In order to investigate the unusual oxidation properties of a meso-substituted porphyrin, tetrakis(3,5-di-tert-butylhydroxyphenyl)-porphyrin (H[2]T[t]BHPP), X-ray crystallography and computer modelling have been used. The crystal structure of a number of complexes of TtBHPP (Pd(II), Zn(II), Ni(II), Fe(III)Cl and Ha[4][2+]), its oxidation product, H[2]PDM, and (H[2]O)ZnTPP have been determined. The Pd(II) and Zn(II) complexes have unusual structures, with approximately 28 cyclohexane solvent molecules per unit cell very loosely bound within the lattice. The Ni(II) complex has the most extensively ruffled core reported for a metalloporphyrin, with a short Ni-N bond distance 1.913(3)A. The crystal structures of H[2]PDM.6H[2]O and [H[4]T[t]BHPP][2+][Zn(CF[3]COO)[4]][2-]. 6H[2]O show interesting clathrate-like structures with extensive intermolecular hydrogen-bonding. The oxidised porphyrin, H[2]PDM, has a tetraquinone structure in the solid state which contrasts with the proposed diquinone/diphenol structure found in solution. Molecular Mechanics and Molecular Orbital calculations were used to investigate both geometric and electronic structures of the porphyrins and their oxidised counterparts. Due to the size and complexity of these calculations and the lack of experimental data these methods were not as useful as anticipated. The difference in behaviour of various metallo complexes of T[t]BHPP to oxidation is attributed to electronic effects rather than the geometric structures of the metalloporphyrins.