Table 1. Selected bond lengths (Å).

Ca—O1	2.2696 (9)
Ca—O2W	2.3265 (10)
Ca—O1W	2.3434 (10)
S1—C13	1.7686 (12)
S1—C14	1.7891 (12)
S2—C13	1.7037 (12)
O1—C11	1.2494 (14)
N1—C11	1.3448 (15)
N1—C1	1.4184 (15)
N2—C18	1.1518 (16)
C11—C12	1.4684 (16)
C12—C13	1.3996 (17)
C12—C18	1.4325 (17)