Influence of the presence of divalent first-row transition metal ions on the structure of sodium(i) salts of 1,2,3,4-benzenetetracarboxylic acid (H4bta)

Abstract

Three different sodium(I)-containing salts of 1,2,4,5-benzenetetracarboxylic (H₄bta) of formula [Na₄(bta)(H₂O)₁₂] (1), [Na₂M(H₂bta)₂(H₂O)₈]·2H₂O] [M = Mn (2) and Ni (3)] were synthesized and their structures were solved by single crystal X-ray diffraction methods. Compound 1 crystallises in orthorhombic system, space group Pc2₁b with a = 6.9997(4) Å, b = 16.4260(9) Å, c = 20.3312(18) Å, V = 476.30(15) ų and Z = 4. Compounds 2 and 3 crystallize in the monoclinic system, space group C2/m with a = 7.3778(4) Å, b = 20.1493(6) Å, c = 10.4963(4) Å, β = 103.466(8)°, V = 1517.5(11) ų and Z = 2 for 1 and a = 7.2862(4) Å, b = 20.1165(7) Å, c = 10.4032(3) Å, β = 103.366(9)°, V = 1483.52(11) ų and Z = 2 for 2. The structure of 1 consists of layers of four crystallographically independent sodium atoms [two six- (Na(O_w)₆) and two five- (Na(O_w)₃O₂) coordinated] which are bridged by tetrakismonodentate bta⁴⁻ ligands and single and double water molecules. These layers are interlinked through hydrogen bonds involving some of the coordinated water molecules and free carboxylate-oxygen atoms to afford a 3-D network. Compounds 2 and 3 are isostructural: their structures are made up of chains with regular alternating pairs of Na⁺ and single M²⁺ cations [M = Mn (2) and Ni (3)], two water molecules acting as bridges between each pair of metal ions. Two water molecules (at M) and two carboxylate-oxygen atoms from two H₂bta²⁻ ligands (at Na) which are coordinated to the metal ions in trans positions build distorted octahedral surroundings. The H₂bta²⁻ group acts as a bismonodentate ligand toward adjacent sodium atoms through 1,3-carboxylate oxygens. These neutral chains are interlinked through hydrogen bonds involving free carboxylate-oxygen atoms and coordinated and crystallization water molecules to afford a 3-D structure.