvinyl alcohol–polyethyleneimine (PVOH–PEI) and polyvinyl alcohol–polydiallyldimethyl ammonium chloride (PVOH–PDADMAC) were investigated. At 90% relative humidity the PVOH–PEI material retains a PVOH-rich component that is detected in a cross-polarization NMR experiment and is therefore assumed to be relatively immobile. The barrier properties of this material are also largely retained at this relative humidity. Under the same conditions of humidity no signal is detected in the cross-polarization NMR experiment for the PVOH–PDADMAC system and the barrier properties of the PVOH–PDADMAC system are compromised. The persistence of the more rigid domains in the PVOH–PEI material is used to explain the barrier properties of this blend at high relative humidity. For the PVOH–PDADMAC system the cross-polarization signal is recovered and the barrier properties of the blend are restored to their original level as the humidity is lowered.

Synthesis of a series of dichloroamino- and dihalosulfonamido-1,3,5-triazines and investigation of their hindered rotation and stereodynamic behaviour by NMR spectroscopy

Mono-substituted 1,3,5-triazines (s-triazines) have been prepared and characterised by NMR spectroscopy. The room temperature 13C NMR spectra of dichloroamino-s-triazines show three signals for the triazine ring, clearly indicating that C(2) and C(3) are in inequivalent environments. At elevated temperatures, two of the signals broaden and coalesce. Conversely, a number of dihalosulfonamido-s-triazine compounds were found to display only one signal for C(2) and C(3), indicating that the degree of π-bonding in the exocyclic C–N bond in these compounds is less significant. The low temperature exchange limits for the dihalosulfonamido-s-triazine compounds are reported.

Molybdenum-mediated methoxycarbonylation of propargyl halides: molecular and crystal structure of the vinylmolybdenum(II) complex [Mo(bipy)(CO)2(C5H7O2)(py)]BF4

Treatment of a methanolic suspension of [PPh4][Mo(bipy)(CO)3X](bipy = 2,2′-bipyridine, X = Cl or Br) held at –17 °C with propargyl (prop-2-ynyl) chloride or bromide yields the cis-dicarbonylmolybdenum complexes [Mo(bipy)(CO)2(C5H7O2)X][X = Cl (1) or Br (2)], which are believed to contain an η3-oxacyclobutenyl ligand formed by methoxycarbonylation of the propargyl moiety. Reaction of complex (1) or (2) with Na(O2CC2F5), or with AgBF4 in acetone followed by pyridine, yields [Mo(bipy)(CO)2(C5H7O2)(O2CC2F5)](3) and [Mo(bipy)(CO)2(C5H7O2)(py)]BF4(4)(py = pyridine) respectively, in which the mode of bonding of the C5H7O2 ligand has changed from η3-alkyl to σ-vinyl. Crystal structure analysis shows that in the molecule (4) the molybdenum atom is seven-co-ordinate being bonded to bipy [2.241 (7), 2.164(7)A], pyridine [2.275(8)A], two carbonyl groups [1.936(10), 1.983(11)A], and the bidentate C5H7O2 ligand [Mo–O 2.164(6) and Mo–C 2.155(10)A].