Salt forms of the monoazo dye Mordant Orange 1

The crystal structures of eight salt forms of the carboxylate-functionalized monoazo dye Mordant Orange 1 are presented and discussed, primarily in terms of their coordination behaviour. The relatively non-polar metals Mg and Li give the solvent-separated ion-pair structures hexaaquamagnesium bis{2-hydroxy-5-[( E )-(4-nitrophenyl)diazenyl]benzoate} tetrahydrate, [Mg(H 2 O) 6 ](C 13 H 8 N 3 O 5 ) 2 ·4H 2 O, and tetraaqualithium 2-hydroxy-5-[( E )-(4-nitrophenyl)diazenyl]benzoate dihydrate, [Li(H 2 O) 4 ](C 13 H 8 N 3 O 5 )·2H 2 O, respectively. The alkaline earth metals Sr and Ba give isostructural catena -poly[[[(dimethylformamide)strontium(II)]-μ-aqua-bis{μ-2-hydroxy-5-[( E )-(4-nitrophenyl)diazenyl]benzoato}] dimethylformamide disolvate] and the barium(II) analogue, {[ M (C 13 H 8 N 3 O 5 ) 2 (DMF)(H 2 O)]·2DMF} n ( M = Sr, Ba; DMF is dimethylformamide, C 3 H 7 NO), and a crystallographic mirror plane passes through the metal centre and the DMF ligand. These are 1D coordination polymers that propagate via M —O— M bridges where the O atom is from a carboxylate group or from a water ligand. For the Na, Rb and mixed Cs/Na salt forms, namely, poly[tetra-μ-aqua-diaquabis{μ-2-hydroxy-5-[( E )-(4-nitrophenyl)diazenyl]benzoato}disodium(I)], [Na 2 (C 13 H 8 N 3 O 5 ) 2 (H 2 O) 6 ] n , poly[tetra-μ-aqua-bis{μ-2-hydroxy-5-[( E )-(4-nitrophenyl)diazenyl]benzoato}dirubidium(I)], [Rb 2 (C 13 H 8 N 3 O 5 ) 2 (H 2 O) 4 ] n , and poly[tetra-μ-aqua-diaquabis{μ-2-hydroxy-5-[( E )-(4-nitrophenyl)diazenyl]benzoato}caesium(I)sodium(I)], [NaCs(C 13 H 8 N 3 O 5 ) 2 (H 2 O) 6 ] n , the nitro substituent was found to be as competitive in its ability to bond to metal as the carboxylate group. For Na, this gave a 1D coordination polymer, where Na 4 units link through the length of the azo anions and via bonds to both nitro and carboxylate groups. For both the Rb and the mixed Cs/Na salt forms, higher metal coordination numbers and more extensive bridging interactions give 3D coordination polymers.