Two new bis(dipivaloylmethanate)nitrato-bis(triphenylphosphine oxide)lanthanide(III) complexes [Eu(dpm) 2 (NO 3 )-(tppo) 2 ] (1) and [Tb(dpm) 2 (NO 3 )(tppo) 2 ] have been prepared in monomeric form. The structural behavior of these coordination compounds is significantly different from those of [Eu 2 (dpm) 6 ] and [Tb 2 (dpm) 6 ] dimeric complexes. The photoluminescent properties of the monomeric and dimeric complexes are dependent on the energy positions of the low-lying ligand-to-metal charge-transfer (LMCT) state, which may be correlated with the chelating and chelate bridging [a]