Charged Molecular Alloys: Synthesis and Characterization of the Binary Anions Pd₇As₁₆^4- and Pd₂As₁₄^4-

Pd(PCy3)2 (Cy = cyclohexyl) reacts with As73- in en/tol solvent mixtures to give Pd2As144- (2) and Pd7As164- (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 As75- groups bound to square-planar Pd(III) centers linked by a Pd−Pd bond (dPd-Pd = 2.7144(6) Å). Anion 4 has a highly distorted capped trigonal prismatic Pd7 core stabilized by 2 As5-, 2 As2-, and 2 As- 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”.