Browsing by Author "Sailaja Sunkari"

Now showing 1 - 7 of 7

Extended molecular networks based on Zn and Cd imparting N-substituted imidazole
(Elsevier S.A., 2010) Ashish Kumar Singh; Mahendra Yadav; Sanjay Kumar Singh; Sailaja Sunkari; Daya Shankar Pandey
Synthesis of complexes with the formulations [M(CPI)2Cl2] (M = Zn, 1; M = Cd, 4) and [M(CPI)6](X)2 (M = Zn, X = NO3-, 2; X = ClO4-, 3; M = Cd, X = NO3-, 5; X = ClO4-, 6) have been achieved from the reactions of MCl2, M(NO3)2·xH2O and M(ClO4)2·xH2O (M = Zn, Cd) with 1-(4-cyanophenyl)-imidazole (CPI). Complexes 1-6 have been characterized by elemental analyses and spectral studies (IR, 1H, 13C NMR, electronic absorption and emission). Molecular structures of 1, 2, 3 and 6 have been determined crystallographically. Weak interaction studies on the complexes revealed presence of various interesting motifs resulting from C-H···N, C-H···Cl and π-π stacking interactions. The complexes under study exhibit strong luminescence at ∼450 nm in DMSO at room temperature. © 2009 Elsevier B.V. All rights reserved.
Influence of metal to ligand molar ratios on the supramolecular structure formation of Cu(II) with diaminopropane and iodide: Synthesis, structure, spectroscopic and DFT studies
(2014) Bhagwan Kharediya; Madhulata Shukla; Satyen Saha; Sailaja Sunkari
Two new copper(II) complexes with 1,3-diaminopropane and iodide, viz., [{Cu ((1,3-diaminopropane)2 I (I3))}] (1) and [{Cu ((1,3 diaminopropane)2(I)2)}] (2) have been synthesized under self assembly conditions and structurally characterised to observe the structural variations brought about by varying ligand molar ratios, towards studying the effect of external factors on supramolecular structure formation, with a long term goal of obtaining magnetic materials. Corresponding to the variation in metal to ligand molar ratios from one to two, totally different products are obtained whose gross structural features are entirely different. The formation of 1, is unpredicted under given synthetic conditions and hence is interesting. The formation of 2, is as generally expected for the reacting components under given conditions. In case of 1, the metal ion's choice to adopt a square pyramidal geometry by coordinating to two ligand units and a coordinated iodide, even in the absence of sufficient moles of ligand, as in 2, is due to sub-molar ligand ratios complemented by weak hydrogen bonding interactions, operating between the ligand amino hydrogens and coordinated iodide and uncoordinated triiodide moiety. This approach of providing sub-molar amounts of ligand to the metal to satisfy its coordination requirements, appear to be a promising strategy towards obtaining novel solid systems of material relevance. Both the complexes are characterised structurally and spectroscopically. Further, both the structures were satisfactorily modelled by calculations based on Density Functional Theory (DFT), and their UV-visible spectra were analyzed in depth with the help of Time Dependent DFT (TD-DFT).© 2014 Elsevier B.V. All rights reserved.
Novel structures based on 1-(4-cyanophenyl)-imidazole resulting from weak bonding interactions
(2009) Ashish Kumar Singh; Mahendra Yadav; Prashant Kumar; Sanjay Kumar Singh; Sailaja Sunkari; Daya Shankar Pandey
Mono-nuclear complexes [M(CPI)6](X)2 (M = Co, X = NO3- 1; M = Ni, X = NO3- 2; M = Cu, X = ClO4- 3) and [Cu(CPI)4(H2O)2](NO3)2 4, based on novel bridging ligand 1-(4-cyanophenyl)-imidazole (CPI) are reported. The complexes have been characterized by elemental analyses, spectral studies and their molecular structures have been authenticated by single crystal X-ray diffraction analyses. In molecular species 1-3 metal centers are coordinated octahedrally by six CPI ligands wherein cyanophenyl rings of six ligands about the complex cations are involved in face-to-face π-π interaction with six co-planar molecules to afford unprecedented 2D sheet. Along 'c'-axis it gives a beautiful rim like motif. In complex 4, coordination about metal center Cu is distorted octahedral with four CPI ligands in the equatorial position and two water molecules occupying axial positions. In this complex hydrogen bonding interactions between the coordinated water molecules and nitrate anions results in a 1D straight chain along 'a'-axis and 2D sheets having hexagonal cavity filled by nitrate ions. The complexes upon excitation at 275-285 nm exhibit luminescences with emission maxima centered at 438-445 nm attributable to the ligand CPI at room temperature. © 2009 Elsevier B.V. All rights reserved.
Synthesis, structure, UV-Vis-IR spectra, magnetism and theoretical studies on CuII[(2-aminomethyl)pyridine](thiocyanate)2 and comparisons with an analogous CuII complex
(Elsevier Ltd, 2011) Madhulata Shukla; Nitin Srivastava; Satyen Saha; T.R. Rao; Sailaja Sunkari
The title complex was synthesized under self-assembly conditions using Cu(acetate)2·H2O, 2-amp (= 2-aminomethylpyridine) and KSCN, and was characterized by IR, elemental analysis and single crystal structural analysis, and its spectral and RT magnetic properties were investigated. The asymmetric unit consists of a square planar Cu(II) center, with two ligand N atoms and two anionic Ns forming the square plane. In the unit cell, the monomeric complex assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu2+. Further, the structure was satisfactorily modeled by calculations based on Density Functional Theory (DFT), and the UV-Vis and IR spectra are analyzed in depth with the help of Time Dependent DFT (TDDFT). The results indicate that the absorption maxima are at relatively high energy and are mainly assigned to π → π transitions (in pyridine), with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d-d transition band. Also, it has been found that when the ligand ratio is modified, the formation of Cu(2-amp)2(SCN)2 takes place under the same self-assembly conditions, whose structure only has been recently reported. Structural, spectral and theoretical comparisons are presented for both complexes. © 2010 Elsevier Ltd. All rights reserved.
Temperature influence on supramolecular structure formation. Synthesis, structure, spectral and DFT studies of Cu(II)-azide systems with symmetric diamines
(Elsevier Ltd, 2013) Bhagwan Kharediya; Sailaja Sunkari
Three new Cu(II) complexes, viz. [{Cu2((1,3-diaminopropane) 2(N3)4}2] (1), [Cu((1,3- diaminopropane)2(-N3)2] (2) and [Cu(en) 2(N3)2] (3), with symmetric amines and azide ligands have been synthesized under self-assembly conditions and structurally characterized, towards understanding the influence of temperature in directing the final structure formation. Interestingly, temperature plays a decisive role in the final structure formation, leading to the formation of a tetramer 1 at low temperature (LT) and a monomer 2 at room temperature (RT) in the case of the Cu(II)-1,3-diaminopropane-N3 system. However, such a temperature influence has not been observed in the case where ethylene diamine is a ligand. Irrespective of the crystallization temperature, the Cu(II)-en-azide system always affords compound 3 only. The stability of both 1 and 2 is further confirmed by Single Point Energy calculations, which corroborate the experimental observations. © 2013 Elsevier Ltd. All rights reserved.
Tetranuclear Copper(II) Complexes with Simultaneous Phenoxo and Azido Bridges - Synthesis, Structural and Magnetic Studies
(Wiley-Blackwell, 2018) Priyanka Pandey; Nidhi Dwivedi; Goulven Cosquer; Masahiro Yamashita; Sailaja Sunkari
Tetradentate Schiff base ligands with multiple coordinaton sites are one of the best choice for the construction of multinuclear metal complexes. Coupled with auxiliary ligands under self assembling conditions, the scope for generating new structures increases manifold due to various structure directing factors in operation. Though, phenoxo or azido bridged copper(II) systems have been investigated thoroughly from structural and magnetic aspects, the literature is scanty with combined phenoxo and azido bridged systems. In a study on the effect of synthetic conditions on the structures generated and associated magnetic properties, two new tetranuclear copper complexes, viz., [Cu4(L1)2(μ-N3)2(N3)2] (1) and [Cu4(L2)2(μ-N3)2(N3)2] (2) where L1=N,N′-Bis(salicylidene)diaminopropane (salpn) and L2=N,N′-Bis(salicylidene)diaminobenzene (salophen) with both phenoxo and azido bridges are reported. The tetranuclear cluster is made of two inversion related dimers built of phenoxo bridged Cu1 and Cu2 with distorted square planar and square pyramidal geometries respectively. These dimers are bridged by symmetrically bridging azides leading to a tetranuclear core. The contrasting magnetic behavior inspite of same coordination environments, antiferromagnetic in 1 (J1=−2.17 cm−1; J2=−28.15 cm−1) and ferromagnetic in 2 (J1=−74.7 cm−1; J2=146.5 cm−1), is understood in terms of lower bridge angles and closer separation between copper centers in 2 than in 1. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Water square (uudd) in novel CuII framework structures built from isomeric (aminomethyl)pyridines and oxalate: Synthesis, structure, spectral and DFT studies
(Elsevier Ltd, 2013) Madhulata Shukla; Bhagwan Kharediya; Nitin Srivastava; Satyen Saha; Sailaja Sunkari
A perfect water square in uudd configuration, built from solvent waters has been isolated from a hybrid metal-organic host [Cu(3-aminomethyl)pyridine oxalateOH2·2H2O]n under self assembly conditions, stabilizing the supramolecular framework through cooperative hydrogen bonding interactions, a rare occurrence among water clusters. The present findings with detailed crystallographic and theoretical studies add to our knowledge regarding the understanding of the contribution of water clusters to the stability and function of biological assemblies as well as the anomalous properties of water. © 2013 Elsevier Ltd. All rights reserved.