The thermal properties of a synthetic LDH, intercalated with benzoate or terephthalate, are investigated using powder X-ray diffraction. After synthesis at 75 degrees C, both are found to show expanded interlayer structures, the benzoate intercalate resulting in a slightly larger interlayer distance (15.4 Angstrom compared to 14.0 Angstrom). The LDH terephthalate is stable to 250 degrees C, but the LDH benzoate interlayer spacing collapses to about 9.0 Angstrom at less than 100 degrees C. This process is reversible on rehydration. Evidence is also found of anion ordering in the [110] plane, with a superlattice parameter of root 3a, in the case of LDH benzoate. Synthesis at 200 degrees C and 10 atm (HTP) is shown to result in very different properties. The LDH benzoate (HTP) shows no interlayer expansion, whilst the LDH terephthalate (HTP) shows the same room temperature structure as before, but is thermally unstable, collapsing to a layer spacing of about 8.8 Angstrom by 150 degrees C. Again, this layer collapse is reversible on rehydration. These new properties are explained as being a result of the high-temperature and -pressure synthesis favoring an Mg:Al ratio of 3:1 as opposed to 2:1 in the "normal" structure. An intermediate, regularly interstratified structure is also identified at 75 degrees C in LDH terephthalate (HTP), consisting of alternating collapsed and expanded layers. This is the first such structure observed in an LDH-like material and demonstrates the importance of forces between layers which are not immediate neighbors. In almost all the above cases the hydroxides in opposing faces of adjacent layers are found to be prismatic, resulting in a three-layer repeat distance and a rhombohedral unit cell (AC=CB=BA=AC). The one exception to this is the case of collapsed LDH terephthalate (HTP) layers, where the interlayer is octahedral (AC-AC); this can be rationalized in terms of the rigidity of the bifunctional terephthalate molecule, which binds to both faces of the interlayer region, so constraining its possible geometry. The consequence of this is that the regularly interstratified LDH terephthalate (HTP) 75 degrees C structure has a six-layer repeat and rhombohedral unit cell (AC=CB-CB=BA-BA=AC-AC), the expanded interlayers being prismatic, whilst the collapsed ones are octahedral.