Polymorphism and metal-metal interactions on [Rh(Cl)(CO)(2)(Hpz(R))] complexes

The novel pyrazoles containing 3-[4-n-hexyloxyphenyl] (hp), 3-[4-n-octyloxy phenyl] (op) and 3-[4-n-decyloxyphenyl] (dp) substituents, Hpz(R) (R = hp, op, dp; 1-3), and their corresponding Rh(l) compounds [Rh(Cl)(LL)(Hpz(R))] (LL = 2,5-norbornadiene NBD, 1,5-cyclooctadiene COD, 2CO; R = hp, op, dp;,4 -12) have been prepared and characterised. The influence of the pyrazol sub stituent on the properties of the Rh(l) complexes has been analysed. Two cr ystalline polymorphs (yellow and red) have been isolated for [Rh(Cl)(CO)(2) (Hpz(dp))] (12) in contrast to the single red crystalline form isolated for the related complexes [Rh(Cl)(CO)(2)(Hpz(R))] (R = hp, op; 10 and 11). X-r ay crystal structures of the red forms of 10-12 as well as the yellow one o f 12 have been solved. The red compounds display one-dimensional stacking o f square-planar molecules with metal-metal interactions along the c-axis. T he yellow form consists of dimeric unities held together by Cl bridges, and without the one-dimensional metal-metal contacts. In both cases an intramo lecular hydrogen bond was present, being stronger in the yellow form than i n the red one. Thermochromic behaviour has also been observed for these dic arbonyl complexes. No liquid crystals properties were found for the new com pounds, however, the double melting behaviour observed for 10-12 could be c losely related to mesomorphism. (C) 2001 Elsevier Science B.V. All rights r eserved.