Six novel series of mononuclear ortho-palladated and ortho-platinated metallomesogens have been obtained by combination of rod-like heteroaromatic liquid crystals with bent or half-disc-shaped 1,3-diketonate units. The synthesis of these molecules was achieved by ortho-metallation of rod-like 2-phenylpyrimidines and 2-phenylpyridines, with formation of the corresponding chloro-bridged dinuclear metallomesogens. Ligand exchange with alkoxy-substituted thallium 1,3-diphenyl-1,3-diketonates led to the desired mononuclear metallomesogens, incorporating a rod-like ortho-metallated heteroaromatic core and bent or half-disc-shaped 1,3-diketonate ligands. The liquid crystalline properties of these molecules were investigated using polarized light optical microscopy, differential scanning calorimetry and X-ray scattering. By increasing the number of alkyl chains attached to the 1,3-diketonate units, a transition from lamellar (SmA, SmC) and nematic to two distinct types of hexagonal columnar phases (Colh) was found, but no cubic phase could be detected. In the Colh phases, depending on the number of attached chains, either only one or two molecules are organized side-by-side within the columns. However, apart from the number of alkyl chains, their distribution on the 1,3-diketonate units is of importance to the mesophase behavior. Elongation of the calamitic subunit (2,5-diphenylpyrimidines) stabilizes smectic phases and Colh phases having two molecules in their cross-section (edge-to-edge dimers). The ortho-metallated 2-phenylpyridine unit has, for the first time, been introduced into metallomesogens. However, ortho-palladated and ortho-platinated 2-phenylpyridines are either non-mesogenic or have significantly lower mesophase stabilities than the corresponding pyrimidine derivatives. Replacement of palladium by platinum does not significantly influence the mesophase type, but it can have a mesophase-stabilizing effect, due to stronger d8–d8 closed-shell interactions between the Pt atoms.