Ligand directed structural diversity and magnetism in copper(ii)-azido assemblies with isomeric aminopyridines: synthesis, structure, magnetism and theoretical studies.

Four new copper complexes, viz. [{Cu(2-aminopyridine)(N3)2(H2O)}2]n (1), [Cu3(3-aminopyridine)2(N3)6]n (2), [{Cu(3-aminopyridine)(N3)2}2]n (3), and [Cu(4-aminopyridine)2(N3)2]n (4), have been synthesized with isomeric aminopyridines, viz. 2-aminopyridine (2-ap), 3-aminopyridine (3-ap), and 4-aminopyridine (4-ap), to probe the role of ligand and reactant molar ratios in directing the polynuclear assemblage and the associated magnetic properties. Ligand geometry is quite influential as can be seen through the versatile structures formed, viz. a hydrogen bonded layer of µ-1,1 azide bridged Cu dimers in 1; a network of two different types of dimers (Cu1-Cu2 & Cu3-Cu3') involving µ-1,1; µ-1,3; µ-1,1,3; & µ-1,1,3,3 azide bridges in 2; a ladder structure in which µ-1,1 azide bridges form the rungs and µ-1,3 azide bridges form the rails of the ladder in 3; and a 1-D polymer chain involving µ-1,1 azide bridges in 4. Consistent with the bridge geometry, compounds 1 & 2 display ferromagnetic interactions, while 3 & 4 display antiferromagnetic interactions. The rather unexpected antiferromagnetic interactions in 3, in spite of µ-1,1 azide bridged rungs may be due to the crossover near the bridge angle. The ferromagnetic interactions in 1 and 2 are supported by DFT calculations.

Design, synthesis and pharmacological evaluation of pyrimidobenzothiazole-3-carboxylate derivatives as selective L-type calcium channel blockers.

L-type voltage gated calcium channels play essential role in contraction of various skeletal and vascular smooth muscles, thereby plays important role in regulating blood pressure. Dihydropyridine receptors have been targeted for development of newer antihypertensive agents, one of the structurally analogs nucleus dihydropyrimidines have been reported earlier by us as a potential agent toward development of calcium channel modulator. A pre-synthetic QSAR was run and on the basis of structure activity relationship a series of twenty three molecules was synthesized and studied by myosin light chain kinase assay (MLCK), Angiotensin Converting Enzyme (ACE) colorimetric assay, non-invasive blood pressure (NIBP) and invasive blood pressure (IBP) methods. Molecules with significant efficacy were studied for their single crystal X-ray diffraction, molecular docking, molecular dynamics and post-synthetic QSAR. The NIBP and IBP methods screened molecules with better percentage inhibition versus time compared to standard drug Nifedipine. The lead compound ethyl 2-methyl-4-(3-nitrophenyl)-4H-pyrimido [2,1-b] [1,3] benzothiazole-3-carboxylate (26) presented a triclinic structure with polymeric chain packing in lattice. 26 exhibited IC50 on MLCK assay of 2.1±1.7 µM with selectivity of L-type calcium channels and comparative to Nifedipine. It offered satisfactory physicochemical properties with partition coefficient of (ClogP) 4.64. Its pharmacokinetic profile is also good with Cmax at 0.40 µg/ml by oral route with Tmax reaching in 0.5 h which means in 30 min. 26 also exhibits superior t1/2 of 5.4 h and oral bioavailability of (F) 56.75% with an AUC0-∞ of 0.84 µg h/ml. Molecular docking studies indicates toward the interaction of lead compound via hydrogen bonds with Lys144, Glu181 and Asp183, it forms the Van der Walls interactions with Ser18, Asp20, Asn187, Pro185, Glu180, Glu181 and Arg10 with Glide score and Glide energy to be -3.602 and -47.098, respectively. Post-synthetic QSAR of newly synthesized molecules indicates toward improvement with respect to steric descriptor which contributed negatively in former series.

Development of selective DprE1 inhibitors: Design, synthesis, crystal structure and antitubercular activity of benzothiazolylpyrimidine-5-carboxamides.

Decaprenylphosphoryl-b-D-ribose 20-epimerase (DprE1) is a potential drug target for development of antitubercular agents. Structure based drug discovery approach yielded twenty novel derivatives of benzothiazolylpyrimidine-5-carboxamides (7a-t) which were synthesised by three component one pot reaction involving benzothiazolyl oxobutanamide, thiourea and substituted aromatic benzaldehydes. These derivatives were evaluated for antitubercular activity to determine MIC and compound 7a, 7e, 7f and 7o were found to be potentially active against Mycobacterium tuberculosis (H37Rv). Log P of these compounds was found to be between 2.0 and 3.0 making them suitable for oral dosing. DprE1 selectivity and pharmacokinetic studies were carried out for these compounds of which 7a and 7o were found to be highly selective and bioavailability was found to be above 52% by oral dose. Crystal structure of 7a was studied and molecular packing was determined, it exhibited a triclinic crystal lattice arrangement having hydrogen bonded dimeric arrangement. Drug receptor interactions were studied which exhibited docking in the active site of receptor with hydrogen bonding, hydrophobic interactions, vdW interactions with amino acid residues such as Cys387, Asn385, Lys418, Tyr314, Gln334 and Lys367 respectively. 3D QSAR analysis was carried out by kNN-MFA method to determine and develop theoretical model, best suitable model was found to be based on Simulated Annealing k-Neariest Neighbour Molecular Field Analysis (SA kNN-MFA). The model provided with hydrophobic descriptors in positive side indicating the need of bulky groups, steric and electronegative descriptors in negative coordinates hints with contribution by the electronegative substitutions as favourable and desirable moieties for enhancing the activity. The q(2), q(2)_se and Pred_r(2)se were found to be 0.5000, 0.6404 and 1.0094 respectively. A pharmacophore model was generated which suggested for necessity of aromatic, aliphatic carbon centre and hydrogen bond donor for development of newer DprE1 selective inhibitors.

Novel three-dimensional coordination polymers of lanthanides with sulfate and oxydiacetic acid.

Three three-dimensional coordination polymers, viz. poly[[diaqua-µ4-oxydiacetato-di-µ4-sulfato-dipraseodymium(III)] hemihydrate], [Pr2(C4H4O5)(SO4)2(H2O)2]·0.5H2O, (I), poly[[diaquadi-µ3-oxydiacetato-µ3-sulfato-dineodymium(III)] 1.32-hydrate], [Nd2(C4H4O5)2(SO4)(H2O)2]·1.32H2O, (II), and poly[[diaquadi-µ3-oxydiacetato-µ3-sulfato-disamarium(III)] 1.32-hydrate], [Sm2(C4H4O5)2(SO4)(H2O)2]·1.32H2O, (III), were obtained by hydrothermal reactions of the respective lanthanide oxides and ZnSO4 with oxydiacetic acid (odaH2). The Nd(3+) and Sm(3+) compounds form isomorphous crystal structures in which the lanthanide cations are nine-coordinate, having a tricapped trigonal prismatic coordination. The Pr(3+) compound has an entirely different crystal structure in which two types of coordination polyhedra are observed, viz. nine-coordinate (trigonal prism) and ten-coordinate (bicapped square antiprism). The sulfate anions show various coordination modes, one of which has only rarely been observed crystallographically to date.

l-Histidinium dipicrate dihydrate.

In the title mol-ecular salt, C6H11N3O2 (2+)·2C6H2N3O7 (-)·2H2O, the histidine mol-ecule exists as a histidinium dication, being protonated at the N atom of the imidazole ring. The charges are balanced by two picrate anions and the compound crystallizes as a dihydrate. In the crystal, the components are linked via N-H⋯O and O-H⋯O hydrogen bonds and weak C-H⋯O inter-actions, forming a three-dimensional supermolecular structure.

A new end-on azido bridged Mn(III) single-chain magnet and its dimeric single molecule magnet polymorph. Synthesis, structure and magnetic properties of [Mn(5-Clsalpn)N3]n and phenoxo bridged [Mn(5-Clsalpn)N3]2.

An end-on azido bridged Mn(III) coordination chain polymer [Mn(5-Clsalpn)N3]n (complex 1) and its dimeric polymorph, [Mn(5-Clsalpn)N3]2 (complex 2), where 5-Clsalpn is N,N'-bis(5-chlorosalicylidene)-1,3-diaminopropane, were prepared. Complex 1, which is obtained as two concomitant polymorphs (1a and 1b) with nearly identical molecular structures but different crystal packing, has µ-1,1(end-on) azido bridges. This single atom bridge is unsymmetrical and leads to a -1 cm(-1) antiferromagnetic interaction among Mn(III) centers of the one-dimensional coordination polymer. Mn(III) anisotropy is manifested through Jahn-Teller elongation along the N(azido)-Mn-N(azido) axis, and results in single-chain magnet behavior. The phenoxo-bridged dimer (complex 2) has terminal azido ligands and a ferromagnetic interaction is mediated by the unsymmetrical bis-phenoxo bridge. Mn(III) anisotropy is manifested through Jahn-Teller elongation along an N-Mn-O axis, and results in single molecule magnet behavior. The dimers are organized into a two-dimensional network structure via Cl···Cl and Cl···H-phenyl interactions which are also ferromagnetic.

Increase in oxidative stress at low temperature in an antarctic bacterium.

Association between cold stress and oxidative stress was demonstrated by measuring the activity of two antioxidant enzymes and the level of free radicals generated in two batches of cells of an Antarctic bacterium Pseudomonas fluorescens MTCC 667, grown at 22 and 4°C. Increase in oxidative stress in cells grown at low temperature was evidenced by increase in the activity of an enzyme and also in the amount of free radicals generated, in the cold-grown cells. The association between cold stress and oxidative stress demonstrated in this investigation bolsters the concept of interlinked stress response in bacteria.

Polymorphism in the nitrate salt of the [Mn(acetylacetonate)2(H2O)2]+ ion.

The crystallization of [Mn(acac)(2)(H(2)O)(2)](+) from solutions containing excess nitrate leads to the formation of four polymorphs. All polymorphs contain two different types of complex ions, one containing essentially coplanar acac ligands and the other in which the two acac ligands together assume a chair conformation. Molecular modelling using DFT (density-functional theory) calculations shows that the coplanar conformation is the electronically stable one. The hydrogen bonding between the trans-water molecules and the nitrate ion produces a one-dimensional chain of 12-membered rings, which are further organized into a two-dimensional network via a lattice water molecule. Lattice-energy calculations have been carried out to compare the stabilities of the four polymorphs.

Cerium(IV)-lanthanide(III)-pyridine-2,6-dicarboxylic acid system: coordination salts, chains, and rings.

A series of new heterometallic compounds containing cerium(IV) and lanthanide(III) with pyridine-2,6-dicarboxylic acid (dipicH(2)) have been synthesized. Depending on the Ln(III) ion and preparation conditions, we obtained four types of compounds. Type-I: one-dimensional coordination polymer, [Ln(dipicH)(H(2)O)(4)Ce(dipic)(3)].7H(2)O; Ln = La (1), Ce (2), or Pr (3). Type-II: ionic compound, [Ln(dipicH)(H(2)O)(6)][Ce(dipic)(3)].7H(2)O; Ln = Nd (4), Sm (5), Eu (6), Gd (7), or Dy (8). Type-III: octanuclear cluster incorporating a six-membered coordination ring, [Ln(H(2)O)(7)Ln(dipic)(H(2)O)(4)(Ce(dipic)(3))(2)](2).nH(2)O; Ln = La (9) n = 24, Ce (10) n = 24, Pr (11) n = 24, or Nd (12) n = 26. Type-IV: hexanuclear cluster incorporating a four-membered coordination ring, [(Ln(H(2)O)(5))(2)(Ce(dipic)(3))(4)(2H(+))].nH(2)O; Ln = Nd (13) n = 34, Sm (14) n = 26, Eu (15) n = 26, or Gd (16) n = 26. Crystal structures were determined for compounds 1-16. Tb and heavier lanthanides all form compounds isomorphous with Type-IV compounds. The observed structural variety is a consequence of the interplay of lanthanide contraction and kinetic effects involving water molecules, free as well as clusters, ranging in size from 6 to 26. A metal-centered luminescence sensitized by dipic ligand was observed in compounds containing Eu(III) and Dy(III) ions. Direct chelation, as opposed to bridging coordination, leads to enhanced luminescence. Resolved EPR spectra were observed for the Gd(III) compounds which are dependent on the coordination environment.

Solvent water tapes in two hydrates of mu-oxo-bis[bis(2,2'-bipyridine-kappa2N,N')(sulfato-kappaO)iron(III)].

The title compound, [Fe2O(SO4)2(C10H8N2)4], crystallizes as two different hydrates, viz. 11H2O, (I), and 15H2O, (II). The complex is binuclear, in which the two FeIII atoms are coordinated in an octahedral geometry to four N atoms from the two bipyridine ligands, to one O atom from the sulfate ion and to an oxide ion on a twofold axis, which acts as a bridge between the symmetry-related units. The Fe...Fe separation is 3.556 (4) A and the Fe-O-Fe angle is 161.6 (2) degrees in (I); the corresponding values are 3.544 (1) A and 165.8 (2) degrees in (II). In (II), one of the O atoms of the sulfate ion is disordered over two positions. In both compounds, the solvent water molecules form slightly different one-dimensional hydrogen-bonded networks which pass along the c axis of the unit cell. In (I), three solvent water molecules and, in (II), one solvent water molecule, are situated on the twofold axis. In both (I) and (II), the central O atom of the metal complex lies on a twofold axis.

Silver(I) complexes of 2-(2-aminoethyl)pyridine: nitrate and perchlorate salts of bis[mu-2-(2-aminoethyl)pyridine-kappa(2)N:N']disilver(I).

2-(2-Aminoethyl)pyridine (2-aep, C7H10N2) acts as a bridging ligand in bis[mu-2-(2-aminoethyl)pyridine-kappa(2)N:N']disilver(I) dinitrate, [Ag2(2-aep)2](NO3)2, and bis[mu-2-(2-aminoethyl)pyridine-kappa(2)N:N']disilver(I) diperchlorate, [Ag2(2-aep)2](ClO4)2. Both salts contain the dinuclear [Ag2(2-aep)2]2+ cation, which possesses a crystallographic inversion center. The Ag...Ag distance is 3.1163 (5) A for the nitrate and 3.0923 (3) A for the perchlorate salt, and may indicate a weak d(10)-d(10) interaction in each case. Essentially linear coordination of the AgI atom is perturbed by weak coordination to the anionic O atoms. These latter interactions organize the dinuclear cations into one-dimensional polymeric chains in the crystals of the two salts.

Synthesis and structure of coordination polymers of Ag(I) with isomeric (aminomethyl)pyridines. Formation of a novel circular helicate and 2-D networks via Ag...Ag contacts and coordination shell expansion under anion control.

Reaction between Ag(I) salts and the three isomers of (aminomethyl)pyridines, viz., 2-amp, 3-amp, and 4-amp, lead to either discrete or polymeric (1-D and 2-D) structures influenced by anions and closed shell Ag.Ag contacts. Characterization data for Ag(2-amp)BF(4) (1) follow: monoclinic, space group C2/c, with a = 16.788(2) A, b = 11.5719(6) A, c = 11.3864(7) A, beta = 123.671(8) degrees, and Z = 8. For Ag(2)(2-amp)(3)(PF(6))(2) (2): monoclinic, space group P2(1)/a, with a = 10.029(7) A, b = 20.291(12) A, c = 13.907(6) A, beta = 95.38(5) degrees, and Z = 4. For Ag(2)(3-amp)(3)(PF(6))(2) (4): triclinic, space group P1, with a = 10.4482(7) A, b = 11.1468(9) A, c = 12.2720(11) A, alpha = 81.018(7) degrees, beta = 80.668(6) degrees, gamma = 80.977(6) degrees, and Z = 2. For Ag(4-amp)BF(4).0.75CH(3)CN (5): orthorhombic, space group C222(1), with a = 9.272(2) A, b = 16.164(12) A, c = 27.851(2) A, and Z = 8. For Ag(4-amp)PF(6) (6): monoclinic, space group P2(1)/m, with a = 5.2089(7) A, b = 14.3950(17) A, c = 7.0149(14) A, beta = 96.538(14) degrees, and Z = 2. While Ag(I) is 2-coordinate in 1, 5 and 6, it shows 3-coordination in 2 and 4. Compound 1 consists of a 1-D polymeric cation chain with interchain Ag...Ag contacts and the anions sitting on the edges of the chains. The dication in 2 is held in the form of a circular helicate by closed shell Ag...Ag interactions. Compound 4 generates a 2-D network with channels big enough to accommodate the anions. Compound 5 is a 2-D chiral network of chains connected by Ag...Ag contacts. Compound 6 shows a simple 1-D chain structure with an alternating arrangement of cationic chains and anions.

Synthesis, structure, and magnetic properties of [MnIII(salpn)NCS]n, a helical polymer, and the dimer [MnIII(salpn)NCS]2. Weak ferromagnetism in [MnIII(salpn)NCS]n related to the strong magnetic anisotropy in Jahn-Teller MnIII (salpnH2 = N,N'-bis(salicylidene)-1,3-diaminopropane).

Dimeric [Mn(salpn)NCS](2)(1) and polymeric [Mn(salpn)NCS](n)(2) are formed by the reaction of Mn(CH(3)CO(2))(2).4H(2)O, the schiff base, and thiocyanate. The formation of the two polymorphic forms is solvent and temperature dependent. 1: orthorhombic, space group Pbca, with a = 12.573(2) A, b = 13.970(7) A, c = 18.891(9) A, and Z = 8. 2: orthorhombic, space group Pna2(1), with a = 12.5277(14) A, b = 11.576(2) A, c = 11.513(2) A, and Z = 4. The dimers in 1 are held together by weak noncovalent S...pi (phenyl) interactions leading to a chain along the a-axis. Each monomeric unit of the polymer in 2 is related to its adjacent ones by a 2-fold screw axis leading to a helix along the c-axis. The exchange coupling is nondetectable in the dimer. The magnetic susceptibility of the helical chain fits a classical chain law with J = -3.2 cm(-1) and shows a weak ferromagnetic ordering below 7 K due to spin canting effects.

Complexes of Ag1 with cationic ligands: bis[(pyridylmethyl)ammonio]silver(I) salts.

Bis[(2-pyridylmethyl)ammonio]silver(I) trinitrate, [Ag(C(6)H(9)N(2))(2)](NO(3))(3), (I), and bis[bis[(4-pyridylmethyl)ammonio]silver(I)] hexakis(perchlorate) dihydrate, [Ag(C(6)H(9)N(2))(2)](2)(ClO(4))(6).2H(2)O, (II), are rare examples of complexes with cationic ligands. In (I), the Ag(+) cation has a T-shaped [2+1] coordination involving the pyridine N atoms and a nitrate O atom, while in (II) there are three independent two-coordinate Ag complex cations (two with the Ag atoms on independent inversion centres) and disordered ClO(4)(-) ions. The crystal structures reveal the role of hydrogen bonding in stabilizing these complexes.

Synthesis, Structure, and Magnetic Properties of Mn(salpn)N(3,) a Helical Polymer, and Fe(salpn)N(3), a Ferromagnetically Coupled Dimer (salpnH(2) = N,N'-bis(Salicylidene)-1,3-diaminopropane).

The preparation, crystal structures, and variable temperature magnetic susceptibility data are presented for two azido-bridged Schiff base complexes of Mn(III) and Fe(III). Mn(salpn)N(3) (1), where salpn is the dianion of N,N'-bis(salicylidene)-1,3-diaminopropane, crystallizes in the orthorhombic system, space group Pna2(1), with a = 11.947(2) Å, b = 11.818(2) Å, c = 11.227(5) Å, and Z = 4. Fe(salpn)N(3) (2) crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.199(7) Å, b = 14.081(6) Å, c = 12.017(3) Å, beta = 105.19(3) degrees, and Z = 4. In 1, salpn coordinates in the equatorial mode, with two azide ions coordinating in axial positions. The azide ions act as "end-to-end" (&mgr;-(1,3)) bridges, leading to an infinite helical chain propagating along the crystallographic c axis. In striking contrast, 2 has a dimeric structure in which the Schiff base adopts a cis-octahedral coordination mode. The dimer is held together by two "head-on" (&mgr;-(1,1)) bridging azide ions. The polymeric compound, 1, is weakly antiferromagnetic (J = -4.03 cm(-)(1), H(ex) = -2J summation operatorS(i)()S(i)()(+1)), while 2 is weakly ferromagnetic (J = 0.76 cm(-)(1), H(ex) = -2JS(1)S(2)).

Synthesis, Crystal Structure, Magnetic Properties, and EPR of Cu(bp3ca)Br(2).H(2)O (bp3ca = 2,2'-Bipyridine-3,3'-dicarboxylic Acid). Ferromagnetic Interactions via Unsymmetrical Bromide Bridges.

Cu(bp3ca)Br(2).H(2)O crystallizes in the triclinic space group P&onemacr; with a = 10.622(2) Å, b = 10.832(2) Å, c = 14.684(2) Å, alpha = 106.13(1) degrees, beta = 105.91(1) degrees, gamma = 102.74(1) degrees, and Z = 2. The asymmetric unit consists of a bis &mgr;-bromo unsymmetrically dibridged dimer which is further linked to its inversion-related partner to form a dimer of dimers. Weak intertetramer contacts are also observed. The magnetic data for this compound were fit to a linear tetramer model to give J(1) = J(3) = -8.69 x 10(-)(3) cm(-)(1), J(2) = 91.52 cm(-)(1), and the intertetramer interaction J' = -1.187 cm(-)(1) with g = 1.93. EPR data are consistent with the magnetic data. This system is compared to its previously reported chloro counterpart, which differs markedly in both structure and magnetic properties.

Synthesis and Structural Investigations of [Mn(3)O(4)(phen)(4)(H(2)O)(2)](NO(3))(4).2.5H(2)O: A Water-Bound Complex Obtained by Cerium(IV) Oxidation.

The trinuclear manganese complex [Mn(3)O(4)(phen)(4)(H(2)O)(2)](NO(3))(4).2.5H(2)O, 1 (where, phen = 1,10-phenanthroline), has been synthesized by the Ce(IV) oxidation of a concentrated solution of manganese(II) acetate and phen in 1.6 N nitric acid. The complex crystallizes in the triclinic space group P&onemacr; with a = 10.700(2) Å, b = 12.643(3) Å, c = 20.509(4) Å, alpha = 78.37(3) degrees, beta = 83.12(3) degrees, gamma = 82.50(3) degrees, and Z = 2. The structure was solved by direct methods and refined by least-squares techniques to the conventional R (R(w)) factors of 0.055 (0.076) based on 4609 unique reflections with F(o) >/= 6.0sigma(F(o)). The structure of the cation consists of an oxo-bridged Mn(3)O(4)(4+) core, with the geometry of the manganese atoms being octahedral. The coordination polyhedron of one of the manganese atoms (Mn(1)) consists of two &mgr; oxo ligands and two pairs of nitrogen atoms of two phen moieties, whereas that of each of the remaining two manganese atoms consists of three &mgr;-oxo ligands, two nitrogen atoms of a phen moiety, and the oxygen atom of a water molecule. The complex represents the second example for water coordination to manganese(IV) centers in complexes with a Mn(3)O(4)(4+) core. Optical spectra in ligand buffer (pH 4.5) reveal complete conversion of the complex into a Mn(III)Mn(IV) species. The observed room-temperature (298 K) magnetic moment of 3.75 &mgr;(B) indicates the presence of strong antiferromagnetic coupling in the complex.