Search

Cool cages!The use of phosphonates has led to formation of a family of manganese(II)–lanthanide(III) heterometallic cages with structurally beautiful cores (see figure). Magnetic studies show antiferromagnetic interactions within the manganese centers and huge entropy change in the {Mn4Gd6} complex, which, in principle, can be used for ultralow temperature cooling.

The ligand N,N‐diisobutyl‐N′‐(4‐nitrobenzoyl)selenourea (4‐NO2‐C6H4CONHCSeNiBu2) (1) and its complex {bis[N,N‐diisobutyl‐N′‐(4‐nitrobenzoyl)selenoureato]lead(II)} [(4‐NO2‐C6H4CONHCSeNiBu2)PbII] (2) have been synthesized, and their structures determined by single‐crystal X‐ray methods. Compound 2was employed as a single‐source precursor (SSP) for the deposition of PbSe thin films by aerosol‐assisted chemical vapor deposition (AACVD) in the temperature range 250–500 °C on glass substrates. The films obtained at low temperature consist of globular‐shaped crystallites, whereas at higher temperature (ca. 500 °C) wirelike morphologies are dominant. PbSe nanocrystals were also prepared from compound 2by solution thermolysis at 200–250 °C. Photoluminescence (PL) life time measurements based on the time‐correlated single‐photon‐counting (TCSPC) technique showed significantly faster PL decay in as‐prepared PbSe nanocrystals relative to previous reports. The purity and elemental composition of the as‐deposited PbSe thin films and nanocrystals were determined by energy‐dispersive X‐ray analysis (EDX).

Tetraalkoxy‐substituted [2.2]paracyclophane‐1,9‐dienes can be prepared in three steps from dithia[3.3]paracyclophanes. A mixture of pseudo‐geminal and pseudo‐ortho diastereomers is produced and the pure compounds can be separated by fractional crystallization. The solid state structures of these diastereomers reveal strongly distorted aromatic rings consistent with high levels of ring strain. Reaction of these diastereomers with the second generation Grubbs catalyst shows that only the pseudo‐geminal isomer can be ring opened to give cis,trans‐distrylbenzenes. The origin of this selectivity is discussed and the photoisomerization of the as‐formed cis,trans‐product to the all transisomer is demonstrated.

A series of novel complexes [Ln2(N3)(nic)2(OH)3(Hnic)(H2O)]n(Ln = YIII1and GdIII2; Hnic = nicotinic acid) and [Sm4(N3)2(nic)4(OH)6(Hnic)2(H2O)2]n(3) have been hydrothermally synthesized and structurally characterized by single‐crystal X‐ray analysis. Complexes 1, 2and 3have similar structures and consist of [Ln2(N3)(nic)2(OH)3(Hnic)(H2O)] units that are linked to neighboring units through end‐on azido, μ2and μ3hydroxo, and bridging carboxylato groups to form 1D infinite chains. In all the complexes the 1D chains propagate parallel to crystallographic a‐axis to give rise to a ribbon‐like chain structure. All the compounds exhibit excellent catalytic performance in olefin epoxidation reactions, which is reflected in high turnover numbers. Good expoxide selectivity was obtained in the cases of cyclooctene and 1‐hexene. The possibility of easy recycling makes these catalysts highly promising candidates for addressing industrial needs and environmental concerns.

AbstractMulti heavy atom cluster compounds like K2PtBr6offer a way forward to solve, de novo, unknown protein structures by powder diffraction involving dispersive (measured at two X-ray wavelengths) and isomorphous intensity differences as a complement to micro-crystallography or by using both approaches in combination. Towards this end, using the ESRF high resolution synchrotron X-ray powder diffraction beamline ID31, we have recorded high quality protein powder diffractograms at the platinum LIII and bromine K absorption edges, as well as reference wavelengths, for K2PtBr6bound to lysozyme. These experiments were conducted at 80K to protect the sample against X-radiation damage as much as possible and also to fix the K2PtBr6bound state, which seemed to show instability at room temperature. With multiple powder pattern analysis we extracted intensities and showed the PtBr6bound in lysozyme using ‘omit electron density maps’. In addition the wavelength dispersive Fourier around the Br K edge shows up the bromine signal at PtBr6binding site 1 in one of the six samples tested. To better understand the chemical properties of this heavy atom compound we have elucidated the detailed binding behaviour using single crystal analyses with time-resolved freeze quenching after soak times of 10, 90 and 170 minutes. Whilst the quick soaking of 10 to 30 minutes, used at ESRF ID31 shows clear binding there is increasing binding strength with increasing soak time. Thus, these time-resolved analytical chemistry results show that further heavy atom signal optimizations are possible. Prospects for extending our approach to the yet larger isomorphous and wavelength dispersive signal case of Ta6Br12bound to lysozyme are also described.

SmI2/H2O reduces cyclic 1,3‐diesters to 3‐hydroxyacids with no over reduction. Furthermore, the reagent system is selective for cyclic 1,3‐diesters over acyclic 1,3‐diesters, and esters. Radicals formed by one‐electron reduction of the ester carbonyl group have been exploited in intramolecular additions to alkenes. The ketal unit and the reaction temperature have a marked impact on the diastereoselectivity of the cyclizations. Cyclization cascades are possible when two alkenes are present in the starting cyclic diester and lead to the formation of two rings and four stereocenters with excellent stereocontrol.

No Abstract

Ideal kombiniert: Optisch reine 3,4‐disubstituierte 1‐Pyrroline, die aus entsprechenden meso‐Pyrrolidinen durch biokatalytische Desymmetrisierung mit Monoaminoxidase N (MAO‐N) erhalten wurden, reagieren mit Carbonsäuren und Isocyaniden in einer Ugi‐Mehrkomponentenreaktion hoch diastereoselektiv zu substituierten Prolylpeptiden mit großer Bedeutung in der Pharmazie.

AbstractThe synthesis, spectroscopic characterization and crystal structures of two uranyl complexes, [UO2(SALEN)(DMF)] (1) and [UO2(BPHA)2(DMF)] (2){SALEN = N,N′-ethylenebis(salicylimine), DMF = N,N-dimethylformamide, BPHA = N-phenyl benzohydroxamate} are described. The coordination geometry around the metal center in the mononuclear complexes can be best described as distorted pentagonal bipyramidal with an almost linear uranyl moiety. In addition to the van der Waal´s interactions, the crystal packing in the complexes is stabilized by weak intermolecular C–H…O hydrogen bonds involving the uranyl oxygen atoms, so generating two-dimensional arrays in both crystal structures.

No Abstract

No Abstract

Quick on the uptake: Following its identification during a targeted search, the intriguing crystal structure of 3,3′,4,4′tetratrimethylsilylethynylbiphenyl was investigated. Simple removal of the included solvent provides an organic crystal with an open microporous structure that has a striking similarity to that of zeoliteA see picture. Reversible adsorption of nitrogen and hydrogen gases at 77K confirms that the microporosity is permanent.

Aufnahmefähig: Die außergewöhliche Kristallstruktur von 3,3′,4,4′Tetratrimethylsilylethinylbiphenyl wurde untersucht. Durch Entfernen eingeschlossener Solvensmoleküle entsteht ein organischer Kristall mit einer weitmaschigen mikroporösen Struktur, die derjenigen von ZeolithA verblüffend ähnlich ist siehe Bild. Experimente zur reversiblen Adsorption von Stickstoff oder Wasserstoff bei 77K bestätigten, dass die Mikroporen permanent bestehen bleiben.

Thin films of silver are deposited from tetraphenyldioxoimidodiphosphinato silver(I) [Ag{(OPPh2)2N}]4· 2H2O (1) and silver(I) triflouoroacetate CF3COOAg (2) single‐source precursors (SSPs) by the aerosol‐assisted (AA)CVD method. The complex (1) is a tetramer with linear and distorted tetrahedral coordination modes at silver. Two types of films, silvery and brownish, are observed from both SSPs due to the temperature gradient in the AACVD reactor. The as‐deposited films are characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray (EDX) analysis, and ultraviolet/visible (UV‐vis) spectroscopy methods.

The synthesis of octaazaphthalocyanine (AzaPc) derivatives, with bulky phenoxyl substituents placed at eight peripheral positions and containing either H+, Ni2+or Zn2+ions in their central cavity, is described. The required precursors, derivatives of pyrazine‐2,3‐dicarbonitrile, were prepared using a nucleophilic aromatic substitution reaction between 2,6‐diisopropylphenol or 2,6‐diphenylphenol and 5,6‐dichloropyrazine‐2,3‐dicarbonitrile. Analysis of the resulting AzaPcs by UV/Visible and 1H NMR spectroscopy confirms that steric isolation of the AzaPc cores was enforced both in solution and in the solid state. X‐ray diffraction studies of single crystals of the AzaPcs reveal that solvent inclusion takes place in each case. Of particular significance is the finding that the zinc derivative of 2,3,9,10,16,17,23,24‐octa‐(2,6‐diisopropylphenoxy)octaazaphthalocyanine provides nanoporous cubic crystals, containing massive (8 nm3) solvent‐filled voids, similar to those of the analogous phthalocyanine derivative. Exchange of the included solvent within the voids can be readily achieved by using a number of alternative solvents including water. Based on the observed loading of included water, the internal volume of this nanoporous cubic crystal appears to be more hydrophilic than its phthalocyanine counterpart.

No Abstract

No Abstract

For the RNA world hypothesis to be accepted, the constitutional self‐assembly of RNA will have to be demonstrated. Conceptually, the simplest route to RNA involves nucleotide polymerisation. Activated pyrimidine nucleotides can be derived from arabinose‐3‐phosphate under potentially prebiotic conditions, but the prebiotic synthesis of this sugar phosphate has not hitherto been investigated. The results of synthetic approaches involving phosphorylation, phosphate migration and 2,3‐CC bond construction are described herein.

No Abstract

No Abstract

Two N-substituted phenylene diamines, C30H28N2S2O4(I) and C30H28N2S2O5(II), have been synthesized, and characterized by spectroscopic and single crystal X-ray analyses. Intermolecular N—H···O and C—H···O hydrogen bonds link the molecules of (I) into centrosymmetric dimers, which are further joined by C—H···O hydrogen bonds to form one-dimensional polymeric chain propagating along the [100] direction. The two molecules, A and B, in the asymmetric unit of (II) are connected by a pair of N—H···O hydrogen bonds forming a characteristic R22(14) dimeric ring centered at (0.245, 0.510, 0.252). The interlinking of adjacent dimers in (II) via C—H···O hydrogen bonds generates infinite one-dimensional ABBAAB… polymeric chain along the [101] direction.

Two novel homologous series of phthalocyanines were prepared from 2,2‐dialkylindane and 2,2‐dialkyl‐1,3‐benzodioxole precursors. It was anticipated that attaching alkyl chains to five‐membered rings, fused to the peripheral sites of the phthalocyanine ring, would result in the adoption of an out‐of‐plane configuration and thereby discourage cofacial aggregation, to provide an analogy with picket‐fence porphyrins. This strategy proved partially successful. Some members of the series of phthalocyanines derived from 2,2‐dialkyl‐1,3‐benzodioxoles, in which the alkyl chains are linked to the phthalocyanine via a cyclic ketal, form spin‐coated thin films in which the phthalocyanine cores are perfectly isolated. This behaviour is associated with the formation of a disordered crystal that appears as a mesophase in the thermal profile of these materials. However, the phthalocyanines derived from 2,2‐dialkylindanes display a columnar mesophase over a wide temperature range, with some liquid crystalline derivatives at ambient temperature. A single‐crystal X‐ray diffraction structure of the octahexyl derivative of this series shows how the columnar assembly accommodates the out‐of‐plane alkyl chains by tilting the macrocyclic plane of the phthalocyanine components with respect to the axis of the column. This study helps to emphasise the importance of both the steric and electronic effects of substituents on the packing behaviour of phthalocyanines in the condensed phase, and especially the role of electron‐donating oxygen atoms directly attached to the ring.

A series of thorium(iv) perrhenato- and pertechnetato-complexes with P&z.dbd;O donor ligands have been prepared and characterised both in the solid state and in solution. Isostructural complexes of general formula [Th(MO4)4(L)4], where M = Re or Tc and L = triethylphosphate (TEP) (2 and 7), tri-iso-butylphosphate (TiBP) (3 and 8) and tri-n-butylphosphine oxide (TBPO) (4 and 9) have been prepared from the novel starting materials [Th(ReO4)4]·4H2O (1) and [Th(TcO4)4]·4H2O (6). The reaction of 1 or 6 with triphenylphosphine oxide (TPPO) in MeOH has also led to the synthesis of [Th(MO4)3(TPPO)3(OCH3)(HOCH3)] (M = Re (5) or Tc (10)). While the structural characterisation of 4 and 9 has been previously described, we report for the first time the structural characterisation of 2 and 5, with a partial structural refinement of 3. Vibrational spectroscopic analysis confirms that the Tc complexes not characterised by single crystal X-ray diffraction are indeed isostructural with the perrhenate complexes with the same P&z.dbd;O donor ligand. In all cases, monodentate coordination of the Group 7 tetraoxo anion is observed. 31P NMR spectroscopy indicates that in all the phosphine oxide-based complexes there is one dominant solution species. For the phosphate based systems, the presence of pertechnetate appears to inhibit P&z.dbd;O donor ligand complexation in solution, whereas a significant proportion of each phosphate remains coordinated to ThIV when perrhenate is present as the counter ligand. These results give some indication as to the mechanism of pertechnetate co-extraction with tetravalent cations in the presence of tri-n-butyl phosphate in the Plutonium and Uranium Recovery by Extraction (PUREX) process.

In this work we present some experimental evidence of the existence of carbonyl–π electron cloud interactions. Such interactions are analogous to anion–π interactions, which have been predicted to be energetically favourable in the case of electron deficient aromatic rings. UV-Visible spectroscopy and cyclic voltammetry results obtained for 9,10-anthraquinone, 1,1′-bis-9,10-anthraquinone, poly(9,10-anthraquinone-1,4-diyl) and other 1,4-diaryl substituted anthraquinone derivatives are described. It was found that the steric hindrance occurring between the carbonyl groups and the adjacent aromatic substituent forces the plane of the anthraquinone moiety and that of the aromatic substituent to adopt a nearly orthogonal conformation, resulting in relatively strong carbonyl–π interactions that affect both the UV-Vis absorption spectrum and the reduction potential of the compound. Moreover, in the case of thiophene substituted derivatives, the torsion angle between the anthraquinone moiety and its aromatic substituent is smaller and therefore carbonyl–π interaction effects are not observed in these compounds.

Two N-substituted phenylene diamines C27H24N2S3O4(I) and C29H25N2S2O4Cl (II), acyclic precursors leading to quinoxaline derivatives, have been synthesized, and characterized by spectroscopic and X-ray structural studies. The molecules of compounds (I) and (II) are linked through intermolecular N—H···O and C—H···O hydrogen bonds into centrosymmetric dimers, with characteristic R22(14) and R22(26) rings, which combine to form infinite polymeric chains propagating along the [001] direction. Additional intermolecular C—H···O hydrogen bonds connect the molecules of (I) into two-dimensional sheet of R44(32) rings in the ab-plane and one-dimensional C(7) chain propagating along the [100] direction in (II). The combination of two-dimensional sheets in the ab-plane (in I) and one-dimensional C(7) chains along the [100] direction (in II) with the polymeric chains along the [001] direction generates a three-dimensional supramolecular assembly in (I) and a two-dimensional framework in (II).

2,2′‐Biphenol‐ and (R/S)‐ and (R)‐1,1′‐bi(2‐naphthol)‐based polysulfones were synthesized by classical step‐growth polymerizations and by entropically‐driven ring‐opening polymerizations (ED‐ROPs) of the corresponding macrocyclic oligomers (MCOs). To facilitate comparisons, the polysulfone derived from 4,4′‐cyclohexylidenebisphenol was synthesized similarly. ED‐ROP was also used to prepare copolymers. The molecular weights obtained using ED‐ROP were generally higher than those obtained using the classical step growth method. The MCOs required as the starting materials for ED‐ROPs were prepared by classical high dilution syntheses using the biphenols and bis(4‐chlorophenyl)sulfone in the presence of base. The cyclic dimer from a high dilution synthesis using (R)‐1,1′‐bi‐2‐naphthol and the cyclic dimer from a similar synthesis using 4,4′‐cyclohexylidenebisphenol were isolated as pure compounds by column chromatography and the molecular structures determined by single crystal X‐ray diffraction. Copyright © 2006 John Wiley & Sons, Ltd.

The synthesis and crystal structures of a family of decametallic CrIII“molecular wheels” are reported, namely [Cr10(OR)20(O2CR′)10] [R′=Me, R=Me (1), Et (2); R′=Et, R=Me (3), Et (4); R′=CMe3, R=Me (5), Et (6)]. Magnetic studies on 1–6reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R′) the nearest neighbour Cr⋅⋅⋅Cr magnetic exchange coupling is more antiferromagnetic for the ethoxide‐bridged (R=Et) cluster than for the methoxide analogue. In complexes 2, 4and 6the overall coupling is weakly antiferromagnetic resulting in diamagnetic (S=0) ground states for the cluster, whilst in 1and 5it is weakly ferromagnetic thus resulting in very high‐spin ground states. This ground state has been probed directly in the perdeuterated version of 1([D]1) by inelastic neutron scattering experiments, and these support the S=15 ground state expected for ferromagnetic coupling of ten CrIIIions, and they also indicate that a single J‐value model is inadequate. The ground state of 5is large but not well defined. The trends in Jon changing R are further supported by density functional calculations on 1–6, which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1and 2, and 5and 6are the result of relatively small changes in Jthat happen to cross J=0, hence changing the sign of J.

Solid-state decomposition of [V3O(O2CPh)6(H2O)3]Cl at 300 °C followed by alcoholysis of the product gives the new vanadium complexes [V6O6(PhCO2)6(CH3O)6(CH3OH)3] (1), [V6O6(PhCO2)6(C2H5O)6(C2H5OH)3] (2), [V6O6(PhCO2)6(C3H7O)6(C3H7OH)3] (3), [V6O6(PhCO2)6(C4H9O)6(C4H9OH)3] (4) and [V4O4(OCH3)6(O2CPh)2(HOCH3)2] (5). Complexes 2, 3and 5have been crystallographically characterised. DC magnetic susceptibility studies on complex 3shows antiferromagnetic coupling leading to a S= 0 spin ground state.

No Abstract

No Abstract

No Abstract

No Abstract

We report the syntheses and crystal structures of NH411LnIIIPMo11O392·xH2O where Ln every trivalent lanthanide cation except promethium in which two lacunary PMo11O397−anions sandwich an 8-coordinate LnIIIcation to yield the complex anion, LnIIIPMo11O39211−. The 14 salts crystallise in two different space groups, C2cor P1, but the LnIIIcontaining anions are isostructural across the whole series, a very rare example of such a complete study. Solid state and solution 31P NMR, Raman and IR spectroscopies have been used to prove the stability of LnPMo11O39211−in aqueous solution. As expected, the LnIIIcation contracts across the series and the Ln–O bond distances decrease uniformly. Interestingly, the splitting in the νP–Omode within the PMo11O397−unit increases uniformly across the series, which we attribute to the stronger interaction with the smaller, higher charge density LnIIIcation as the series is traversed. For the 31P NMR measurements a direct comparison of Lanthanide Induced paramagnetic Shift could be made with the analogous PW11O39211−complexes.

The reaction of Ni(NO3)2·6H2O with H3thme (trihydroxymethylethane) in the presence of NaOMe leads to a tetranuclear Ni4 complex with a cubane-like structure. Intramolecular ferromagnetic interactions [J = 10 cm⁻¹ based on H = −J(S1·S2 + S1·S3 + S1·S4 + S2·S3 + S2·S4 + S3·S4)] lead to an S = 4 ground state stabilized by 40 cm⁻¹ from the first S = 3 excited state. Magnetization vs. field studies at different temperatures above 2 K suggest the presence of an axial magnetic anisotropy. Single-crystal magnetization measurements show a single-molecule-magnetic behavior below T = 0.5 K with fast relaxation of the magnetization due to resonant quantum tunneling. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

We report a carboxylate triangle consisting of three manganeseii centres which is made from manganeseii carbonate and pivalic acid. The magnetic exchange within the triangle is extremely weak, and antiferromagnetic. Several models have been used to fit the magnetic data, and the best fit uses two weak antiferromagnetic coupling constants of J1 −0.588 cm−1and J2 −0.855 cm−1. Exchange interactions between the metal centres has been calculated using DFT adopting all the three possible Heisenberg models for a trinuclear system and the results are compared with experimental values. Spin density distribution is used to analyse the nature of the coupling between the metal centres. EPR spectroscopy has been used to explore the nature of the ground state. Recrystallisation of the trinuclear compound from MeCN gives a polymer, while oxidation in air leads to a known compound—an edge-sharing bitetrahedral MnIII2MnII4 cage.

The first structural characterization of an actinide complex with coordinated perrhenate is reported, [UO₂(ReO₄)₂(TPPO)₃] (1). In this {UO₂}2+ complex two [ReO₄]− anions and three TPPO (triphenylphosphine oxide) P&z.dbd;O donor ligands are coordinated in the equatorial plane in a cisoid arrangement. This bonding arrangement, and apparent strain observed in the equatorially bonded ligands, is attributed to the solid state packing in adjacent molecules in which hydrophobic TPPO ligands form an effective “shell” around a hydrophilic core of two UO₂(ReO₄)₂ moieties. Solid state vibrational spectroscopy (infrared and Raman), 31P CP MAS NMR and elemental analysis are also consistent with the formula of 1. Solution state vibrational spectroscopy and 31P NMR measurements in EtOH indicate the lability of the TPPO and [ReO₄]− groups. The photolytic generation of peroxide in EtOH solutions of 1 leads to the formation of trace quantities of [{(UO₂)(TPPO)₃}₂(µ₂-O₂)][ReO₄]₂, 2, in which the coordinated [ReO₄]− groups of 1 have been displaced by bridging O₂2−, derived from atmospheric O₂. Finally, attempts to synthesise a {NpO₂}+ analogue of 1 have resulted only in the formation of [NpO₂(TPPO)₄][ReO₄], 3, in which [ReO₄]− acts solely as a counter anion. From these results it can be concluded that [ReO₄]− will bond to {UO₂}2+, but will be readily displaced by a more strongly coordinating ligand (e.g. peroxide) and will not coordinate to an actinyl cation with a lower charge, {NpO₂}+, under the same reaction conditions.

The first structural characterization of an actinide complex with coordinated perrhenate is reported, UO2ReO42TPPO31. In this UO22complex two ReO4−anions and three TPPO triphenylphosphine oxide PO donor ligands are coordinated in the equatorial plane in a cisoidarrangement. This bonding arrangement, and apparent strain observed in the equatorially bonded ligands, is attributed to the solid state packing in adjacent molecules in which hydrophobic TPPO ligands form an effective “shell” around a hydrophilic core of two UO2ReO42moieties. Solid state vibrational spectroscopy infrared and Raman, 31P CP MAS NMR and elemental analysis are also consistent with the formula of 1. Solution state vibrational spectroscopy and 31P NMR measurements in EtOH indicate the lability of the TPPO and ReO4−groups. The photolytic generation of peroxide in EtOH solutions of 1leads to the formation of trace quantities of UO2TPPO32µ2-O2ReO42, 2, in which the coordinated ReO4−groups of 1have been displaced by bridging O22−, derived from atmospheric O2. Finally, attempts to synthesise a NpO2analogue of 1have resulted only in the formation of NpO2TPPO4ReO4, 3, in which ReO4−acts solely as a counter anion. From these results it can be concluded that ReO4−will bond to UO22, but will be readily displaced by a more strongly coordinating ligand e.g.peroxide and will not coordinate to an actinyl cation with a lower charge, NpO2, under the same reaction conditions.

The synthesis and characterisation of a range of cobalt pivalate cage complexes are reported. The cages include: a dinuclear Co^II complex; an oxo-centred Co^III triangle; tetranuclear Co^II heterocubanes and butterflies; tetranuclear heterovalent cobalt butterflies and hexanuclear edge-sharing bitetrahedra; heterovalent penta-, hexa- and hepta-nuclear cages based on {M4O4} heterocubane cores; and a tetradecanuclear cage based on heterocubanes sharing edges and vertices. Spectroscopic studies suggest that some of these cores are retained in solution, but that only in the Co^III triangle is the structure including ligands retained. A scheme is proposed to account for the many structures observed, which may be applicable to other polymetallic cage complexes.

The synthesis and characterisation of a range of cobalt pivalate cage complexes are reported. The cages include: a dinuclear CoIIcomplex; an oxo‐centred CoIIItriangle; tetranuclear CoIIheterocubanes and butterflies; tetranuclear heterovalent cobalt butterflies and hexanuclear edge‐sharing bitetrahedra; heterovalent penta‐, hexa‐ and hepta‐nuclear cages based on {M4O4} heterocubane cores; and a tetradecanuclear cage based on heterocubanes sharing edges and vertices. Spectroscopic studies suggest that some of these cores are retained in solution, but that only in the CoIIItriangle is the structure including ligands retained. A scheme is proposed to account for the many structures observed, which may be applicable to other polymetallic cage complexes.

No Abstract

No Abstract

The preparation and properties of fourteen novel paramagnetic [NiIIx] aggregates bridged by pivalate, pyrazolinolate and in most cases hydroxide are reported. A rich structural diversity has been achieved by changing the nature of the alkali of the base used during the synthesis, leading to the nuclearities [NiII4NaI4] (2, 3, 4), [NiII5NaI4] (5, 6, 7), [NiII5LiI6] (8), [NiII8MI2] (M=K (9, 10), Rb (11, 12), Cs (13, 14) and [NiII8] (15). All compounds have been characterised by single‐crystal Xray diffraction; however, full crystallographic details are given only for the representative molecules [Ni4Na4(fpo)4(piv)8(Hpiv)8] (2), [Ni5Na4(OH)2(mpo)4(piv)8(Hpiv)2(MeCN)2] (5), [Ni5Li6(OH)2(fpo)2(piv)12(Hpiv)4] (8), [Ni8K2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (9), [Ni8Rb2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (11), [Ni8Cs2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (13) and [Ni8(OH)4(mpo)2(PhCH2CO2)10(Hmpo)8] (15). Variable‐temperature bulk magnetisation measurements have been performed for each type of complex. The [NiII4NaI4] clusters show intramolecular antiferromagnetic coupling and a spin ground state of S=0. Complexes of the type [NiII5NaI4] also display antiferromagnetic superexchange, leading to an S=1 spin ground state. The molecule with nuclearity [NiII5LiI6], in contrast, exhibits ferromagnetic interactions, resulting in the presence of low energy states with high multiplicity, and a spin ground state S>1. The [NiII8MI2] and [NiII8] clusters have the same topology of spin carriers, which display predominantly antiferromagnetic interactions to yield a diamagnetic ground state. The coupling within these octanuclear NiIIclusters is rationalised in terms of the nature of the Ni‐O‐Ni angles within the core.

The preparation and properties of fourteen novel paramagnetic [Ni^IIx] aggregates bridged by pivalate, pyrazolinolate and in most cases hydroxide are reported. A rich structural diversity has been achieved by changing the nature of the alkali of the base used during the synthesis, leading to the nuclearities [Ni^II4Na^I4] (2, 3, 4), [Ni^II5Na^I4] (5, 6, 7), [Ni^II5Li^I6] (8), [Ni^II8M^I2] (M=K (9, 10), Rb (11, 12), Cs (13, 14) and [Ni^II8] (15). All compounds have been characterised by single-crystal Xray diffraction; however, full crystallographic details are given only for the representative molecules [Ni4Na4(fpo)4(piv)8(Hpiv)8] (2), [Ni5Na4(OH)2(mpo)4(piv)8(Hpiv)2(MeCN)2] (5), [Ni5Li6(OH)2(fpo)2(piv)12(Hpiv)4] (8), [Ni8K2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (9), [Ni8Rb2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (11), [Ni8Cs2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (13) and [Ni8(OH)4(mpo)2(PhCH2CO2)10(Hmpo)8] (15). Variable-temperature bulk magnetisation measurements have been performed for each type of complex. The [Ni^II4Na^I4] clusters show intramolecular antiferromagnetic coupling and a spin ground state of S=0. Complexes of the type [Ni^II5Na^I4] also display antiferromagnetic superexchange, leading to an S=1 spin ground state. The molecule with nuclearity [Ni^II5Li^I6], in contrast, exhibits ferromagnetic interactions, resulting in the presence of low energy states with high multiplicity, and a spin ground state S>1. The [Ni^II8M^I2] and [Ni^II8] clusters have the same topology of spin carriers, which display predominantly antiferromagnetic interactions to yield a diamagnetic ground state. The coupling within these octanuclear Ni^II clusters is rationalised in terms of the nature of the Ni-O-Ni angles within the core.

We report the cyclo‐depolymerization of poly(propylene terephthalate) to give a mixture of cyclic oligomers in 94% yield, the characterization of the mixture by 1H‐NMR spectroscopy, matrix assisted laser desorption ionization time of flight mass spectrometry and gel permeation chromatography. The major cyclic oligomer in the mixture was shown to be the cyclic dimer. It was isolated and its X‐ray crystal structure determined. Some entropically‐driven ring‐opening polymerizations of the cyclic oligomers were carried out. So too were some copolymerizations using mixtures of the cyclic oligomers and those derived similarly from poly(ethylene terephthalate) and poly(butylene terephthalate). 13C‐NMR spectroscopic analysis showed that the copolymers were random. Copyright © 2003 John Wiley & Sons, Ltd.

We report the cyclo-depolymerization of poly(propylene terephthalate) to give a mixture of cyclic oligomers in 94% yield, the characterization of the mixture by ¹H-NMR spectroscopy, matrix assisted laser desorption ionization time of flight mass spectrometry and gel permeation chromatography. The major cyclic oligomer in the mixture was shown to be the cyclic dimer. It was isolated and its X-ray crystal structure determined. Some entropically-driven ring-opening polymerizations of the cyclic oligomers were carried out. So too were some copolymerizations using mixtures of the cyclic oligomers and those derived similarly from poly(ethylene terephthalate) and poly(butylene terephthalate). ¹³C-NMR spectroscopic analysis showed that the copolymers were random. Copyright © 2003 John Wiley & Sons, Ltd.

The pentahapto-bonded cyclooctadienylmolybdenum complexes [Mo(CO)₂(L₂)(1–3:5,6-η-C₈H₁₁)][BF₄] (L₂ = Ph₂P(CH₂)_nPPh₂, n = 1, (dppm), 1a; n = 2, (dppe), 2a) are synthesised by reaction of [MoBr(CO)₂(L₂)(1–3-η:5,6-C₈H₁₁)] with Ag[BF₄] in CH₂Cl₂; [Mo(CO)₂(dppm)(1–5-η-C₈H₁₁)][BF₄], 1b, is obtained from [MoBr(CO)₂(dppm)(1–3-η:4,5-C₈H₁₁)] by an identical procedure. Related syntheses afford [Mo(CO)₂{P(OMe)₃}₂(1–5-η-C₈H₁₁)][BF₄], 4b, and [Mo(CO)₂(CNBut)₂(1–3:5,6-η-C₈H₁₁)][BF₄], 5a. The complexes [Mo(CO)₂(NCMe)₃(η3-C₈H₁₁)]+ (η3-C₈H₁₁ = 1–3-η:5,6-C₈H₁₁, 1–3-η:4,5-C₈H₁₁) are precursors to [Mo(CO)(CNBut)₃(1–3:5,6-η-C₈H₁₁)][BF₄], 6a, [Mo(CO)(CNBut)₃(1–5-η-C₈H₁₁)][BF₄], 6b and [Mo(CO)₂(norborna-2,5-diene)(1–3:5,6-η-C₈H₁₁)][BF₄], 7a. The X-ray crystal structures of complexes 1a and 6b have been determined. NMR spectroscopic investigations on the 1–5-η-C₈H₁₁ complexes 1b, 4b and 6b, indicate a high barrier to rotation of the metal group with respect to the cyclooctadienyl ring. Complexes 1a, 1b and 2a undergo ligand addition reactions with accompanying η5 → η3 hapticity conversion at the cyclooctadienyl ligand to yield adducts [Mo(CO)₂(L')(L₂)(η3-C₈H₁₁)]+ (L' = NCMe or CO, L₂ = dppm or dppe, η3-C₈H₁₁ = 1–3-η:5,6-C₈H₁₁ or 1–3-η:4,5-C₈H₁₁, not all combinations). The facility of these processes is strongly dependent upon the identity of the variables L₂ and C₈H₁₁.

Nickel and cobalt heterocubanes have been synthesised from dinuclear complexes. The use of 8-hydroxyquinaldine leads to a rhombohedral distortion in two faces of the cubes. Both cubes were studied by paramagnetic NMR, which shows that they are stable in solution. Magnetic measurements show that the coupling within both molecules is overall antiferromagnetic. The magnetic data for the nickel cube has been modelled, and shows that the coupling consists of two ferromagnetically coupled pairs which are antiferromagnetically coupled to give a diamagnetic ground state.

The reaction of the complex [Ni₂(H₂O)(piv)₄(Hpiv)₄] (1) (Hpiv = pivalic acid) with Hppo (3-phenylpyrazolin-5-one) in the presence of a base of an alkaline-earth metal (MII = MgII, SrII or BaII) has led to three different NiII clusters whose structures are controlled by the nature of MII. The formulae of the new heteronuclear cages are [Ni₆Mg₂(OH)₂(ppo)₄(piv)₁₀(Hppo)₄(MeOH)₂] (2), [Ni₈Sr(OH)₂(ppo)₆(piv)₁₀(Hppo)₅(Hpiv)₂(MeCN)] (3) and [Ni₈Ba(OH)₂(ppo)₆(piv)₁₀(Hppo)_5.3(Hpiv)_0.7(MeCN)₂] (4). Magnetic measurements indicate that the spin ground state of 2 consists of two independent S = 3 units, while the presence of two non-interacting S = 2 fragments in the molecule is postulated for compounds 3 and 4.

The new bis-iminophosphorane complexes [UO₂Cl{η3-CH(Ph₂PNSiMe₃)₂}(thf)] (1) and [UO₂Cl{η3-N(Ph₂PNSiMe₃)₂}(thf)] (2) are synthesised from the reaction of [UO₂Cl₂(thf)₃] with Na[CH(Ph₂PNSiMe₃)₂] (NaI) and Na[N(Ph₂PNSiMe₃)₂] (NaII), respectively. Both 1 and 2 form dinuclear complexes in the absence of a coordinating solvent. The reactivity of 1 has been explored. The crystal structures of 1 and 2 have been determined. They display distorted pentagonal bipyramidal geometry with ligands I and II both bonding in a tridentate chelating manner which is shown to remain intact in solution. Complex 1 contains a U–C bond that is out of the equatorial plane by 0.842(3) Å in contrast to 2 where the U–N bond is close to the equatorial plane (0.154(3) Å). This difference in geometry results in an unusual low energy electronic absorption band for 1 originating from C → U LMCT supported by molecular orbital calculations at the DFT level.