Gravar-mail: Crystal structures of the 1:1 salts of 2-amino-4-nitro­benzoate with each of (2-hy­droxy­eth­yl)di­methyl­aza­nium, tert-but­yl(2-hy­droxy­eth­yl)aza­nium and 1,3-dihy­droxy-2-(hy­droxy­meth­yl)propan-2-aminium