Subrata Das

Two Polymorphic Forms of a Six-Coordinate Mononuclear Cobalt(II) Complex with Easy-Plane Anisotropy: Structural Features, Theoretical Calculations, and Field-Induced Slow Relaxation of the Magnetization

A mononuclear cobalt(II) complex [Co(3,5-dnb)2(py)2(H2O)2] {3,5-Hdnb = 3,5-dinitrobenzoic acid; py = pyridine} was isolated in two polymorphs, in space groups C2/c (1) and P21/c (2). Single-crystal X-ray diffraction analyses reveal that 1 and 2 are not isostructural in spite of having equal formulas and ligand connectivity. In both structures, the Co(II) centers adopt octahedral {CoN2O4} geometries filled by pairs of mutually trans terminal 3,5-dnb, py, and water ligands. However, the structures of 1 and 2 disclose distinct packing patterns driven by strong intermolecular O-H···O hydrogen bonds, leading to their 0D→2D (1) or 0D→1D (2) extension. The resulting two-dimensional layers and one-dimensional chains were topologically classified as the sql and 2C1 underlying nets, respectively. By means of DFT theoretical calculations, the energy variations between the polymorphs were estimated, and the binding energies associated with the noncovalent interactions observed in the crystal structures were also evaluated. The study of the direct-current magnetic properties, as well as ab initio calculations, reveal that both 1 and 2 present a strong easy-plane magnetic anisotropy (D > 0), which is larger for the latter polymorph (D is found to exhibit values between +58 and 117 cm(-1) depending on the method). Alternating current dynamic susceptibility measurements show that these polymorphs exhibit field-induced slow relaxation of the magnetization with Ueff values of 19.5 and 21.1 cm(-1) for 1 and 2, respectively. The analysis of the whole magnetic data allows the conclusion that the magnetization relaxation in these polymorphs mainly takes place through a virtual excited state (Raman process). It is worth noting that despite the notable difference between the supramolecular networks of 1 and 2, they exhibit almost identical magnetization dynamics. This fact suggests that the relaxation process is intramolecular in nature and that the virtual state involved in the two-phonon Raman process lies at a similar energy in polymorphs 1 and 2 (∼20 cm(-1)). Interestingly, this value is recurrent in Co(II) single-ion magnets, even for those displaying different coordination number and geometry.

Experimental observation and theoretical investigation of a novel Cd(II) complex with π-hole interactions involving nitro groups

Some of our group recently demonstrated combining theory and a statistical survey of the Cambridge Structural Database (CSD) that the interaction between the π-holes of nitro groups and electron-rich atoms is somewhat directional (Chem. Commun., 2015, 51, 1491–1493). In this communication, we present a joint experimental and theoretical study on a novel cadmium(II) complex, [Cd(C7H3N2O6)2(C12H8N2)2]·H2O·DMF (1) [where C7H4N2O6 = 3,5-dinitrobenzoic acid and C12H8N2 = 1,10-phenanthroline] to unravel the important role of this π-hole interaction.

An efficient stereo-controlled synthesis of bis-pyrimido-[4,5-d]-pyrimidine derivatives via aza-Diels–Alder methodology and their preliminary bioactivity

The one-pot synthesis of novel fused bis-pyrimido-[4,5-d]pyrimidine derivatives by a three-component reaction of 6-[(dimethylamino)methylene]1,3-dimethylaminouracil, terephthalaldehyde and amino derivatives has been depicted. The structures of the compounds were established by studying various spectroscopic methods and single-crystal X-ray crystallography. The long range W-coupling constant in 1H-NMR spectra is an infrequent example, where our synthesized novel compounds show such a distinctive constant. The synthetic strategy provides an efficient way to synthesise bis-pyrimidine-fused heterocycles that can be explored for further potential pharmaceutical or biological activities.

Environment-friendly and solvent-free synthesis of symmetrical bis-imines under microwave irradiation

Abstract A short library of symmetrical bis-imines has been constructed efficiently from the reaction between dialdehydes and mono amines or diamines and mono aldehydes under microwave irradiation catalyzed by p-toluenesulphonic acid. The methodology is associated with shorter reaction time, good yields and simple workup.

Two-Stage Conversion of High Free Fatty Acid Jatropha curcas Oil to Biodiesel Using Brønsted Acidic Ionic Liquid and KOH as Catalysts

Biodiesel was produced from high free fatty acid (FFA) Jatropha curcas oil (JCO) by two-stage process in which esterification was performed by Brønsted acidic ionic liquid 1-(1-butylsulfonic)-3-methylimidazolium chloride ([BSMIM]Cl) followed by KOH catalyzed transesterification. Maximum FFA conversion of 93.9% was achieved and it reduced from 8.15 wt% to 0.49 wt% under the optimum reaction conditions of methanol oil molar ratio 12 : 1 and 10 wt% of ionic liquid catalyst at 70°C in 6 h. The ionic liquid catalyst was reusable up to four times of consecutive runs under the optimum reaction conditions. At the second stage, the esterified JCO was transesterified by using 1.3 wt% KOH and methanol oil molar ratio of 6 : 1 in 20 min at 64°C. The yield of the final biodiesel was found to be 98.6% as analyzed by NMR spectroscopy. Chemical composition of the final biodiesel was also determined by GC-MS analysis.

Cadmium(II) complexes containing N,N′-dimethylviolurate as ligand or counteranion: synthesis, characterization, crystal structures and DFT study

N,N′-dimethylvioluric acid mono hydrate (HDMV) (1·H2O) and two cadmium(II) complexes with N-donor ligands of formula [Cd(DMV)2(benzim)2]·2H2O (2) (benzim = benzimidazole) and [Cd(H2O)4(py)2](DMV)2 (3) (py = pyridine) have been synthesized. Free N,N′-dimethyl violuric acid mono hydrate (HDMV) and the complexes have been fully characterized by elemental analysis, IR, 1H and 13C NMR spectral methods, fluorescence spectroscopy, TGA and structural X-ray crystallography. HDMV (1·H2O) which remains in keto-oxime form in the solid state transforms to the nitroso-enolato form in the complexes [(2) and (3)]. A typical R12(6) motif with a bifurcating hydrogen bond is observed in all three structures. Dimethylviolurate anion acts as a bidentate ligand in (2), whereas in (3) it is present as a counter-ion, outside the coordination sphere. In addition, DFT-D3 calculations have been performed to study interesting noncovalent interactions observed in the solid states of (1) and (2) with special interest in the lone pair (lp)–π interactions and their interplay with π–π interactions.

6-[(Dimethyl­amino)methyl­ene­amino]-1,3-dimethyl­pyrimidine-2,4(1H,3H)-dione dihydrate

Uracil, the pyrimidine nucleobase, which combined with adenine forms one of the major motifs present in the biopolymer RNA, is also involved in the self-assembly of RNA. In the title compound, C9H14N4O2·2H2O, the asymmetric unit contains one dimethylaminouracil group and two water molecules. The plane of the N=C—NMe2 side chain is inclined at 27.6 (5)° to the plane of the uracil ring. Both water molecules form O—H⋯O hydrogen bonds with the carbonyl O atoms of the uracil group. Additional water–water hydrogen-bond interactions are also observed in the crystal structure. The O—H⋯O hydrogen bonds lead to the formation of a two-dimensional hydrogen-bonded network cage consisting of two dimethylaminouracil groups and six water molecules.

Two mixed-ligand cadmium(II) compounds bearing 5-nitrosopyrimidine and N-donor aromatic blocks: self-assembly generation, structural and topological features, DFT studies, and Hirshfeld surface analysis

Using the mixed-ligand strategy, two novel cadmium(II) coordination compounds, namely, the discrete 0D dimer [Cd2(μ2-H2Vi)4(benzim)2]·2MeOH (1) and the 1D coordination polymer [Cd(μ2-DMV)(DMV)(2-apy)]n (2), were self-assembled in aqueous methanol medium under ambient conditions from the cadmium(II) nitrate–H3Vi/HDMV–benzim/2-apy system {where H3Vi = violuric acid [5-(hydroxyimino)pyrimidine-2,4,6(1H,3H,5H)-trione], benzim = benzimidazole, HDMV = N,N′-dimethylvioluric acid [5-(hydroxyimino)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione], and 2-apy = 2-aminopyridine}. Both products were isolated as crystalline solids and were structurally characterized. The violurate ligands adopt a tridentate bridging mode in 1, whereas in 2 simultaneous coordination modes [bis(bidentate) bridging + bidentate] are displayed by dimethylviolurate ligands. The nature of the substituent on the violurate ring and the presence of different N-donor ligands play a role in the generation of distinct products. The crystal structures of 1 and 2 reveal a number of strong intermolecular hydrogen bonds that are responsible for the 0D → 3D (1) or 1D → 2D (2) structure extension, resulting in rather complex H-bonded networks. These networks were topologically classified as underlying nets with the sqc2 and 3,4L18 topologies in 1 and 2, respectively. By means of DFT calculations (BP86-D3/def2-TZVPD), the computation of the energetic features of the different noncovalent interactions, such as lone pair (lp)–π, π–π, and C–H/π, was performed aiming at rationalizing their roles in the crystal packing of 1 and 2. Notably, the lp–π interactions observed in 2 present one of the shortest lp–π distances (2.74 A) reported to date. Hirshfeld surface analysis was also carried out to provide qualitative and quantitative insights into the intermolecular interactions in 1 and 2. Furthermore, luminescence properties of the compounds were investigated.

An X-ray crystallographic study of C-5 and C-6 substituted 1,3-dimethyl-6-aminouracil architectures

Uracil, one of the four RNA bases is a vital component in the complex processes of molecular genetics. The correct functioning of these processes depends on the types of bonds formed by uracil with the surroundings. This communication elaborates the versatile potential of 1,3-dimethyl-6-aminouracil (L1) to form its 5-, 6- position substituted derivatives with different significant molecular packing behaviours. Presently, five crystals (L2-L6) have been synthesised and their crystallographic architectures are glimpsed in this paper. Analysis of crystal packing shows supra-molecular behaviours through hydrogen bonding and π-π interactions among the molecules in maintaining the integrity of the structures. The ligand 6,6’-diamino-1,1’,3,3’-tetramethyl-5,5’-(benzylidene)bis[pyrimidine-2,4(1H,3H)-dione] was observed to be stabilised in a helical arrangement.Graphical AbstractVersatile potential of 1, 3-dimethyl-6-aminouracil to form its 5-, 6- position substituted derivatives e.g. 6,6’-diamino-1,1’,3,3’-tetramethyl-5,5’-(benzylidene)bis[pyrimidine-2,4(1H,3H)-dione] in a helical arrangement.

6,6′-Diamino-1,1′,3,3′-tetra­methyl-5,5′-(4-chloro­benzyl­idene)bis­[pyrimidine-2,4(1H,3H)-dione]

The title compound, C19H21ClN6O4, is a 1:2 adduct of p-chlorobenzaldehyde and uracil. It crystallizes with two molecules in the asymmetric unit. The two uracil units in the same molecule are connected by a pair of strong N—H⋯O hydrogen bonds. The packing is stabilized by N—H⋯O, C—H⋯O and C—H⋯N interactions.