In the title compound, C16H13NO4, the carbazole ring system is almost planar with non-H atoms possessing a mean deviation from planarity of 0.037 Å. The two ester groups are orientated trans to one another and tilted slightly from the mean plane of the carbazole ring system, making dihedral angles of 8.12 (6) and 8.21 (5)°. In the crystal, mol-ecules are linked by pairs of N-H⋯O hydrogen bonds forming inversion dimers. The dimers are linked by parallel slipped π-π inter-actions, forming slabs propagating along the b-axis direction [inter-centroid distance = 3.6042 (8) Å, inter-planar distance = 3.3437 (5) Å, slippage = 1.345 Å].

The title compound, C16H13NO6, exhibits a biphenyl unit with a dihedral angle between the two aryl rings of 56.01 (5)°. The two ester groups vary slightly from planarity, with ar-yl-ester dihedral angles of 4.57 (5) and 16.73 (5)°. The nitro group is turned from the aromatic unit with an ar-yl-nitro dihedral angle of 48.66 (4)°. In the crystal, mol-ecules are connected by weak C-H⋯O inter-actions, forming a three-dimensional network.

The title compound, C16H12N2O8, exhibits two near-planar aromatic ester groups with ar-yl-ester dihedral angles of 2.1 (2) and 4.2 (3)°. The dihedral angle between the aromatic rings is 58.0 (1)°. The two nitro groups are tilted slightly from the plane of the aromatic rings, making dihedral angles of 14.1 (1) and 8.2 (2)°. In the crystal, mol-ecules are connected by weak C-H⋯O inter-actions, forming a three-dimensional network.