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 crystalstructures 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