Paul E. Y. Milne

New routes to copper–lanthanoid complexes I: via a metallomacrocycle

We report the synthesis and structure of a novel hexanuclear copper complex of the anion of 6-methyl-2-hydroxypyridine (MeL), which undergoes reaction with lanthanum nitrate to give [La8Cu12(OH)24(NO3)22(MeLH)13(H2O)6][NO3]2[MeLH]2·CH2Cl2, a copper–lanthanoid complex with several unique structural features.

New routes to copper–lanthanoid complexes–via a metal dimer

The synthesis and structure of a dimeric copper complex of 6-chloro-2-hydroxypyridine [CILH] is reported; treatment with lanthanum nitrate gives a novel LaCu3 complex, and with ytterbium nitrate gives a new Yb2Cu2 complex, both of which are also structurally characterised.

Synthesis, crystal structures and thermal decomposition studies of a series of copper–lanthanoid complexes of 6-methyl-2-pyridone

A series of mixed copper-Ianthanoid complexes have been synthesised and structurally characterised. All the compounds were made from the reaction of [Cu6Na(mhp)12]NO3(mhp is the anion of 6-methyl-2-pyridone) with hydrated lanthanoid nitrates in methanol. In each case X-ray crystallographic analysis revealed a central Cu2O2 ring bridged to peripheral lanthanoid (Ln) atoms by mhp ligands. For early lanthanoids (La, Ce and Nd) the complex has a stoichiometry [Ln2Cu2(OMe)2(mhp)4(NO3)4(Hmhp)2-(MeOH)4], in which the Ln atoms are nine-co-ordinate, with approximate tricapped-trigonal prismatic, geometry. For later lanthanoids (Gd, Dy and Yb) the stoichiometry is [Ln2Cu2(OMe)2(mhp)4(NO3)4-(Hmhp)2(MeOH)2] and the Ln atoms are eight-co-ordinate, with a geometry that can be related to a dodecahedron. For Ln = Sm a disordered co-ordination sphere results, presumably caused by the intermediate ionic radius of Sm leading to very similar stabilities for the eight- and nine-co-ordinate structures. Thermal decomposition studies of these complexes have also been carried out which indicate that decomposition occurs initially to monometallic oxides or oxide carbonates, followed by production of the mixed-oxide phase Ln2CuO4(for Ln = La, Nd, Gd or Dy) or Ln2Cu2O5(for Ln = Er or Yb). In most cases CuO is also found. All oxide and oxide-carbonate phases have been characterised by X-ray powder diffraction.

NEW HIGH-SPIN CLUSTERS FEATURING TRANSITION METALS

Three possible routes to polynuclear transition metal complexes are discussed. The first route, oligomerization induced by desolvation of small cages, is exemplified by synthesis of a dodecanuclear cobalt cage, and by reactions which give octa– and dodecanuclear chromium cages. The second route involves linking cages through organic spacers, and is illustrated by use of phthalate to link together cobalt and nickel cages. For the nickel case a complex consisting of four cubanes and a sodium octahedron is found. The third route involves the use of water to introduce hydroxide bridges into cages. One method of introducing water is to use hydrated metal salts; the transformation of a Cu6Na cage into a Cu12La8 illustrates this approach. Alternatively, adventitious water within solvents can be used as a source, and this approach has led to a Co24 cage. The structures and magnetic properties of these various cages are discussed.

The photoinitiated cyclopolymerization of dienes in the creation of novel polymeric systems and three-dimensional networks

In this article we describe the photo-initiated cyclopolymerization of 5-, 6- and 7-centre dienes. We find that substituted dienes can be cyclopolymerized in sunlight or by the use of a low-power UVA sunlamp of broad spectral range (320–400 nm). Unless activated by suitable electron withdrawing groups the cyclopolymerization can often be slow and incomplete. However, when suitably activated the polymerization rates can approach those for acrylates. In particular diallylamine, its quaternary salts, which can often be obtained as ionic fluids, and diallylamide, can be subjected to fairly rapid photocyclopolymerization to give robust coatings and adhesives. This discovery augments, and gives a different dimension, to the acrylate and methacrylate monomer and polymer systems that are already commercially available.

Novel UV cured coatings and adhesives based on the photoinitiated cyclopolymerization of derivatives of diallylamine

A new family of non-acrylate UV cured three-dimensional polymeric networks for coatings and adhesives based on the photoinitiated cyclopolymerization of diallylamine salts and diallylamides using a low power (75 W) UVA domestic sunlamp is described.

Use of a hexanuclear copper complex as a ligand transfer agent : crystal structures of hexakis(6-methyl-2-pyridone)iron(III) nitrate and tetrakis(6-methyl-2-pyridone)bis(nitrato)cobalt(II)

Abstract The hexanuclear copper complex [Cu6Na(MeL)12][NO3](1) (where MeL = C6H6NO, the anion of 2-hydroxy-6-methylpyridine) undergoes ligand transfer reactions with solid hydrated transition metal nitrates. With iron(III) nitrate the salt [Fe(MeLH)6][NO3]3 (2) results, while with cobalt(II) nitrate the complex [Co (MeLH)4(NO3)2] (3) is formed. Both compounds have been characterized by X-ray crystallography, which reveals that in both cases the metals have regular octahedral coordination geometries, and that the protonated ligands are involved in either inter- or intra-molecular hydrogen bonding.

Reactions of copper pyridonate complexes with hydrated lanthanoid nitrates

Twenty new copper–lanthanoid complexes have been prepared. The route involves reaction of preformed copper pyridonate complexes with hydrated lanthanoid nitrates in a variety of solvents. Structural characterisation of eleven of these complexes gave some indications of how the structure is controlled in these compounds. Reaction of [Cu 6 Na(mhp) 12 ][NO 3 ] (mhp = 6-methyl-2-pyridonate) with hydrated lanthanum nitrate in CH 2 Cl 2 leads to a high-nuclearity complex containing a Cu 12 La 8 core. The twelve Cu atoms are arranged in a cuboctahedron surrounded by a cube of eight La atoms. Similar reactions involving 6-chloro-, 6-bromo- and 6-fluoro-2-pyridonate led to tetranuclear complexes which fall into three distinct structural groups. Consideration is given to the factors governing the choice of structural group.

Multi-frequency single-crystal and powder electron paramagnetic resonance spectroscopy of [Cu2(chp)4](chp = 6-chloro-2-pyridonate)

Powder and single-crystal X- and Q-band EPR spectra show evidence for both intra- and inter-dimer exchange in [Cu2(chp)4](chp = 6-chloro-2-pyridonate). The antiferromagnetic intradimer exchange gives rise to a singlet ground state and a thermally accessible S= 1 excited state which is described by the spin-Hamiltonian parameters (from single-crystal measurements at 120 K)gzz= 2.30, gxx= 2.07, gyy= 2.05, |D|= 0.275 cm–1 and |λ|(=|E/D|)= 0.01. Dzz and gzz are colinear with the Cu—Cu vector. Interdimer exchange between neighbouring triplet state molecules is apparent by both a highly temperature dependent linewidth and an ‘extra’ feature at geff≈ 2.1, the intensity of which rapidly falls with decrease in temperature. Analysis of the linewidth variation with temperature from single-crystal measurements at X-band leads to an interdimer exchange parameter of J′≈ 0.15 cm–1. The extra feature arises from averaging of the S= 1 signals of individual dimers under the action of interdimer exchange and occurs over only a narrow range of orientations in the single crystal.

Pyrolysis of stabilised phosphorus ylides as a route to new hetero carbenes

Abstract Flash vacuum pyrolysis of sulphonyl- and sulphinyl-stabilised phosphorus ylides results in loss of either phosphine or phosphine oxide to generate thio-, sulphinyl- and sulphonyl-carbenes which undergo a variety of rearrangement and insertion processes to give stable products. The first case of phosphine extrusion from a s-oxo ylide is reported, giving access to benzotriazolyl acetyl carbene which rearranges to an acetyl benzotriazine and 2-cyanoacetophenone.