Moments Of Compounds Research Articles

The New Complexes of Selected Transition Metal Ions with a Ligand Formed by Condensation of Isatin with Amino Acid: Spectral, Thermal, and Magnetic Properties

The new complexes of 2-[(2-oxo-1,2-dihydroindol-3-ylidene)amino]butanoic acid, LH (where L = C12H11N2O3), with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) of general formulae MLCl·nH2O, for Co(II), Ni(II) and Cu(II), and ML2·H2O for Mn(II) and Zn(II), where n = 1, 2 depending on M(II) ions, are synthesized. The complexes crystallize in a monoclinic system, and upon heating in the air (293–1173 K) decompose in three steps forming eventually the corresponding oxides of the metals(II). In the course of this process the organic ligand decomposes releasing the molecules of H2O, CO2, NH3, CO, hydrocarbons, and additionally HCl for Co(II), Ni(II) and Cu(II) complexes. Magnetic moments of compounds are determined in the ranges of 76–303 and 2–300 K. All analyzed compounds, except that of Zn(II), demonstrate the paramagnetic properties with the ferro- and antiferromagnetic interactions between molecular centres.

New complexes of 3,4-dimethoxyphenylacetic acid with selected transition metal ions: Spectral, thermal, and magnetic properties

3,4-Dimethoxyphenylacetates of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) of general formula M(C10H11O4)2·nH2O, where n = 1, 2 or 4 depending on M(II) ions, are obtained. The complexes crystallize in monoclinic or triclinic systems. The carboxylate groups act as bidentate chelating or bridging ligands. On heating in the air (293–1173 K) they decompose in three steps finally forming oxides of the corresponding metals(II) or their mixtures. Magnetic moments of compounds were determined in the ranges of 76–303 and 4–300 K.

X-ray circular magnetic dichroism in the presence of strong spin fluctuations

The use of X-ray magnetic circular dichroism (XMCD) spectra for determininghe t magnitude of atomic magnetic moments in compounds of rare-earth and transition elements is discussed. The standard sum rule approach often yields a magnitude of moments that is often smaller than values obtained from magnetic measurements. We attribute this to strong spin fluctuations in the surface layers in which XMCD signals form. A way of determining the values of local magnetic moments in the presence of strong fluctuations is proposed and tested.

The X-ray magnetic dichroism, the sum rule and spin fluctuations on the surface of manganite (LaPrCa)MnO3

The problem of determining the magnitude of the atomic magnetic moments in compounds with rare-earth and transition elements using the X-ray magnetic circular dichroism (XMCD) is investigated. The standard sum rules approach usually gives the moment values by several times smaller than their bulk values obtained from the direct magnetic measurements. We attribute this to the strong spin fluctuations in the surface layer which actually formed the soft XMCD signal. A method of determining the value of the local magnetic moments in the presence of strong fluctuations is proposed. The magnetic interactions in La0.5Pr0.2Ca0.3MnO3 are investigated by x-ray absorption spectroscopy, XMCD and bulk magnetization measurements. The proposed procedure is used to determine the values of atomic magnetic moments of transition and rare-earth elements as well as net magnetization on the surface and in the bulk from experimental Mn L2,3 and Pr M4,5 XMCD spectra.

Conformational analysis of arylphosphine selenides

We have carried out the conformational analysis by the methods of dipole moments and quantum chemistry [DFT B3PW91/6-31G(d), B3PW91/6-311++G(3df, 3pd)] of bis[(4-chlorophenyl)ethyl]phosphine selenide (I) and bis-[(4-tert-butylphenyl)ethyl]phosphine selenide (II), which are promising initial materials for the synthesis of various organophosphoselenium compounds. Their structural formulas are presented in the scheme. The coeffi cients of the calculation equations and the experimental dipole moments of phosphine selenides I, II are compiled in Table 1. The most probable conformers of compounds I, II according to the quantum-chemical calculations are given below (hydrogen atoms are not shown). The energies, theoretical dipole moments and those computed using the vector-additive scheme for the conformational isomers of compounds I, II are presented in Table 2. In phosphine selenide I according to the data of B3PW91/6-31G(d) the energy minimum corresponds to conformer IА possessing a symmetric structure. However the calculation in an extended basis indicates the energy prevalence of conformer IB. Taking into consideration that the dipole moment values of conformer IB calculated in both bases is in better agreement with the experimental fi nding than those of conformer IA the results of B3PW91/6-311++G(3df,3pd) concerning the energy preference of conformer IB apparently should be regarded Table 1. Coeffi cients of calculation equations and experimental dipole moments of compounds I, II

A blue-green-emitting 3D supramolecular compound: synthesis, crystal structure and effect of solvents and temperature on the luminescent properties

A blue-green-emitting three-dimensional supramolecular compound (C10O2N2H8)(C9O7H6) (1) was synthesised under hydrothermal conditions and structurally characterised by elemental analysis, IR spectrum, 1H NMR and single-crystal X-ray diffraction. The crystal belongs to triclinic system with P 1¯ space group. The crystal structure is stabilised by O–H…O, O–H…N hydrogen bonds and π–π interactions (π–π stacking distance is 3.282 Å). Compound 1 exhibits intense green luminescence in solid state at 298 K (λem = 546 nm). In addition, absorption and fluorescence characteristics of compound 1 have been investigated in different solvents (DMSO, CH3CN and CH3OH). The results show that compound 1 exhibits a large red shift in both absorption and emission spectra as solvent polarity increases (polarity: DMSO>CH3CN>CH3OH), indicating a change in dipole moment of compound 1 upon excitation. Although the emission spectra of compound 1 in CH3OH are close to it in dimethyl sulfoxide (DMSO), it is revealed that the luminescence behaviour of compound 1 depends not only on the polarity of environment but also on the hydrogen bonding properties of the solvent. Meanwhile, temperature strongly affects the emission spectra of compound 1. Emission peaks of compound 1 were blue shift at 77 K than those at 298 K in both solid state (ca. 142 nm) and solution (ca. 6–23 nm), which was due to the non-radiative transition decreases at low temperature. Moreover, the quantum yield and fluorescence lifetime of compound 1 were also measured, which increased with increasing polarity of solvent, lifetime in DMSO at 298 K (τ1 = 0.92 μs, τ2 = 8.71 μs) was the longest one in solvents (298 K: τ1 = 0.87–0.92 μs, τ2 = 7.50–8.71 μs; 77 K: τ1 = 0.72–0.90 μs, τ2 = 6.88–7.45 μs), which was also shorter than that in solid state (298 K: τ1 = 1.13 μs, τ2 = 7.50 μs; 77 K: τ1 = 0.97 μs, τ2 = 8.97 μs). This was probably because of the weak polarity environment of compound 1 in solid state.

Ferromagnetism, paramagnetism, and thermally induced magnetism in photomagnetic CrIII/MnII and CrIII oxalates with the 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f]quinolinium cation

Single crystals of the new cationic chromene, 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f-quinolinium iodide (C25H20NO)I (1), were synthesized. The crystal structure of the new compound was studied, and quantum chemical calculation for the open and closed forms were carried out. The bifunctional compounds containing mono- and bimetallic 3d metal (tris)oxalates with the chromenium cation, (C25H20NO)3[Cr(C2O4)3] · 4H2O (2) and (C25H20NO)[CrMn(C2O4)3] · H2O (3), were prepared. Compound 1 is paramagnetic due to low-lying thermally excited states of the chromene molecules. At low temperatures (∼2 K), the paramagnetic states are frozen, and the compound becomes diamagnetic. Compound 2 is paramagnetic and its magnetic properties are determined mainly by the Cr3+ ions and the thermally induced paramagnetic states of the chromene molecules. At high temperatures, the magnetic moment of compound 3 consists of the contributions of the paramagnetic Cr3+ and Mn2+ ions and the thermally induced paramagnetic states of chromenes. At low temperatures (2–3 K), the thermally induced magnetism of organic molecules is frozen, and the magnetically ordered (and, probably, spin-glass) state is observed in the two-dimensional network of metal oxalates (Tc = 3 K in the zero magnetic field). The UV irradiation leads to an increase in the magnetic moment of the compound in the paramagnetic region due to the generation of radiation defects.

Nature of PO Bonds in Phosphates

Making use of a combination of ab initio calculated geometries, orbital energies, and orbital spatial distributions as well as experimental information about bond lengths, bond energies, vibrational frequencies, and dipole moments, the nature of the terminal PO bond in phosphates such as (MeO)(3)PO was probed and compared to the case in MeO-P=O where P is trivalent and a PO pi bond is thus assumed to exist. We find that the MeO-P and terminal PO bond lengths in (MeO)(3)PO are essentially the same as in MeO-P=O and the terminal PO lengths are substantially shorter than single P-OMe bond lengths. We also find that the HOMO orbital energies in the two compounds are within 0.1 eV of one another and that these orbitals have spatial characteristics much like one would expect of a bonding pi orbital connecting two atoms from different rows of the periodic table. Using this data, making a comparison to the more familiar bonding arising in N(2), CO, and BF, and taking note of the dipole moments in compounds known to possess dative bonds, we conclude that it is best to represent the terminal PO bond in phosphates in terms of valence-bond structures such as (MeO)(3)P=O in which the formal charges are P(0)O(0) and where a single PO pi bond exists. However, when it comes to characterizing the PO antibonding pi* orbitals, significant differences arise. Electronic structure methods were able to identify the pi* orbital of MeO-P=O and to determine its energy (the MeO-P=O(-) anion is even bound). Similar attempts to identify the PO pi* orbital in the unbound (MeO)(3)P=O(-) anion lead us to conclude that this anion state is probably so strongly coupled to the continuum (i.e., to states corresponding to (MeO)(3)P=O plus a free electron) that it is so short lived as to be undetectable in experiments.

Antiferromagnetism in Mn5Si3: the magnetic structure of the AF2 phase at 70 K

The antiferromagnetic structure of the AF2 phase of Mn5Si3, stable between the Neel point at 99 K and the transition to a second antiferromagnetic AF1 phase at 66 K, has been determined from unpolarized neutron integrated intensity measurements on single-crystal and powder samples. The paramagnetic phase adopts the hexagonal D88 structure, Z=2, with Mn1 and Mn2 atoms in a fourfold and a sixfold site respectively. With the onset of long-range magnetic order the symmetry is reduced to orthorhombic. The orthorhombic cell dimensions at 70 K are a=6.89856(1), b=11.89120(2) and c=4.79330(1) A and these are related to those of the hexagonal cell, ah etc., by a approximately=ah, b approximately= square root 3ah and c approximately=ch. The orthorhombic cell is C-face centred, space group Ccmm, with Z=4. Magnetic reflections indexed on this cell have h+k odd corresponding to a (010) magnetic propagation vector. Zero-field neutron polarimetry on a single crystal shows that there are no components of moment parallel to the c axis. A magnetic structure in which the Mn1 and one-third of the Mn2 atoms have no ordered moment and the remaining Mn2 atoms a moment of 1.48(1) mu B directed parallel and antiparallel to b gives a good fit to both the powder and single-crystal intensities. This structure differs significantly from previous models, but it is coherent with current ideas about the stability of Mn moments in compounds with B-subgroup elements. Its relation to the recently revised structure of the low-temperature AF1 phase is discussed.

DIPOLE MOMENTS OF SOME PHENYL AND CHLOROPHENYL PHOSPHORUS-HALOGEN COMPOUNDS

Abstract The electric dipole moments of o-ClC6H4PCl2 1, C6H5PF4 2, o-ClC6H4PF4 3, C6H5P(O)F2 4, C6H5P(O)HF 5. C6H5P(O)H(OH) 6, and o-ClC6H4P(O)Cl2 7, were determined in dilute benzene solution at 25°C. The phosphoryl bond moment PO in compounds 4, 5, and 7 was estimated using simple bond-additivity calculations. The results obtained were 4.55D, 3.64D, and 5.52D for compounds 4, 5, and 7, respectively. Dipole moments for compounds 2 and 3 were also calculated theoretically using INDO MO techniques. The calculated values differed from the experimental values by about 12%.

Concentration dependence of the Fe moments in rare earth iron compounds

A linear relationhip has been found between the hyperfine fields observed at the various Fe sites in rare earth iron compounds R x Fe y and the relative number of near neighbour Fe atoms corresponding to these sites. From these results it is concluded that the concentration dependence of the magnitude of the Fe moments in these compounds is largely determined by the local environment.

Dipole moments of nitro derivatives of indazole

The dipole moments of indazole and a number of its nitro derivatives in dioxane solution were measured. The directions of the vectors of the dipole moments of indazole in the tautomeric 1-H and 2-H forms were determined to solve the problems associated with the tautomerism and the position of the substituents in the molecules. The experimental values of the dipole moments, of the investigated compounds were compared with the values calculated via a vector additive scheme. As a result it was shown that the mononitro and dinitro derivatives of indazole exist primarily in the 1-H tautomeric form, whereas the trinitro and tetranitroindazoles exist in the 2-H tautomeric form. The ratios of the isomers were calculated for compounds that have dipole moments intermediate between the 1-H and 2-H forms. A deviation between the experimental and calculated dipole moments of compounds containing two nitro groups in the ortho position was established; this may be explained by disruption of the coplanarity of the molecules or by deviation from additivity because of the introduction of strong electron-acceptor substituents.

Dipole moments of complex compounds of aluminum hydride

1. The authors have determined the dipole moments of the compounds AlH3-nCln·NEt3, AlCl3·NMe3, and AlHCl2· Et2O. 2. The dipole moments of the compounds varied linearly with the same increment (about 0.6 D) when the hydrogen atom is replaced by chlorine. 3. The authors estimated the dipole moments of the compounds AlH3·Et2O and AlH2Cl·Et2O. 4. They calculated the dipole moments of the donor — acceptor bonds Al - N and Al - O.

Dirole moments of compounds of the selenophene series

Dirole moments of compounds of the selenophene series