Low-spin Ground State Research Articles

Synthesis and structure of cis-dichlorobis(2-phenylazopyridine)chromium(II), an inert chromium(II) compound

Recent studies have shown 2-phenylazopyridine (Azpy) to be a useful departure from polypyridyl type ligands in coordination chemistry; frequently lower oxidation states are stabilized by this ligand. We have prepared and studied [Cr(Azpy) 2Cl 2] which is surprisingly inert for a chromium(II) complex. The compound crystallizes in the space group P2 1/ c with a = 7.953(3), b = 21.189(11), c = 12.922(12) Å, β = 114.80(5)° and Z = 4. Based on 6777 reflections the structure has been refined to R = 0.030 and R w = 0.038. The complex is six-coordinated with cis-chlorides, cis-azo and trans-pyridyl groups. The overall symmetry is close to C 2. The azo NN distances are elongated to 1.282 and 1.314 Å, significantly longer than observed in free azo groups. The magnetic moment of 2.8 BM is independent of temperature indicating an orbitally non-degenerate low-spin ground state. In acetonitrile the spectrum shows a band in the red at 1470 nm which is assigned as ligand-metal charge transfer, consistent with earlier interpretations on similar compounds. The compound is stable to air oxidation in acetonitrile or methylene chloride; cyclic voltammetry in these solvents yields potentials of 0.508 and −0.185 V, both appearing to be one electron transfers. The complex is a non-electrolyte in acetonitrile, nearly unchanged over 24 h. However, chloride ions are slowly replaced at 50 °C in this solvent by 2,2′-bipyridyl; this reaction is pseudo-first order in complex with a rate constant of 4.0 ± 0.3 × 10 −7 s −1. All data indicate the presence of a strong chromium-Azpy pi-interaction.

Synthesis, characterization, and antitumor activity of iron(II) and iron(III) complexes of α-N-heterocyclic carboxaldehyde thiosemicarbazones

Complexes of iron(II) and iron(III) with 1-formylisoquinoline thiosemicarbazone (1-iqtsc-H), 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone (4-Me-5-NH 2-1-iqtsc-H) and 4-( m-aminophenyl)-2-formylpyridine thiosemicarbazone (4- m-NH 2ph-2-pytsc-H) were synthesized and characterized by elemental analysis, conductance measurements, magnetic susceptibilities (from room temperature down to liquid N 2 temperature), and Mössbauer, electronic, and infrared spectral studies. On the basis of these studies, a highly distorted, high-spin, five-coordinate structure for Fe(HL)SO 4 (HL= 1-iqtsc-H, 4-Me-5-NH 2-1-iqtsc-H or 4- m-NH 2ph-2-pytsc-H) and a distorted, low-spin, octahedral structure for Fe(HL)Cl 2 are suggested. The EPR spectra of iron(III) complexes show that all have d xy low-spin ground state. All these complexes have been screened for their antitumor activity against the P 388 lymphocytic leukemia test system in mice and have been found to possess significant activity at the dosages employed.

On the Fe-CO molecule

Using a perturbational configuration interaction approach, it is found that the Fe-CO molecule has a low-spin ground state (i.e. 3∑−), at variance with similar compounds formed by the first transition elements of this series (e.g. Sc and Ti). Binding energies, interatomic distances and vibration frequencies have been calculated for the 3∑− state as well as for the 5∑− high-spin state.

Electronic-structure calculation of point defects in silicon

Density-functional theory allows studies of ground-state properties of a many-electron system from first principles. Using Green-function technique and the local density (or local spin-density) approximation, it is possible to calculate charge (ion) states, total energies, donor- and acceptor levels, and spin-densities of point defects in semiconductors. Focussing on existing open questions and controversies, we present results of recent theoretical studies of single substitutional and interstitial chalcogens and 3d transition-metal impurities in silicon. For the chalcogen point defects S, Se and Te we identify their positions in the silicon lattice as the substitutional site. For 3d impurities in silicon we obtain spin-multiplicities and donor and acceptor levels in good agreement with available experimental data. The early 3d interstitial and the late 3d substitutional ions are predicted to have low-spin ground-states which is in conflict with the generally accepted model of Ludwig and Woodbury (LW). A large number of predictions will be offered to be tested by future experimental studies.

Additions and Corrections: Synthesis of Two Bis-m-quinomethanes. An Experimental Study of Connectivity Effects on the Equal-Parity Criterion for Low-Spin Ground States in Alternant Non-Kekule Molecules

Additions and Corrections: Synthesis of Two Bis-m-quinomethanes. An Experimental Study of Connectivity Effects on the Equal-Parity Criterion for Low-Spin Ground States in Alternant Non-Kekule Molecules

Excitation and ionization of Mo and W in GaAs.

We study the electronic structure of the Mo 4d and W 5d impurities in GaAs, using the cluster approach within the multiple-scattering X\ensuremath{\alpha} formalism; results are also given for the Cr 3d isovalent impurity. Multiplet structures for the systems are evaluated through the approach of Fazzio, Caldas, and Zunger. Our results indicate that the Mo and W impurities will present a low-spin ground state in the 2+ oxidation state (acceptor), and that the observed luminescence lines are not related to the $^{5}\mathrm{}^{5}$${\mathrm{T}}_{2}$ internal transition of the isolated substitutional Mo and W impurities.

Theoretical investigation of the electrical and optical activity of vanadium in GaAs.

We study the excitation and ionization processes at the isolated substitutional vanadium impurity in GaAs. The electronic structure is solved through the spin-restricted version of the multiple-scattering X\ensuremath{\alpha} method to obtain the relevant mean-field energies, and correlation effects are evaluated through the Fazzio-Caldas-Zunger multiplet approach. The similar systems GaP:V, InP:V are also investigated. Our results for GaAs:V point to the occurrence of an acceptor level at \ensuremath{\sim}${E}_{c}$-0.16 eV, the donor level appearing very close to or within the valence band. The V-related midgap acceptor should then be related to some complex defect involving vanadium. We also suggest that ${\mathrm{V}}^{2+}$ in these compounds is present in the low-spin ground state $^{2}\mathrm{E}$..AE

Synthesis of two bis-m-quinomethanes. An experimental study of connectivity effects on the equal-parity criterion for low-spin ground states in alternant non-Kekule molecules

Synthesis of two bis-m-quinomethanes. An experimental study of connectivity effects on the equal-parity criterion for low-spin ground states in alternant non-Kekule molecules

Prediction of a low-spin ground state in the GaAs:V2+ impurity system.

All 3d impurities observed to date in tetrahedral semiconductors have a high-spin ground state, in agreement with Hund's rule. Using first-principles self-consistent Green's-function calculations for substitutional GaAs:V within the local-spin-density formalism, we predict that the as yet unobserved ground state of GaAs:${\mathrm{V}}^{2+}$ is of the low-spin type. The origin of this unusual ground state is explained.

Quadridentate versus quinquedentate co-ordination of some N5and N3O2macrocyclic ligands and an unusual thermally controlled quintet ⇌ singlet spin transition in an iron(II) complex

The complexes [FeIIL(CN)2]·xH2O of the macrocyclic Schiff-base ligands L1–L3 derived from the condensation of 2,6-diacetylpyridine with 3,6-diazaoctane- 1,8-diamine (L1), 3,7-diazanonane1,9-diamine (L2), and 3,6-dioxaoctane-1,8-diamine (L3) have been prepared and their magnetic susceptibilities and Mossbauer spectra studied over the temperature range 80–300 K. The complexes of the N5 macrocycles L1 and L2 have low-spin (S= 0) ground states and are assigned six-co-ordinate structures in which the macrocycle acts as a quadridentate ligand with one secondary amine group unco-ordinated. This contrasts with the situation in all previously characterised complexes of these macrocycles (containing other metal ions and/or other axial ligands) where all five potential donor atoms are co-ordinated in a pentagonal planar arrangement. The exceptional structure of the present complexes is attributed to the ligand-field stabilization energy associated with the low-spin, approximately octahedral configuration generated by the strong field cyanide ligands. The magnetic properties of [FeL3(CN)2]·H2O exhibit a complex variation with temperature. The thermodynamically stable forms are high-spin (S= 2) at ambient temperature and low-spin (S= 0) below 150 K while between 150 and 200 K the stable form appears to contain approximately equal numbers of high-spin and low-spin molecules. The structure of the low-spin form is believed to be six-co-ordinate, with one ether oxygen of the macrocycle unco-ordinated while the high-spin form may have either a six- or a seven-co-ordinate structure.

Theoretical investigations of Fe porphyrins. V. Low‐lying electronic states of bisammineporphinatoiron(III)

AbstractAb initio CI calculations are reported on the lowest doublet, quartet, and sextet states of [FeIII(P)(NH3)2]+. The low‐spin ground state is calculated as (dxy2 (dπ)3 with dxy(dπ)4 higher by 0.15 eV. The near‐ir bands at ∼1 eV observed in low‐spin ferriheme proteins are attributed to (π → dπ) transitions. The lowest high‐spin state is 6A1g, and the near‐ir transitions of the high‐spin ferriheme proteins observed at ∼1.2 eV are attributed to higher 6[tripsextet] excited states [i.e., ring triplet, metal sextet]. The 30‐ps “triplet” transient populated with low quantum yield observed in laser‐flash studies on FeIII(TPP)CI [TPP = tetrapbenylporphyrin] may be an 1[tripsextet] state.

Theoretical evidence for low-spin ground states of early interstitial and late substitutional 3d transition-metal ions in silicon.

Ground-state total energies and spins have been calculated for all interstitial and substitutional $3d$ ions in crystalline Si by use of spin-unrestricted density-functional theory plus the linear muffintin-orbital Green's-function method. The calculated deep donor and acceptor levels reproduce for the first time all experimentally observed transitions. The early $3d$ interstitial ions and the late $3d$ substitutional ions are calculated to have low spin. This is in conflict with the generally accepted model due to Ludwig and Woodbury.

The Spin Density Wave Hartree-Fock State in almost Half-Filled Hubbard Systems with Infinite Repulsion

It is shown that a spin density wave (SDW) Hartree-Fock (HF) state corresponds to the low-spin ground state in almost half-filled Hubbard systems with infinite repulsion. The SDW HF state has a long range ferromagnetic spin ordering. This suggests that the low-spin ground state does not indicate absence of ferromagnetism.

Electronic and Magnetic Properties of Interstitial 3d Impurities in Silicon

AbstractSelf-consistent spin-unrestricted all-electron Green's function calculations are reported for the first time for a series of interstitial 3d impurities in silicon. The calculations, performed within the selfinteraction- corrected local-spin-density fromalism show: (i) not all 3d impurities follow Hund's rule: Tio, Ti−, Vo, V+ and Co2+ have a low-spin ground state, (ii) the angular momentum part gL of g-value is quenched due to p-d hybridization effects, (iii) covalency explains also the chemical trends in the central hyperfine coupling constants, (iii) chemical trends in donor andacceptor transitions are reproduced and are consistent with a high-spin to lowspin transition at the low-Z end and high-Z end of the 3d series, (iv) A number of predictions are offered.

ChemInform Abstract: A NEW SERIES OF HEPTAMOLYBDONICKELATE(IV) AND MANGANATE(IV). INVESTIGATION OF THE UNUSUAL MAGNETIC AND ELECTRONIC SPECTRAL BEHAVIOR OF THE NICKEL(IV) COMPOUND

AbstractDie neuen isomorphen Heteropolymolybdate (I) und (II) mit bislang unbekannter l :7(Ni/Mn : Mo)‐Stöchiometrie werden durch Oxidation wäßriger, Ammoniumheptamolybdat und NiSO4 ‐ 6 H2O bzw. MnSO4 ‐ 4 H2O enthaltender Lösungen mit KzSzOg dargestellt.

A New Series of Heptamolybdonickelate(IV) and Manganate(IV). Investigation of the Unusual Magnetic and Electronic Spectral Behavior of the Nickel(IV) Compound

Abstract Two new heteropolymolybdates of nickel(IV) and manganese(IV) of composition K2H8NiMo7O28·6H2O and K2H8MnMo7O28·4H2O with a hitherto unknown 1 : 7 (Ni/Mn : Mo) stoichiometry are reported. X-Ray powder patterns show that they are isomorphous. The electronic spectrum of the nickel(IV) compound exhibits four absorption bands at 16.4, 17.5, 18.3, and 24×103 cm−1, and the room temperature magnetic moment of the compound is abnormally high, 1.78 μB. The rationale for these observations is that there are Ni3+ impurity which occupy interstitial positions in the crystal lattice and as a consequence of dynamic Jahn-Teller distortion the high-spin 4A2g(4T1g) state of the Ni3+ ion lies close to the low-spin ground state 2A1g(2Eg) to get thermally populated to an appreciable extent leading to significant triplet state contribution.

ChemInform Abstract: LASER PHOTOELECTRON SPECTROSCOPY OF MANGANESE HYDRIDE (MNH‐) AND IRON HYDRIDE (FEH‐): ELECTRONIC STRUCTURES OF THE METAL HYDRIDES, IDENTIFICATION OF A LOW‐SPIN EXCITED STATE OF MANGANESE HYDRIDE (MNH), AND EVIDENCE FOR A LOW‐SPIN GROUND STATE OF IRON HYDRIDE (FEH)

Chemischer InformationsdienstVolume 14, Issue 31 Physical Inorganic Chemistry ChemInform Abstract: LASER PHOTOELECTRON SPECTROSCOPY OF MANGANESE HYDRIDE (MNH-) AND IRON HYDRIDE (FEH-): ELECTRONIC STRUCTURES OF THE METAL HYDRIDES, IDENTIFICATION OF A LOW-SPIN EXCITED STATE OF MANGANESE HYDRIDE (MNH), AND EVIDENCE FOR A LOW-SPIN GROUND STATE OF IRON HYDRIDE (FEH) A. E. STEVENS, A. E. STEVENSSearch for more papers by this authorC. S. FEIGERLE, C. S. FEIGERLESearch for more papers by this authorW. C. LINEBERGER, W. C. LINEBERGERSearch for more papers by this author A. E. STEVENS, A. E. STEVENSSearch for more papers by this authorC. S. FEIGERLE, C. S. FEIGERLESearch for more papers by this authorW. C. LINEBERGER, W. C. LINEBERGERSearch for more papers by this author First published: August 2, 1983 https://doi.org/10.1002/chin.198331005Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume14, Issue31August 2, 1983 RelatedInformation

Laser photoelectron spectroscopy of MnH− and FeH−: Electronic structures of the metal hydrides, identification of a low-spin excited state of MnH, and evidence for a low-spin ground state of FeH

The laser photoelectron spectra of MnH− and MnD−, and FeH− and FeD− are reported. A qualitative description of the electronic structure of the low-spin and high-spin states of the metal hydrides is developed, and used to interpret the spectra. A diagonal transition in the photodetachment to the known high-spin, 7Σ+, ground state of MnH is observed. An intense off-diagonal transition to a state of MnH, at 1725±50 cm−1 excitation energy, is attributed to loss of an antibonding electron from MnH−, to yield a low-spin quintet state of MnH. For FeH− the photodetachment to the ground state is an off-diagonal transition, attributed to loss of the antibonding electron from FeH−, to yield a low-spin quartet ground state of FeH. A diagonal transition results in an FeH state at 1945±55 cm−1; this state of FeH is assigned as the lowest-lying high-spin sextet state of FeH. An additional excited state of MnH and two other excited states of FeH are observed. Excitation energies for all the states are reported; vibrational frequencies and bond lengths for the ions and several states of the neutrals are also determined from the spectra. The electron affinity of MnH is found to be 0.869±0.010 eV; and the electron affinity of FeH is determined to be 0.934±0.011 eV. Spectroscopic constants for the various deuterides are also reported.

Crystal structure of Bis(2,2':6',2''-terpyridyl)cobalt(II) iodide dihydrate at 295 K and at 120 K

The crystal structure of the title compound, [CO(C15H11N3)2] 12.2H2O, has been determined by single crystal X-ray diffraction methods at 295 K and at 120 K, being refined by least squares to residuals of 0.051 and 0.035 respectively for 982 and 1024 'observed' reflections at these temperatures. Both structures are based on a P42/n tetragonal cell, a c. 8.9, c c. 19.4 �, Z 2, in which only a quarter of the cation is independent, being located about a site of 4 symmetry. At room temperature (μoff c. 3.2 BM) Co-N (central, distal) are 1.942(7), 2.104(5) � diminishing to 1.912(5), 2.083(4) � at 120 K, with μoff c. 2.2 BM, corresponding to a fully populated low-spin ground state.

Yields and isomeric ratio of xenon and krypton isotopes from thermal neutron fission ofU235

The experimental cumulative yields of /sup 85/Kr/sup m/, /sup 87/Kr, /sup 88/Kr, /sup 133/Xe/sup g/, /sup 135/Xe/sup m/, and /sup 135/Xe/sup g/ and the independent isomeric yield of /sup 133/Xe/sup m/ in the thermal neutron fission of /sup 235/U have been measured by the gas chromatographic method. The independent yields of /sup 133/Xe/sup g/, /sup 135/Xe/sup m/, and /sup 135/Xe/sup g/ were deduced with the aid of /sup 133/I and /sup 135/I data. The isomeric yield ratios of /sup 133/Xe and /sup 135/Xe have been computed and compared with theoretical values since they have the same high spin state J = 11/2/sup -/ and low spin ground state J = 3/2/sup +/. The influence of the shell effect on the fission isomeric yield ratio is discussed. From the measured independent yield of Xe isotopes plus the reported data, the Xe-isotopic distribution curve has been constructed. The curve is compared with the isotopic distribution curves of Xe isotopes formed in 11.5 GeV proton interactions with /sup 238/U and Cs isotopes formed in 24 GeV proton interactions with /sup 238/U. Upon fitting the yield curves we find that only those products with N/Z> or =1.48 fit a curve typical of a binarymore » fission process.« less