Monash University
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Advances in rare earth and alkaline earth 8-quinaldinolate and pyrazolate chemistry

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posted on 2017-02-03, 03:41 authored by Urbatsch, Aron
This thesis is concerned with two primary themes. Firstly, it describes the synthesis and structural characterisation of new homoleptic rare earth/alkaline earth (RE/AE) heterobimetallic complexes involving a 8-hydroxyquinoline derivative (2-methyl-8-hydroxyquinoline, 8-quinaldine, HMQ) accessed via pseudo-solid-state rearrangement reactions at elevated temperatures. Secondly, it focuses on the synthesis and characterisation of air- and moisture-sensitive RE and AE metal complexes of new unsymmetrically substituted pyrazolate ligands. These pyrazolate complexes were synthesised by either redox transmetallation/protolysis reactions involving the pyrazole and the organomercurial Hg(C6F5)2, or by direct reaction of the metal with the pyrazole after activation of the free metals by iodine. This work contributes significantly to the number of structurally characterised heterobimetallic RE/AE compounds containing HMQ. It also greatly broadens the insight into the coordination behaviour of unsymmetrically substituted pyrazolate ligands. Chapter 2 describes the synthesis and characterisation of homoleptic RE/AE heterobimetallic derivatives of 8-quinaldinolate. Rearrangement reactions between powdered RE(MQ)3 and AE(MQ)2 metal chelates in the presence of the flux 1,2,4,5-tetramethylbenzene (TMB) at elevated temperatures afforded the trinuclear and linear [Ln2AE(MQ)8]•xTMB (AE = Mg; Ln = Eu, Gd, Tb; x = 1/3; Ln = Er; x = 0; AE = Ca; Ln = La, Eu; x = 0) complexes. They also produced the homometallic [Mg4(MQ)8] complex and the structurally similar heterobimetallic [Sc2Mg2(MQ)8(OH)2]•2TMB species. Furthermore, the tetranuclear [Eu3Ba(MQ)11]•2TMB was structurally characterised. PXRD measurements on the bulk powders confirmed the presence of the structurally characterised complexes. Chapter 3 expands the pseudo-solid-state syntheses of homoleptic MQ complexes to include alkali metals and small inorganic anions. The polymeric [RbLn(MQ)4]n (Ln = Tb, Er) complexes and the unprecedented monomeric [KYb2(MQ)7] species, as well as the dimeric [Cs2(MQ)2(HMQ)2] complex are amongst the isolated structures. Furthermore, the first example of the η1(O)-μ3-η1(O’):η1(O’):η1(O’)-η1(O’’) carbonate ligation mode was found in the heteroleptic [Ln3(MQ)7CO3] (Ln = Eu, Er) complexes. In addition, the tetranuclear complexes [Eu4(MQ)8(μ4-O)Cl2] and [Eu4(MQ)8Cl4] showed a μ4-O cage derivative in the former, and a more linear arrangement of the ligands in the latter, both containing bridging chloro ligands. Crystallisation from an Et2O suspension yielded the triangular [Eu3(MQ)8(OH)]•2Et2O complex. Part of this research was undertaken on the MX1 beamline at the Australian Synchrotron. Chapter 4 investigates the synthesis and structural characterisation of divalent complexes of the unsymmetrically substituted 3-(2’-thienyl)-5-(trifluoromethyl)pyrazolate (ttfpz) ligand. Redox transmetallation/protolysis reactions in donor solvents produced the [M(ttfpz)2(thf)4] (M = Yb, Ca, Sr, Ba; thf = tetrahydrofuran) and [M(ttfpz)2(dme)n] (M = Ca, Sr, Yb, n = 2; M = Ba, n = 3; dme = 1,2-dimethoxyethane) complexes. The monomeric structures exhibit η2-bound pyrazolate ligands with eight-coordinate metal atoms for all complexes, except for the ten-coordinate barium complex [Ba(ttfpz)2(dme)3]. Chapter 5 is devoted to the synthesis and characterisation of trivalent [RE(ttfpz)3(solv)x] complexes. The same synthetic pathway, as described in Chapter 4, afforded the monomeric tris-thf complexes [RE(ttfpz)3(thf)3]•nsolv (RE = La, solv = PhMe, n = 0.5; RE = Sm, n = 0) and the bis-thf derivatives [RE(ttfpz)3(thf)2] (RE = Sc, Y, Ho, Lu). Reactions in dme led to the isolation of [RE(ttfpz)3(dme)2]•nsolv (RE = La, n = 0; solv = Et2O, n = 1; Eu, solv = dme, n = 1). Iodine activation reactions yielded [Tb(ttfpz)3(thf)3]•thf and also the hydrolysed [Er2(ttfpz)2(μ2-OH)2(dme)4]I2•2(ttfpzH) complex. In the pseudo-octahedral tris-thf derivatives, the pyrazolate and thf ligands display a change from a facial to a meridional arrangement corresponding with the change of the RE metal from La to Tb. Finally, in Chapter 6 the synthesis of some new symmetrically and unsymmetrically substituted pyrazoles and their complexation with a variety of metals is described. 3,5-Di-(2-furanyl)pyrazole (fu2pzH), 3,5-di-(2-thienyl)pyrazole (t2pzH) and the unsymmetrical 3-phenyl-5-(2-thienyl)pyrazole (PhtpzH) and 3-(2-furanyl)-5-(2-naphthyl)pyrazole (fu2nappzH) were synthesised and spectroscopically and structurally characterised. They were used in redox transmetallation/protolysis reactions in donor solvents and gave the divalent [Ca(Phtpz)2(thf)4] and [Ca(fu2nappz)2(thf)4•thf complexes, the trivalent [La(fu2pz)3(thf)3]•2thf and the dimeric hydroxide-bridged [Yb2(Phtpz)4(OH)2(thf)4]•3.5thf complex. Iodine activation reactions were further established as a general route to these pyrazolate complexes. They gave [Ba(Phtpz)2(thf)4] and the divalent [Yb(Phtpz)2(dme)2] complex. Moreover, [Yb(Phtpz)I(thf)4] is a heteroleptic iodo-containing species bearing an iodo ligand in a transoid arrangement with the Phtpz ligand. Part of this research was also undertaken on the MX1 beamline at the Australian Synchrotron.


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Principal supervisor

Peter C. Junk

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Doctor of Philosophy

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Faculty of Science

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