Gary D. Fallon

Spectroscopy of Naphthalene Diimides and Their Anion Radicals

Naphthalene diimides 1–4 having different N,N-disubstitution undergo single electron reduction processes either chemically or electrochemically to yield the corresponding radical anion in high yield. This study concentrates on 1, bearing pentyl side chains connected through the diimide nitrogens, and compares the results obtained against those bearing isopropyl, propargyl, and phenylalanyl side chains. Compound 1 exhibits mirror image absorption and fluorescence in the near-UV region in CH2Cl2 and dimethylformamide that is typical of monomeric N,N-dialkyl-substituted naphthalene diimides. In toluene, excimer-like emission is observed, which suggests ground-state complexes involving 1 are formed. X-Ray crystallography has been used to characterize 1 in the solid state. Cyclic voltammetry enables the reversible potentials for [NDI]0/– and [NDI]−/2– type processes to be measured. Bulk one-electron reduction of 1–4 is characterized by dramatic changes in the absorption and emission spectra. Additionally, highly structured EPR (electron paramagnetic resonance) signals from dimethylformamide solutions of the radical anions of 1–3 have been obtained and are consistent with coupling between the unpaired electron and the naphthalene diimide nitrogens and hydrogens and the NCH hydrogens of the appropriate side chains. The overall structure of the EPR spectrum is substituent-dependent. These changes in spectroscopic output upon an electronic input may be described as a simple ‘on/off’ switching mechanism with which to apply a ‘bottom-up’ approach to molecular device manufacture.

Modifying the properties of platinum(IV) complexes in order to increase biological effectiveness

The preparation of a series of novel Pt(IV) complexes containing the anionic polyfluoroaryl ligands, 2,3,5,6-tetrafluorophenyl (p-HC6F4), 2,3,5,6-tetrafluoro-4-methoxyphenyl (p-MeOC6F4) and pentafluorophenyl (C6F5) are described. The crystal structure of a representative complex, [Pt(p-MeOC6F4)2(O2CEt)2(en)] (en = ethane-1,2-diamine) was determined and confirms the trans arrangement of the carboxylato ligands. Reduction potentials of the series of complexes reveal that replacement of equatorial chloro ligands by polyfluoroaryl ligands makes reduction substantially more difficult. They also confirm previously reported trends in that complexes having axial carboxylato ligands are more readily reduced than those having axial hydroxo ligands. Reduction potentials and in vitro activities showed no obvious correlations. Moderate to high activity was observed for many complexes in the series, including some of those that were very difficult to reduce.

Manipulation of reaction pathways in redox transmetallation–ligand exchange syntheses of lanthanoid(II)/(III) aryloxide complexes

Redox transmetallation/ligand exchange reactions of lanthanoid metals (Ln), Hg(C6F5)2 and HOAr(OMe) (Ar(OMe) = C6H2-2,6-Bu(t)-4-OMe), in thf (tetrahydrofuran) gave, for Ln = Yb, [Yb(OAr(OMe))2(thf)3], and for Ln = Sm, a mixture of [Sm(II)(OAr(OMe))2(thf)3] and mainly [Sm(III)(Ar(OMe))3(thf)] x thf. X-Ray structure determinations show the divalent complexes to have distorted square-pyramidal stereochemistry with transoid thf and OAr(OMe) ligands in the basal plane. Treatment of [Yb(OAr(OMe))2(thf)3] with diethyl ether or PhMe at room temperature gave [Yb(OAr(OMe))2] or [Yb(OAr(OMe))2] x 0.5 PhMe. For lanthanoids Ln = Nd, Er or Y, the reactions with Hg(C6F5)2 and HOAr(OMe) yielded complex product mixtures, from one of which the novel erbium aryloxide fluoride cage [Er3(OAr(OMe))4(mu2-F)3(mu3-F)2(thf)4] x thf x 0.5 C6H14 was isolated. The cage core consists of a triangle of Er atoms joined to two mu3-fluoride ligands and three further mu2-fluorides bridge adjacent Er atoms. One of the Er atoms is six-coordinate with additionally two OAr(OMe) ligands whilst the other two have one OAr(OMe) and two thf ligands and are seven coordinate. Substitution of Hg(C6F5)2 by Hg(CCPh)2 in the redox transmetallation/ligand exchange reactions gave the new derivatives [Ln(OAr(OMe))3(thf)] x thf (Ln = La, Pr, Nd, Sm, Gd, Ho) in good yields whilst Ln = Yb gave [Yb(OAr(OMe))2(thf)3]. Recrystallisation of [Sm(OAr(OMe))3(thf)] x thf from dme (1,2-dimethoxyethane) yielded [Sm(OAr(OMe))3(dme)]. Structural characterisation of [Ln(OAr(OMe))3(thf)] x thf (Ln = Nd, Ho) and [Sm(OAr(OMe))3(dme)] showed monomeric four-coordinate distorted tetrahedral and five-coordinate distorted square-pyramidal complexes respectively. For the smaller lanthanoids Ln = Y, Er or Lu, reactions with Hg(CCPh)2 and HOAr(OMe) gave the mixed aryloxide/alkynide complexes [Ln(OAr(OMe))2(CCPh)(thf)2]. Oxidation of the divalent ytterbium aryloxide [Yb(OAr(OMe))2(thf)3] by Hg(CCPh)2 in thf gave the analogous [Yb(OAr(OMe))2(CCPh)(thf)2]. The erbium alkynide [Er(OAr(OMe))2(CCPh)(thf)2] x 0.25 C6H14 has distorted square-pyramidal stereochemistry with transoid OAr(OMe) and thf ligands in the basal plane and a rare (for Ln) terminal alkynide ligand in the apical position. The reactive Lu-C bond in the [Lu(OAr(OMe))2(CCPh)(thf)2] complexes could be slowly cleaved by free HOAr(OMe) in hydrocarbon solvents, yielding Lu(OAr(OMe))3 species and fortuitous partial hydrolysis of [Er(Ar(OMe))2(CCPh)(thf)2] gave the dimeric [Er(OAr(OMe))2(mu-OH)2]2.

The molecular structures and magnetic properties of μ3-tetranuclear β-diketonate copper complexes [Cu(bzac)(μ3-OC2H4OCH3)]4 and [Cu(μ-dbm)(μ3-OC2H4OCH3)]4

Abstract [Cu(bzac)(OC 2 H 4 OCH 3 )] 4 1 ( I ) and [Cu(dbm)(OC 2 H 4 OCH 3 ] 4 1 ( II ) have been shown to be tetrameric in the solid state. Compound I has a pseudo-cubane type structure with μ 3 -alkoxide oxygens occupying four bridging positions. Two methoxy oxygens are also within bonding distance of copper(II) ions. Compound II has a stepped configuration with a chelate ring and alkoxide oxygens as bridging centres. None of the methoxy oxygens is clearly chelating. Magnetic susceptibility data versus temperature data to 4 K for the complexes show antiferromagnetic coupling which can be treated by “pairs of equal dimers” procedures. The complexes decompose in stages at temperatures below 350°C at atmospheric pressure to give CuO.

The structure of hydrated lead(II) dimethylacetate, [Pb6(O2CCH(CH3)2)12] 4H2O: A hexanuclear carboxylate

Abstract Hydrated lead(II) dimethylacetate forms hexanuclear units [Pb6(O2CCH(CH3)212]4H2O in the solid state consisting of a ring of four lead atoms linked by oxygen atoms belonging to chelated carboxylates, with two further lead atoms linked to the ring by bridging carboxylate oxygens. Water molecules are coordinated to four lead atoms. There are pairs of Pb atoms with 7, 6 and 5-fold coordination in the molecular unit. The hexanuclear molecularity is retained in solution but Pb207 NMR measurements indicate different 5-coordinate sites are formed.

The crystal structure of Ba2Ti9O20: a hollandite related compound

Ba2Ti9O20 crystallizes in the triclinic system with unit cell dimensions (from single crystal data) a = 14.358(4), b = 14.095(4), c = 7.477(1) A, α = 95.53(3), β = 100.55(3), γ = 89.95(2)°, and space group P1, z = 4. The structure was solved using Patterson (“P1” method) and Fourier techniques. Of the 8625 unique reflections measured by counter techniques 3767 with I ≧ 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.057 (Rω = 0.054). The structure of Ba2Ti9O20 is very similar to that of hollandite except that additional barium ions replace oxygen ions and disrupt the tunnel walls resulting in the formation of cavities, rather than tunnels, that contain two barium ions per cavity.

Organolanthanoids: VII. The crystal and molecular structure of dibromo-η5-cyclopentadienyltris(tetrahydrofuran)ytterbium(III)☆

Abstract Crystals of dibromo-η 5 -cyclopentadienyltris(tetrahydrofuran)ytterbium(III) are monoclinic, P 2 1 / n (C 2 n 5 , No. 14), with a 15.310(15), b 16.900(17), c 7.968(8) A, β 96.66(5)° and Z = 4. The ytterbium is pseudo-octahedrally coordinated by a cyclopentadienyl ligand, trans bromines, and mer tetrahydrofuran ligands, and the ytterbium—oxygen distance trans to cyclopentadienyl is longer than the other ytterbium—oxygen bonds.

Self-assembling mixed porphyrin trimers – the use of diaxial Sn(IV)porphyrin phenolates as an organising precept

Abstract Tin(IV)porphyrin phenolates are the stable product of the equilibrium-based condensation reaction of phenols with tin(IV)porphyrin dihydroxide in an organic medium. Their formation is characterised by significant shifts (1–5 ppm) of the phenolic protons within the recorded 1 H NMR spectra. To demonstrate the inherent simplicity of their formation and the flexibility in choice of phenolic ligand towards the design and fabrication of more elaborate assemblies and arrays we have constructed two different mixed porphyrin trimer families in which the porphyrin units differ in their orientation to the central porphyrin unit using Sn–O, Ru(III)–N and Zn(II)–N interactions. In one of these cases, 5 molecular components are self-assembled in one-pot to form a cofacially stacked mixed porphyrin trimer with high yield.

Systematic differences in electrochemical reduction of the structurally characterized anti-cancer platinum(IV) complexes [Pt{((p-HC6F4)NCH2)2}-(pyridine)2Cl2], [Pt{((p-HC6F4)NCH2)2}(pyridine)2(OH)2], and [Pt{((p-HC6F4)NCH2)2}(pyridine)2(OH)Cl].

The putative platinum(IV) anticancer drugs, [Pt{((R)NCH(2))(2)}(py)(2)XY] (X,Y=Cl, R=p-HC(6)F(4) (1a), C(6)F(5) (1b); X,Y=OH, R=p-HC(6)F(4) (2); X=Cl, Y=OH, R=p-HC(6)F(4) (3), py = pyridine) have been prepared by oxidation of the Pt(II) anticancer drugs [Pt{((R)NCH(2))(2)}(py)(2)] (R=p-HC(6)F(4) (4a) or C(6)F(5) (4b)) with PhICl(2) (1a,b), H(2)O(2) (2) and PhICl(2)/Bu(4)NOH (3). NMR spectroscopy and the X-ray crystal structures of 1b, 2 and 3 show that they have octahedral stereochemistry with the X,Y ligands in the trans-position. The net two electron electrochemical reduction of 1a, 2 and 3 has been studied by voltammetric, spectroelectrochemical and bulk electrolysis techniques in acetonitrile. NMR and other data reveal that reduction of 1a gives pure 4a via the elimination of both axial chloride ligands. In the case of 2, one end of the diamide ligand is protonated and the resulting -NH(p-HC(6)F(4)) group dissociated giving a [Pt{N(p-HC(6)F(4))CH(2)CH(2)NH(p-HC(6)F(4))}] arrangement, one pyridine ligand is lost and a hydroxide ion retained in the coordination sphere. Intriguingly, in the case of reduction of 3, a 50% mixture of the reduction products of pure 1a and 2 is formed. The relative ease of reduction is 1>3>2. Testing of 1a, 2 and 3 against L1210 and L1210(DDP) (DDP = cis-diamine-dichloroplatinum(II)) mouse leukaemia cells shows all to be cytotoxic with IC(50) values of 1.0-3.5 μM. 2 and 3 are active in vivo against AHDJ/PC6 tumor line when delivered in peanut oil despite being hard to reduce electrochemically, and notably are more active than 4a delivered in this medium whilst comparable with 4a delivered in saline/Tween.

Endiandric acid, a novel carboxylic acid from Endiandra introrsa(Lauraceae): X-ray structure determination

X-Ray crystal structure analysis shows that endiandric acid, a constituent of the Australian tree Endiandra introrsa, has the novel racemic structure (1), (1RS,3RS,6SR,7SR,10SR,11RS,12RS,13RS)-(6-phenyltetracyclo[5.4.2.03,13010,12]trideca-4,8-dien-11-yl]acetic acid.