Charged molecular alloys: synthesis and characterization of the binary anions Pd(7)As(16)(4-) and Pd(2)As(14)(4-).

Pd(PCy(3))(2) (Cy = cyclohexyl) reacts with As(7)(3-) in en/tol solvent mixtures to give Pd(2)As(14)(4-) (2) and Pd(7)As(16)(4-) (4) as the [K(2,2,2-crypt)](+) salts. The anions were characterized by EDX, ESI-MS, and single-crystal X-ray diffraction. Anion 2 formally contains two norbornadiene-like As(7)(5-) groups bound to square-planar Pd(III) centers linked by a Pd-Pd bond (d(Pd)(-)(Pd) = 2.7144(6) A). Anion 4 has a highly distorted capped trigonal prismatic Pd(7) core stabilized by 2 As(5)(1-), 2 As(2)(2-), and 2 As(3-) anions. The 6 Pd(I) ions are in distorted 5-coordinate environments whereas the lone Pd(II) ion is square planar. Complexes 2 and 4 are rare examples of organic-free, homoleptic transition metal anions containing group 15 elements, and they represent an emerging class of charged "molecular alloys".