Lanthanide complexes of triazolylDO3A have been used to prepare bimetallic d−f hybrid complexes in which the triazolyl pendant arm coordinates to both the lanthanide and a transition-metal ion, and their properties have been compared with those of analogous systems in which the lanthanide triazoloDO3A domain is separated from the rhenium chromophore by an alkyl spacer. The triazole-bridged system has been shown to facilitate energy transfer from the chromophore to the lanthanide but also exhibits reduced affinity of the triazole nitrogen for the lanthanide center. In contrast, the system in which the two domains are separated by a spacer shows phosphate-independent relaxometric properties and has potential as a bimodal contrast agent for MRI luminescence.

5-Chloro-2'-deoxyuridine (C9H1 tC1N2Os) crystallizes in the space group P21 with one molecule per asymmetric unit and with unit-cell dimensions a= 9.118 (8), b = 5-090 (5), c= 11"992 (8) A and fl= 107040 ' (3). The structure was solved by Patterson interpretation methods and the positional and thermal parameters were refined by the method of least squares, using anisotropic temperature factors for the nonhydrogen atoms. The final R index for the 1228 reflexions used in the refinement process is 0.038 and the standard deviations in the bond lengths and angles are about 0.005 A, and 0"3 ° respectively.