Powder neutron diffraction and magnetic susceptibility measurements of the antiferromagnetic phases of Mn_xNi_1-xO,Mn_xCo_1-xO, (Mn_xFe_1-x)_zO and (Co_xFe_1-x)_zO reveal that the magnetic moments of unlike ions are always effectively collinear, despite the presence of competing anisotropies. The magnetic moments of Mn_xNi_1-xO (x = 0.24,0.48 and 0.77) at 5K are confined to (111) planes by dipole-dipole forces, and the small trigonal exchangestrictions are the products of opposed antiferromagnetic Mn²⁺-Mn²⁺ and ferromagnetic Ni²⁺-Mn²⁺ nearest neighbour interactions. In Mn_xCo_1-xO (x = 0.05, 0.10, 0.25,0.36) at 5K, the orbital degener- acy of Co²⁺ is removed by both Jahn-Teller (J.T) and spin-orbit coupling (S.O) mechanisms, leading to orthorhombic or triclinic symmetries and partially quenched Co²⁺ moments. Monoclinic symmetry is observed for 0.51<x<0.67, and Jahn-Teller stabilisations and spin-only Co²⁺ moments are evident. The cobalt concentration is too small to support a cooperative J.T stabilisation in Mn_0.83Co_0.17O, where a magnetostriction (c/a < 1) is observed (in agreement with previous AFMR results). Previous results for Co_xNi_1-xO, and those for Mn_xCo_1-xO, (Mn_xFe_1-x)_zO (x = 0.05, 0.1, 0.12, 0.23, 0.36,0.56,0.66,0.89) and (Co_xFe_1-x)_zO (x = 0.04,0.12,0.50,0.63,0.81) at 5K indicate that the anisotropy order for the iron group monoxides is CoO>MnO»Fe_zO≈NiO. The weak trigonal anisotropy of Fe²⁺ correlates with the near-cubic symmetries of (Co_xFe_1-x)_z( (x = 0.04,0.12) and (Mn_xFe_1-x)_zO (0.1<x<0.66), and a tetragonal (c/a>1) magnetostriction of Fe²⁺ is observed in (Co_xFe_1-x)_zO with x > 0.5. Measurements of vacancy-ferric interstitial ratios for (Mn_xFe_1-x)_zO and (Co_xFe_1-x)_zO suggest that non-stoichiometry is accommodated by 6:2 or 8:3 defect clusters in the former, and by larger units in the latter. The observed magnetic moments of defective samples are normally larger than those calculated according to a previous model for Fe_zO, and require the postulation of partial antiferromagnetic order around the clusters. The room temperature Mossbauer effect parameters of (Mn_xFe_1-x)_zO (0<x<0.975,0.910<z<1.0) indicate that while Fe²⁺ and Mn²⁺ ions are randomly distributed over octahedral sites, ferric ions are localised around defect clusters.

Submitted in the fulfillment of the requirement for the Master's Degree in Chemistry,Durban University of Technology, 2017. / Knoevenagel condensation reaction is a useful protocol for the formation of C=C bond in organic synthesis. This protocol is extensively utilized by synthetic chemist to generate dynamic intermediates or end-products such as perfumes, polymers, pharmaceuticals and calcium antagonists. The reaction is catalyzed by bases such as ammonia, primary and secondary amines, quaternary ammonium salts, Lewis acids, catalysts containing acid-base sites, which are carried out under homogeneous conditions. This necessitates the use of organic solvent which generate the large volumes of solvent waste. From green chemistry perspective, solvent free heterogeneous catalysts have received considerable attention. Since, these heterogeneous catalysts not only avoid the use of organic solvents but also suppress side reactions such as self-condensation and oligomerisation leading in better selectivity and product yield. In recent years, therefore, the use of heterogeneous catalyst, their recovery and reusability are in demand in industry. The use of cobalt, iridium and platinum hydroxyapatites, MgO/ZrO2, MgO/HMCM- earlier been reported in the literature, and used as heterogeneous catalysts for the Knoevenagel condensation of aldehydes and esters. Based on these evidences, we envisioned that MgO and VMgO could also be used as heterogeneous catalysts for this reaction. Magnesium oxide was synthesized from three precursors, viz. magnesium nitrate, magnesium carbonate and magnesium acetate. Magnesium oxide prepared from magnesium nitrate precursor was found to be the optimum giving an 81 % product yield. Vanadium-magnesium oxide catalysts with different vanadium loadings; 1.5, 3.5 and 5.5 wt. %, were synthesized by wet impregnation of magnesium oxide with aqueous ammonium metavanadate solution. The synthesized catalysts were characterized by ICP-AES, FTIR, Powder XRD, SEM-EDX and TEM. The Knoevenagel condensation reactions between benzaldehyde and ethyl cyanoacetate were carried out in a 100 mL two-necked round bottom flask equipped with a reflux condenser, magnetic stirrer and a CaCl2 guard tube. An equimolar quantity (10 mmol) of substrates and 0.05g of catalyst were added to the flask and heated at 60 °C, stirred vigorously for the required time. The yields were determined using GC-FID equipped with a capillary column. Elemental composition of the catalysts (vanadium and MgO) was determined by ICP-AES. IR spectra of MgO showed that magnesium oxide was the only phase present in the catalysts prepared from different precursors. The 1.5 and 5.5 wt. % VMgO showed weak bands attributed to pyrovanadate and orthovanadate phases present in small quantities. The phases manifested more with the increase in the vanadium concentration (3.5 and 5.5 wt. % VMgO). The diffraction patterns of all the catalysts showed the existence of MgO and magnesium orthovanadate. The morphology of the catalysts with increasing vanadium was more affected by precursor treatment rather than chemical differences. Electron microscopy showed that the VMgO surface is only sparingly covered with vanadium and MgO showed stacked with large rounded particles. Good to excellent yields were obtained for the MgO catalysts: MgO(1) 68 %, MgO(2) 65 %, MgO(3) 72 %, MgO(P) 73 % and MgO(DP) 82 %. Excellent yields were obtained for the VMgO catalysts: 1.5VMgO 83 %, 3.5VMgO 91 % and 5.5VMgO 97 %. The 5.5VMgO catalyst was found to be the optimum catalyst and was further tested for it activity using different aldehyde substrates. Excellent yields of the products were obtained for benzaldehyde 97 %, nitrobenzaldehyde 94 %, bromobenzaldehyde 96 %, chlorobenzaldehyde 93 % and methoxybenzaldehyde 95%. / M