title: Synthesis and characterisation of homometallic and heterometallic Co(II)/4f complexes: investigation of magnetic properties
Creators: name: Collet, Alexandra Foteini Tsampika
Publisher: name: University of Glasgow
Year: 2019
Subjects: subject: polynuclear coordination complexes, cobalt complexes, lanthanide complexes, microwave synthesis, solvothermal synthesis, single crystal X-ray diffraction, magnetic properties.

description: The work presented in this thesis describes the directed synthesis, structural and magnetic characterisation of new Co(II), Co(II)-4f and 4f complexes, using a range of polydentate ligands. The aim of this work was to synthesise new Co(II)-based complexes, in the presence or absence of 4f ions, where the cobalt centre would adopt different coordination numbers and geometries, in an attempt to tune the magnetic properties. We managed to isolate twenty new complexes and depending on the ligand employed they can be categorised in five groups. Complexes [CoII(H2bic)Cl] (1), [CoII9(Hbic)4(bic)2Cl4] (2) and [CoII9(Hbic)4(bic)2Cl4]·12H2O (2·12H2O) were synthesised using the ligand bicine (= H3bic, N,N-Bis(2-hydroxyethyl)glycine) by employing solvothermal and microwave−assisted synthesis. Complexes 1, 2 and 2·12H2O were magnetically characterised and only 2 shows the onset of out-of-phase ac signals at low temperature. The second family consists of three Co(II)/Co(III) complexes with the same triangular motif and with the Co(II) in a trigonal bipyramidal geometry: [CoIICoIII2(μ3-OH)(μ-pz)4(DBM)3]∙2THF (3∙2THF), [CoIICoIII2(μ3-OH)(μ-pz)4(DBM)3]∙2MeCN (4∙2MeCN) and [CoIICoIII2(μ3-OH)(μ-pz)4(acac)3] (5), where Hpz = pyrazole, HDBM = dibenzoylmethane and Hacac = acetylacetone. Magneto-structural analysis showed that complexes 3∙2THF and 4 show field-induced slow magnetic relaxation, while 5 shows only the onset of the out-of-phase signals at low temperature. The third group consists of polynuclear Co(II)-based complexes incorporating substituted phosphonate ligands along with dimethylpyrazole (= Hdmpz), exhibiting nuclearities from two to nine metal centres. These complexes are: [CoII9(tBuPO3)3(dmpz)12(Hdmpz)6]∙xMeCN∙yH2O (6∙xMeCN∙yH2O), [CoII3(tBuPO3)2(Hdmpz)4Br2] (7), [CoII8(EtPO3)3(dmpz)10(Hdmpz)6]∙xMeCN∙yH2O (8(MeCN)), [HNEt3][CoII8(EtPO3)3(dmpz)10(Hdmpz)6][ClO4]∙xDCM∙yH2O (9a(DCM)), [HNEt3][CoII8(EtPO3)3(dmpz)10(Hdmpz)6][ClO4]∙0.75(Hdmpz)∙2.25DCE∙H2O (9b(DCE)), [CoII3(dmpz)4(Hdmpz)2Cl2] (10), [HNEt3][CoII6(PhPO3)3(dmpz)6(Hdmpz)6][ClO4]∙DCM (11∙DCM) and [HNEt4]2[CoII2(dmpz)2Cl4] (12), where tBuPO3H2 = tert-butylphosphonic acid, EtPO3H2 = ethylphosphonic acid and PhPO3H2 = phenylphosphonic acid. Complexes 6 and 7 were magnetically characterised and ac magnetic studies showed only the onset of out-of-phase ac signals for 6, whereas complex 7 does not display slow magnetic relaxation. The next group is a family of six-coordinate mononuclear LnIII complexes which was obtained by utilising the ligand tricyclohexylphosphine oxide (= Cy3PO), with molecular formula [LnIII(Cy3PO)2Cl3(EtOH)]·yEtOH, where LnIII = Tb (13), Dy (14), Ho (15), Er (16) and Y (17), and y = 0.5 for 14 and y = 1 for 13, 15−17. Magnetic studies for complexes Tb (13), Dy (14) and Ho (15) revealed that only Dy (14) displays field-induced slow magnetic relaxation. The last family of complexes incorporates the ligand 2,6-bis[4(1-N-phenyl-3-methyl-pyrazolium-5-one)carbonyl]pyridinium trichloride (= [H5L]·3Cl) leading to a variety of 4f and Co(II)-4f complexes with nuclearities from one to nine metal centres. These complexes are [LaIII9(L2−)7(NO3)4(CO3)4(OH)(H2O)8]·xMeCN·yH2O (18·xMeCN·yH2O), [HNEt3][CeIII3(HL−)2(NO3)7(H2O)2][Cl]·xMeCN·yH2O·zEt2O (19a) and [HNEt3][CeIII3(HL2−)(H2L)(NO3)7(H2O)2][Cl]·xMeCN·yH2O·zEt2O (19b), [DyIII(HL−)2(H2O)4][Cl]·xMeCN·yH2O (20·xMeCN·yH2O), [CoII2LnIII(L2−)2(NO3)2.3Cl0.7(MeCN)] where Ln = La (21) and Ce (22), [HNEt3][CoIIDyIII2(L2−)4(HL−)(H2O)2]·xMeCN·yH2O (23·xMeCN·yH2O) and [GdIII6(L2−)4(OH)4(O2−)(MeOH)6(H2O)2][NO3]3.75[Cl]0.25∙xMeOH∙yH2O (24∙xMeOH∙yH2O). Magnetic studies were carried out only for the Co(II)-4f complexes, with complex 23 exhibiting field-induced slow magnetic relaxation.