title: Element-Element Bonds. IX.(1) Structures of Tetrakis(trifluoromethyl)diphosphane and -diarsane: Experimental and Theoretical Investigations.
abstract: X-ray structure determinations of tetrakis(trifluoromethyl)diphosphane (2c, mp -82 degrees C, triclinic, P&onemacr;; Z = 1, a = 529.7(3) pm, b = 681.6(2) pm, c = 802.8(3) pm, alpha = 108.58(1) degrees, beta = 99.66(1) degrees, gamma = 103.29(1) degrees, wR2 = 0.204) and -diarsane (3c, mp -52 degrees C, monoclinic, P2(1)/c; Z = 2, a = 769.5(3) pm, b = 750.0(3) pm, c = 960.7(2) pm, beta = 105.26(1) degrees, wR2 = 0.115), both at -100(3) degrees C, reveal the molecules to adopt the trans conformation in the solid. Compared with the tetramethyl derivatives, the E-E (224.6(2)/246.3(1) pm, E = P, As) and E-C (188.3(4)/201.3(7) pm) bonds are elongated by 4.5/4.8 pm and 3.4/3.4 pm, respectively. From gas electron diffraction studies of diphosphane 2c a mixture of 85(10)% trans and 15(10)% gauche conformers can be deduced; diarsane 3c shows the trans form exclusively. The molecular parameters (E-E, 224.8(11)/245.2(6); E-C, 189.6(4)/ 201.2(4) pm) agree excellently with those determined for the crystalline state. As a result of quantum chemical calculations at Hartree-Fock and hybrid density functional levels of theory using 6-311+G basis sets, the gauche conformer of hydrazine derivative 1c and the trans conformer of diarsane 3c are clearly lowest in energy. However, for diphosphane 2c the gauche and not the trans form is found to be slightly more stable. Variations of calculated E-E and E-C bond lengths are analyzed and compared with corresponding values of the parent compounds E(2)H(4) (1a to 3a) as well as the tetramethyl derivatives 1b to 3b.
authors.affiliation: Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, Anorganisch-Chemisches Institut, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Strasse 8, D-48149 Münster, Germany, Institut für Anorganische Chemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Strasse 2, D-06120 Halle, Germany, and Institut für Physikalische und Theoretische Chemie, Eberhard-Karls-Universität, Auf der Morgenstelle 8, D-72076 Tübingen, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Becker
authors.forename: Winfried
authors.initials: W
authors.lastname: Golla
authors.forename: Joseph
authors.initials: J
authors.lastname: Grobe
authors.forename: Karl Wilhelm
authors.initials: KW
authors.lastname: Klinkhammer
authors.forename: Duc
authors.initials: D
authors.lastname: Le Van
authors.forename: Andreas H.
authors.initials: AH
authors.lastname: Maulitz
authors.forename: Otto
authors.initials: O
authors.lastname: Mundt
authors.forename: Heinz
authors.initials: H
authors.lastname: Oberhammer
authors.forename: Martin
authors.initials: M
authors.lastname: Sachs