Structural and energetic features of the binuclear titanium carbonyls Ti-2(CO)(n) (n = 12, 11, 10) have been examined using density functional theory. The lowest-energy Ti-2(CO)(12) structure is a singlet structure consisting of two Ti(CO)(6) units linked by Ti-Ti double bonds of lengths 3.0-3.2 angstrom. A similar slightly higher energy triplet Ti-2(CO)(12) structure is found with longer Ti-Ti bonds (3.37-3.62 angstrom), considered to be formal single bonds. The energy required for the dissociation of Ti-2(CO)(12) into two Ti(CO)(6) fragments is 18.5 +/- 2 kcal/mol higher than the energy required for the dissociation of V-2(CO)(12) into two V(CO)(6) fragments. For the unsaturated Ti-2(CO)(11) system, the lowest-energy structures contain a four-electron-donor bridging eta(2)-mu-CO group and 10 terminal CO groups with formal Ti-Ti double bonds in the singlet structures and formal Ti-Ti single bonds in the triplet structures. Similarly, the most favored geometries for the more highly unsaturated Ti-2(CO)(10) contain two four-electron-donor bridging eta(2)-mu-CO groups with formal Ti-Ti double bonds for the singlet structures and formal Ti-Ti single bonds for the triplet structures. Higher-energy triplet Ti-2(CO)(10) structures are found with two or three two-electron-donor semibridging CO groups and formal Ti=Ti triple bonds of length 2.7-2.8 angstrom.