The reaction of hydrated magnesium or calcium 4-nitrobenzoate (4-nba) generated in situ, with imidazole (Im) results in the formation of the complexes [Mg(H 2 O) 2 (Im) 2 (4-nba) 2 ] 1 and [Ca(H 2 O) 3 (Im)(4-nba) 2 ]⋅Im 2, which exhibit the same metal:4-nba:Im ratio but different degrees of hydration. Complex 1 crystallizes in the triclinic Pī space group and the Mg atom is located on an inversion centre, while 2 crystallizes in the monoclinic P2 1

The aqueous reaction of [Mg(H 2 O) 6 ]Cl 2 with the in situ generated sodium salt of 4-nitrobenzoic acid (4-nbaH) and N-methylimidazole (N-MeIm) results in the formation of the dinuclear complex [Mg(H 2 O)(N-MeIm) 2 (4-nba) 2 ] 2 1 (4-nba = 4-nitro benzoate), while the direct reaction of [Mg(H 2 O) 6 ]Cl 2 with sodium 4-nba leads to the formation of the mononuclear complex, [Mg(H 2 O) 6 ](4-nba) 2 ⋅2H 2 O 2. In the centrosymmetric dimer 1, each Mg atom is coordinated to an aquo ligand, two monodentate N-MeIm ligands and a monodentate 4-nba ligand. The second 4-nba ligand functions as a bridging bidentate ligand, linking the metal centers and completes the hexacoordination around each Mg(II). The dimeric molecules of 1 are linked into a one-dimensional chain along b with the aid of intra-as well as intermolecular H-bonding interactions between the coordinated water and the free oxygen atom of the monodentate 4-nba ligand. In the mononuclear complex [Mg(H 2 O) 6 ](4-nba) 2 ⋅2H 2 O 2, the Mg(II) is located on an inversion center and its structure consists of an octahedral [Mg(H 2 O) 6 ] 2+ dication, a free uncoordinated 4nba anion and a lattice water molecule. One of the H atoms attached of the lattice water is disordered over two positions. The hexaaquomagnesium(II) dication, the 4-nba anion and the lattice water molecule are linked by intra-and intermolecular H-bonding interactions resulting in the formation of alternating layers of [Mg(H 2 O) 6 ] 2+ dications and 4-nba anions in the crystallographic bc plane. The lattice water molecules are situated between the cations, while the 4-nba anions are arranged antiparallel to each other along b.

The organic diammonium salt N,N′-dibenzyl-N,N,N′,N′-tetramethylethylenediammonium dibromide dihydrate, (dbtmen)Br 2 ⋅2H 2 O (1), was prepared by the reaction of N,N,N′,N′-tetramethylethylenediamine (tmen) with benzyl bromide. 1 crystallizes in the triclinic space group P 1 with the following unit cell dimensions for C 20 H 34 Br 2 N 2 O 2 (M = 494⋅31): a = 8⋅6672(6) Å, b = 11⋅7046(8) Å, c = 11⋅7731(8) Å, α = 76⋅988(8)°, β = 88⋅978(8)°, γ = 76⋅198(8)°, V = 1129⋅26(13) Å 3 , Z = 2. Three components, namely the (dbtmen) 2+ dication, two bromide anions and two crystal water molecules constitute the structural arrangement of 1. H 2 O molecules are linked to bromide anions via O-H⋅⋅⋅Br hydrogen bonding interactions resulting in the formation of a four-membered {O 2 Br 2 } cyclic dibromide. The {O 2 Br 2 } units and the dications are arranged as alternating layers extending in the crystallographic bc plane. The arrangement of anions and cations may be viewed as a typical lamellar structure. The crystal water molecules can be removed by heating 1 at 140°C and the anhydrous dibromide thus formed can be fully rehydrated as evidenced by IR spectra and X-ray powder patterns.

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The reaction of barium carbonate with 4-nitrobenzoic acid (4-nbaH) results in the formation of a Ba(II) coordination polymer, catena-poly[[(pentaaqua)(4-nitrobenzoato-O,O′)barium(II)](μ-4-nitrobenzoato-O,O′)] 1. The polymeric compound [[Ba(H 2 O) 5 (4-nba-O,O′)](μ-4-nba-O,O′)] n 1 was characterized by elemental analysis, IR and UV-Vis spectra, weight loss studies, X-ray powder diffraction and its structure determined. In 1 five water molecules are coordinated to the central metal and one of the 4-nba ligands is bonded to Ba(II) in a bidentate manner (4-nba-O,O′) through the carboxylate O atoms. The [(pentaaqua)(4-nitrobenzoato-O,O′)barium(II)] units are linked into an infinite one-dimensional chain along b-axis with the aid of the second 4-nba anion, which functions as a bridging bidentate (μ-4-nba-O,O′) ligand. This results in nine coordination around each Ba(II) ion in the coordination polymer. A long Ba⋅⋅⋅Ba distance of 6⋅750(1) Å is observed between adjacent Ba(II) ions in the chain and the oxygen atoms of the carboxylate group and the nitro functionalities of the 4-nba ligand are involved in several O-H⋅⋅⋅O and C-H⋅⋅⋅O interactions.