The luminescence properties of trans-dioxo rhenium(V) and osmium(VI) [d2] and square-planar platinum(II) and palladium(II) [d8] transition metal complexes have been studied as a function of temperature and pressure. Both types of complexes studied have idealized D4h point group symmetry with the d2 systems representing the tetragonally compressed limit of a six-coordinate complex in the D4h point group and the d8 systems representing the tetragonally elongated limit. The observed luminescence in both classes of complexes has been assigned as a metal-centered (d → d) 3Eg → 1A1g transition. The application of external pressure provides a means to induce minor changes in the molecular geometries of these model systems that reveal the delicate interplay between structural and electronic properties. Pressure-dependent spectroscopic data are analyzed quantitatively using theoretical models adapted from high-resolution low-temperature spectra where emitting state displacements along vibrational coordinates are determined from resolved vibronic structure. These combined experimental and theoretical techniques allow for a full characterization of the ground and emitting state potential energy surfaces and their explicit dependence on structural parameters.