Polymorphism and metal–metal interactions on [Rh(Cl)(CO)2(HpzR)] complexes

The novel pyrazoles containing 3-[4-n-hexyloxyphenyl] (hp), 3-[4-n-octyloxyphenyl] (op) and 3-[4-n-decyloxyphenyl] (dp) substituents, HpzR (R=hp, op, dp; 1–3), and their corresponding Rh(I) compounds [Rh(Cl)(LL)(HpzR)] (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 substituent on the properties of the Rh(I) complexes has been analysed. Two crystalline polymorphs (yellow and red) have been isolated for [Rh(Cl)(CO)2(Hpzdp)] (12) in contrast to the single red crystalline form isolated for the related complexes [Rh(Cl)(CO)2(HpzR)] (R=hp, op; 10 and 11). X-ray crystal structures of the red forms of 10–12 as well as the yellow one of 12 have been solved. The red compounds display one-dimensional stacking of square-planar molecules with metal–metal interactions along the c-axis. The yellow form consists of dimeric unities held together by Cl bridges, and without the one-dimensional metal–metal contacts. In both cases an intramolecular hydrogen bond was present, being stronger in the yellow form than in the red one. Thermochromic behaviour has also been observed for these dicarbonyl complexes. No liquid crystals properties were found for the new compounds, however, the double melting behaviour observed for 10–12 could be closely related to mesomorphism.