Criteria for liquid crystal formation in 5-alkoxy-, 5-alkylamino-, and 5-alkanoyl-tropolone complexes of transition metals (Cu(II), Zn(II), Ni(II), Co(II), UO(2)(VI), VO(IV)). The first uranium metallomesogen. Crystal structure of bis(5-hexadecyloxytropolonato)copper(II).
The mesophase properties of bis(5-alkoxytropolonato)copper(II) complexes are reported and interpreted in terms of d-layer spacings, which indicate considerable intertwining of the alkyl chains. The mesogenic properties depend on the nature of the 5-substituent: to be mesogenic, it must be alkoxy with n > 8, and may not be 5-alkanoyl or 5-alkylamino. The nature of the metal is also important: to be mesogenic, it may be Cu(II) or UO(2)(VI) but not Ni(II), Zn(II), Co(II), or VO(IV). The crystal structure of bis(5-hexadecyloxytropolonato)copper(II) shows how, even in the crystalline state, molecular packing is dominated by the interactions between alkyl chains, together with copper-oxygen interactions. In the Cu(II) complexes, strong interactions occur between Cu atoms and O atoms of neighboring molecules. These are stronger than alkyl-alkyl interactions and therefore dominate alkyl-alkyl interactions between neighbors which otherwise govern the possibility and nature of mesogenic properties. The Cu.O interactions disrupt alkyl-alkyl chain interactions enough to produce a mesophase; such interactions do not obtain in the T(d)() Zn(II) and Co(II) complexes, and indeed, these complexes are not mesogenic. Likewise, alkyl chain interactions by the oxygens of the UO(2)(VI) lead to a mesophase, and U constitutes the heaviest metal ever placed into a mesogenic molecule. In the case of VO(IV), analogous synthetic steps from VOSO(4) led to a new series of binuclear complexes [(VO)(2)(SO(4))(5-alkoxytropoloato)(2)].
Elliott
James M
JM
Department of Chemistry, University of Missouri-Rolla, Rolla, Missouri 65409, USA.
Chipperfield
John R
JR
Clark
Stephen
S
Teat
Simon J
SJ
Sinn
Ekkehard
E