Search

The synthesis of six N,N′-substituted thiourea ligands (L1a–L3b) was achieved in two steps. A corresponding extensive series of Cu(I), Cu(II), Ni(II) and Zn(II) complexes (1–24) with varying formulations were synthesised from these ligands by the reaction of a 1 : 1 or a 1 : 2 mixture of Cu(II), Ni(II) and Zn(II) perchlorate or chloride salts. Complexes 1–24 have been comprehensively characterised by mass spectrometry, elemental analysis, UV-vis., IR, and 1H and 13C{1H} NMR spectroscopies where applicable. The X-ray crystal structures were obtained for eight examples: [(L1a)2Cu]ClO4 (1), [(L1c)2Zn](ClO4)2 (4), [(L2a)2Cu]ClO4 (6), [(L2c)2Ni](ClO4)2 (7), [(L1b)2Cu](ClO4) (15), [(L1b)CuCl] (16), [(L4)2CuCl2] (19) and [(L3b)CuClO4] (21). These studies reveal that L1c and L2c represent ligands that have undergone cleavage during reaction with the metal salt; L4 represents an intramolecular rearrangement (via a Hugershoff reaction) of L2b; and in most cases Cu(II) is reduced to Cu(I) during the ligand reaction. The X-ray crystal structures also reveal that 1, 4, 6, 15 and 16 are monometallic species in the solid state; that Cu(I) in 1, 6, 15 and 16 and Zn(II) in 4 are arranged in a distorted tetrahedral geometry; that Cu(I) in 21 adopts a trigonal planar geometry; and that in 7 and 19 the Ni(II) and Cu(II) centres, respectively, possess square planar geometry. Preliminary studies on the biological activity (using the Malaria Sybr Green I Fluorescence assay) of the thiourea containing complexes suggests that the d10 complexes, and increased ligand stoichiometries, may afford higher potency. [ABSTRACT FROM AUTHOR]

We report two tripodal frameworks, mono(2,2′-bipyrid-6-yl)bis(2-pyridyl)methanol (L1) and bis(2,2′-bipyrid-6-yl)mono(2-pyridyl)methanol (L2) which have one and two bipyridyl arms, respectively. Both ligands form complexes with the first row transition metals. Both ligands appear to overcome the steric strain involved in twisting the ligand to produce an octahedral complex and the solid state structures in general show more octahedral character than complexes of the related ligand, tris(2,2′-bipyrid-6-yl)methanol (L3). Continuous Shape Mapping (CShM) calculations based on crystallographic data reveal that L1 is incapable of enforcing a trigonal prismatic (TP) co-ordination geometry in the solid state, surprisingly even upon co-ordination to metals with no stereochemical preference such as cadmium (S(TP) = 7.15 and S(Oh) = 3.95). However, ligand L2 clearly maintains an ability to enforce a trigonal prismatic conformation which is demonstrated in the crystal structures of the MnII and CdII complexes (S(TP) = 0.75 and 1.09, respectively). While L3 maintains near-TP configurations in the presence of metal ions with strong octahedral preferences, L2 distorts towards predominantly octahedral co-ordination geometries, increasing in the order CoII ＜ NiII ＜ FeII and no trigonal prismatic structures. [ABSTRACT FROM AUTHOR]

The co-ordination chemistry of a tristhiourea tris(2-pyridylmethyl)amine ligand (L1) with a series of transition metal ions has been investigated. Crystallographic data show that large metal ions, with no geometrical preferences, such as Mn(ii) and Cd(ii), will form seven co-ordinate monocapped octahedral complexes, while smaller metal ions such as Zn(ii) favour five co-ordinate trigonal bipyramidal structures. In a similar manner to the related bisthiourea complexes, the Ni(ii) complex shows a strong preference for octahedral geometries resulting in the ligand binding asymmetrically. Spectroscopic (IR and NMR), spectrometric (MS) as well as electrochemical data for these complexes are reported. [ABSTRACT FROM AUTHOR]

Three new chromophoric anthraquinone-based multidentate ligands have been synthesised in a step-wise manner from 1,8-dichloroanthraquinone. The ligands each comprise two dipicolyl amine units and react with trivalent lanthanide ions to form monometallic complexes of the form [Ln(L)](OTf)3 as indicated by MS studies and elemental analyses. Supporting DFT studies show that the monometallic species are highly favoured (＞1000 kJ mol−1) over the formation of a 2 : 2 dimetallic congener. Both ligands and complexes absorb light efficiently (ε∼ 104 M−1 cm−1) in the visible part of the spectrum, with λabsca. 535–550 nm through an intramolecular charge transfer (ICT) transition localised on the substituted anthraquinone unit. In all cases the complexes show a fluorescence band at ca. 675 nm due to the ICT emitting state. The corresponding Nd(iii), Yb(iii) and Er(iii) complexes also reveal sensitised near-IR emission characteristic of each ion following excitation of the ICT visible absorption band at 535 nm. [ABSTRACT FROM AUTHOR]

Facile conjugation of a luminescent cyclometalated PtII complex with a DO3A-derived GdIII moiety yields a hybrid species with visible luminescence and enhanced relaxivity. [ABSTRACT FROM AUTHOR]

Trivalent lanthanide ions offer remarkable opportunities in the design of bioimaging agents: this review presents an accessible discussion of their application in both optical and magnetic resonance imaging. Aspects of molecular design, control over key physical properties and biological compatibility are discussed in this context, together with developments and opportunities as responsive probes and in multimodal imaging. [ABSTRACT FROM AUTHOR]

An investigation into the co-ordination chemistry of tris(6-pivaloylamino-2-pyridylmethyl)amine (TPPA) shows a preference for capped octahedral geometry when no additional donors are present. This tripodal ligand yields capped octahedral complexes upon co-ordination to a series of first row transition metals when the counter-ion is a perchlorate, bromide or iodide ion. The exact geometry has been confirmed by shape mapping calculations. The largest variation from the capped octahedral geometry is observed in the case of nickel(ii), indicating a greater octahedral preference of this metal ion. [ABSTRACT FROM AUTHOR]

The radiometal 64Cu is now widely used in the development of diagnostic imaging agents for positron emission tomography (PET). The present study has led to the development and evaluation of a novel chelating agent for 64Cu: the new monothiourea tripodal ligand 1-benzoyl-3-{6-[(bis-pyridin-2-ylmethyl-amino)-methyl]-pyridin-2-yl}-thiourea (MTUBo). X-ray crystallographic analysis has shown this ligand forms a mononuclear complex with copper(ii) and co-ordinates via a trigonal bipyramidal N4S array of donor atoms. Promisingly, cell uptake studies revealed that 64Cu-MTUBo selectively accumulates in EMT-6 cells incubated under hypoxic conditions which may result from its relatively high CuII/I redox potential. Small-animal PET imaging and ex vivo biodistribution studies in EMT-6 tumor bearing BALB/c mice revealed significant tumor uptake after 1 h p.i., yielding tumor-to-muscle (T/M) and tumor-to-blood (T/B) ratios of 8.1 and 1.1, respectively. However, injection of 64Cu-acetate resulted in similar uptake indicating that the observed uptake was most likely non-specific. Despite showing high in vitro stability, it is likely that in vivo the complex undergoes transchelation to proteins within the blood in a relatively short timeframe. For comparison, the hypoxia imaging agent 64Cu-ATSM was also evaluated in the same murine tumor model and showed about 60% higher tumor uptake than 64Cu-MTUBo. [ABSTRACT FROM AUTHOR]

Bis(2,2′-bipyrid-6′-yl)ketone has been shown to co-ordinate to Zn(ii) to form either a dinuclear hemiketal complex in methanol solutions or mononuclear complexes in acetonitrile. The ligand readily complexes to the late transition metals in acetonitrile to yield mononuclear complexes (Mn(ii), Co(ii), Ni(ii),Zn(ii) and Cd(ii)) however for Fe(ii) only dinuclear complexes [Fe2{(2-bipy)2C(OMe)O−}2][ClO4]2could be isolated. The solid state structures of the mononuclear complexes exhibit varying degrees of distortion compared to an anticipated planar array of bipyridyl donors. [ABSTRACT FROM AUTHOR]

The investigation into the substitution and addition chemistry of Re(σ2-terpy)(CO)3Cl shows that the chloride in Re(σ2-terpy)(CO)3Cl (1) may be substituted for acetonitrile to give [Re(σ2-terpy)(CO)3(CH3CN)][PF6] (2), but in the cationic complex [Re(σ2-terpyMe)(CO)3Cl][PF6] (4), where the pendant pyridine has been methylated, substitution of the chloride could not be achieved using standard conditions. However, use of [Re(σ2-terpyMe)(CO)3I][PF6] (3) results in the formation of [Re(σ2-terpyMe)(CO)3(CH3CN)][PF6]2(5). The acetonitrile ligand in complex 2was found to be labile and could be substituted by pyridine donors. [ABSTRACT FROM AUTHOR]

A tripodal tris-8-aminoquinoline ligand was synthesised in high yield viathe Bucherer reaction. The septa-dentate ligand was found to give isolable complexes when coordinated with transition metals. Complexes of zinc(ii), cadmium(ii) and cobalt(iii) were isolated and their solid state structures were determined by single crystal X-ray diffraction. The solid state structures of these complexes were compared to the solution 1H NMR data which was obtained for each complex. The two first row metals both gave octahedral six coordinate structures, although the two metals were coordinated by a differing donor set of heteroatoms. The cadmium complex was found to contain a seven coordinate cadmium centre in the solid state. DFT calculations were carried out in order to give an indication as to why the two different six coordinate binding modes were encountered. [ABSTRACT FROM AUTHOR]

The 3-chloromethylpyridyl bipyridine fac tricarbonyl rhenium cation is a thiol-reactive luminescent agent with a long luminescence lifetime and large Stokes shift that is demonstrated by co-localisation studies to accumulate in mitochondria. This represents the first application of a 3MLCT luminescent agent for the specific targeting of a biological entity in imaging. [ABSTRACT FROM AUTHOR]

The co-ordination of a series of terpyridine-N-oxide ligands to the Cu(ii) ion is reported. Addition of two equivalents of ligand results in the formation of the expected 2 : 1 six co-ordinate product, while the addition of one equivalent of ligand allows the isolation of 1 : 1 species if the ligand has a meridonal binding mode. The five complexes isolated were characterised in the solid state by X-ray crystallography while they are studied in solution using EPR, UV-vis spectroscopy and IR spectroscopy. [ABSTRACT FROM AUTHOR]

Europium complexes of a series of terpyridine-N-oxide ligands have been prepared and structurally characterised by crystallographic studies. While the addition of three equivalents of terpyridine-1 -oxide or terpyridine-1,1'-bisoxide results in complexes with nine co-ordinate tricapped trigonal prismatic or monocapped square antiprismatic geometries, respectively, three equivalents of the terpyridine-1, 1',1'-trisoxide yields an unexpected 8 co-ordinate geometry. Luminescence studies of the three complexes in acetonitrile show a typical europium emission spectra, dominated by the 5D0-7F2 transition. While no simple trend in the relative quantum yields could be ascertained, the terpyridine-1-oxide complex was observed to have the most intense luminescence for this set of complexes. [ABSTRACT FROM AUTHOR]

UV-visible titrations, 1H NMRD experiments and molecular docking studies show that emissive anthraquinone appended dimetallic lanthanide complexes bind to DNA. The strength of binding and the observed relaxivity behaviour depend on the nature of the substituted anthraquinone core. [ABSTRACT FROM AUTHOR]

We report the facile and efficient synthesis of a novel cryptand using a one-pot method involving a Pd(ii)-catalysed carbonylation reaction. The crystal structure of the corresponding CuIIcryptate is also described. [ABSTRACT FROM AUTHOR]

We report the facile and efficient synthesis of a novel cryptand using a one-pot method involving a Pd(ii)-catalysed carbonylation reaction. The crystal structure of the corresponding CuIIcryptate is also described. [ABSTRACT FROM AUTHOR]

Unlike their octahedral analogues, copper(II) compounds with trigonal prismatic stereochemistry undergo an elongation of two bonds in cis positions due to a Jahn-Teller effect, a behavior that can also occur in slightly twisted octahedra. [ABSTRACT FROM AUTHOR]

Unlike their octahedral analogues, copper(ii) compounds with trigonal prismatic stereochemistry undergo an elongation of two bonds in cispositions due to a Jahn–Teller effect, a behavior that can also occur in slightly twisted octahedra. [ABSTRACT FROM AUTHOR]

A series of lipophilic and hydrophilic fac tricarbonyl rhenium bisimine complexes have been prepared, their membrane-permeabilities explored in liposomes and their potential for application in fluorescence microscopy cell imaging demonstrated in the first application of MLCT-fluorescent rhenium complexes in cell imaging. [ABSTRACT FROM AUTHOR]

The synthesis of six N , N '-substituted thiourea ligands (L1a-L3b) was achieved in two steps. A corresponding extensive series of Cu(I), Cu(II), Ni(II) and Zn(II) complexes (1-24) with varying formulations were synthesised from these ligands by the reaction of a 1 : 1 or a 1 : 2 mixture of Cu(II), Ni(II) and Zn(II) perchlorate or chloride salts. Complexes 1-24 have been comprehensively characterised by mass spectrometry, elemental analysis, UV-vis., IR, and 1 H and 13 C{ 1 H} NMR spectroscopies where applicable. The X-ray crystal structures were obtained for eight examples: [(L1a) 2 Cu]ClO 4 (1), [(L1c) 2 Zn](ClO 4 ) 2 (4), [(L2a) 2 Cu]ClO 4 (6), [(L2c) 2 Ni](ClO 4 ) 2 (7), [(L1b) 2 Cu](ClO 4 ) (15), [(L1b)CuCl] (16), [(L4) 2 CuCl 2 ] (19) and [(L3b)CuClO 4 ] (21). These studies reveal that L1c and L2c represent ligands that have undergone cleavage during reaction with the metal salt; L4 represents an intramolecular rearrangement ( via a Hugershoff reaction) of L2b; and in most cases Cu(II) is reduced to Cu(I) during the ligand reaction. The X-ray crystal structures also reveal that 1, 4, 6, 15 and 16 are monometallic species in the solid state; that Cu(I) in 1, 6, 15 and 16 and Zn(II) in 4 are arranged in a distorted tetrahedral geometry; that Cu(I) in 21 adopts a trigonal planar geometry; and that in 7 and 19 the Ni(II) and Cu(II) centres, respectively, possess square planar geometry. Preliminary studies on the biological activity (using the Malaria Sybr Green I Fluorescence assay) of the thiourea containing complexes suggests that the d 10 complexes, and increased ligand stoichiometries, may afford higher potency.

The co-ordination chemistry of a tristhiourea tris(2-pyridylmethyl)amine ligand () with a series of transition metal ions has been investigated. Crystallographic data show that large metal ions, with no geometrical preferences, such as Mn(ii) and Cd(ii), will form seven co-ordinate monocapped octahedral complexes, while smaller metal ions such as Zn(ii) favour five co-ordinate trigonal bipyramidal structures. In a similar manner to the related bisthiourea complexes, the Ni(ii) complex shows a strong preference for octahedral geometries resulting in the ligand binding asymmetrically. Spectroscopic (IR and NMR), spectrometric (MS) as well as electrochemical data for these complexes are reported.

Three new chromophoric anthraquinone-based multidentate ligands have been synthesised in a step-wise manner from 1,8-dichloroanthraquinone. The ligands each comprise two dipicolyl amine units and react with trivalent lanthanide ions to form monometallic complexes of the form [Ln(L)](OTf)3 as indicated by MS studies and elemental analyses. Supporting DFT studies show that the monometallic species are highly favoured (>1000 kJ mol(-1)) over the formation of a 2 : 2 dimetallic congener. Both ligands and complexes absorb light efficiently (ε ∼ 10(4) M(-1) cm(-1)) in the visible part of the spectrum, with λabsca. 535-550 nm through an intramolecular charge transfer (ICT) transition localised on the substituted anthraquinone unit. In all cases the complexes show a fluorescence band at ca. 675 nm due to the ICT emitting state. The corresponding Nd(iii), Yb(iii) and Er(iii) complexes also reveal sensitised near-IR emission characteristic of each ion following excitation of the ICT visible absorption band at 535 nm.

An investigation into the co-ordination chemistry of tris(6-pivaloylamino-2-pyridylmethyl)amine (TPPA) shows a preference for capped octahedral geometry when no additional donors are present. This tripodal ligand yields capped octahedral complexes upon co-ordination to a series of first row transition metals when the counter-ion is a perchlorate, bromide or iodide ion. The exact geometry has been confirmed by shape mapping calculations. The largest variation from the capped octahedral geometry is observed in the case of nickel(ii), indicating a greater octahedral preference of this metal ion.

The radiometal (64)Cu is now widely used in the development of diagnostic imaging agents for positron emission tomography (PET). The present study has led to the development and evaluation of a novel chelating agent for (64)Cu: the new monothiourea tripodal ligand 1-benzoyl-3-{6-[(bis-pyridin-2-ylmethyl-amino)-methyl]-pyridin-2-yl}-thiourea (MTUBo). X-ray crystallographic analysis has shown this ligand forms a mononuclear complex with copper(II) and co-ordinates via a trigonal bipyramidal N4S array of donor atoms. Promisingly, cell uptake studies revealed that (64)Cu-MTUBo selectively accumulates in EMT-6 cells incubated under hypoxic conditions which may result from its relatively high Cu(II/I) redox potential. Small-animal PET imaging and ex vivo biodistribution studies in EMT-6 tumor bearing BALB/c mice revealed significant tumor uptake after 1 h p.i., yielding tumor-to-muscle (T/M) and tumor-to-blood (T/B) ratios of 8.1 and 1.1, respectively. However, injection of (64)Cu-acetate resulted in similar uptake indicating that the observed uptake was most likely non-specific. Despite showing high in vitro stability, it is likely that in vivo the complex undergoes transchelation to proteins within the blood in a relatively short timeframe. For comparison, the hypoxia imaging agent (64)Cu-ATSM was also evaluated in the same murine tumor model and showed about 60% higher tumor uptake than (64)Cu-MTUBo.

The synthesis of a thiourea substituted derivative of tris(pyridyl-2-methyl)amine (TPA) is reported. Two of the three pyridine rings are substituted in the 6-position with benzoylthiourea groups. These thiourea groups undergo intramolecular hydrogen bonding to form six-membered rings which leaves one N-H group available to form hydrogen bonds with other molecules. This reports details how the complexation of this new ligand with transition metal ions yields complexes with differing geometries. Seven co-ordinate Mn(II) and Cd(II), six co-ordinate Ni(II) and five co-ordinate Co(II), Cu(II) and Zn(II) complexes have been isolated.

A Zn 2+ specific GdDOTA derivative containing two bis-(3-pyrazolyl) units was prepared and characterized. Unlike a previously reported Zn 2+ binding agent, the new agent binds to human albumin both in the presence and absence of Zn 2+ .

We report the facile and efficient synthesis of a novel cryptand using a one-pot method involving a Pd(II)-catalysed carbonylation reaction. The crystal structure of the corresponding Cu(II) cryptate is also described.

The synthesis of the novel ligand tris(2,2'-bipyrid-6-yl) methanol (L(1)) is described. Co-ordination of the ligand to the first row transition metals (Mn(2+)-Zn(2+)) as well as Cd(2+) showed that the ligand formed complexes close to trigonal prismatic in geometry in the solid state. Analysis of the geometry of the co-ordination spheres showed varying degrees of trigonal prismatic and octahedral character. For each d-electron configuration, this could be related to the relative differences in ligand field stabilisation energies for the two geometries.

The synthesis of a new functionalised bis-macrocyclic ligand (L1) is described together with the corresponding Ln(III) complexes, Ln(2)- (Ln = Gd(III), Eu(III)). Phosphorescence measurements on Gd(2)- at 77 K allowed the ligand-centred triplet state ((3)pi-pi*) to be estimated at ca. 28500 cm(-1). Steady state and time-resolved measurements confirmed emission from the f-centred excited state ((5)D(0)) for Eu(2)-. (1)H NMRD profiles revealed the longitudinal proton relaxivity (r(1)) of Gd(2)- to be 8.3 mM(-1)s(-1)(30 MHz, 25 degrees C). The interaction of Cu(II) and Hg(II) with the lanthanide complexes was probed using luminescence and relaxivity measurements. Addition of Cu(II) (10 eq.) resulted in quenching of the Eu(III) emission, but no increase in r(1) of the Gd(III) dimer. Addition of Hg(II) (10 eq.) caused changes to the hypersensitive emission bands of Eu(III) together with an increase in r(1) of Gd(2)- to be 10.3 mM(-1)s(-1)(30 MHz, 25 degrees C) suggesting a net increase in hydration at the Gd(III) centres.

A tripodal tris-8-aminoquinoline ligand was synthesised in high yield via the Bucherer reaction. The septa-dentate ligand was found to give isolable complexes when coordinated with transition metals. Complexes of zinc(ii), cadmium(ii) and cobalt(iii) were isolated and their solid state structures were determined by single crystal X-ray diffraction. The solid state structures of these complexes were compared to the solution (1)H NMR data which was obtained for each complex. The two first row metals both gave octahedral six coordinate structures, although the two metals were coordinated by a differing donor set of heteroatoms. The cadmium complex was found to contain a seven coordinate cadmium centre in the solid state. DFT calculations were carried out in order to give an indication as to why the two different six coordinate binding modes were encountered.

Unlike their octahedral analogues, copper(II) compounds with trigonal prismatic stereochemistry undergo an elongation of two bonds in cis positions due to a Jahn-Teller effect, a behavior that can also occur in slightly twisted octahedra.

The co-ordination of a series of terpyridine-N-oxide ligands to the Cu(ii) ion is reported. Addition of two equivalents of ligand results in the formation of the expected 2 : 1 six co-ordinate product, while the addition of one equivalent of ligand allows the isolation of 1 : 1 species if the ligand has a meridonal binding mode. The five complexes isolated were characterised in the solid state by X-ray crystallography while they are studied in solution using EPR, UV-vis spectroscopy and IR spectroscopy.

A series of lipophilic and hydrophilic fac tricarbonyl rhenium bisimine complexes have been prepared, their membrane-permeabilities explored in liposomes and their potential for application in fluorescence microscopy cell imaging demonstrated in the first application of MLCT-fluorescent rhenium complexes in cell imaging.

The homohexanuclear complexes [Ni2[Ni(L1)]4](BF4)4 x MeCN, 1, [Pd2(Pd(L2)]4](BF4)4, 2, and the heteropentanuclear aggregate [Cu2[Ni(L3)]3](PF6)2, 3, all adopt a 'pinwheel' type structural motif via thiolate bridging between square-planar Ni(II) or Pd(II) and between trigonal planar Cu(I) centres, respectively.