A series of novel heterometallic square complexes with the general molecular formulas {fac-Br(CO)(3)Re[mu-(pyterpy)(2)M]}(4)(PF6)(8) and {(dppf)Pd[mu-(pyterpy)(2)Ru]}(4)(PF6)(8)(OTf8 (4), where M = Fe (1), Ru(2), or Os (3), pyterpy is 4 '-(4 ' ' ' -pyridyl)-2,2 ' :6 ' ,2 " -terpyridine, dppf = 1,1 " -bis(diphenylphospkino)ferrocene and OTf is trifluoromethanesulfonate; were prepared by self-assembly between BrRe(CO)(5) or(dppf)Pd(H2O)(2)(OTf)(2) and (pyterpy)2M(PF6)2. The obtained NMR spectra, IR spectra, electrospray ionization mass spectra, and elemental analyses are ah consistent with the proposed square structures incorporating terpyridyl metal complexes as bridging ligands. Multiple redox processes were observed in all square complexes. All four complexes display strong visible absorptions in the region 400-600 nm, which are assigned as metal (Fe, Ru, or Os)-to-ligand (pyterpy) charge transfer (MLCT) bands. Square 3 exhibits an additional weak band at 676 nm, which is assigned to an Os-based (MLCT)-M-3 band. For:each complex, the bands centered between 279 and 377 nm are assigned as pyterpy-based pi-pi* bands and the Re-based MLCT band. Square 3 is luminescent in room-temperature solution, while squares 1, 2, and 4 do-not have any detectable luminescence under identical experimental conditions.