N. N. Adarsh

A Novel, Air-Stable Phosphine Ligand for the Palladium-Catalyzed Suzuki−Miyaura Cross-Coupling Reaction of Chloro Arenes

A novel, air-stable phosphine ligand, prepared from readily available 2-bromonitrobenzene and vinylmagnesium bromide, combines with Pd(CH(3)CN)(2)Cl(2) to afford an effective catalyst for Suzuki-Miyaura cross-coupling of aryl, heteroaryl, and allyl chlorides with phenylboronic acid.

Metal–organic frameworks derived from bis-pyridyl-bis-amide ligands : Effect of positional isomerism of the ligands, hydrogen bonding backbone, counter anions on the supramolecular structures and selective crystallization of the sulfate anion

Three new metal–organic frameworks, namely [Co(μ-L1)2(Cl)2]n1, [Cd(µ-L1)2(NO3)2]n2 and [{Co(μ-L1′)(H2O)4}.SO4·3(H2O)]n3 (L1 = N,N′-bis-(4-pyridyl)isophthalamide, L1′ = N,N′-bis-(3-pyridyl)isophthalamide) have been synthesized and characterized. The single crystal structures of 1–3 and the free ligand L1 are discussed in the context of the effect of positional isomerism of the ligands, hydrogen bonding backbone and counter anions on the supramolecular structural diversities observed in these MOFs. Selective crystallization of the sulfate anion from a mixture of L1′, CoSO4, Co(NO3)2, Co(ClO4)2, Co(OAc)2, Co(BF4)2 was evident from the isolation of 3 which was confirmed by powder X-ray diffraction, elemental analysis and IR data.

Zn(II) metal–organic frameworks (MOFs) derived from a bis-pyridyl-bis-urea ligand: effects of crystallization solvents on the structures and anion binding properties

The Reaction of N,N′-bis-(3-pyridyl)ethylene-bis-urea (BPEBU) with ZnSO4 in 2:1 ligand:metal ratio in various crystallization solvents afforded four metal–organic frameworks (MOFs), namely [{Zn(H2O)3(SO4)(µ-BPEBU)}·EG·2H2O]n2, [{Zn(µ-BPEBU)2(H2O)2}.SO4·2H2O.2THF}n3, [{Zn(µ-BPEBU)2(H2O)2}·SO4·2H2O.2acetone}n4 and [{Zn(µ-BPEBU)2(H2O)2}·SO4·2H2O·2(1,4-dioxane)}n5, which were mainly characterized by single cyrstal X-ray diffraction. MOFs 3–5 are found to be isomorphous. The study revealed that the crystallization solvents affected the structures; the single crystal structure of the free BPEBU was also discussed in the context of the conformation and ligating topology of the ligand found in the reported MOFs. When the MOFs syntheses were performed in a competitive environment wherein other oxo-counter anions such as NO3−, ClO4− and CF3SO3− were present, the isolated MOFs turned out to be the corresponding sulfate MOFs 2–4 indicating interesting sulfate selectivity.

Supramolecular Synthons in Noncovalent Synthesis of a Class of Gelators Derived from Simple Organic Salts: Instant Gelation of Organic Fluids at Room Temperature via in Situ Synthesis of the Gelators

The supramolecular synthon approach has been employed to synthesize noncovalently a series of low molecular mass organic gelators (LMOGs) derived from benzylammonium salts of variously substituted benzoic acids. The majority of the salts (75%) prepared showed interesting gelation properties. Instant gelation of an organic fluid, namely methyl salicylate, was achieved at room temperature by using most of the gelator salts by in situ synthesis of the gelators. Table top rheology and scanning electron microscopy (SEM) were used to characterize the gels. Single crystal X-ray diffraction studies revealed the presence of both 1D and 2D supramolecular synthons. X-ray powder diffraction (XRPD) studies indicated the presence of various crystalline phases in the fibers of the xerogels. By using these data, a structure-property correlation has been attempted and the working hypothesis for designing the gelator has been reinforced.

An unprecedented all helical 3D network and a rarely observed non-interpenetrated octahedral network in homochiral Cu(II) MOFs: effect of steric bulk and π–π stacking interactions of the ligand backbone

Two bis-pyridyl-bis-amide based chiral ligands derived from L-phenylalanine and L-alanine resulted in an unprecedented all helical 3D network and a rarely observed microporous octahedral network in the corresponding homochiral Cu(II) MOFs. This remarkable structural difference displays the effect of amino acid side chain and ligating topology of the ligands on the supramolecular structures in these MOFs.

Folding and Unfolding Movements in a [2]Pseudorotaxane

A new dibenzo[24]crown-8 derivative (1) was synthesized and functionalized with aromatic moieties such as naphthalene and coumarin units. These two fluorophores are known to form an effective FRET (Forster resonance energy transfer) pair, and this formed the basis for the design of this host crown ether derivative. Results of the steady-state and time-resolved fluorescence studies confirmed the resonance energy transfer between the donor naphthalene moiety and acceptor coumarin fragment, while NMR spectra and computational studies support a folded conformation for the uncomplexed crown ether 1. This was found to form an inclusion complex, a [2]pseudorotaxane type with imidazolium ion derivatives as the guest molecules with varying alkyl chain lengths ([C(4)mim](+) or [C(10)mim](+)). The host crown ether (1) tends to adopt an open conformation on formation of the interwoven inclusion complex (1·[C(4)mim](+) or 1·[C(10)mim](+)). This change in conformation, from the folded to a open one, was predicted by computational as well as (1)H NMR studies and was confirmed by single crystal X-ray structure for one (1·[C(4)mim](+)) of the two inclusion complexes. The increase in the effective distance between the naphthalene and coumarin moieties in the open conformation of these inclusion complexes was also supported by the decrease in the effective FRET process that was operational between naphthalene and coumarin moieties in the free molecule (1). Importantly, this inclusion complex formation was found to be reversible, and in the presence of a stronger base/polar solvent, such as triethyl amine/DMSO, the deprotonation/effective solvation of the cationic imidizolium ions ([C(4)mim](+) or [C(10)mim](+)) resulted in decomplexation or dethreading with restoration of the original emission spectra for 1, which signifies the subsequent increase in the FRET process. Thus we could demonstrate that a molecular folding-unfolding type of movement in the crown ether derivative could be induced by chemical input as an imidazolium ion.

Combinatorial library of primaryalkylammonium dicarboxylate gelators: a supramolecular synthon approach.

Following the supramolecular synthon approach, a combinatorial library comprising 35 organic salts derived from 7 dicarboxylic acids (malonic-, succinic-, adipic-, L-tartaric-, maleic-, phthalic-, and isophthalicacid) and 5 primaryalkyl amines Me-(CH2)n-NH2 (n = 11-15) was prepared and scanned for gelation. About 66% of the salts in the combinatorial library were found to show moderate to good gelling ability in various polar and nonpolar solvents including commercial fuels such as petrol. The majority of the salts having a rigid, unsaturated anionic backbone (maleate, phthalate, and isophthalate) did not show gelation; only the corresponding hexadecylammonium salts showed gelation. Some of the representative gels were characterized by rheology, small-angle neutron scattering (SANS), optical microscopy (OM), and scanning electron microscopy (SEM). Single-crystal structures of two gelator and two nongelator salts were also discussed in the context of supramolecular synthon and structure-property correlation.

Crystal engineering of Fe(II) spin crossover coordination polymers derived from triazole or tetrazole ligands.

The past decade has witnessed intense research activity in the area of Fe(II) spin crossover coordination polymers, which are structurally diverse and functionally intriguing materials. In this endeavor, a less exploited series of ligands have been selected among various N-donor triazole and tetrazole molecules. Developing conventions that allow the tailoring of such functional materials with predictable architecture and properties is an important objective and current interest in crystal engineering. However, detailed knowledge on the structure-property correlation is still scanty due to the small number of crystal structures of such compounds. The principal focus is to decipher the effect of various supramolecular factors such as intermolecular interactions, hydrogen bonding etc., on the resultant Fe(II) coordination polymers. This tutorial review aims at highlighting some of the developments of such structurally diverse and functionally intriguing 1D polymeric chains, 2D and 3D networks built from triazole or tetrazole ligands exhibiting fascinating spin crossover phenomena.

Metalla-macro-tricyclic cryptands: anion encapsulation and selective separation of sulfate via in situ crystallization

A conformationally flexible bis-pyridyl-bis-amide ligand, namely N,N′-bis-(3-pyridyl)isophthalamide (L1), has been exploited to synthesize metalla-macro-tricyclic cryptands by reacting it with various Cu(II) salts having different counteranions. Out of the five coordination compounds, namely [{Cu(μ-L1)2(H2O)2}·SO4·2H2O·X] (1a), [{Cu(μ-L1)(H2O)4}·SO4·3H2O]∝ (1b), [{Cu(μ-L1)2(H2O)2}·SiF6·CH3OH·4H2O]∝ (2), [{Cu(μ-L1)2(μ-Cl)}·ClO4]∝ (3) and [{Cu(μ-L1)2(H2O)}·(NO3)2·2H2O·X]∝ (4a) (X = disordered solvents), compounds such as 1a, 2 and 3 are metallacryptands, of which 3 is the first example of a polymeric metalla-macro-tricyclic cryptand. The effect of the conformation-dependent ligating topology and hydrogen bonding backbone of ligand L1, and counteranions on the formation of metallacryptands is discussed. Interestingly, an important anion, namely SO42−, has been separated by concomitantly crystallizing 1a and 1b from a complex mixture of anions, such as SO42−, NO3− and ClO4−, by following an in situ crystallization technique. Magnetic interactions in 3 have been investigated as a typical example. Weak antiferromagnetic coupling is observed in 3, as expected given the topology of the networks.

Single-walled metal-organic nanotube built from a simple synthon.

A conformationally flexible triazole-carboxylic acid ligand derived from an L-amino acid, namely, 4 H-1,2,4-triazol-4-yl-acetic acid (αHGlytrz), has been exploited to synthesize a structurally diverse and functionally intriguing metal-organic framework with CuSiF6. The crystal structure reveals a novel single-walled metal-organic nanotube (SWMONT), namely, {[Cu3(μ3-OH)(H2O)3(Glytrz)3]⋅SiF6⋅8 H2O⋅X}∞ (1), (where X = disordered lattice water molecules) having a pore size as large as zeolites. Compound 1 was synthesized as crystals, as powder, or as layers by precipitation/electrodeposition. Mercury intrusion porosimetry demonstrates the ability of this material to store metallic mercury, after a pressure treatment, contrary to previous literature examples.