Nitrochloranilic acid: a novel asymmetrically substituted quinoid bridging ligand for design of coordination polymers

Abstract

A series of alkali salts and transition metal complexes of a novel asymmetrically substituted quinoid ligand, 3-nitro-6-chloro-2,5-dihydroxyquinone (nitrochloranilic acid, H₂NCA) was prepared and characterised. The nitrochloranilate moiety readily binds to transition metals either as a terminal bidentate or a bridging (bis)bidentate ligand. Therefore it is capable of forming coordination polymers of various topologies, and is a promising building block that may be used for design of metal–organic frameworks. We have prepared and structurally characterised three of its alkali salts, sodium hydrogen nitrochloranilate trihydrate (NaHNCA·3H₂O), sodium nitrochloranilate trihydrate (Na₂NCA·3H₂O) and potassium nitrochloranilate dihydrate (K₂NCA·2H₂O). The first series of coordination compounds includes mononuclear {[Ni(bpy)₂(NCA)]·EtOH, [Cu(phen)₂(NCA)]·EtOH and (Hpy)₂[Mn(H₂O)₂(NCA)₂] (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, Hpy = pyridinium)} and binuclear units {[Cu(bpy)(NCA)]₂}, as well as 1D linear {[Cu(H₂O)(MeCN)(NCA)]_n}, zig-zag {[Co(phen)(NCA)]·EtOH}_n and ladder-like polymers {[Mn₂(NCA)₂(H₂O)₅·3.5H₂O]_n}.