Gavin Vaughan

Ligand-to-metal ratio controlled assembly of tetra- and hexanuclear clusters towards single-molecule magnets.

A simple template-mediated route, starting from triethalolamine 1, sodium hydride or caesium carbonate, and iron(III) chloride led to the six- and eight-membered iron coronates [Na c [Fe6[N(CH2CH2O)3]6]]+ (2) and [Cs c (Fe8[N(CH2CH2O)3]8]]+ (3). In the reaction of N-methyldiethanolamine 4 (H2L1) or N-(2,5-dimethylbenzyl)iminodiethanol 6 (H2L2) with calcium hydride followed by addition of a solution of iron(III) chloride, the neutral unoccupied coronands [Fe6Cl6(L1)6] (5) and [Fe6Cl6(L2)6] (7) were formed. Subsequent exchange of the chloride ions of 7 by bromide or thiocyanate ions afforded the ferric wheels [Fe6Br6(L2)6] (8) or [Fe6(NCS)6(L2)6] (9), respectively. Titration experiments of solutions of dianion (L1)2- with iron(III) chloride in THF revealed interesting mechanistic details about the self-assembling process leading to 5. At an iron/ligand ratio of 1:1.5 star-shaped tetranuclear [Fe[Fe(L1)2]3] (11) was isolated. However, at an iron/ligand ratio of 1:2, complex 11 was transformed into the ferric wheel 5. It was shown, that the interconversion of 5 and 11 is reversible. Based on the mechanistic studies, a procedure was developed which works for both the synthesis of homonuclear 11 and the star-shaped heteronuclear clusters [Cr[Fe(L1)2]3] (12) and [Al[Fe(L1)2]3] (13). The structures of all new compounds were determined unequivocally by single-crystal X-ray analyses.

X-ray transfocators: focusing devices based on compound refractive lenses.

A tunable X-ray focusing and/or monochromating device, called a transfocator, is described. Examples of its implementation on ID11 at the ESRF are given.

A key step in the formation of acrylic acid from CO2 and ethylene: the transformation of a nickelalactone into a nickel-acrylate complex

The reaction of a nickelalactone with dppm, resulting in the formation of a stable binuclear Ni(I) complex with an acrylate, a Ph2P- and a dppm bridge, models a key step in the formation of acrylic acid from CO2 and ethylene.

Synthesis of ionisable [2 × 2] grid-type metallo-arrays and reversible protonic modulation of the optical properties of the [CoII4L4]8+ species

The new bis-hydrazone based ligands A and B form ionisable [2 x 2] grid-type transition metal complexes whose properties may be modulated by multiple protonation/deprotonation as shown by the reversible change in optical properties of the [Co2(II)L4]8+ complexes depending on their protonation state.

X-ray microscopy in four dimensions

Three-dimensional X-ray diffraction (3DXRD) microscopy offers the possibility of time-resolved mapping of structures down to the micrometer scale 1 , 2 , 3 , 4 , 5 , 6 , i.e. four-dimensional studies. In this review, the principles of the 3DXRD microscope are described and various examples of its applications are presented.

Self-assembly of tetrahedral and trigonal antiprismatic clusters [Fe4(L4)4] and [Fe6(L5)6] on the basis of trigonal tris-bidentate chelators.

In a one-pot reaction, the tetranuclear iron chelate complex [Fe4(L4)4] 6 was generated from benzene-1,3,5-tricarboxylic acid trichloride (4), bis-tert-butyl malonate (5a), methyllithium, and iron(II) dichloride under aerobic conditions. Alternatively, hexanuclear iron chelate complex [Fe(L5)6] 7 was formed starting from bis-para-tolyl malonate (5b) by employing identical reaction conditions to those applied for the synthesis of 6. The clusters 6 and 7 are present as racemic mixtures of homoconfigurational (delta,delta,delta,delta)/(lambda,lambda,lambda,lambda)-fac or (delta,delta,delta,delta,delta,delta)/(lambda,lambda,lambda,lambda,lambda,lambda)-fac stereoisomers. The structures of 6 and 7 were unequivocally resolved by single-crystal X-ray analyses. The all-iron(III) character of 6 and 7 was determined by Mössbauer spectroscopy.

Recognition‐Directed Supramolecular Assemblies of Metal Complexes of Terpyridine Derived Ligands with Self‐Complementary Hydrogen Bonding Sites

The synthesis and X-ray structures of three metal complexes with terpyridine-derived ligands that contain amino-pyrimidine and amino-pyrazine moieties are presented. They have been designed in view of directing their self-assembly into specific supramolecular arrays through molecular recognition interactions. The solid-state structures indeed reveal extensive hydrogen-bonded networks. The Co complex 4a with PF6- counterions builds a two-dimensional infinite interwoven grid through strong double hydrogen bonds (d(N-H-N) =2.918-3.018 A) between the amino groups and the N atoms of the rings, with all H-bonding sites saturated. Changing the anions to BF4- in 4b leads to a similar infinite but partially broken grid with a quarter of the H-bonding sites unsaturated (d(N-H-N)=2.984-3.206 A). In the case of the Zn complex 12 with triflate anions, half of the hydrogen bonds are formed. Only one of the two orthogonal ligands has hydrogen bonds (d(N-H-N) = 3.082, 3.096 A) to the neighbouring complexes and thus builds linear, supramolecular, polymeric chains. These structural differences are mainly attributed to crystal-packing effects caused by the different anions. The data presented here may also be regarded as a prototype for the generation of organised arrays through sequential self-assembly processes.

Atomic structure of Zr–Cu glassy alloys and detection of deviations from ideal solution behavior with Al addition by x-ray diffraction using synchrotron light in transmission

The atomic structure of Zr–Cu binary amorphous alloys was studied using real space pair distribution functions derived from x-ray diffraction. The structure can be modeled by an ideal solution approximation because of relatively weak Cu–Zr atomic interactions. Addition of Al to Zr–Cu metallic glasses modifies the atomic structure in the short and medium range order because of the strongly attractive interaction between Al and Zr atoms. These interactions generate strong deviations from the ideal solution behavior.

Structural Effects of Proline Substitution and Metal Binding on Hexameric Cyclic Peptoids

L-Proline and N-methoxyethyl glycine have been included in novel cyclic hexameric peptoids. Supramolecular coordination with Na(+) triggered the formation of the first 1D metal-organic framework based on peptoids.

TiC-NiAl composites obtained by SHS: a time-resolved XRD study

Self-propagating high-temperature synthesis (SHS) has been performed in the quaternary Al–Ni–Ti–C system in order to obtain intermetallic–ceramic composites. These kind of reaction synthesis are very fast (linear velocity of the synthesis front is in the range 1–100 mm/s) and the productivity would be very high from the industrial point of view. Nevertheless,this characteristic is a negative point when synthesis mechanism and kinetics must be studied. There are only a few tools with enough time resolution in order to study these kinds of fast reactions. Synchrotron radiation (ESRF,Grenoble) has been employed to follow the reactions in situ on a time-scale of 100 ms. Powder diffraction patterns were recorded in this time-interval using a high-speed CCD camera coupled to an image intensifier X-ray sensitive detector with 10241024 pixels frames. As the reactions proceed patterns from the pre-heated, reaction front,post-heated and cooling zones of the reaction were sampled. The phases occurring during the reactions were identified and information of the reaction mechanism and the nucleation kinetics were obtained. SEM was used to characterize the final microstructure. # 2002 Published by Elsevier Science Ltd.