• Volume 124, Issue 6

November 2012,   pages  1143-1450

• Foreword

• Mechanism of -O-O- bond activation and catalysis by RuIII-pac complexes (pac = polyaminocarboxylate)

This paper presents the mechanistic aspects of the -O-O- bond activation by the Ru-pac (pac = polyaminocarboxylate) complex leading to the formation of various catalytic active species, viz. [RuIII(pac)(OOH)]2−, [RuIV(pac)(OH)] and [RuV(pac)(O)], and their reactivity towards oxidation of a few organic compounds.

• Helical chirality induction of expanded porphyrin analogues

Expanded porphyrin analogues with unique figure-eight conformation were prepared by way of useful pyrrole intermediates such as bis(azafulvene)s and 2-borylpyrrole. Supramolecular chirogenesis of cyclooctapyrrole O1 with 32𝜋-cycloconjugation was successfully applied to determine absolute configuration of chiral carboxylic acids. Dinuclear CuII complex of cyclooctapyrrole O2 with interrupted 𝜋-conjugation was resolved by HPLC into enantiomers and their helical handedness was determined by theoretical simulation of their CD spectral pattern. Enantioselective induction of helicity in the metal helicate formation in the presence of a chiral promoter was demonstrated by using (𝑅)-(+)-1-(1-phenyl)ethylamine that favoured 𝑃, 𝑃 helicity. Dinuclear CoII complexes of cyclotetrapyrroletetrapyridine O3 were found to be substitution labile and pick up amino acid anions in water. Those amino acid complexes of O3Co2 were rendered to adopt a particular unidirectional helical conformation preferentially depending on the ligated amino acid anion.

• Organometallic complexes of the platinum metals: Synthesis, structure, and catalytic applications

Reaction of a group of N-(aryl)picolinamides (pic-R) with [Ru(PPh3)2(CO)2Cl2] in refluxing 2-methoxyethanol in the presence of a base affords hydrido complexes of two types (1-R and 2-R), which are geometric isomers. Similar reaction with N-(naphthyl)picolinamide (pic-nap) yields an organoruthenium complex (3) via formation of a hydrido intermediate. Reaction of 2-(arylazo)phenols (ap-R) with [Ir(PPh3)3Cl] in refluxing ethanol affords a mono-hydrido intermediate (4-R), a di-hydrido intermediate (5-R) and an organoiridium complex (6-R) as the final product, where the azo-ligand is coordinated as CNO-donor. Reaction of ap-R ligands with [Rh(PPh3)3Cl] yields organorhodium complexes (7-R) analogous to 6-R, but without any hydrido intermediate. N-(2'-hydroxyphenyl)benzaldimines (hpbz-R) react with [Rh(PPh3)3Cl] to yield a group of organorhodium complexes (8-R), where the hpbz-R ligands are coordinated in CNO-fashion. Upon interaction with [Ir(PPh3)3Cl] 2-(2',6'-dimethylphenylazo)-4-methylphenol (dmap) undergoes a methyl C-H activation and affords organoiridium complex 9, while 2-(2'-methylphenylazo)-4-methylphenol (mmap) undergoes a phenyl C-H activation and gives organoiridium complex 10. Reaction of benzaldehyde thiosemicarbazones (bztsc-R) with [Pd(PPh3)2Cl2], carried out with the expectation of inducing CNS-mode of coordination, actually has yielded complexes (11-R) where the bztsc-R is coordinated in an uncommon NS-mode forming a fivemembered chelate ring associated with a restricted rotation around the imine (C=N) bond. These palladium complexes are found to catalyse C-C cross coupling reactions very efficiently. Crystal structures of selected complexes of each type have been determined by X-ray crystallography.

• Digestive ripening: a synthetic method par excellence for core-shell, alloy, and composite nanostructured materials

The solvated metal atom dispersion (SMAD) method has been used for the synthesis of colloids of metal nanoparticles. It is a top-down approach involving condensation of metal atoms in low temperature solvent matrices in a SMADreactor maintained at 77 K.Warming of the matrix results in a slurry ofmetal atoms that interact with one another to form particles that grow in size. The organic solvent solvates the particles and acts as a weak capping agent to halt/slow down the growth process to a certain extent. This as-prepared colloid consists of metal nanoparticles that are quite polydisperse. In a process termed as digestive ripening, addition of a capping agent to the as-prepared colloid which is polydisperse renders it highly monodisperse either under ambient or thermal conditions. In this, as yet not well-understood process, smaller particles grow and the larger ones diminish in size until the system attains uniformity in size and a dynamic equilibrium is established. Using the SMAD method in combination with digestive ripening process, highly monodisperse metal, core-shell, alloy, and composite nanoparticles have been synthesized. This article is a review of our contributions together with some literature reports on this methodology to realize various nanostructured materials.

• Electronic structures of ruthenium complexes encircling non-innocent ligand assembly

Electronic structural forms of selected mononuclear and dinuclear ruthenium complexes encompassing redox non-innocent terminal as well as bridging ligands have been addressed. The sensitive valence and spin situations of the complexes have been established in the native and accessible redox states via detailed analysis of their crystal structures, electrochemistry, UV/VIS/NIR spectroelectrochemistry, EPR signatures at the paramagnetic states and DFT calculations. Mononuclear complexes exhibit significant variations in valence and spin distribution processes based on the simple modification of the non-innocent ligand frameworks as well as electronic nature of the co-ligands, 𝜎-donating or 𝜋-accepting. Dinuclear complexes with modified pyrazine, 𝑝-quinone and azo-derived redox-active bridging ligands show complex features including redoxinduced electron-transfer (RIET), remote metal to metal spin-interaction in a three-spin metal-bridge-metal arrangement as well as electron-transfer driven chemical transformation (EC).

• Simple tertiary phosphines to hexaphosphane ligands: Syntheses, transition metal chemistry and their catalytic applications

Designing efficient phosphorus-based ligands to make catalysts for homogeneous catalysis has been a great challenge for chemists. Despite a plethora of phosphorus ligands ranging from simple tertiary phosphines to polyphosphines are known, the enthusiasm to generate new ones is mainly due to the demand from industry for economical and robust catalytic system operational under normal atmospheric conditions. In this context, we have developed new synthetic methodologies for making unusual inorganic ring systems containing trivalent phosphorus centres, novel phosphorus-based multidentate and hybrid ligands and explored their rich transition metal chemistry and catalytic applications. We have also fine tuned a few existing ligand systems with donor functionalities to employ them in homogeneous catalysis. The details are summarized in this account.

• Reactions of a stable dialkylsilylene and their mechanisms

Various reactions for a stable dialkylsilylene, 2,2,5,5-tetrakis(trimethylsilyl)silacyclopentane-1,1-diyl (1), are summarized and their mechanisms are discussed. Silylene 1 isomerizes to the corresponding silaethene via the 1,2-trimethylsilyl migration. Reduction of 1 with alkali metals affords the corresponding radical anion 1.− with a relatively small 29Si hfs constant (2.99 mT) and a large g-factor (g = 2.0077) compared with those for trivalent silyl radicals. Photo-excitation of 1 generates the corresponding singlet excited state (1$^{1\ast}$) with the lifetime of 80.5 ns. The excited state reacts with C=C double bond compounds including benzene, naphthalene, and (𝐸)- and (𝑍)-2-butenes. Although the thermal reactions of 1 with haloalkanes occur via radical mechanisms, the insertion into O-H, Si-H and Si-Cl bonds proceeds concertedly via the threemembered cyclic transition states. The reaction of 1 with H2SiCl2 gives the Si-Cl insertion product exclusively, while the quantitative insertion to Si-H bond occurs when Me2SiHCl is used as a substrate. The origin of the rather unusual Si-H/Si-Cl selectivity is elucidated using DFT calculations. Silylene 1 adds to C=C, C≡C, and C=O 𝜋 bonds to afford the corresponding silacycles as stable compounds. The importance of the carbonyl silaylides during the reactions of silylenes with aldehydes and ketones is emphasized.

• Cu(II) complexes of glyco-imino-aromatic conjugates in DNA binding, plasmid cleavage and cell cytotoxicity

Binding of metal complexes of C2-glucosyl conjugates with DNA has been established by absorption and fluorescence studies. Conformational changes occurred in DNA upon binding have been studied by circular dichroism. All these studies are suggestive that the metal complexes bind to DNA through intercalation. Binding of di-nuclear copper complex 5 was found to be stronger when compared to the other complexes studied. Copper complexes were found to cleave the plasmid DNA in the absence of oxidizing or reducing agent, whereas, zinc complexes do not cleave. Metal complexes have shown toxicity to the HeLa and MCF-7 cell lines.Morphological studies, western blot and FACS analysis are suggestive of apoptotic cell death induced by the metal complexes. Di-nuclear copper complexes were found to be better as compared to the mononuclear ones in binding, plasmid cleavage and also in causing more cell death.

• Cu(I)/Cu(II) templated functional pseudorotaxanes and rotaxanes

Threaded complexes like pseudorotaxanes, rotaxanes based on Cu(I)/Cu(II) ions have shown to be promising for the construction of mechanically interlocked molecular-level architectures. In this short review, we focus on the synthetic strategies developed to construct pseudorotaxanes and rotaxanes using Cu(I)/Cu(II) ions as template. Further, brief discussions on chemical and mechanical properties associated with some of the selected to Cu(I)/Cu(II) based pseudorotaxanes and rotaxanes are presented.

• Linear, branched and network polysilanes with thienyl/furyl substituted sila-alkyl side chains and their applications for the synthesis of fluorescent silver nanoparticles/clusters

The scope of Wurtz coupling and catalytic dehydrocoupling methods for the synthesis of functional polysilanes of compositions, [RR'Si]$_n$ (linear), [(PhMeSi)$_x$-co-(RSi)$_{1−x}$]$_n$ (branched) and [RSi]$_n$ (network) [R = Et3SiCH2CH2, 2-Fu/2-ThMe2SiCH2CH2 (Fu = Furyl, Th = Thienyl), 𝑛-Hex or Ph; R' = H or Me] is presented. By virtue of 𝜎-delocalized silicon backbone and variable HOMO-LUMO band gap energies, these polymers are found to be promising candidates as reducing agents for Ag(I) ions in toluene/cyclo-hexane and provide a simple approach for ‘size-controlled’ synthesis of silver nanoparticles (AgNPs) as well as fluorescent polymer-silver nanocomposites.

• Chalcogenated Schiff bases: Complexation with palladium(II) and Suzuki coupling reactions

Chalcogenated Schiff bases of 5-chloroisatin (L1-L3), 2-(methythio)benzaldehyde (L4), 2-acetylpyridine (L5) and benzaldehyde (L6-L7) have been synthesized. Both the carbonyl groups of 5- chloroisatin appear to be reactive (noticed for the first time) for making &gt;C=N bond, of course one at a time only. The 1H, 13C{1H}, 77Se{1H} and 125Te{1H} NMR spectroscopy have been used to establish the coexistence of two products, which were found in the ratio 53:47 (E = S), 55:45 (E = Se) and 81:19 (E = Te). The larger amount is of the one in which C=O group away from NH is derivatized. The two products are not separable. Palladium complexes (1-4) of Schiff bases of other three aldehydes were synthesized. The ligands as well as complexes were characterized by multinuclear NMR spectroscopy. The crystal structures of [Pd(L4/L5)Cl][ClO4] (1/2) have been solved. The Pd-Se bond lengths are 2.4172(17) and 2.3675(4) Å, respectively for 1 and 2. The Pd-complexes (3-4) of L6-L7 were explored for Suzuki-Miyaura coupling and found promising as 0.006 mol % of 3 is sufficient to obtain good conversion with TON up to $1.58 \times 10^4$.

• Click-generated triazole based ferrocene-carbohydrate bioconjugates: A highly selective multisignalling probe for Cu(II) ions

Two Cu2+-specific colorimetric sensors, based on ferrocene-carbohydrate bioconjugates, 2, C46H56O20N6Fe and 3, C28H33O10N3Fe were designed and synthesized in good yields. Both the compounds, 2 and 3, behave as very selective and sensitive chromogenic and electrochemical chemosensor for Cu2+ ion in aqueous environment (CH3CN/H2O (2:8, $v/v$). The analytical detection limit (ADL) for receptor 2 was $7.5 \times 10^{−7}$ M. The considerable changes in their absorption spectra of 2 and 3 are accompanied by the appearance of a new low energy (LE) peak at 630 nm (2: $\epsilon = 1600$ M-1 cm-1 and 3: 822 M-1 cm-1). This is further accompanied by a strong colour change from yellow to dark green that allows the prospective for naked eye’ detection of Cu2+ ion.

• Metal derivatives of heterocyclic-2-thiones: Variable donor ability, C-S rupture and new structural motifs

The chemistry of thio-ligands based on heterocyclic-2-thiones, namely, pyridine-2-thione (SNC5H5), imidazolidine-2-thione (SN2C3H6), imidazoline-2-thione (SN2C3H4), 1-methyl-imidazoline-2-thione (SN2C4H6) and thiazolidine-2-thione (S2NC3H5) with coinage and some other metals are described. The synthesis, solvent effect, isolation of new products after C-S rupture and crystal structure are also discussed. For example, copper(I) bromide with 1-methyl-imidazoline-2-thione (SN2C4H6) in acetonitrile formed CuI trinuclear complex, {Cu3($\kappa^1$-Br)3(𝜇-SN2C4H6)3}·CH3CN. This reaction in the presence of chloroform involved C-S bond rupture, oxidation of sulphur to sulphate and bromination of ring and formed a tetranuclear cluster, Cu4($\kappa^1$-N-(N2C4H5Br)4($\mu_4$-O)(𝜇-Br)6] (N2C4H5Br = 2-bromo-1-methyl-imidazole). The reaction of copper(I) chloride with 1-methyl-imidazoline-2-thione (SN2C4H6) in acetonitrile also involved C-S rup ture and formed a chloro-bridged dinuclear complex [Cu2{$\kappa^2$-N,N-(N2C4H5)2S}2(𝜇-Cl)2Cl2] {(N2C4H5)2S = 1, 1'-dimethyl-2,2'-di-imidazolyl sulphide}. Significantly copper(I) bonded to more polarisable iodide ion (Cu-I) does not involve C-S rupture and in this case it formed CuI polynuclear complex, {Cu2(𝜇-I)2(𝜇-SN2C4H6)2}$_n$. Both copper(I) chloride and copper(I) bromide with 1-methyl-imidazoline-2-thione in dimethyl sulphoxide involved C-S rupture and oxidation of sulphur to sulphate and formed a sulphate chelated CuII complex, [CuII{$\kappa^2$-N,N-(N2C4H5)2S}($\eta^2$-O,OSO2)($\kappa^1$-OH2)]. Imidazolidine-2-thione (SN2C3H6) with copper(I) chloride/bromide in dimethyl sulphoxide gave a sulphate bridged polynuclear complex, [CuII{$\kappa^2$-N,N-(N2C3H5)2S}(𝜇-O,OSO2)($\kappa^1$-OH2)]$_n$ {(N2C3H5)2S = 2,2'-thio-di-2-imidazoline}. Other metals such as silver, zinc, cadmium and mercury formed monomers or dimers.

• Mechanistic studies of copper(II)-mediated oxidation of vic-dioxime to furoxan

The oxidation of vic-dioximes to furoxans by copper(II) perchlorate in acetonitrile as the oxidant has been discussed. This method was found to be applicable for a broad range of vic-dioximes. Copper complexes of 1,10-phenanthroline derived furoxans were isolated by oxidation of the corresponding copper(II) complexes of 1,10-phenanthroline based dioximes. In exploring the mechanism of copper(II)-mediated oxidative cyclization of vic-dioxime, a transient blue species was observed in the reaction pathway. Based on the spectroscopic signatures and reactivity patterns, the intermediate was proposed to be a dioximatecopper(II)-dinitrosoalkene complex. These results along with the role of metal ion and solvent in the oxidative transformation reaction are discussed in this review.

• Crystallization of organically templated phosphomolybdate cluster-based solids from aqueous solution

The paper reports the synthesis and structural characterization of several organic-inorganic solids involving phosphomolybdate clusters. The Strandberg-type {P2Mo$^{\text{VI}}_5$O23} and the lower-valent {P4Mo$^V_6$O31} cluster based solids were isolated in the presence of $en$ (ethylenediamine) by controlling pH of the reaction medium. The lower-valent cluster invariably requires the presence of a suitable metal cation for further stabilization. A detailed investigation of the system was carried out where three different weak acids viz. oxalic acid, succinic acid and glycine were used in the entire pH range (1-12). Our results establish that the organic amine ($en$) is alone capable of reducing the molybdenum core in the absence of an organic acid at a suitable pH. Hence, pH of the reaction medium combined with suitable temperature favours the formation of lower-valent phosphomolybdate cluster. Higher pH favours the precipitation of a new sodium hydrogen phosphate.

• Calixarenes: Versatile molecules as molecular sensors for ion recognition study

This article presents a brief account on designing of calixarene-based molecular sensor for recognition of various metal ions and anions and also different analytical techniques to monitor the recognition event. This review focuses only on calix[4]arene derivatives, in which mainly the lower rim is modified incorporating either crown moiety to make calix-crown hybrid ionophore to encapsulate metal ions or some fluoregenic inorganic and organic moieties to use it as signalling unit. In order to investigate effect of conformation of the calixarene unit and steric crowding on ion selectivity, designing of these molecules have been made using both the cone and 1,3-alternate conformations of the calixarene unit and also incorporating bulky tert-butyl group in few cases to impose controlled steric crowding. Among various ions, here focuses are mainly on biologically and commercially important alkali metal ion such as K+, toxic metal ions such as Hg2+, Pb2+, Cd2+, important transition metal ion such as Cu2+ and toxic anion like F. The techniques used to monitor the recognition event and also to determine binding constants with strongly interacting ions are fluorescence, UV-vis and 1H NMR spectroscopy. Most of the ionophores reported in this review have been characterized crystallographically, however no structural information (except one case) are incorporated in this article, as it will occupy space without significant enhancement of chemistry part. Different factors such as size of the ionophore cavity, size of metal ion, coordination sites/donor atoms, steric crowding and solvents, which determine selectivity have been discussed. Response of ion recognition process to different analytical techniques is another interesting factor discussed in this article.

• Synthesis, characterization and phosphotriesterase mimetic activity of some Zn(II) and Cu(II) complexes

We report here the synthesis and characterization of a few phenolate-based ligands bearing tertamino substituent and their Zn(II) and Cu(II) metal complexes. Three mono/binuclear Zn(II) and Cu(II) complexes [Zn(L1)(H2O)].CH3OH.H2O (1) (H2 L1 = 6,6′-(((2-dimethylamino)ethylazanediyl)bis(methylene))bis(2, 4-dimethylphenol), [Zn2(L2)2] (2) (H2L2 = 2,2′-(((2-dimethylamino)ethyl)azanediyl)bis(methylene)bis(4-methylphenol) and [Cu2(L3)2.CH2 Cl2] (3) (H2L3 = (6,6′-(((2-(diethylamino)ethyl)azanediyl)bis(methylene)) bis(methylene))bis(2,4-dimethylphenol) were synthesized by using three symmetrical tetradendate ligands containing N2O2 donor sites. These complexes are characterized by a variety of techniques including; elemental analysis, mass spectrometry, 1H, 13C NMR spectroscopic and single crystal X-ray analysis. The new complexes have been tested for the phosphotriesterase (PTE) activity with the help of 31P NMR spectroscopy. The 31P NMR studies show that mononuclear complex [Zn(L1)(H2O)].CH3OH.H2O (1) can hydrolyse the phosphotriester i.e., p-nitrophenyl diphenylphosphate (PNPDPP), more efficiently than the binuclear complexes [Zn2(L2)2] (2) and [Cu2(L3)2.CH2Cl2] (3). The mononuclear Zn(II) complex (1) having one coordinated water molecule exhibits significant PTE activity which may be due to the generation of a Zn(II)-bound hydroxide ion during the hydrolysis reactions in CHES buffer at pH 9.0.

• Fabrication of optochemical and electrochemical sensors using thin films of porphyrin and phthalocyanine derivatives

This paper describes the fabrication of thin films of porphyrin and metallophthalocyanine derivatives on different substrates for the optochemical detection of HCl gas and electrochemical determination of L-cysteine (CySH). Solid state gas sensor for HCl gas was fabricated by coating meso-substituted porphyrin derivatives on glass slide and examined optochemical sensing of HCl gas. The concentration of gaseous HCl was monitored from the changes in the absorbance of Soret band. Among the different porphyrin derivatives, meso-tetramesitylporphyrin (MTMP) coated film showed excellent sensitivity towards HCl and achieved a detection limit of 0.03 ppm HCl. Further, we have studied the self-assembly of 1,8,15,22-tetraaminometallophthalocyanine (4𝛼-MTAPc; M = Co and Ni) from DMF on GC electrode. The CVs for the self-assembled monolayers (SAMs) of 4𝛼-CoIITAPc and 4𝛼4-NiIITAPc show two pairs of well-defined redox couple corresponding to metal and ring. Using the 4𝛼-CoIITAPc SAM modified electrode, sensitive and selective detection of L-cysteine was demonstrated. Further, the SAM modified electrode also successfully separates the oxidation potentials of AA and CySH with a peak separation of 320mV.

• Photocytotoxic lanthanide complexes

Lanthanide complexes have recently received considerable attention in the field of therapeutic and diagnostic medicines. Among many applications of lanthanides, gadolinium complexes are used as magnetic resonance imaging (MRI) contrast agents in clinical radiology and luminescent lanthanides for bioanalysis, imaging and sensing. The chemistry of photoactive lanthanide complexes showing biological applications is of recent origin. Photodynamic therapy (PDT) is a non-invasive treatment modality of cancer using a photosensitizer drug and light. This review primarily focuses on different aspects of the chemistry of lanthanide complexes showing photoactivated DNA cleavage activity and cytotoxicity in cancer cells. Macrocyclic texaphyrin-lanthanide complexes are known to show photocytotoxicity with the PDT effect in near-IR light. Very recently, non-macrocyclic lanthanide complexes are reported to show photocytotoxicity in cancer cells. Attempts have been made in this perspective article to review and highlight the photocytotoxic behaviour of various lanthanide complexes for their potential photochemotherapeutic applications.

• Computational tools for mechanistic discrimination in the reductive and metathesis coupling reactions mediated by titanium(IV) isopropoxide

A theoretical study has been carried out at the B3LYP/LANL2DZ level to compare the reactivity of phenyl isocyanate and phenyl isothiocyanate towards titanium(IV) alkoxides. Isocyanates are shown to favour both mono insertion and double insertion reactions. Double insertion in a head-to-tail fashion is shown to be more exothermic than double insertion in a head-to-head fashion. The head-to-head double insertion leads to the metathesis product, a carbodiimide, after the extrusion of carbon dioxide. In the case of phenyl isothiocyanate, calculations favour the formation of only mono insertion products. Formation of a double insertion product is highly unfavourable. Further, these studies indicate that the reverse reaction involving the metathesis of N,N'-diphenyl carbodiimide with carbon dioxide is likely to proceed more efficiently than the metathesis reaction with carbon disulphide. This is in excellent agreement with experimental results as metathesis with carbon disulphide fails to occur. In a second study, multilayer MM/QM calculations are carried out on intermediates generated from reduction of titanium(IV) alkoxides to investigate the effect of alkoxy bridging on the reactivity of multinuclear Ti species. Bimolecular coupling of imines initiated by Ti(III) species leads to a mixture of diastereomers and not diastereoselective coupling of the imine. However if the reaction is carried out by a trimeric biradical species, diastereoselective coupling of the imine is predicted. The presence of alkoxy bridges greatly favours the formation of the d,l (±) isomer, whereas the intermediate without alkoxy bridges favours the more stable meso isomer. As a bridged trimeric species, stabilized by bridging alkoxy groups, correctly explains the diastereoselective reaction, it is the most likely intermediate in the reaction.

• 𝜇-Phenoxo-𝜇-pseudohalide and 𝜇-pseudohalide dinuclear, tetranuclear and one-dimensional complexes: magneto-structural correlation and interesting type of solid state isomerism

Five Schiff base ligands have been utilized to explore metallo-pseudohalide (azide or cyanate) systems. These ligands are the 1:1 condensation products of 3-methoxysalicylaldehyde with ethanolamine (H2L1)/1-(2-aminoethyl)-piperidine (HL2)/ 4-(2-aminoethyl)-morpholine (HL3) or salicylaldehyde with 1-(2-aminoethyl)-piperidine (HL4)/4-(2-aminoethyl)-morpholine (HL5). The derived complexes are as follows: Four heterobridged 𝜇-phenoxo-$\mu_{1,1}$-azide/cyanate dinickel(II) compounds of composition [Ni$^{\text{II}}_2$ (HL1)3($\mu_{1,1}$-N3)]$\cdot$3H2O (1), [Ni$^{\text{II}}_2$ (L2)2($\mu_{1,1}$-N3)(N3)(H2O)]·CH3CH2OH (2), [Ni$^{\text{II}}_2$ (L3)2-($\mu_{1,1}$-N3)(CH3CN)(H2O)](ClO4)·H2O·CH3CN (3) and [Ni$^{\text{II}}_2$ (HL1)3($\mu_{1,1}$-NCO)]·2H2O (4); Two $\mu_{1,3}$-azide bridged tetranickel(II) compounds [{NiII(L4)($\mu_{1,3}$-N3)(H2O)}4] (5) and [{NiII(L5)($\mu_{1,3}$-N3)(H2O)}4] (6); Two $\mu_{1,3}$-azide/cyanate one-dimensional compounds [CuIIL5($\mu_{1,3}$-NCO)]$_n$·2𝑛H2O (7) and [CuIIL5($\mu_{1,3}$-N3)]$_n$·2𝑛H2O (8). Except compound 5 which shows overall antiferromagnetic coupling, other compounds exhibit overall ferromagnetic interaction. Syntheses, crystal structures, magnetic properties, density functional theoretical (DFT) calculations and experimental/theoretical magneto-structural correlations have been carried out which have revealed some interesting observations on composition/topology, magneto-structural correlations and solid state isomerism. The results have been already published. The present report deals with a review of the salient and interesting features of these works.

• Study of $\eta^6$- cyclic 𝜋-perimeter hydrocarbon ruthenium complexes bearing functionalized pyridyl diketones: Isolation of complexes with $\kappa^2$-N∩O and $\kappa^4$-N∩O bonding modes of ligands

Chelating mono- and di-pyridyl functionalized 𝛽-diketones, viz. 1-phenyl-3-(2-pyridyl) propane-1,3-dione (pppdH) and 1,3-di(2-pyridyl)propane-1,3-dione ($dppdH$) ligands yielded new water soluble $\eta^6$-arene ruthenium(II) complexes of the formulation [($\eta^6$-arene)Ru($\kappa^2$-N-O-pppdH)Cl]+ (arene = C6H6 1, p$^i$PrC6H4Me 2, C6Me6 3) and [($\eta^6$-arene)2Ru2($\kappa^4$-N-O-$dppd$)Cl2]+ (arene = C6H6 4, 𝑝-$^i$PrC6H4Me 5, C6Me6 6), as their (complexes 1-4, 6) PF6 salt or (complex 5) BF4 salt. The complexes were obtained by treatment of respective precursors, [($\eta^6$-arene)Ru(𝜇-Cl)Cl]2 (arene = C6H6, 𝑝-$^i$PrC6H4Me, C6Me6) in 1:2 and 1:1 molar ratio with pppdH and $dppdH$ in the presence of NH4PF6/NH4BF4. All the complexes have been characterized on the basis of FT-IR and NMR spectroscopic data as well as by elemental analysis. Molecular structures of representative complexes 2, 5 and 6 have been confirmed by single crystal X-ray diffraction studies. The $O-C-C-C-O$' fragment of the coordinated ligand (pppdH) is neutral in complexes 1-3 and that of the $dppdH$ ligand existed as a neutral as well as concomitantly uninegative fashion in complexes 4-6 due to the delocalization of 𝜋-electrons.

• Rhomboidal [Cu4] coordination cluster from self-assembly of two asymmetric phenoxido-bridged Cu2 units: Role of $\mu_{1,1}$-azido clips

The coordination cluster [Cu2(𝜇-OMe)($\mu_{1,1}$-N3)(𝜇-bcp)(N3)]2 (1; Hbcp = 2,6-bis(2-benzoyl-4-chloro-phenylimino)-methyl)-4-methylphenol, forming a new member within the rapidly growing family of Cu4 cluster complexes, has been synthesized and structurally characterized by X-ray crystallography. The complex crystallizes in the monoclinic system, space group P21/𝑐, with unit cell parameters a = 14.620(7) Å, b = 17.923(8) Å, c = 15.008(7) Å, 𝛽 = 115.815(14)° and Z = 2. It is the first example of a rhomboidal [Cu4] compound formed from $\mu_{1,1}$-azido clipping of two methoxido bridged [Cu2] complexes showing asymmetric coordination from benzophenone oxygen atoms and terminal azido groups.

• Single crystal growth of europium and ytterbium based intermetallic compounds using metal flux technique

This article covers the use of indium as a potential metal solvent for the crystal growth of europium and ytterbium-based intermetallic compounds. A brief view about the advantage of metal flux technique and the use of indium as reactive and non-reactive flux are outlined. Large single crystals of EuGe2, EuCoGe3 and Yb2AuGe3 compounds were obtained in high yield from the reactions of the elements in liquid indium. The results presented here demonstrate that considerable advances in the discovery of single crystal growth of complex phases are achievable utilizing molten metals as solvents.

• Metal azides under pressure: An emerging class of high energy density materials

Metal azides are well-known for their explosive properties such as detonation or deflagration. As chemically pure sources of nitrogen, alkali metal azides under high pressure have the ability to form polymeric nitrogen, an ultimate green high energy density material with energy density three times greater than that of known high energetic materials. With this motive, in this present work, we try to address the high-pressure behaviour of LiN3 and KN3 by means of density functional calculations. All the calculations are performed with the inclusion of van derWaals interactions at semi empirical level, as these materials are typical molecular solids. We found that both LiN3 and KN3 are structurally stable up to the studied pressure range of 60 GPa and 16 GPa, respectively. At ambient conditions both the materials are insulators with a gap of 3.48 eV (LiN3) and 4.08 eV (KN3) and as pressure increases the band gap decreases and show semiconducting nature at high pressures.We also found that the compressibility of both the crystals is anisotropic which is in good agreement with experiment. Our theoretical study proved that the materials under study may have the ability to form polymeric nitrogen because of the decrease in interazide ion distance and possible overlapping of N atomic orbitals.

• Mechanism of unusual polymorph transformations in calcium carbonate: Dissolution-recrystallization vs additive-mediated nucleation

Unusual transformation of one CaCO3 phase to another has been reported by the process of dissolution-recrystallization and under the influence of additive. In one case, while metastable vaterite transforms to another metastable phase aragonite by simple refluxing in distilled water, it instead transforms thermodynamically stable phase calcite upon refluxing in its mother-liquor’. This is explained by the process of dissolution-recrystallization. In another case, aragonite is preferentially synthesized over calcite in the presence of molten lauric acid as an additive.

• Synthesis, characterization and cytotoxic activity of palladium (II) carbohydrate complexes

Carbohydrate containing pyridyl triazole ligands, 5-deoxy-1,2-𝑂-isopropylidene-5-(4-(2-pyridyl)-1H-1,2,3-triazole-1-yl)-𝛼-D-xylofuranose (2a), 3-𝑂-Benzyl-5-deoxy-1,2-𝑂-isopropylidene-5-(4-(2-pyridyl)-1H-1,2,3-triazol-1-yl)-𝛼-D-xylofuranose (2b), methyl-5-deoxy-2,3-𝑂-isopropylidene-5-(4-(2-pyridyl)-1H-1,2,3-triazol-1-yl)-𝛽-D-ribofuranoside, (2c) and 6-deoxy-1,2:3,4-di-𝑂-isopropylidene-6-(4-(2-pyridyl)-1H-1,2,3-triazol-1-yl)-𝛼-D-galactopyranose (2d) were prepared by the click’ reaction of 2-ethynyl pyridine with the corresponding azides. The palladium complexes were synthesised by the reaction of pyridyl triazole ligands with [Pd(COD)Cl2] in dichloromethane. All the compounds were characterized by NMR, IR, mass and elemental analysis. Structural characterization of the ligand 2a was done by X-ray crystallography. The ligands and complexes were tested for their cytotoxic activity on different cell lines like A549 (human alveolar adenocarcinoma cells), Neuro2a (mouse neuroblastoma cells), HeLa (cervical carcinoma cancer cells), MDA-MB-231 (human breast adenocarcinoma cells) and MCF7 (human breast adenocarcinoma cells). The complexes showed considerable cytotoxicity while the ligands were non-toxic on the tested cell lines.

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• # Journal of Chemical Sciences

Volume 132, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019