Abstract
The two title compounds, 4a C(19)H(19)N(2)O(3)P and 4b C(17)H(15)N(2)O(3)P, are not isotypic. The tetra-cyclic ring systems are essentially planar. The phospho-nate groups are similarly oriented. Compound 4a crystallizes in P1 with Z' = 1; mol-ecules are linked in inversion-symmetric pairs by classical hydrogen bonds N-H⋯O=P, forming rings of graph set R (2) (2)(12). Compound 4b crystallizes in P2(1)/c with Z' = 2; the two independent mol-ecules are linked by a hydrogen-bond system analogous to that of 4a, but the ring systems subtend an inter-planar angle of 55.84 (1)°. For 4a, the hydrogen bonding combines with ring stacking in pairs to form a ribbon structure parallel to the b axis. For 4b, the classical hydrogen bonding combines with two 'weak' hydrogen bonds C-H⋯O to form a layer structure parallel to the ac plane. Non-spherical atom scattering factors were employed (using the program NoSpherA2) to avoid the problem of badly fitting reflections in high-resolution data (2θ(max) ca 105° using Mo Kα radiation).