Mössbauer and electronic spectral characterization of homo-bimetallic Fe(III) complexes of unsymmetrical [N10] and [N12] macrocyclic ligands

The homo-bimetallic complexes of stoichiometry Fe2(L)ClO4(ClO4)2 where L are novel unsymmetrical [N10] (L1.2HClO4) and [N12] (L2.2HClO4) macrocyclic ligands, have been prepared. The ligands were obtained from an in situ capping reaction of the reactive substrate, N,N'-bis(N-ethylaniline)hydrazine-1,2-diimine with a mixture of aniline or 1,3-diaminopropane and HCHO in presence of HClO4. The compounds have been characterized by elemental analyses, conductometric, IR, FAB-mass and electronic spectral studies. IR data of complexes suggest coordination from unsymmetrical aza sites as a tridentate (N,N,N) or tetradentate (N,N,N,N) ligand. mu(eff) values of the complexes suggest presence of antiferromagnetically coupled (Fe3+-Fe3+=S5/2-S5/2) spin exchange. M?ssbauer parameters of the complexes support (+/-3/2)-->(+/-1/2) nuclear transition in high-spin configurations of Fe(III) nuclei of the homo-bimetallic complexes with the presence of Kramer's double degeneracy.     

Wrapped weighted exponential distributions

We have developed a new class of circular distributions named wrapped weighted exponential distributions. The estimation of unknown parameters along with some characteristics of these distributions is also investigated. Some theorems that relate the distribution to some other circular distributions are established and we clarify their modeling potential using a classical data set on movements of sea stars.     

Structural Studies of Coupling Products Formed Between (C6H5)CH=N(C6H5) and the M(C5H5)(6,6-dmch) Fragments (M?=?Ti, Zr; dmch?=?dimethylcyclohexadienyl)

Abstract  

The reactions of Ti(C₅H₅)(6,6-dmch)(PMe₃) and Zr(C₅H₅)(6,6-dmch)(PMe₃)₂ with two equivalents of C₆H₅C(H)=N(C₆H₅) have led to couplings of the imines to the 1,5 (terminal) positions of the 6,6-dmch ligands. In both cases the PMe₃ ligands are lost, and the metal complexes each attain 18 electron configurations via η⁵-(C₅H₅), η³-allyl, and bis(π-amide) coordination. The complexes each crystallize in the monoclinic space group P2₁/c. For the titanium complex, a = 10.4336(1) ?, b = 9.0407(1) ?, c = 32.5547(6) ?, β = 94.2939(5)°, V = 3062.17(7) ?³, D_calc = 1.264 at 200(1) K. For the zirconium complex, a = 13.8900(3) ?, b = 10.0873(2) ?, c = 22.4543(6) ?, β = 90.7638(7)°, V = 3145.85(12) ?³, D_calc = 1.322 at 150(1) K.     

Piperidines: a new class of urease inhibitors

A variety of piperidines (2-12, 14-26) with variable substituents at N-atoms have been synthesized and evaluated as urease inhibitors. The synthesized compounds showed varying degree of urease inhibitory activity ranging from 31.97 to 254 microM. The size and electron-donating or -withdrawing effects of substituents influence the activity, which lead to the formation of urease inhibitors.     

Solvent effects on the structural and formyl substrate reactivity properties of a nitrogen/sulfur-ligated zinc hydroxide complex

The solution structural and formyl substrate reactivity properties of a nitrogen/sulfur-ligated zinc hydroxide complex, [(bmnpaZn)2(mu-OH)2](ClO4)2 (1, bmnpa = N,N-bis-2-(methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine), in acetonitrile and methanol are reported. In CH3CN, 1 has a binuclear cation [(bmnpaZn)2(mu-OH)2]2+ that is stabilized by secondary hydrogen bonding and CH/pi interactions involving the bmnpa chelate ligand. In CH3OH, 1 undergoes reaction with solvent to yield a zinc methoxide species, as determined by 1H NMR and electrospray mass spectral analysis. Treatment of 1 with methyl formate in CH3CN results in stoichiometric hydrolysis of the formyl ester to produce [(bmnpa)Zn(O2CH)]ClO4 (2) and methanol. The formate complex was identified via independent synthesis and characterization (X-ray crystallography, 1H and 13C NMR, FTIR, LRFAB-MS, conductance, and elemental analysis). In the solid state, 2n has a formate-bridged coordination polymer-type structure. However, in CH3CN, 2 behaves as 1:1 electrolyte, indicating cleavage of the polymer structure into mononuclear [(bmnpa)Zn(O2CH)]ClO4 species. Treatment of 1 with a stoichiometric amount of formanilide in CH3CN for 48 h at 45 degrees C results in decomposition of the zinc hydroxide complex to yield the free bmnpa ligand and an inorganic solid, presumably a zinc hydroxide or oxide species. Treatment of 1 with a stoichiometric amount of ethyl formate in CD3OD results in rapid, quantitative transesterification of the formyl carboxylate ester. A control reaction indicates that this transesterification reaction does not occur on the same time scale in the absence of the catalyst. Treatment of 1 with an excess of ethyl formate in CD3OD results in catalytic formyl carboxylate ester transesterification, with approximately 1000 turnovers in 60 min at 22(1) degrees C. Treatment of a CD3OD solution of 1 (0.5 equiv) with formanilide (1 equiv) results in the formation of aniline, d3-methyl formate, and the zinc formate complex 2. While aniline is produced stoichiometrically, the yield of d3-methyl formate varied from 30 to 50%, and the yield of 2 varied from 50 to 70% in repetitive experiments. Formation of both d3-methyl formate and 2 indicates that both methanolysis and hydrolysis reactions take place.     

Solvent-enhanced magnetic ordering temperature for mixed-valent chromium hexacyanovanadate(II), Cr(II)0.5Cr(III)[V(II)(CN)6].zMeCN, magnetic materials

The reaction of V(III)(THF)3Cl3 with NEt(4)CN in acetonitrile (MeCN) forms (NEt4)3[V(III)(CN)6].4MeCN (1), which after characterization was used as a molecular building block toward the synthesis of Prussian blue structured magnets. The reaction of 1 with [Cr(II)(NCMe)4](BF4)2 forms Cr(II)(0.5)Cr(III)[V(II)(CN)6].zMeCN via internal electron transfer, whose structure and magnetic properties are dependent on the degree of solvation, z. When solvated, Cr(II)(0.5)Cr(III)[V(II)(CN)6].1.2MeCN (2) is a mixture of crystalline and amorphous fractions that yield a material with two magnetic phases: bulk ferrimagnetic phase/crystalline [faced-centered-cubic lattice with a = 10.55(2) A] and cluster-glass phase/amorphous. The bulk ferrimagnetic phase exhibits a critical temperature, Tc, of 110 K, while the amorphous cluster-glass phase exhibits a freezing temperature, Tf, of approximately 25 K. Amorphous Cr(II)(0.5)Cr(III)[V(II)(CN)6].0.1MeCN (3) was determined to be the pure cluster-glass phase. This is an overall enhancement of 85 K (350%) in the magnetic ordering temperature via solvation, z. The coercivity was also increased 4-fold from 890 (2) and 3900 Oe (3) via desolvation.     

Structure and magnetic properties of a hydroxo-bridged copper(II) distorted cubane stabilized via supramolecular hydrogen bonding with an ionic hexafluoroacetylacetonate

Tetranuclear [Cu(II)4(OH)4(aib)4)](hfac)4 (1; aib = 2-methyl-2-amino-4-iminopentane; hfac = hexafluoroacetylacetonate) forms from the reaction of aqueous ammonia and Cu(hfac)2.2H2O in acetone. The structure of 1 reveals that four noncoordinating hfac- counterions stabilize the distorted cubane complex via multiple H-bonding contacts. Magnetic susceptibility studies reveal that cubane-like 1 is best described as a pair of independent antiferromagnetically coupled dimers with g = 2.10 and J/kB = -298 K (207 cm(-1)) (H = -2JS1.S2).     

Development of superconducting phases in BSCCO and Ba-BSCCO by sol spray process

The effects of barium substitution for Bi or Sr sites on the growth of superconducting phases have been studied. The sol spray process has been used to synthesis the Bi-Sr-Ca-Cu-O (BSCCO) and Ba-BSCCO homogeneous ceramic powders. Thermogravimetric (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques were employed to characterize the synthesized materials. The electrical resistance was measured by classical d.c. fourprobe technique. It has been observed that sol spray process has affected the physico-chemical properties of the materials and also avoid the use of chelating agent as in the case of sol gel process. In addition to the Bi₂Sr₂CaCu₂O₈ (2212) phase Ba doped specimens also contained Bi₂Sr₂Ca₂Cu₃O₁₀ (2223), BaBiO₃, BaCuO₂ and CuO phases. The results revealed that the specific effect of barium-doping on either sites (Bi or Sr) seems to avoid the formation of higher volume fraction of the low T _c phase and promoting the formation of BiBaO₃, BaCuO₂ and CuO along with formation of a high T _c 2223 phase. The substitution of Ba on either sites (Bi or Sr) lower the sintering temperature for the formation of high T _c (small volume fraction) however, the Ba doped specimens also contained non-superconducting phases.     

Structural Studies of [Ru(1,8-naphthyridine)<Subscript>4</Subscript>]<Superscript>2+</Superscript> and [Ru(1,5-cyclooctadiene)(1,8-naphthyridine)<Subscript>2</Subscript>]<Superscript>2+</Superscript> as their Tetraphenylborate Salts

Abstract  

The previously reported [Ru(naph)₄]²⁺ complex (naph = 1,8-naphthyridine) has been prepared by a simplified route using [RuCl₂(1,5-COD)] _x (COD = cyclooctadiene) as starting material and isolated as its tetraphenylborate salt. The salt crystallizes in the monoclinic space group P2₁/n with a = 13.6531(3) ?, b = 12.5389(4) ?, c = 20.0349(5) ?, β = 96.5884(15)o, V = 3407.22(16) ?, D _calc = 1.300 at 150(1) K. The dication has crystallographically imposed inversion symmetry. Although the iron analogue has been found to have a coordination number of eight, the ruthenium complex is only six-coordinate, which is achieved by the presence of two monodentate and two bidentate 1,8-naphthyridine ligands. The observation of a higher coordination number for Fe(II) vs. Ru(II) can be explained by the high spin nature of the iron complex. A byproduct complex, [Ru(1,5-COD)(naph)₂][B(C₆H₅)₄]₂, could also be synthesized, isolated pure, and structurally characterized. The organometallic complex possesses an 18 electron configuration by virtue of the dicationic metal center being coordinated by the diene ligand and all four nitrogen lone pairs. This salt crystallizes in the triclinic space group \textP[`1] {\text{P}}\bar{1} with a = 12.9538(3) ?, b = 14.9485(3) ?, c = 17.4291(3) ?, α = 69.0649(11)o, β = 78.3211(9)o, γ = 78.5629(10)o, V = 3057.50(11) ?³, D _calc = 1.293 at 150(1) K.     

Texture transformations and orientational properties of lyotropic nematics in magnetic field

Dynamics of changes of the morphological properties and processes of orientation in lyotropic nematic mesophases by application of external magnetic field have been investigated in detail. The dynamics of changes of the optical birefringence values in nematic‐calamitic mesophase vs. time has been determined. The optical mappings of nonequilibrium magnetically induced textures, which have been observed for this mesophase during orientational process, and changes of birefringence vs. time are presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)