APdCu(Se2)(Se3) (A = K and Rb):: New quaternary copper palladium polyselenides with unusual metal-selenium coordination

Two novel metal polyselenides, PdCu(Se-2)(Se-3) (I) and RbPdCu(Se-2)(Se-3) (II), have been synthesized from solvothermal reactions in superheated ethylenediamine at 160 degreesC. The isostructural compounds crystallize in the monoclinic space group P2(1)/m, Z = 2, with a = 6.145(1) Angstrom, b = 7.268(1) Angstrom, c = 8.865(2) Angstrom, beta = 102.41(3)degrees for I, and a = 6.253(1) Angstrom, b = 7.267(1) Angstrom, c = 8.993(2) Angstrom, beta = 102.28(3)degrees for II. Their crystal structures are two-dimensional networks with (2)(infinity)[PdCu(Se-2)(Se-3)](-) anionic layers built from one-dimensional (1)(infinity)[Pd(Se-2)(Se-3)](2-) "chains" that are "stitched" together by tetrahedrally coordinated Cu atoms. The DSC data show that I and II are stable up to 400 degreesC and decompose at ca. 436 and 424 degreesC, respectively. Both compounds are narrow band-gap semiconductors with estimated band gaps of about 0.7 eV (I) and 0.8 eV (II), respectively. They are the first structurally characterized quaternary copper palladium polychalcogenides with a (Se-2)(2-) and a (Se-3)(2-) fragment, both exhibiting interesting and unusual metal-selenium coordination.