Specifically, we're talking C-D-G (1-2-5 in C), as the first basic group; then Bb-F-Eb (5-2-1 in Eb). Together, they form a C-7 11, six note chord (C-Eb-G-Bb-D-F).
These two groups were chosen because there are no repeating notes, which means they form a hexatonic (6 note) scale (C-D-Eb-F-G-Bb), which can also be viewed as the triad pair of C min. and Bb Maj.