Ganapathi Anantharaman

Extended metal-organic solids based on benzenepolycarboxylic and aminobenzoic acids

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 MC12·nH2O (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(OH2)3]∞ (2), [Sr(2-aba)2(OH2)22·H2O)]∞ (3), [Ba(2-aba)2(OH2)]∞ (4), respectively. While the calcium ions in2 are hepta-coordinated, the strontium and barium ions in3 and4 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 complexes3 and4. Complexes [Mg(H2O)6(4-aba)2·2H2O] (5), [Ca(4-aba)2(H2O)2] (6) prepared from 4-aminobenzoic acid reveal more open or layered structures. Interaction of 2-mercaptobenzoic acid with MCl2·6H2O (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) (OH2)4n·n(C4H12N2)·4nH2O] (btec = 1,2,4,5-benzene tetracarboxylate) (M = Co9; Ni10; Zn11) have been synthesized from 1,2,4,5-benzene tetracarboxylic acid in the presence of piperazine. These compounds are made up of extensively hydrogen-bonded alternating layers of anionic M-btec co-ordination polymer and piperazinium cations. Compounds2- 11 described herein form polymeric networks in the solid-state with the aid of different coordinating capabilities of the carboxylate anions hydrogen bonding interactions.

Molecular zinc phosphonates: synthesis and X-ray crystal structures of [{(ZnMe)4(THF)2}{tBuPO3}2] and [{(ZnEt)3(Zn(THF))3}{tBuPO3}4{μ3-OEt}]

The reactions of zinc alkyls with tert-butylphosphonic acid in 2 : 1 and 1 : 1 molar ratios afforded [[(ZnMe)(4-)(THF)2][tBuPO3]2] (2) and [[(ZnEt)3(Zn(THF))3][tBuPO3]4[mu3-OEt]] (3), respectively. Compounds 2 and 3 have been fully characterised by means of spectroscopic and analytical methods. Single-crystal X-ray diffraction studies revealed that zinc phosphonates 2 and 3 are tetra- and hexa-nuclear, respectively. This is in contrast to the dodecanuclear zinc phosphonate [[Zn2(THF)2(ZnEt)6Zn4(mu4-O)][(tBuPO3)8]] (1) obtained in a 1.5 : 1 reaction between zinc alkyls and tBuP(O)(OH)2.

Organoaluminum chemistry with low valent aluminum — recent developments

The chemistry of mono and divalent aluminum has progressed very significantly in the last decade. Many fascinating and unusual results and novel structures of products have been realized. The monomeric form of divalent aluminum does not exist but dimers are well known and characterized. Stable Al(I) derivatives in both monomeric and tetrameric forms have been synthesized and structurally characterized. A common feature in these compounds is the use of bulky organic substituents. The chemistry of some of these compounds has also been explored. The monomeric Al(I) derivative, [HC(MeCNAr)2]Al, very recently synthesized, exhibits interesting addition and insertion reactions with alkyne, carbon dioxide and silyl azide at room temperature.

Aluminum Substituted Cobalt Ferrite (Co−Al−Fe) Nano Adsorbent for Arsenic Adsorption in Aqueous Systems and Detailed Redox Behavior Study with XPS

Arsenic [As(III) and As(V)] adsorption on aluminum substituted cobalt ferrite (Co-Al-Fe) ternary metal oxide adsorbent is reported by means of qualitative and quantitative spectroscopy tools. IR and Raman active signals were observed around 810-920 cm-1 band indicate different As-OHcomplexed and As-Ouncomplexed stretching vibrations on to the adsorbent. The adsorption behavior of arsenic (III and V) onto these adsorbents is studied as a function of contact time, different concentrations, and pH conditions. The kinetics study on adsorption were performed to understand nature of adsorption which supports the Pseudo Second Order (PSO) model. The adsorption isotherms study indicates Freundlich type of adsorption. The maximum adsorption capacity of Co-Al-Fe adsorbent is observed around 130 and 76 mg g-1 for As(III) and As(V) systems, respectively. Detailed XPS study of As 3d, Fe 2p, Co 2p, and O 1s spectra has been reported in explaining the redox behavior and ligand exchange reactions in supporting arsenic adsorption mechanism.

Chiral and achiral helical coordination polymers of zinc and cadmium from achiral 2,6-bis(imidazol-1-yl)pyridine: Solvent effect and spontaneous resolution

AbstractFour 2D helical coordination polymers (CPs) (1–4) were synthesized using achiral 2,6-bis (imidazol-1-yl)pyridine (pyim2) ligand with metal nitrates (metal = zinc and cadmium), which showed that variation in the solvent condition leads to difference in geometry around the central metal ion and results in chiral/achiral behaviour of these CPs. By using (pyim2), [trans-Zn(pyim2)2(NO3)2]n (1) was obtained by unary solvent (MeOH), while [trans- Cd(pyim2)2(NO3)2]n (2) was formed under binary solvent mixtures (DMF/MeOH). On the other hand, in ternary solvent mixture (DMF/MeOH/H2O) it resulted into an achiral {[trans-Zn(pyim2)2(H2O)2] ·(NO3)2}n (3) and homochiral {[cis-Cd(pyim2)2(H2O)2] ·(NO3)2}n (4) coordination polymer, respectively. The homochiral behaviour of the coordination polymer (4) was further studied by solid state CD spectra and also its optical behaviour was analyzed by polarimetry. Graphical AbstractFour solvent dependent 2D coordination polymers (CPs) 1-4, containing helical chains were synthesized using achiral ligand 2,6-bis(imidazol-1-yl)pyridine (pyim2), with zinc nitrate and cadmium nitrate. Single crystal X-ray analysis revealed, 1-3 are achiral frameworks whereas, 4 is homochiral in nature which is further confirmed by CD spectroscopy and polarimetry.

Structural diversity and luminescence properties of coordination polymers based on mixed ligands, 2,5-bis(imidazol-1-yl)thiophene (thim2) and aromatic multicarboxylates

Seven new CPs, {[Zn(thim2)(o-BDC)]·(H2O)2}n (1), [Co(thim2)(m-BDC)]n (2), {[M(thim2)(HBTC)]·(H2O)}n [M = Co(3) and Zn(4)], {[M(thim2)(OBA)]·(H2O)2}n [M = Co(5) and Zn(6)], [Mn2(thim2)2(m-BDC)2(H2O)]n (7) [o-H2BDC = phthalic acid, m-H2BDC = isophthalic acid, H3BTC = trimesic acid, H2OBA = 4,4′oxybis(benzoic acid)], have been prepared by hydro/solvothermal reaction of different metal salts with 2,5-bis(imidazol-1-yl)thiophene (thim2) in the presence of various multicarboxylic acids. CP 1 exhibits a 2D herringbone pleated network structure. CP 2 reveals a 2D + 2D = 3D polycatenated framework composed of a 2D parallel pleated network. CPs 3 and 4 show isostructural 2D herringbone pleated networks. CPs 5 and 6 are also isostructural and form a 2D layer structure arranged in a ⋯ABAB⋯ pattern in the crystal lattice. CP 7 forms a 3D framework consisting of 1D [Mn2(m-BDC)2(H2O)]n chains linked by thim2. The structures of all five type of CPs indicate that different multicarboxylate coligands play an important role in structural variation. The thermal stabilities of all the CPs (1–7) were monitored by TGA. Furthermore, solid state photoluminescence was investigated for 1, 4 and 6 at room temperature.

Anion triggered and solvent assisted structural diversity and reversible single-crystal-to-single-crystal (SCSC) transformation between 1D and 2D coordination polymers

An anion induced structural variation from 1D to 2D was studied for four coordination polymers (CPs) synthesized from an angular ditopic ligand 2,6-bis(imidazol-1-yl)pyridine (pyim2) under different solvent conditions, namely {[Zn(pyim2)2]·(PF6)2}n (1) (1D), {[trans-Cd(pyim2)2(DMF)2]·(PF6)2·(DMF)2}n (2) (1D), {[trans-Cd(pyim2)2(H2O)2]·(NO3)2}n (3) (2D) and {[trans-Cd(pyim2)2(H2O)2]·(PF6)·(NO3)·(H2O)2}n (4) (1D). An anion triggered single-crystal-to-single-crystal (SCSC) transformation was observed from 1D to 2D by counteranion exchange from PF6− to NO3− and vice versa. In addition, the cause for SCSC transformation involving the metal–ligand bond breaking/formation phenomenon and enhancement/decrement of the network dimensionality is discussed. The anion/solvent exchange transformations were confirmed directly through single crystal X-ray diffraction, IR spectroscopy, PXRD and elemental analysis. Furthermore, the thermal and solid state photoluminescence properties of 1–4 were analyzed.

Coordination polymers built with transition metal sulphates and angular 2,5-bis(imidazol-1-yl)thiophene (thim2): synthesis, structure and photoluminescent properties

The reactions of angular tritopic ligand 2,5-bis(imidazol-1-yl)thiophene (thim2) with different metal sulphates afforded six new CPs {[M(thim2)(SO4)(H2O)2]2·(thim2)·(H2O)}n [M = Zn (1); Mn (2)], {[Cd(thim2)(SO4)(H2O)]·(H2O)}n (3) and {[M(thim2)2(SO4)]·(H2O)x}n [M = Co, x = 7, (4); Ni, x = 7 (5); Cu, x = 6.5 (6)]. CPs 1 and 2 are isostructural with a 1D double chain propagating in a wave like fashion. Whereas, CP 3 exhibits a layered 2D network and in the case of 4–6 an isostructural 3D framework containing a 1D rhombic channel was obtained. In all the CPs there is an interesting sulphate ion binding mode to the metal centers, such as four membered M2O4 rings (1 and 2), six membered (Cd2SO3) 1-D chain (3) and MSO4 (4–6) 1-D chain, which is further linked by thim2 to form inorganic organic hybrid type systems. The stability of CPs (1–6) was monitored by TGA and a solid state photoluminescence study was carried out for 1 and 3 at room temperature.

Coordination polymers based on copper carboxylates and angular 2,5-bis(imidazol-1-yl)thiophene (thim2) ligand: sequential structural transformations

Four CPs [Cu(thim2)(OOCCH3)2]n (1), [Cu2(thim2)(μ2-OOCC6H5)4]n (2), [Cu2(thim2)2(μ2-OOCC6H5)2(OOCC6H5)2]n (3) and {[Cu2(thim2)2(μ2-OH2)(OOCC6H5)4]·4H2O} (4) have been synthesized and characterized. 1D helical CP (1) was formed by using copper acetate and 2,5-bis(imidazol-1-yl)thiophene (thim2), whereas addition of two equivalents of benzoic acid resulted in the formation of a 1D zig-zag chain (2) consisting of paddle wheel copper benzoate units. Interestingly, CP 2 undergoes one pot sequential SC–SC transformations in an A–B–C manner to another kinetically more stable 1D ladder type chain (3) in the presence of air and excess ligand in solution before forming a thermodynamically stable 2D network (4) in mother solution. The cause for these transformations (2–4) and the magnetic behavior (1–3) of the CPs have been discussed.

Architectures varying from discrete molecular units to 2-dimensional coordination polymers and photoluminescence behavior of zinc and cadmium comprising an anionic zwitterion of rigid 4,5-dicarboxy-1,3-dimethyl-1H-imidazolium iodide

A rigid imidazolium dicarboxylate ligand, 4,5-dicarboxy-1,3-dimethyl-1H-imidazolium iodide (H2DDII), was synthesized and employed in the construction of metal complexes or coordination polymers (CPs) comprising an anionic zwitterion (DDI−), namely, [Zn(Cl)(H2O)2(DDI)]·(H2O) (2), {[Zn2(DDI)3(H2O)2]·I}n (3), [Zn2(DDI)2I]·2H2O (4), [Zn(DDI)2(H2O)3]·(H2O)2 (5) and [Cd(DDI)2]n (6). In addition, the ligand upon crystallization forms a zwitterion, [HDDI, (1)] by losing HI and shows both intra- and intermolecular H-bonding and an interesting intermolecular CO⋯C short contact. The carboxylate unit of the ligand exhibits terminal monodentate and bidentate chelate modes of coordination. The stoichiometric ratio of metal to ligand, nature of base, type of metal salt and solvent conditions affected the architectures and dimensionality of 2–6 from zero dimensional monomers and dimers to 2D coordination polymers (CPs). Complex 2 forms a discrete molecular unit extended by supramolecular interactions to form 2D rectangular sheets. In 3, a crown shaped macrocycle results in a 2D herringbone CP and extends to a 3D supramolecular architecture on account of a coordination network containing trapped iodide as counter anions. Complex 4 forms a dimer with coordinated iodide ions and forms an infinite 1D ladder shaped supramolecular architecture. Complex 5 forms another discrete molecular unit different from 2, and extends to a 3D architecture through supramolecular interactions. Complex 6 forms a 2D CP with Cd(II) forming an interesting “fish scale pattern” and lacks any counter anion or solvent molecules. Additionally, the thermal stability of complexes 2–6 was analyzed by thermogravimetric analysis. In addition, the solid state photoluminescence properties of H2DDII and compounds 2–6 were investigated at room temperature.