Kristallstruktur des Benzol‐Addukts des 1,2,3,4‐Tetramethylcyclobutadien‐nickel(II)‐chlorids, (C8H12, NiCl2)2, C6H6

Abstract

Crystals of 1,2,3,4‐tetramethylcyclobutadiene‐nickel dichloride, C₈H₁₂NiCl₂, are monoclinic, a = 16,01, b = 8,01, c = 16,45 Å; β = 111° 5′; Z = 8; Space group P2_1/n. Crystals of the benzene containing solvate, 2C₈H₁₂NiCl₂, C₆H₆, lose benzene rapidly but are stable for several days when enclosed in glass tubes. The unit cell of the solvate is monoclinic, a = 8,311, b = 11,944, c = 12,715 Å; β = 103° 2′; space group P2₁/c; it contains 4 molecules of complex plus 2 molecules of benzene. The approximate structure has been derived by standard methods and refined by least‐squares analysis to an R factor of 0,069. The molecule, as it exists in the solvate, is a dimer, C₈H₁₂Ni₂Cl₄C₈H₁₂. Each Ni atom has on one side the four atoms of the cyclobutadiene ring (Ni‐C, 2,00 to 2,05 Å), and on the other side 3 Cl neighbours, two shared with the second Ni to form a 4‐membered ring (Ni‐Cl, 2,35 Å) and one unshared (Ni‐Cl, 2,26 Å). The cyclobutadiene ring is planar and appears to be square or very nearly so (C‐C, 1,40 to 1,45 Å). The methyl groups are displaced outwards (i.e. away from the Ni atom) by 0,12 to 0,19 Å, probably as a result of steric interference with the Cl atoms. The benzene rings lie between, and approximately parallel to, pairs of C₈H₁₂ groups belonging to different molecules, and undergo a strong rotational disorder in their own planes.