New macrocyclic reagents for heavy metals

Vasilescu, Ioana Monica (2010) New macrocyclic reagents for heavy metals. PhD thesis, James Cook University.

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A series of potentially pentadentate, unsymmetrical, mixed donor systems of type I, based on the corresponding 'symmetrical' macrocycles synthesised over many years in the author's laboratory, have been synthesised during the course of this project. Chapter 1 includes a review of these latter ligands along with aspects of their metal ion chemistry towards Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ag(I) and Pb(II) and serves as a background for the author's (related) results presented in subsequent chapters of the thesis.

[Figure of Type I]

X = S or O Y = NH, S or O n = 2 or 3 m = 2 or 3

The synthesis of the new unsymmetrical macrocycles involved, in each case, the Schiffbase condensation between the appropriate linear di- or tri-amine and unsymmetrical dialdehyde precursors, followed by in situ reduction of the resulting diimine. The preparation of the unsymmetrical dialdehyde precursors is also described. The extensive organic ligand synthetic studies resulted in successful isolation and characterisation of a range of 17- and 18-membered, unsymmetrical, mixed-donor rings which are described in Chapter 2.

Selected crystalline Ni(II), Cu(II), Cd(II) and Ag(I) complexes of the new 17-membered mixed donor macrocycles suitable for X-ray diffraction analysis were isolated: [NiLCl]⁻ Cl·3H₂O(L = 138), [NiLCl]Cl·0.125CH₃CN·3.75H₂O (L = 142), [CuLCl₂]·CH₃CN(L = 138), [CuLCl₂]·CH₃CN(L = 142), [CuLCl]Cl·2.375H₂O(L = 141), [CdL(NO₃) ₂]·CH₃OH (L = 138), [CdL(NO₃)] (NO₃)·CH₃CH₂OH (L = 132), [AgL]PF₆ (L = 132) and [AgL]PF₆ (L = 141) as well as the metal-free diprotonated nitrate salt (LH₂)(NO₃)₂ (L = 137). The results of the corresponding X-ray studies, presented in Chapter 3, revealed that the Ni(II) species display distorted octahedral geometries, with the respective macrocycles acting as pentadentate ligands. Cu(II) yields both five and six coordinate complexes in which the respective macrocycles act as both tridentate and pentadentate ligands; the coordination geometries vary from close to square pyramidal to distorted square pyramidal and distorted octahedral - largely reflecting the different affinities of the macrocyclic donors for this metal ion in each case. In the Cd(II) complexes the metal is seven-coordinate and binds to all the ligand donors with nitrate groups completing the coordination sphere. Ag(I) yielded complexes of two different structural types: in the first of these, the coordination geometry around silver can be described as close to square pyramidal, with the central metal coordinating to all five donors of the macrocyclic ring, while in the second, a one-dimensional coordination polymer was obtained.

The thermodynamic stabilities of the above unsymmetrical 17-membered rings were investigated with respect to their Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ag(I) and Pb(II) complexation in 95 percent methanol. The stabilities for these systems were found to follow the Irving-Williams order. The magnitude of the log K values obtained is strongly influenced by the number of nitrogen donors present in the macrocyclic donor set. The results confirmed previous observations that metal ion recognition can be 'tuned' by changing both the available donor set and the spatial arrangement of the respective donors for a given donor set in the macrocyclic backbone. Thus, for example, ligand I (X = Y = S, n = m = 2) showed very good discrimination for Ag(I) over Pb(II) relative to the other systems investigated, with a difference between the log K values of the respective complexes of 7.5.

The development of a simple procedure for modeling the metal complex stability constants of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ag(I) and Pb(II) complexes of dibenzosubstituted, 17-membered mixed-donor macrocycles of both symmetrical and unsymmetrical derivatives of the present type is described in Chapter 4. In general, quite good agreement with the experimentally determined log K values was obtained across the ligand series investigated. In addition, the results provide a means for predicting log K values for complexes of other systems of type I (n = m = 2) for which experimental data is not yet available.

Finally, previously documented ligand design strategies for achieving Ag(I) discrimination were successfully applied to the design and synthesis of a new Nbenzylated S₃N₂-donor macrocycle, which was demonstrated to show enhanced selectivity for Ag(I) over Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) in both log K and bulk membrane transport studies. The silver complex is at least 10⁵ more stable than any of the remaining complexes investigated. Suitable crystals for X-ray diffraction analysis were isolated for this complex. The structure of the complex cation (see II) shows that all macrocyclic donors coordinate to the Ag(I) centre, with the latter adopting a distorted square pyramidal geometry.

[Figure of Type II]

The current study demonstrates the structural diversity and metal ion discrimination behaviour that is possible from the use of potentially pentadentate ligands of general type I containing different donor set combinations – with different metal ion affinities – when reacted with transition and post-transition ions of the type mentioned above.

Item ID: 39167
Item Type: Thesis (PhD)
Keywords: inorganic chemistry; ligand synthesis; macrocycles; macrocyclic ligands; metal-ion selectivity; pentadentate ligands
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Baldwin, Darren S., Bowden, Bruce F., Duckworth, Paul A., Lindoy, Leonard F., Mccool, Brian J., Meehan, George V., Vasilescu, Ioana M., and Wild, S. Bruce (2002) New macrocyclic ligands: XIV. synthesis and X-ray structures of potentially pentadentate ligands incorporating non-symmetrically arranged N₄S⁻, N₃OS⁻, N₂O₂S⁻ and N₂S₂O-heteroatoms. Australian Journal of Chemistry, 55 (9). pp. 597-603.

Adam, Kenneth R., Baldwin, Darren S., Lindoy, Leonard F., Meehan, George V., Vasilescu, Ioana M., and Wei, Gang (2003) Metal-ion recognition. Modeling the stability constants of some mixed-donor macrocyclic metal ion complexes—a simple model. Inorganica Chimica Acta, 352. pp. 46-50.

Vasilescu, Ioana M., Bray, David J., Clegg, Jack K., Lindoy, Leonard F., Meehan, George V., and Wei, Gang (2006) Rational ligand design for metal ion recognition. Synthesis of a N-benzylated N2S3-donor macrocycle for enhanced silver(I) discrimination. Dalton Transactions , 2006 (43). pp. 5115-5117.

Lindoy, Leonard F., Meehan, George V., Vasilescu, Ioana M., Kim, Hyun Jee, Lee, Ji-Eun, and Lee, Shim Sung (2010) Transition and post-transition metal ion chemistry of dibenzo-substituted, mixed-donor macrocycles incorporating five donor atoms. Coordination Chemistry Reviews, 254 (15-16). pp. 1713-1725.

Date Deposited: 05 Aug 2015 23:43
FoR Codes: 03 CHEMICAL SCIENCES > 0302 Inorganic Chemistry > 030207 Transition Metal Chemistry @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 100%
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