title: Preparation, Spectroscopic Characterization, and Theoretical Study of the [Pd(4)(dmb)(4)(PPh(3))(2)]Cl(2) Complex (dmb = 1,8-Diisocyano-p-menthane) and Its Organometallic Polymer {[Pd(4)(dmb)(5)](CH(3)CO(2))(2)}(n)(): The First Examples of 58-Electron Linear Pd(4) Clusters.
abstract: The title compounds [Pd(4)(dmb)(4)(PPh(3))(2)]Cl(2) (1) and {[Pd(4)(dmb)(5)](CH(3)CO(2))(2)}(n)() (2) were prepared from the reactions Pd(2)(dba)(3).CHCl(3) + 2dmb + PPh(3) for 1 (dba = dibenzylideneacetone) and Pd(2)(dba)(3).S + excess dmb + Pd(O(2)CCH(3))(2) for 2 (S = benzene or CHCl(3)), 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) Å for 1 and 2.5973(18), 2.6080(18), and 2.6080(18) Å for 2) where the dmb ligands bridge the Pd atoms, forming a catenate. While the PPh(3) 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 nu(PdPd) active modes (nu(1) and nu(2)) are observed at 165 and 86 cm(-)(1), respectively, for 1 (F(PdPd) = 1.44 mdyn Å(-)(1)). On the basis of EHMO (extended Hückel molecular orbital calculations), we predict that the HOMO and LUMO are the two dsigma orbitals arising 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 two Franck-Condon active modes are modes with frequencies of 165 and 86 cm(-)(1), which are assigned to nu(PdPd). The compounds exhibit luminescence at 77 K with lifetimes in the microsecond regime. During the course of this study, use of TCNQ(0) (tetracyanoquinodimethane) as the oxidizing agent during the reaction (instead of CHCl(3) or Pd(O(2)CCH(3))(2)) leads to 3 ([Pd(2)(dmb)(4)(&mgr;-Cl)](TCNQ)(3)), which is the first encapsulated halide ion "M(2)(dmb)(4)" species that is characterized from X-ray crystallography (d(PdCl) = 2.7143(6) Å). X-ray data for 2.4H(2)O: monoclinic, P2(1)/c, a = 19.433(2) Å, b = 15.312(2) Å, c = 29.156(2) Å, beta = 98.841(10) degrees, V = 8572.7(15) Å(3), Z = 4. X-ray data for 3: triclinic, P&onemacr;, a = 13.314(2) Å, b = 13.490(2) Å, c = 14.645(2) Å, alpha = 108.267(10) degrees, beta = 104.834(10) degrees, gamma = 101.221(10) degrees, V = 2303.8(6) Å(3), Z = 1.
authors.affiliation: Département de chimie, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada.
authors.forename: Tianle
authors.initials: T
authors.lastname: Zhang
authors.forename: Marc
authors.initials: M
authors.lastname: Drouin
authors.forename: Pierre D.
authors.initials: PD
authors.lastname: Harvey