Extended metal-organic solids based on benzenepolycarboxylic and aminobenzoic acids

Abstract

This article describes the recent results obtained in our laboratory on the interaction of polyfunctional ligands with divalent alkaline earth metal ions and a few divalent transition metal ions. Treatment of MCl 2 ⋅nH 2 O (M = Mg, Ca, Sr or Ba) with 2-amino benzoic acid leads to the formation of complexes [Mg(2-aba) 2 ] (1), [Ca(2-aba) 2 (OH 2) 3 ] ∞ (2), [{Sr(2-aba) 2 (OH 2) 2 } 2 ⋅H 2 O)] ∞ (3), [Ba(2-aba) 2 (OH 2)] ∞ (4), respectively. While the calcium ions in 2 are hepta-coordinated, the strontium and barium ions in 3 and 4 reveal a coordination number of nine apart from additional metal-metal interactions. Apart from the carboxylate functionality, the amino group also binds to the metal centres in the case of strontium and barium complexes 3 and 4. Complexes [{Mg(H 2 O) 6 }(4-aba) 2 ⋅2H 2 O] (5), [Ca(4-aba) 2 (H 2 O) 2 ] (6) prepared from 4-aminobenzoic acid reveal more open or layered structures. Interaction of 2-mercaptobenzoic acid with MCl 2 .6H 2 O (M = Mg, Ca), however, leads to the oxidation of the thiol group resulting in the disulphide 2,2′-dithiobis(benzoic acid). New metal-organic framework based hydrogen-bonded porous solids [{M(btec) (OH 2) 4 } n ⋅n(C 4 H 12 N 2)⋅4nH 2 O] (btec = 1,2,4,5-benzene tetracarboxylate) (M = Co 9; Ni 10; Zn 11) have been synthesized from 1,2,4,5-benzene tetracarboxylic acid in the presence of piperazine. These compounds are made up of extensively hydrogenbonded alternating layers of anionic M-btec coordination polymer and piperazinium cations. Compounds 2-11 described herein form polymeric networks in the solidstate with the aid of different coordinating capabilities of the carboxylate anions hydrogen bonding interactions.

Synthesis, spectroscopy, thermal studies and supramolecular structures of two new alkali-earth 4-nitrobenzoate complexes containing coordinated imidazole

“…In this context, a rich structural chemistry of the biologically relevant alkali and alkali-earth metals has been recently developed with amino as well as mercapto benzoic acids. [9][10][11][12][13][14][15] As part of an ongoing programme, we are investigating the chemistry of metal complexes of 4-nitrobenzoic acid (4-nbaH) to exploit the H-bonding capabilities of the nitro functionality. [16][17][18] The versatile ligational behaviour of the 4-nitrobenzoate (4-nba) ligand is well documented in the literature.…”

“…In this context, substituted benzene carboxylic acids have been shown to be very useful reagents by several research groups, as evidenced by the impressive array of interesting metal-organic molecular architectures synthesized from these types of ligands. [4][5][6][7][8] The advantage of using benzene-based ligand systems is due to the fact that donor groups like -COOH, -SH, -NH 2 etc. can be anchored onto the rigid six-membered benzene ring and the resulting supramolecular structures will largely depend on the positioning of the donor groups on the ring.…”

catena-Poly[[(pentaaqua)(4-nitrobenzoato-O,O’)barium(II)] (μ-4-nitrobenzoato-O,O’)]: A barium(II) coordination polymer showing O-H⋯O and C-H⋯O interactions

“…It is interesting to note that the reaction of BaCl 2 with 4-abaH (abaH is aminobenzoic acid) in the presence of a weak base results in the formation of the chloride containing compound [BaCl(4-aba)] 22 while the reaction of BaCO 3 with 4-abaH leads to the formation of a hydrated bis(4-aba) complex of barium. 23 With 4-nbaH the use of both the chloride or the carbonate of Ba(II) results in the formation of an identical product.…”

“…1,2 The ready availability of benzene based carboxylic acids in pure form, combined with the fact that the carboxylate group is a versatile donor that can bind in a variety of ways, 3,4 has led to the structural characterization of several metal carboxylates with novel structural features. [5][6][7][8][9][10][11][12] Potential donor groups like -NH 2 , -OH, -SH, or another -COOH can be introduced into the rigid sixmembered ring and the positioning of these groups can be altered with respect to the carboxylate functionality, are additional advantages of using benzene based systems. The introduction of additional groups affects the acidity of the carboxylic acid, which is an important aspect from a synthetic point of view of metal carboxylates.…”

Hydrothermal synthesis and characterisation of amine-templated metal phosphate framework

“…The first row transition metal ions such as Zn 2+ , Co 2+ , Cd 2+ , Fe 2+ are especially commonly used (Ayi, Choudhury and Rao, 2005;Natarajan et al, 2006). Some alkaline metal ions (Ayi et al, 2011), alkaline earth metal ions (Murugavel et al, 2000) and rare earth metal ions (Clearfield and Demadis, 2012) have also been employed as metal nodes for constructing MOF structures.…”