Element‐Element‐Bindungen. XI Kettenbildung bei kristallinen Dimethyldichalkogenanen

Element‐Element Bonds. XI Chain Formation in Crystalline Dimethyldichalkogenanes The structures of dimethyldichalkogenanes (H 3 C) 2 E 2 liquid at room temperature have been determined by single‐crystal x‐ray diffraction { E = S , α‐form 1a , P 2 1 / c ; Z = 4; a = 860.9(5); b = 648.0(4); c = 845.9(4) pm; β = 94.23(4)°; −141 ± 2 °C; β‐form 1b , P 2 1 / c ; Z = 4; a = 518.3(3); b = 1445.6(10); c = 670.9(3) pm; β = 107.30(5)°; −141 ± 2 °C; E = Se , 2 , Fdd 2; Z = 16; a = 2236.6(5); b = 1759.0(9); c = 520.9(2) pm; −120 ± 2 °C; E = Te , 3 , C 2/ c ; Z = 4; a = 1260.8(4); b = 849.1(4); c = 561.0(3) pm; β = 107.04(6)°; −130 ± 2 °C}. As a remarkable result intermolecular E··E interactions indicated by the ratio Q = (E··E)/(E−E) increase gradually in strength when dimethyldisulfane with ordinary van der Waals contacts ( 1a , Q = 1.86; 1b , Q = 1.84) is compared with the selenium ( 2 , Q = 1.54) and the tellurium derivatives ( 3 , Q = 1.38). Taking these E··E contacts into account, an association of the binuclear molecules to pairs can be detected for polymorph 1b , whereas zigzag chains are encountered in the remaining crystal structures ( 1a , E−E··E = 95° and 174°; 2 , 156° and 161°; 3 , 151°). Additionally, by a careful inspection several crystal structures already published by other authors turn out to exhibit similar phenomena. Furthermore, the molecular packing modes of α‐dimethyldisulfane ( 1a ) and elementary chlorine resemble each other, whereas the β‐polymorph 1b and the isotypic crystal structures of β‐dibromo‐ and dichlorodiselane as described by Kniep, Korte und Mootz constitute a pair of polytypoid stacking variants. A similar relationship could be established between the structures of dimethyldiselane ( 2 ) and the homologous ditellane 3 . In comparison with numerous literature data the intermolecular interactions observed with these dimethyldichalkogenanes have to be classified as only weak.