Novel polymetallic 3d and 3d-4f complexes using 2-methyl-8-hydroxyquinoline (mQ) and Aminoethyl phosphonic acid (AEP) have been synthesised. All the complexes have been characterised by elemental analysis, X-ray crystallography, and investigated by magnetic measurements. The introduction covers the significant properties of 8-hydroxyquinoline derivatives ligands, and some previous reports of polymetallic 3d and 3d-4f complexes using 8-hydroxyquinoline (HQ) and its derivatives in literature. In chapter 2, the heterometallic penta-metallic isostructural compounds with a formula of [Ni4Ln(O2CtBu)2(mQ)8]NO3.xMeOH where Ln = NdIII, SmIII, EuIII, GdIII, DyIII and x = 4, 1, 2, 1, 1 respectively have been synthesised, and also characterized by using singleâcrystal X-ray diffraction analyses. The complexes are assembled by the binding action of the eight mQ- ligand with different Harris notation 3.31 and 2.21 bridging modes and two pivalate ligands with 2.11 bridging mode. In chapter 3, two new families of heterometallic tetra-metallic complexes with a formula of [Ni3Ln(mQ)8]NO3.3MeOH.H2O (Ln = SmIII, EuIII, GdIII, TbIII, DyIII, HoIII, YIII, and ErIII) and tri-metallic compounds with a formula of [Ni2Ln(mQ)4(MeO)(MeOH)n(NO3)2].xH2O (where, Ln are the following: LaIII, PrIII, NdIII, SmIII, EuIII, GdIII, TbIII, DyIII, HoIII, YIII, ErIII, whereas n equal ten for LaIII, PrIII, NdIII and nine for the remaining metals, while x equal one for PrIII, NdIII, DyIII, HoIII and two for the remaining metals except ErIII that has zero x value) were prepared and characterised. The tetra-metallic complexes are isostructural and connected by eight fully deprotonated mQ- ligands with different Harris notation 2.21 and 3.31 bridging modes. Correspondingly, the tri-metallic complexes are connected to each other through four mQ- ligands, and methoxy group. In chapter 4, three di-metallic NiII compounds with a formula of [Et2NH2][Ni2(mQ)4X] where X= MeCO2 (1), NO3 (2) and Br (3) are reported and characterised. X-ray crystallography confirmed that the two Ni ions bridged by two mQ- and one (MeCO2) ligands in compound 1, while the two Ni ions bridged by three mQ- ligands in compounds (2) and (3). All the Âµ-mQ- ligands adopt the 2.21 bridging mode. In chapter 5, a new multi-metallic nickel amino-phosphonate complex with a formula of [Ni12(O3PC2H4NH2)2(O2CtBu)10(Âµ3-MeO)6(MeOH)2(Âµ3-OH)2(Âµ4-OH)2(i-PrOH)4].3H2O was obtained. Single-crystal X-ray diffraction revealed a symmetrical crystalline structure containing 12 Ni nuclei connected by aminoethyl phosphonate ligands with 7.322 bridging mode and pivalate ligands.