Charge‐transfer complexes of N‐methyl‐, N‐iso­propyl‐, N‐butyl‐ and N‐iso­butyl­carbazole with 3,5‐di­nitro­benzoic acid

In the title four compounds, C₁₃H₁₁N·C₇H₄N₂O₆, (I), C₁₅H₁₅N·C₇H₄N₂O₆, (II), C₁₆H₁₇N·C₇H₄N₂O₆, (III), and C₁₆H₁₇N·C₇H₄N₂O₆, (IV), the donor and acceptor mol­ecules are stacked alternately to form one‐dimensional columns. In (I), the N‐methyl group of the donor is nearly eclipsed with respect to one of the nitro groups of the neighboring acceptor in a column, whereas the N‐iso­propyl, N‐butyl and N‐iso­butyl groups are in anti positions with respect to one of the nitro groups of the neighboring acceptor in compounds (II)–(IV).