Rare azido-bridged manganese(II) systems: syntheses, crystal structures, and magnetic properties

Two new polymeric azido-bridged manganese complexes of formulas [Mn(N3)2 (bpee)]n (1) and {[Mn(N3)(dpyo)Cl(H2O)2](H2O)}n (2) [bpee, trans-1,2-bis(4-pyridyl)ethylene; dpyo, 4,4'-dipyridyl N,N'-dioxide] have been synthesized and characterized by single-crystal X-ray diffraction analysis and low-temperature magnetic study. Both the complexes 1 and 2 crystallize in the triclinic system, space group P1, with a = 8.877(3) A, b = 11.036(3) A, c = 11.584(4) A, alpha = 72.62(2) degrees, beta = 71.06(2) degrees, gamma = 87.98(3) degrees, and Z = 1 and a = 7.060(3) A, b = 10.345(3) A, c = 11.697(4) A, alpha = 106.86(2) degrees, beta = 113.33(2) degrees, gamma = 96.39(3) degrees, and Z = 2, respectively. Complex 1 exhibits a 2D structure of [-Mn(N3)2-]n chains, connected by bpee ligands, whose pyridine rings undergo pi-pi and C-H...pi interactions. This facilitates the rare arrangement of doubly bridged azide ligands with one end-on and two end-to-end (EO-EE-EE) sequence. Complex 2 is a neutral 1D polymer built up by [Mn(N3)(dpyo)Cl(H2O)2] units and lattice water molecules. The metals are connected by single EE azide ligands, which are arranged in a cis position to the Mn(II) center. The 1D zipped chains are linked by H-bonds involving lattice water molecules and show pi-pi stacking of dpyo pyridine rings to form a supramolecular 2D layered structure. The magnetic studies were performed in 2-300 K temperature range, and the data were fitted by considering an alternating chain of exchange interactions with S = 5/2 (considered as classical spin) with the spin Hamiltonians H = -Ji sigma(S(3i)S(3i+1) + S(3i+1)S(3i+2)) - J2 sigmaS(3i-1)S(3i) and H = -Ji sigmaS(2i)S(2i+1) - J2 sigmaS(2i+1)S(2i+2) for complexes 1 and 2, respectively. Complex 2 exhibits small antiferromagnetic coupling between the metal centers, whereas 1 exhibits a new case of topological ferromagnetism, which is very unusual.     

A study on the fluoride complexes of plutonium(III), samarium(III) and bismuth(III) using fluoride ion-selective potentiometry

Stability constants of the fluoride complexes of Pu(III), Sm(III) and Bi(III) in 1.0M NaClO₄/HClO₄ medium at 23±1°C have been determined by potentiometry using a fluoride ion-selective electrode. Plutonium was reduced to the trivalent state using quinhydrone with an excess to serve as holding reductant. The log values of concentration stability constants log ₁, log ₂, and log ₃ are 3.58, 6.40 and 12.61 for Pu(III), 3.23, 5.81 and 10.54 for Sm(III) and 3.69, 6.13 and 11.04 for Bi(III), respectively. The log ₂ values in all these cases have very large deviation and may be taken only as rough estimates.     

EFFECTS OF IONIC STRENGTH and pH ON THE BINDING OF SANGUINARINE TO DEOXYRIBONUCLEIC ACID

Abstract— The interaction of sanguinarine with DN A has been studied in buffers of various ionic strengths and pH values where the physicochemical properties of DNA remain unchanged. Spectrophotometric analysis using absorption and fluorescence techniques indicates that the complex formed between sanguinarine and DNA is a function of ionic strength and pH. Increasing the salt concentration minimizes the importance of intercalator charge and extrapolation to 1 M [Na+] salt reveals the intercalative abilities, as reflected in binding constants, to be of the same order of magnitude as that of ethidium bromide. The fluorescence of sanguinarine bound to DNA is quenched and can be decreased by [Na +], [Mg²+] and [Ca²+] ions. The influence of pH on the fluorescence spectrum of sanguinarine with increasing concentration of DNA was studied. It is concluded that the binding of sanguinarine to DNA contains a large favourable non-electrostatic interaction and the alkaloid binds more DNA in buffer of low ionic-strength and acidic pH.     

X-ray structures of cobalt(III) complexes with bio-relevant pyrazolyl thiosemicarbazone: Indication of structural changes on the increasing bulkiness of the alkyl substituents on thiosemicarbazone moiety

X-ray crystallographic studies of cobalt(III) complexes of 5-methyl-3-formylpyrazole-N(4)-diethylthiosemicarbazone (HMP_zNEt₂), [Co(MP _z NEt ₂ ) ₂ ]Br·2H ₂ O, 5-methyl-3-formylpyrazole-N(4)-dipropylthiosemicarbazone (HMP_zNPr ₂ ), [Co(MP _z NPr ₂ ) ₂ ]Br·2H ₂ O and 5-methyl-3formylpyrazole-N(4)-dibutylthiosemicarbazone (HMP_zNBu ₂ ), [Co(MP _z NBu ₂ ) ₂ ]Br·H ₂ O, have been reported. In all the three complex species, X-ray crystallography has authenticated a CoN₄S₂ octahedral coordination with the pair of orthogonally coordinated NNS tridentate ligands in the monodeprotonated form of the ligand. The two azomethine nitrogen atoms are trans to each other, while the pyrazolyl ring nitrogens and the thiolato sulfurs are in cis positions. A gradual decrease in the dihedral angle between the coordinating ligands has been observed with increase in the bulkiness of the aliphatic side chains of the substituent on the thiosemicarbazone moieties. In all the three complexes, intraligand C–H···S contacts appear to arrest the free rotation of the side chains about the C(6)–N(5) single bond. ^†Deceased     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. V

Non-isothermal thermal studies of the dehydration of the double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues were carried out where M(I) = TI(I) and M(II) = Mg(II), Co(II), Ni(II), Cu(II) or Zn(II). Thermal parameters like activation energy, order of reaction, enthalpy change, etc. were evaluated from the analysis of TG, DTA and DTG curves. These thermal parameters were compared with those of other series, like NH₄(I), K(I), Rb(I) and Cs(I) studied earlier. On deuteration the nature of dehydration altered in the case of Tl₂Zn(SO₄)₂·6H₂O only. The thermal stability of the salt hyd discussed in relation to the salt hydrates of other series. The role of divalent cation on the thermal properties of dehydration of salt hydrates is also discussed. The order of reaction was always found unity. The values of ΔH were within ≈12–≈16 kcal mol^?1.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. III

Dehydration of double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O where M(I)Rb(I) and M(II)Mg(II), Mn(II), Co(II), Ni(II), Zn(II) and Cu(II) has been studied by derivatograph. Thermal parameters like activation energy, order of reaction, enthalpy change etc. for each step of dehydration have been evaluated from the analyses of TG, DTA and DTG curves and these parameters are compared with corresponding salt hydrates of the NH₄ and K(I) series. These double salt hydrates are deuterated and studied similarly. Activation energies for the first step of dehydration of these salt hydrates increase with the increase of second ionisation potential of the central metal except for Mg. The nature of dehydration changes in the cases of double salt hydrates of Mg(II) and Ni(II) on deuteration. The order of reaction for each case of dehydration has been found to be unity. The enthalpy change per mole of water varies from 11.4 to 17 kcal.     

Rhenium. VIII. Studies on the Formation of Oxofluororhenates (VII) by Conductometry and Thermometry

From conductometric and thermometric titrations of potassium perrhenate with aqueous hydrofluoric acid the existence of the complex species [ReO₄F]^2? has been inferred. Attempts to isolate Oxofluororhenates(VII) from aqueous medium under varying conditions have, however, not been successful.     

Massenspektrometrische-, dta- und tg-untersuchungen an eisencarbonylchalkogeniden Fe2(CO)6X2 (X  S,Se) und Fe3(CO)9X′2 (X′  S,Se, Te)

Mass spectra of Fe₃(CO)₉X₂ (X  S, Se, Te) and Fe₂(CO)₆X′₂ (X′  S, Se) are recorded and their fragmentation pattern given. The thermal decarbonylation has been studied using DTA/TG methods in the temperature range 25–600°C. The results are compared with those obtained from mass-spectroscopic studies. X-ray and magnetic measurements have been carried out on the residues obtained in the decarbonylation process.     

Effect of amines on the ceric ion-initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate R_p is independent of ceric ion concentration and can be expressed by the equation: R_p = k₁ [amine] [monomer] + k₂[monomer]², where k₁ and k₂ are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.     

Generation of potential energy curves for the X1Sigma(+)g, B1Delta(+)g, and B'1Sigma(+)g states of C2 using the effective valence shell Hamiltonian method

Calculations of the ground and excited state potential energy curves of C2 using the third-order effective valence Hamiltonian (Hv3rd) method are benchmarked against full configuration interaction and other correlated single-reference perturbative and nonperturbative theories. The large nonparallelity errors (NPEs) exhibited even by state-of-art coupled cluster calculations through perturbative triples indicate a serious deficiency of these single-reference theories. The Hv method, on the other hand, produces a much reduced NPE, rendering it a viable approximate many-body method for accurately determining global ground and excited state potential energy curvessurfaces.