The title compounds [Pd-4(dmb)(4)(PPh3)(2)]Cl-2 (1) and {[Pd-4(dmb)(5)](CH3CO2)(2)}(n) (2) were prepared from the reactions Pd-2(dba)(3). CHCl3 + 2dmb + PPh3 for 1 (dba = dibenzylideneacetone) and Pd-2(dba)(3). S + excess dmb + Pd(O-2-CCH3)(2) for 2 (S = benzene or CHCl3), in good yields. The stuctures consist of quasi-linear Pd-4(2+) species (d(PdPd) 2.524(10), 2.524(10) and 2.534(10) Angstrom for 1 and 2.5973(18), 2.6080(18), and 2.6080(18) Angstrom for 2) where the dmb ligands bridge the Pd atoms, forming a catenate. While the PPh3 ligands axially coordinate the M-4 structure in 1, a fifth dmb bridges another Pd-4(dmb)(5)(2+) species, forming an organometallic polymer. From Raman spectroscopy, the two v(PdPd) active modes (v(1) and v(2)) are observed at 165 and 86 cm(-1), respectively, for 1 (F(PdPd) = 1.44 mdyn Angstrom(-1)). On the basis of EHMO (extended Huckel molecular orbital calculations), we predict that the HOMO and LUMO are the two d sigma* orbitals;nisi:ng from four interacting Pd atoms via the d(x)2(-y)2, d(z)2, and p(x) M atomic orbitals. This assignment is confirmed by the: UV-vis spectra, in particular from the second-moment band analysis, which indicates that the tune Franck-Condon active modes are modes with frequencies of 165 and 86 cm(-1), which are assigned to v(PdPd). The compounds exhibit luminescence at 77 K with lifetimes in the microsecond regime. During the course of this study, use of TCNQ(o) (tetracyanoquinodimethane) as the oxidizing agent during the reaction (instead of CHCl3 or Pd(O2CCH3)(2)) leads to 3 ([Pd-2(dmb)(4)(mu-Cl)] (TCNQ)(3)), which is the first encapsulated halide ion '"M-2(dmb)(4)" species chat is characterized from X-ray crystallography (d(PdCl) = 2.7143(6) Angstrom). X-ray data for 2 . 4H(2)O: monoclinic, P2(1)/c, a = 19.433(2) Angstrom, b = 15.312(2) Angstrom, c = 29.156(2) Angstrom, beta 98.841(10)degrees, V = 8572.7(15) Angstrom(3), Z = 4. X-ray data for 3: triclinic, P (1) over bar, a = 13.314(2) Angstrom, b = 13.490(2) Angstrom, c = 14.645(2) Angstrom, alpha = 108.267(10)degrees, beta = 104.834(10)degrees, gamma = 101.221(10)degrees, V = 2303.8(6) Angstrom(3), Z = 1.