We isolated the masked cyclo [40]carbon [3]catenane mcC40•(Ma)2 (20% yield) and the masked cyclo[80]carbon [5]catenane mcC80•(Ma)4 (13% yield). These catenanes were fully characterized by 1 H, C and 31 P NMR spectroscopy, and analytical GPC, but none of these techniques provide definitive information on the number of repeat units. At first, attempts at recording MALDI-TOF mass spectra of these two cyclic oligomers were unsuccessful and we tentatively assumed that they were the [3] and [4]catenane. Fortunately, nanoelectrospray ionization mass spectrometry (nESI-MS) gave intense well-resolved molecular ions for both compounds, proving that the larger structure is the [5]catenane, as shown by the excellent fit between the calculated and observed isotopomer pattern (Fig. ). Surprisingly, we were unable to detect any formation of the [4]catenane. Single crystals of the [3]catenane were grown by diffusion of cyclohexane vapor into a solution of mcC40•(Ma)2 in THF. Single crystal X-ray diffraction studies confirmed the interlocked structure (Fig. ). In the solid state, the catenane has Ci symmetry, with half a molecule in the asymmetric unit. Both the diphenylphosphinomethane (dppm) units point towards the Ma macrocycles, in contrast to the conformations adopted in the crystal structures of 3•Ma (one dppm in and one out) and 3•Mb (both dppm units out, i.e. away from the Mb macrocycle; see SI, Section 4). These dppm complexes are conformationally dynamic in solution (in fast exchange by NMR at room temperature) , and the arrangement in the solid state is probably influenced by crystal packing.