Tetrakis(pentafluoroorthotellurate)carbon(IV), C(OTeF5)(4), was synthesized by reaction of CBr4 with BrOTeF5 in SO2ClF solution at -78 degrees C and was isolated as a colorless, crystalline solid that is room-temperature stable in SO2ClF and in the solid state. Both natural abundance and 99% C-13-enriched C(OTeF5)(4) have been characterized in SO2ClF solution by C-13, F-19, and Te-125 NMR spectroscopy. In contrast, C(OTeF5)(4) undergoes rapid decomposition to O(TeF5)(2) and CO2 in CH3CN at 10 degrees C but is stable at -40 degrees C. The X-ray crystal structures of C(OTeF5)(4) and [N(CH3)(4)][B(OTeF5)(4)] were determined at -30 and -170 degrees C, respectively. The averages of four smaller C/B-O-Te bond angles and O center dot center dot center dot O contacts and two larger C/B-O-Te bond angles and O center dot center dot center dot O contacts of C(OTeF5)(4) and the isoelectronic B(OTeF5)(4)(-) anion are consistent with local S-4 symmetry, as predicted by ligand close packing considerations. The existence of three sets of Te-O-C/B-O torsion angles and the energy-minimized geometries of C(OTeF5)(4) and B(OTeF5)(4)(-) also confirm their local S-4 symmetries. The low-temperature, solid-state Raman spectra of C-12/13(OTeF5)(4) and B(OTeF5)(4)(-) were assigned and compared. The energy-minimized geometries, vibrational frequencies, natural charges, and natural bond orders of both species have been calculated using density functional theory methods. The calculated geometries are in accord with the S-4 symmetries assigned for the experimental structures.