Joe B. Gilroy

Monodisperse cylindrical micelles by crystallization-driven living self-assembly

Non-spherical nanostructures derived from soft matter and with uniform size-that is, monodisperse materials-are of particular utility and interest, but are very rare outside the biological domain. We report the controlled formation of highly monodisperse cylindrical block copolymer micelles (length dispersity < or = 1.03; length range, approximately 200 nm to 2 microm) by the use of very small (approximately 20 nm) uniform crystallite seeds that serve as initiators for the crystallization-driven living self-assembly of added block-copolymer unimers with a crystallizable, core-forming metalloblock. This process is analogous to the use of small initiator molecules in classical living polymerization reactions. The length of the nanocylinders could be precisely controlled by variation of the unimer-to-crystallite seed ratio. Samples of the highly monodisperse nanocylinders of different lengths that are accessible using this approach have been shown to exhibit distinct liquid-crystalline alignment behaviour.

High-temperature metal–organic magnets

For over two decades there have been intense efforts aimed at the development of alternatives to conventional magnets, particularly materials comprised in part or wholly of molecular components. Such alternatives offer the prospect of realizing magnets fabricated through controlled, low-temperature, solution-based chemistry, as opposed to high-temperature metallurgical routes, and also the possibility of tuning magnetic properties through synthesis. However, examples of magnetically ordered molecular materials at or near room temperature are extremely rare, and the properties of these materials are often capricious and difficult to reproduce. Here we present a versatile solution-based route to a new class of metal–organic materials exhibiting magnetic order well above room temperature. Reactions of the metal (M) precursor complex bis(1,5-cyclooctadiene)nickel with three different organics A—TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)—proceed via electron transfer from nickel to A and lead to materials containing Ni(II) ions and reduced forms of A in a 2:1 Ni:A ratio—that is, opposite to that of conventional (low Curie temperature) MA2-type magnets. These materials also contain oxygen-based species within their architectures. Magnetic characterization of the three compounds reveals spontaneous field-dependent magnetization and hysteresis at room temperature, with ordering temperatures well above ambient. The unusual stoichiometry and striking magnetic properties highlight these three compounds as members of a class of stable magnets that are at the interface between conventional inorganic magnets and genuine molecule-based magnets.

Main‐Chain Heterobimetallic Block Copolymers: Synthesis and Self‐Assembly of Polyferrocenylsilane‐b‐Poly(cobaltoceniumethylene)

Two metals are better than one: Main-chain heterometallic block copolymers composed of iron- and cobalt-rich blocks (see picture) were synthesized through consecutive photocontrolled ring-opening polymerization (ROP) of sila[1]ferrocenophanes and dicarba[2]cobaltocenophanes followed by oxidation of the cobaltocene-containing block. The redox properties and self-assembly of the resulting block copolymers in solution were also studied.

Pointed-Oval-Shaped Micelles from Crystalline-Coil Block Copolymers by Crystallization-Driven Living Self-Assembly†

Self-assembly of block copolymers in block-selective solvents can lead to a variety of different morphologies with shapeand composition-dependent potential applications in areas as diverse as drug delivery and nanolithography. Amorphous block copolymers usually give rise to spherical micelles in selective solvents, but since the mid 1990s various strategies that promote the formation of other morphologies including cylinders 4] or cylinder networks, disks, helices, Janus micelles, toroids, nanotubes, and other complex forms have been developed. Previous work on the solution self-assembly of diblock copolymers has shown that the presence of crystalline coreforming blocks such as poly(ferrocenyldimethylsilane) (PFS), polyethylene, polyacrylonitrile, polycaprolactone, and poly(ethylene oxide) promote the formation of morphologies with low interfacial curvature such as cylinders and platelets. Moreover, recent studies of PFS block copolymers have revealed that on addition of further unimer, epitaxial growth from the exposed crystalline cores of the ends of cylindrical micelles or the edges of platelets is possible to generate hierarchical micelle architectures such as block co-micelles and scarf structures, respectively. This crystallizationdriven living self-assembly process has enabled the preparation of well-defined self-assembled structures with spatially defined attachment of nanoparticles and oxide surface coatings. Here we report that by using this crystallization-driven living self-assembly approach, the formation of unusual nanoscopic architectures such as pointed ovals and hierarchical pointed-oval-based co-micelle architectures is also possible. We used two types of asymmetric, narrow polydispersity crystalline-coil, PFS core-forming diblock copolymers: firstly, PFS34–P2VP272 (P2VP = poly(2-vinylpyridine)) [17, 19] to generate cylindrical micelles, especially short “seed” micelles, and, second, PFS54–PP290 [18,19] (PP = poly[bis(trifluoroethoxy)phosphazene]; Scheme 1 and Supporting Information Table S1).

Formazans as β-diketiminate analogues. Structural characterization of boratatetrazines and their reduction to borataverdazyl radical anions

Formazans react with boron triacetate to produce boratatetrazines, which can be reduced to yield borataverdazyl radical anions--the first boron containing verdazyl radicals.

Effects of Electron Deficient β-Diketiminate and Formazan Supporting Ligands on Copper(I)-Mediated Dioxygen Activation

Copper(I) complexes of a diketiminate featuring CF(3) groups on the backbone and dimethylphenyl substituents (4) and a nitroformazan (5) were synthesized and shown by spectroscopy, X-ray crystallography, cyclic voltammetry, and theory to contain copper(I) sites electron-deficient relative to those supported by previously studied diketiminate complexes comprising alkyl or aryl backbone substituents. Despite their electron-poor nature, oxygenation of LCu(CH(3)CN) (L = 4 or 5) at room temperature yielded bis(hydroxo)dicopper(II) compounds and at -80 degrees C yielded bis(mu-oxo)dicopper complexes that were identified on the basis of UV-vis and resonance Raman spectroscopy, spectrophotometric titration results (2:1 Cu/O(2) ratio), electron paramagnetic resonance spectroscopy (silent), and density functional theory calculations. The bis(mu-oxo)dicopper complex supported by 5 exhibited unusual spectroscopic properties and decayed via a novel intermediate proposed to be a metallaverdazyl radical complex, findings that highlight the potential for the formazan ligand to exhibit noninnocent behavior.

End-to-End Coupling and Network Formation Behavior of Cylindrical Block Copolymer Micelles with a Crystalline Polyferrocenylsilane Core

Cylindrical block copolymer micelles with a crystalline poly(ferrocenyldimethylsilane) (PFDMS) core and a long corona-forming block are known to elongate through an epitaxial growth mechanism on addition of further PFDMS block copolymer unimers. We now report that addition of the semicrystalline homopolymer PFDMS(28) to monodisperse short (ca. 200 nm), cylindrical seed micelles of PFDMS block copolymers results in the formation of aggregated structures by end-to-end coupling to form micelle networks. The resulting aggregates were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). In some cases, a core-thickening effect was also observed where the added homopolymer appeared to deposit and crystallize at the core-corona interface, which resulted in an increase of the width of the micelles within the networks. No evidence for aggregation was detected when the amorphous homopolymer poly(ferrocenylethylmethylsilane) (PFEMS(25)) was added to the cylindrical seed micelles whereas similar behavior to PFDMS(28) was noted for semicrystalline polyferrocenyldimethylgermane (PFDMG(30)). This suggested that the crystallinity of the added homopolymer is critical for subsequent end-to-end coupling and network formation to occur. We also explored the tendency of the cylindrical seed micelles to form aggregates by the addition of PI-b-PFDMS (PI = polyisoprene) block copolymers (block ratios 6:1, 3.8:1, 2:1, or 1:1), and striking differences were noted. The results ranged from typical micelle elongation, as reported in previous work, at high corona to core-forming block ratios (PI-b-PFDMS; 6:1) to predominantly end-to-end coupling at lower ratios (PI-b-PFDMS; 2:1, 1:1) to form long, essentially linear structures. The latter process, especially for the 2:1 block copolymer, led to much more controlled aggregate formation compared with that observed on addition of homopolymers.

Magnetostructural studies of copper(II)–verdazyl radical complexes

The synthesis, structures, and magnetic properties of several Cu(II) complexes of verdazyl radicals are presented. Reactions of chelating verdazyl radicals with either CuCl2·2H2O or Cu(hfac)2·2H2O produced 1 ∶ 1 Cu ∶ verdazyl complexes with either chloride or hfac ancillary ligands. Structural characterization reveals that the CuCl2 complexes of N,N′-dimethyl-3-(2-pyridyl)-6-oxoverdazyl or N,N′-bis(isopropyl)-3-(2-pyridyl)-6-oxoverdazyl have pseudo-square pyramidal copper ions with verdazyl rings bound in equatorial positions, while the Cu(hfac)2 complex of N,N′-dimethyl-3-(N-methyl-2-imidazolyl)-6-oxoverdazyl is Jahn–Teller distorted pseudo-octahedral and has the verdazyl nitrogen axially bound. Variable temperature magnetic susceptibility studies reveal that equatorially bound verdazyls are strongly antiferromagnetically coupled, while the axially bound radicals are weakly ferromagnetically coupled. Intermolecular magnetic interactions are also an important component of the overall magnetism in these systems.

Transition Metal Complexes of 3-Cyano-and 3-Nitroformazans

The synthesis and characterization of six transition metal complexes of 3-cyano- and 3-nitroformazans are described. Three different formazans were reacted with nickel(II) to produce complexes with bidentate formazan ligands. Mononuclear NiL2 (L = deprotonated formazan) or binuclear hydroxo-bridged (LNi)2(mu-OH) 2 species were produced depending on the steric bulk on the formazan N-aromatic substituents. 1,5-Bis(2-methoxyphenyl)-3-cyanoformazan acts as a tetradentate monoanionic ligand in a copper(II) complex, whereas the analogous 1,5-bis(2-hydroxyphenyl)-3-cyanoformazan binds as a trianion in a tetradentate manner to Fe(III) and Co(III). Crystal structures-the first examples of metal complexes of cyano- or nitroformazans-as well as the electronic spectra of the complexes are discussed in relation to each other as well as that of the uncoordinated formazans.

Photocontrolled Ring-Opening Polymerization of Strained Dicarba[2]Ferrocenophanes: A Route to Well-Defined Polyferrocenylethylene Homopolymers and Block Copolymers

The ring-opening polymerization (ROP) behavior of a variety of substituted 1,1-ethylenylferrocenes, or dicarba[2]ferrocenophanes, is reported. The electronic absorption spectra and tilted solid-state structures of the monomers rac-[Fe(eta(5)-C(5)H(4))(2)(CHiPr)(2)] (7), [Fe(eta(5)-C(5)H(4))(2)(C(H)MeCH(2))] (8), and rac-[Fe(eta(5)-C(5)H(4))(2)(CHPh)(2)] (9) are consistent with the presence of substantial ring strain, which was exploited to synthesize soluble, well-defined polyferrocenylethylenes (PFEs) [Fe(eta(5)-C(5)H(4))(2)(C(H)MeCH(2))](n) (12) and [Fe(eta(5)-C(5)H(4))(2)(CHPh)(2)](n) (13) through photocontrolled ROP. Polymer chain lengths could be controlled by the monomer-to-initiator ratio up to about 50 repeat units and, consistent with the living nature of the polymerizations, sequential block copolymerization with a sila[1]ferrocenophane led to polyferrocenylethylene-polyferrocenylsilane (PFE-b-PFS) block copolymers (14 and 15). PFE polymers 12 and 13 showed two reversible oxidation waves, indicative of appreciable FeFe interactions along the polymer backbone. The diblock copolymers were characterized by NMR spectroscopy, GPC analysis, and cyclic voltammetry.