A series of mononuclear cyclometalated benzo[h]quinolinate platinum and palladium(II) complexes with phosphine ligands, namely, [M(bzq)CIL] (L = PPh2H, Pt 1, Pd 2; PPh2C equivalent to CPh, Pt 3, Pd 4), [Pt(bzq)(PPh2H)(PPh2C equivalent to CPh)]CIO4 5, [Pt(bzq)(PPh2C(Ph) = C(H)PPh2)]CIO4 6, and [Pt(bzq)(C equivalent to CPh)(PPh2C equivalent to CPh)] (7a, 7b), were synthesized. The X-ray crystal structures of 1, 6 center dot CH(3)COCH(3)center dot 1/2CH(3)(CH2)(4)CH3, and 7b-CH3COCH3 have been determined. In 1, the metalated carbon atom and the P atom are mutually cis, whereas in 7b they are trans located. For complex 6, C and N are crystallographically indistinguishable. Reaction of [Pt(bzq)(mu-Cl)](2) with PPh2H and excess of NEt3 leads to the phosphicle-bridge platinum dimer [Pt(bzq)(mu-PPh2)](2) 8 (X-ray). Moderate pi-pi intermolecular interactions and no evident Pt-Pt interactions are found in 1, 7b, and in 8. All of the complexes exhibit absorption bands at high energy due to the intraligand transitions ((IL)-I-1 pi ->pi*) and absorptions at lower energy which are attributed to MLCT (5d) pi ->pi* ((CN)-N-Delta) transition. Platinum complexes show strong luminescence in both solid state and frozen solutions. The influence of the coligands on the photophysics of the platinum complexes has been examined by absorption and emission spectroscopy.