Ramaswamy Murugavel

Cyclopentadiene based low-valent group 13 metal compounds: ligands in coordination chemistry and link between metal rich molecules and intermetallic materials.

Ligands in Coordination Chemistry and Link between Metal Rich Molecules and Intermetallic Materials Sandra Gonzaĺez-Gallardo,† Timo Bollermann,‡ Roland A. Fischer,*,‡ and Ramaswamy Murugavel* †Karlsruhe Institute of Technology (KIT), Institute of Inorganic Chemistry, 76131 Karlsruhe, Germany ‡Lehrstuhl für Anorganische Chemie II, Organometallics & Materials Chemistry, Ruhr-University Bochum, D-44780 Bochum, Germany Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai−400076, India

Noncovalent synthesis of hierarchical zinc phosphates from a single zn(4)o(12)p(4) double-four-ring building block: dimensionality control through the choice of auxiliary ligands

In contrast to the well-known reaction of phosphonic acids RP(O)(OH)(2) with divalent transition-metal ions that yields layered metal phosphonates [RPO(3)M(H(2)O)](n), the 2,6-diisopropylphenyl ester of phosphoric acid, dippH(2), reacts with zinc acetate in methanol under ambient conditions to afford tetrameric zinc phosphate [(ArO)PO(3)Zn(MeOH)](4) (1). The coordinated methanol in 1 can be readily exchanged by stronger Lewis basic ligands at room temperature. This strategy opens up a new avenue for building double-four-ring (D4R) cubane-based supramolecular assemblies through strong intercubane hydrogen-bonding interactions. Seventeen pyridinic ligands have been used to synthesize as many D4R cubanes [(ArO)PO(3)Zn(L)](4) (2-18) from 1. The ligands have been chosen in such a way that the majority of them contain an additional functional group that could be used for noncovalent synthesis of extended structures. When the ligand does not contain any other hydrogen-bonding donor-acceptor sites (e.g., 2,4,6-trimethylpyridine (collidine)), zero-dimensional D4R cubanes have been obtained. The use of pyridine, lutidine, 2-aminopyridine, and 2,6-diaminopyridine, however, results in the formation of linear or zigzag one-dimensional assemblies of D4R cubanes through strong intermolecular C-H...O or N-H...O interactions. Construction of two-dimensional assemblies of zinc phosphates has been achieved by employing 2-hydroxypyridine or 2-methylimidazole as the exo-cubane ligand on zinc centers. The introduction of an alcohol side chain on the pyridinic ligand in such a way that the -CH(2)OH group cannot participate in intracubane hydrogen bonding (e.g., pyridine-3-methanol, pyridine-4-methanol, and 3,5-dimethylpyrazole-N-ethanol) leads to the facile noncovalent synthesis of three-dimensional framework structures. Apart from being useful as building blocks for noncovalent synthesis of zeolite-like materials, compounds 1-18 can also be thermolyzed at approximately 500 degrees C to yield high-purity zinc pyrophosphate (Zn(2)P(2)O(7)) ceramic material.

First alkaline earth metal 3-aminobenzoate (3-aba) complex: 1-D polymeric [Ca(3-aba)2(H2O)2]n assembly

Abstract The reaction of CaCO3 or CaCl2·2H2O with 3-abaH results in the formation of the first alkaline-earth metal complex of 3-abaH [Ca(3-aba)2(H2O)2]n (1) in good yield. The product has been characterized by elemental analysis, IR, UV–vis and 1 H NMR spectral studies, TGA and single crystal X-ray diffraction studies. The molecular structure of 1 is made up of 1-D polymeric chains that are hydrogen-bonded to each other. The Ca2+ ion in 1 is surrounded by eight oxygen atoms in a distorted square-antiprismatic geometry.

Di-, tri-, tetra-, and hexanuclear copper(II) mono-organophosphates: structure and nuclearity dependence on the choice of phosphorus substituents and auxiliary N-donor ligands.

Reactions of 2,6-dimethylphenyl phosphate (dmppH(2)) and 2,6-diisopropylphenyl phosphate (dippH(2)) with copper(II) precursors have been investigated in the presence of auxiliary N-donor ligands, and new structural types of copper phosphates have been isolated. Copper acetate reacts with dmppH(2) in the presence of either 3,5-di-tert-butyl pyrazole (dbpz) or 3,5-dimethyl pyrazole (dmpz), leading to the isolation of tetrameric complex [Cu(dmpp)(dbpz)](4) 1 and hexanuclear cage complex [Cu(6)(PO(4))(dmpp)(3)(OAc)(3)(dmpz)(9)] 2, respectively. Whereas compound 1 is a cubane-shaped cluster whose Cu(4)O(12)P(4) core resembles the double-4-ring (D4R) zeolite SBU, compound 2 is a novel hexanuclear copper complex with an unprecedented structure in metal phosphate chemistry. Use of bulkier dippH(2) in the above reactions, however, yielded metal-free acid-base complexes [(dippH)(dbpz)(dbpzH)] 3 and [(dippH)(dmpz)(dmpzH)] 4, respectively. The reactions carried out between copper acetate and dmppH(2) or dippH(2) in the presence of chelating ligand 1,10-phenanthroline produced structurally similar dimeric copper phosphates [Cu(phen)(dmpp)(CH(3)OH)](2).2CH(3)OH 5 and [Cu(phen)(dipp)(CH(3)OH)](2).2CH(3)OH 6 with a S4R SBU core. Changing the copper source to [Cu(2)(bpy)(2)(OAc)(OH)(H(2)O)].2ClO(4) and carrying out reactions both with dippH(2) and with dmppH(2) result in the formation of trinuclear copper phosphates [Cu(3)(bpy)(3)(dmpp)(2)(CH(3)OH)(3)].2ClO(4).2CH(3)OH 7 and [Cu(3)(bpy)(3)(dipp)(2)(CH(3)OH)(3)].2ClO(4).2CH(3)OH 8. The three copper ions in 7 and 8 are held together by two bridging phosphate ligands to produce a tricyclic derivative whose core resembles the 4=1 SBU of zeolites. Compounds 1-8 have been characterized by elemental analysis and IR, absorption, emission, and EPR spectroscopic techniques. The crystal structures of compounds 1, 2, 4, 5, 6, and 8 have also been established by single-crystal X-ray diffraction studies.

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.

Tetra- and decanuclear iron(III) phosphonates: observance of a rare P-C bond cleavage in a homogeneous medium

Reactions of tert-butylphosphonic acid (tBuPO3H2) with two different Fe(III) precursors have been investigated. The reaction of precursor complex [Fe3(mu3-O)(O2CPh)6(H2O)3]Cl with tBuPO3H2 in pyridine (py) leads to the formation of tetranuclear iron(III)phosphonate [Fe4O(tBuPO3)3(O2CPh)3(py)3Cl] x 3.5 py (1) as single crystals. The change of the Fe(III) source to FeCl3 under similar reaction conditions results in the isolation of decanuclear complex [Fe10(OH)8(HPO4)(tBuPO3)8(tBuPO3H)4(py)8] x 4 py x 5 H2O (2). Compounds 1 and 2 have been characterized by elemental analysis, spectroscopic studies, and single-crystal X-ray diffraction studies. While the structure of 1 could be described as a tetrahedral cluster supported by benzoate and phosphonate ligands, the molecular structure of 2 is unprecedented in metal phosphonate chemistry. In the course of formation of 2, tBuPO3H2 undergoes a rare P-C bond cleavage at room temperature and produces the phosphate anion, which then acts as a template for the construction of a novel decanuclear iron-phosphate-phosphonate with a hitherto unknown core architecture. The temperature dependence of the chiT product in 2 reveals dominant antiferromagnetic interactions between Fe(III) centers.

[3+3] Imine and β-ketoenamine tethered fluorescent covalent-organic frameworks for CO2 uptake and nitroaromatic sensing

Imine and β-ketoenamine based covalent-organic frameworks (COFs) are nitrogen rich organic porous materials which offer enhanced affinity for carbon dioxide. In this article, synthesis, gaseous uptake and chemo-sensing properties of four new 2-D COFs with [3+3] structural motifs have been reported. The COFs have been synthesized from readily available C3-symmetric aldehyde and amine building units via Schiff base condensation. Prior to the synthesis, reactivity and structural integrity of the building blocks were appropriated by a fully characterized model Schiff base (TAPB-Benz) obtained from the condensation of 1,3,5-tris(4′-aminophenyl)benzene (TAPB) and benzaldehyde. Reaction of 1,3,5-tris(4′-aminophenyl)benzene (TAPB) and 1,3,5-tris(4′-amino-3′,5′-isopropylphenyl)benzene (iPrTAPB) with 1,3,5-tris(4′-formylphenyl)benzene (TFPB) and 1,3,5-triformylphluroglucinol (TFP) in dry dioxane and acetic acid (cat.) resulted in the formation of crystalline 2-D frameworks, TAPB-TFPB, iPrTAPB-TFPB, TAPB-TFP and iPrTAPB-TFP. The COFs feature permanent porosity with high surface area and carbon dioxide uptake. Among these, iPrTAPB-TFP revealed the highest surface area of 756 m2 g−1 (Brunauer–Emmett–Teller) and 1515 m2 g−1 (Langmuir) and carbon dioxide uptake of 105 mg g−1 (273 K, 1 atm). Notably with 180 mg g−1 (273 K, 1 atm), TAPB-TFP shows the highest CO2 uptake capacity among all the COFs which is also comparable to previously reported high CO2 uptake capacity COFs. Furthermore, due to the inherent fluorescent capability of triphenylbenzene, the COFs are endowed with fluorescence and fluorescence chemo-sensing ability for polynitroaromatic analytes.

Charge transfer aided selective sensing and capture of picric acid by triphenylbenzenes

A fluorescent chemo-sensor, 1,3,5-tris(4′-(N,N-dimethylamino)phenyl)benzene was synthesized by substituting the N–H protons of 1,3,5-tris(4′-aminophenyl)benzene with methyl groups. The chemo-sensor shows highly selective and remarkable fluorescence quenching in the presence of picric acid with a detection limit of 1.5 ppm. The origin of the selectivity was investigated using absorption, fluorescence emission and 1H NMR spectroscopic techniques. The solid state structure of 1,3,5-tris(4′-(N,N-dimethylamino)phenyl)benzene and its picric acid complex reveals multiple hydrogen bonds (N–H⋯O and C–H⋯O), π–π interactions and electrostatic interactions between 1,3,5-tris(4′-(N,N-dimethylamino)phenyl)benzene and picric acid. The proton transfer process from picric acid to 1,3,5-tris(4′-(N,N-dimethylamino)phenyl)benzene results in the formation of picrate anions and the triply protonated 1,3,5-tris(4′-(N,N-dimethylamino)phenyl)benzene species containing dimethylammonium (–NHMe2+) groups.

One, two, and three methylene phosphonic acid groups (–CH2PO3H2) on a mesitylene ring: synthesis, characterization and aspects of supramolecular aggregation

The ease of substitution of –CH2Br group on the mesitylene ring in a stepwise manner has been exploited to prepare mesitylene mono-, bis-, and tris-methylene phosphonic acids C6H2Me3(CH2PO3H2) (1), C6HMe3(CH2PO3H2)2 (2), and C6Me3(CH2PO3H2)3 (3) in 80–90% yield, through a Michaelis–Arbuzov reaction followed by acid hydrolysis. Compounds 1–4 have been characterized by analytical and spectroscopic (IR, NMR, and MS) techniques. The X-ray structural investigations on all the three compounds reveal that the central mesitylene ring is a robust platform for hosting multiple methylene phosphonic acid groups. Mesitylene mono-methylene phosphonic acid 1, which can be considered as the sterically encumbered modification of benzyl phosphonic acid, interestingly associates as a one-dimensional tubular structure through extensive O–H⋯O hydrogen bonding between adjacent –PO3H2 groups, albeit with no such interactions between the tubes due to the highly hydrophobic nature of the surface. The X-ray structure of mesitylene-1,3-diphosphonic acid 2 reveals that the molecules exhibit a syn-orientation of the –CH2PO3H2, which are involved in extensive P–OH⋯O hydrogen bonding to result in a two-dimensional layered structure. The presence of three –PO3H2 units on the same side of the mesitylene ring in 3 results in a three-dimensional framework solid. The present studies clearly reveal a linear relationship between the dimensionality of the supramolecular structure and the number of phosphonic acid moieties on the mesitylene ring.

Water in organoaluminum chemistry! Three-in-one aluminophosphate clusters that incorporate boehmite repeating units.

Mix and match! Slow introduction of water in the reaction between a monoaryl phosphate and an aluminum alkyl or Al 2 Cl 6 leads to the formation of three-in-one clusters, which constitute aluminophosphate and aluminum hydroxide moieties within the same molecules (see graphic, C and H atoms not shown). Impeding the attack of water by kinetically stabilizing the aluminum alkyl leads to the isolation of a dimeric aluminophosphate, which throws mechanistic insights into the formation of larger clusters.