Synthesis, Spectral Characterization, and Structural Studies of 2-Aminobenzoate Complexes of Divalent Alkaline Earth Metal Ions:  X-ray Crystal Structures of [Ca(2-aba)₂(OH₂)₃]_∞, [{Sr(2-aba)₂(OH₂)₂}·H₂O]_∞, and [Ba(2-aba)₂(OH₂)]_∞ (2-abaH = 2-NH₂C₆H₄COOH)

Abstract

Reactions of alkaline earth metal chlorides with 2-aminobenzoic acid (2-abaH) have been investigated. The treatment of MCl2.nH2O (M = Mg, Ca, Sr or Ba) with 2-abaH in a 1:2 ratio in a MeOH/H2O/NH3 mixture leads to the formation of anthranilate complexes [Mg(2-aba)2] (1), [Ca(2-aba)2(OH2)3]infinity (2), [[Sr(2-aba)2(OH2)2].H2O)]infinity (3), and [Ba(2-aba)2(OH2)]infinity (4) respectively. Alternatively, these products can also be obtained starting from the corresponding metal acetates. Anthranilate complexes 1-4 have been characterized with the aid of elemental analysis, pH measurements, thermal analysis, and infrared, ultraviolet, and NMR (1H and 13C) spectroscopic studies. All the products are found to be thermally very stable and do not melt on heating to 250 degrees C. Thermal studies of complexes 2-4, however, indicate the loss of coordinated and lattice water molecules below 200 degrees C. In the case of the magnesium complex, the analytical and thermogravimetric studies indicate the absence of any coordinated or uncoordinated water molecules. Further, the solid-state structures of metal anthranilates 2-4 have been established by single-crystal X-ray diffraction studies. While the calcium ions in 2 are heptacoordinated, the strontium and barium ions in 3 and 4 reveal a coordination number of 9 apart from an additional weak metal-metal interaction along the polymeric chains. The carboxylate groups show different chelating and bridging modes of coordination behavior in the three complexes. Interestingly, apart from the carboxylate functionality, the amino group also binds to the metal centers in the case of strontium and barium complexes 3 and 4. However, the coordination sphere of 2 contains only O donors. All three compounds form polymeric networks in the solid state with the aid of different coordinating capabilities of the carboxylate anions and O-H...O and N-H...O hydrogen bonding interactions.

Coordination polymer networks with s-block metal ions

“…As mentioned earlier, the calcium coordination polymer with 2-aminobenzoic acid features only oxygen donation towards the cation [84]. The barium derivative [Ba(2-aba) 2 (OH 2 )] however, has the ligands in two different coordination modes, one of which is based on solely O-donation, while the second ligand molecule also involved the N-atom in metal ion coordination.…”

“…Thus, 2-aminobenzoic acid has the amino function placed in the meta position, allowing for a perfect chelate formation when possible (Scheme 10) [84]. Reactions of alkaline earth metal chlorides with 2-aminobenzoic acid (2-abaH) in a 1:2 ratio in a MeOH/H 2 O/NH 3 mixture leads to the formation of anthranilate complexes [Mg(2-aba) 2 …”

Mixed ligand complexes of acesulfame/nicotinamide with earth alkaline metal cations Mg(II), Ca(II), Ba(II) and Sr(II): synthesis and characterization

“…Some complex structures stated have thermochromic, solvatochromic and ionochromic properties depending on deaquation [12]. Also, the alkaline earth metal cation complexes with organic ligands were studied and investigated their bonding parameters by lots of researcher [13][14][15][16][17][18] The importance of studies related with transition metal complexes of nicotinamide acting as vitamin B 3 and used in drug preparation has been increased recently. As a result of spectral investigation of complexes between nicotinamide and these metals, it was determined that it has ability to bind as monodentate ligand through pyridine nitrogen.…”

Synthesis and structural investigation of two metal-organic frameworks constructed from alkaline earth metal cations and organic ligand 5-nitroisophthalic acid (5-NO2-H2BDC)

“…In the past, co-ordination polymers assembled by alkaline earth metal ions have seldom been reported possibly due to the bigger electropositivity of alkaline earth, which results in the difficulty to accept a pair of electrons from ligands. In fact, alkaline earth metal ions with high co-ordination numbers [2] are favored to the reaction of hard base which has stronger ability to present electrons like oxygen of carboxylate group based on the soft and hard acid and base theory. So many works about alkaline earth complexes and patents on the use of these complexes have been studied during the last decade [3][4][5][6][7][8][9][10][11][12][13].…”