Chen, Vanessa; (1999) Magnetic and structural studies of amine inclusion complexes of metal oxyhalides. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is concerned with the structural and magnetic properties of metal oxyhalides, MOX (M= Ti, V, Cr, Fe; X= Cl, Br) and their intercalation chemistry with alkylamines, CnH2n+1NH2 (n= 1-10) and the diamines, such as H2N(CH2)nNH2, n= 2, 3, and 8. The crystal structure of MOX is reported to be of the same type as FeOCl. MOX samples were prepared by solid state reactions and their structures confirmed as orthorhombic by X-ray powder diffraction measurements. The intercalation of CnH2n+1NH2 with MOX occurred easily for TiOC1, TiOBr, VOC1 and VOBr, but could not be performed successfully for CrOC1. TGA analysis studies on (CnH2n+1NH2)yMOX show one step weight losses due to CnH2n+1NH2. The IR spectra of (CnH2n+1NH2)yMOX contain the M-O and M-Cl bands from MOX and the C-H, and N-H bands from CnH2n+1NH2. This is consistent with the MOX and CnH2n+1NH2 remaining unchanged during the intercalation process. On intercalation, CnH2n+iNH2 causes the layers of MOX to be expanded in the (001) direction and the alkyl chains aggregate into a bi-layers tilted at angles of 53° - 69° with respect to the chloride layers. The increase of the basal spacing follows an odd - even alternation which indicates that the orientation of the alkylamine is in a trans-trans conformation. The products of the TiOC1- H2N(CH2)nNH2 intercalations suggest that the orientation of the diamine is arranged in a bilayer with bent molecules. IR spectroscopy, EDAX and quantitative analysis confirmed the formation of substituted products [eg; (C2H7N2)0.50TiOCl0.50, (C2H7N2)0.61TiOCl0.39] after longer reaction times. Magnetic susceptibility measurements showed that the layer compounds MOX and (CnH2n+1NH2)yMOX are paramagnetic materials (apart from CrOCl, which is antiferromagnetic). This is due in part to the frustrated environment of the superexchange interaction between the metal ions. To determine the effective moment of the intercalated samples, the diamagnetic susceptibility from CnH2n+1NH2 had to be taken into the consideration. With intercalation of longer alkylamines, the titanium ions in (CnH2n+1NH2)yMOX showed an increase of effective moment while the vanadium ions showed a decrease of effective moment. These effects might be ascribed to charge transfer between MOX and the amine.

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