Element–Element-Bindungen, IV. Molekül-und Kristallstruktur des Tetramethyldiphosphans und -diarsans /Element–Element Bonds, IV. Molecular and Crystal Structure of Tetramethyldiphosphane and -diarsane

The molecular and crystal structures of the isotypic compounds tetramethyldiphosphane 1 and -diarsane 2 have been determined by single crystal X-ray diffraction (monoclinic; C2/m; Z = 2; 1/2: -155/-144 °C = 540.6(2)/555.8(2); b = 1131.0(6)/l 136.7(6); c -602.5(2)/612.8(2) pm;β = 97.31(3)/95.24(3)°;P-P 221.2(1)/As-As 242.9(1) pm). In accordance with the crystallographically imposed symmetry 2/m, the molecules adopt antiperiplanar conformation. Their crystal structures are closely related to those of the homologues tetramethyldistibane 3 [1] and -dibismuthane 4 [3]. As found for the latter compounds, the E -E units (E = P, As) are also aligned in linear chains, but the intermolecular E···E contacts (P···P 381/As···As 370 pm) do not allow any extended interaction between molecules, which otherwise would result in thermochromic effects.