Doppler-free two-photon excitation spectroscopy and the Zeeman effects of the S1 1B1u(v21=1) <-- S0 1Ag(v=0) band of naphthalene-d8

Doppler-free two-photon excitation spectrum and the Zeeman effect of the S1 1B1u(v21=1) <-- S0 1Ag(v=0) transition of naphthalene-d8 have been measured. 908 lines of Q(Ka)Q(J)KaKc transition of J=0-41, Ka=0-20 were assigned, and the molecular constants of the S1 1B1u(v21=1) state were determined. Perturbations were observed, and those were identified as originating from Coriolis interaction. No perturbation originating from an interaction with triplet state was observed. The Zeeman splittings from lines of a given J were observed to increase with Kc, and those of the Kc=J levels increased linearly with J. The Zeeman effects are shown to be originating from the magnetic moment of the S1 1B1u state, which is along the c axis and is induced by mixing of the S2 1B3u state to the S1 1B1u state by J-L coupling. Rotationally resolved levels were found not to be mixed with a triplet state from the Zeeman spectra. Accordingly, it is concluded that nonradiative decay of an isolated naphthalene excited to low rovibronic levels in the S1 1B1u state does not occur through the intersystem mixing. This is at variance with generally accepted understanding of the pathways of the nonradiative decay.     

Doppler-free two-photon excitation spectroscopy and the Zeeman effects. Perturbations in the 14(0)1 and 1(0)(1)14(0)1 bands of the S1 <-- S0 transition of C6D6

Doppler-free two-photon excitation spectra and the Zeeman effects for the 1 band of the S1 1B2u <-- S0 1A1g transition in gaseous benzene-d6 were measured. Although the spectral lines were strongly perturbed, almost all of the lines near the band origin could be assigned. From a deperturbation analysis, the perturbation near the band origin was identified as originating from an anharmonic resonance interaction. Perturbation centered at K = 28-29 in the 14(0)1 band was analyzed, and it was identified as originating from a perpendicular Coriolis interaction. The symmetry and the assignment of the perturbing state proposed by Schubert et al. (Schubert, U.; Riedle, E.; Neusser, H. J. J. Chem. Phys. 1989, 90, 5994.) were confirmed. No perturbation originating from an interaction with a triplet state was observed in both bands. From the Zeeman spectra and the analysis, it is demonstrated that rotationally resolved levels are not mixed with a triplet state. The intersystem mixing is not likely to occur at levels of low excess energy in the S1 state of an isolated benzene. Nonradiative decay of an isolated benzene in the low vibronic levels of the S1 state will occur through the internal mixing followed by the rotational and vibrational relaxation in the S0 state.     

Observation of the nd 1Delta(g) (n = 6, 7, and 8) Rydberg states of Na2 by optical-optical double resonance spectroscopy: L uncoupling and perturbations

The nd (1)Delta(g) (n = 6, 7, and 8) Rydberg states of Na(2) correlating with the asymptotic limits of Na(3s) + Na(nd) have been observed using high-resolution cw optical-optical double resonance spectroscopy corresponding to the rovibrational transitions X (1)Sigma(g)(+)(v("),J(")) + h nu(pump) --> B (1)Pi(u)(v('),J(')) + h nu(probe) --> nd (1)Delta(g)(v,J). Totals of 104, 83, and 45 identified rovibrational e/f-parity levels in the ranges of v = 0-11, 11 < or = J < or = 83; v = 0-10, 11 < or = J < or = 83; and v = 0-10, 11 < or = J < or = 65, have been assigned to the 6d (1)Delta(g), 7d (1)Delta(g), and 8d (1)Delta(g) states, respectively. Using the observed quantum levels, molecular constants were determined from the Dunham fits of the e-parity levels and the Rydberg-Klein-Rees potential curves were constructed for the nd (1)Delta(g)(n = 6-8) states. The characteristics of the estimated Lambda-doubling splitting constants (q(0), q(v), and mu) with n(= 5-8) of the nd (1)Delta(g) series have been explored. Detailed investigations reveal that the nd (1)Delta(g)(n = 6-8) states involve L uncoupling from the internuclear axis and each of these states is affected by an asymmetric perturbation caused by the up and down adjacent states. The rotational-branch intensity and position anomalies in the observed spectra of the nd (1)Delta(g) series (n = 5-8) of Na(2) lead to the conclusion that due to the effects of the L-uncoupling perturbations, the same l complexes approaching the same ion-core limits result in the same l-mixing processes which lead to the formation of the supercomplexes due to the anisotropy of the molecular-ion [Na(2)(+)(3s)] field. This would open up opportunities to study the effects of L uncoupling and perturbations in the nd series and high Rydberg states of other alkali dimers.     

Proof of large positive zero-field splitting in a Ru2 5+ paddlewheel

We present the synthesis, as well as the structural and magnetic characterization, of [Ru2(D(3,5-Cl2Ph)F)4Cl(0.5H2O)].C6H14 (D(3,5-Cl2Ph)F = N,N'-di(3,5-dichlorophenyl)formamidinate), a Ru2(5+) compound having a 4B(2u) ground state derived from a sigma2pi4delta2pi2delta electron configuration. The persistence of this configuration from 27 to 300 K is shown by the invariance of the Ru-Ru distance. Orientation-dependent magnetic susceptibility (chiT) and magnetization (M(H)) data are in accord with a spin quartet ground state with large magnetocrystalline anisotropy associated with a large axial zero-field splitting (D) parameter. Theoretical fits to chiT and M(H) plots yielded D/kB = +114 K, implying an S = +/-1/2 Kramers doublet ground state at low temperature. Single-crystal and powder EPR data are consistent with this result, as the only observed transition is between the M(s) = +/1/2 Zeeman levels. The g values are g(perpendicular) = 2.182, g(parallel) = 1.970, and D = 79.8 cm(-1). The totality of the results demands D > 0.     

Isotopic variation of experimental lifetimes for the lowest 1 Pi u states of N2

Lifetimes of several (1)Pi(u) states of the three natural isotopomers of molecular nitrogen, (14)N(2), (14)N(15)N, and (15)N(2), are determined via linewidth measurements in the frequency domain. Extreme ultraviolet (XUV)+UV two-photon ionization spectra of the b (1)Pi(u)(v=0-1,5-7) and c(3) (1)Pi(u)(v=0) states of (14)N(2), b (1)Pi(u)(v=0-1,5-6) and c(3) (1)Pi(u)(v=0) states of (14)N(15)N, and b (1)Pi(u)(v=0-7), c(3) (1)Pi(u)(v=0), and o (1)Pi(u)(v=0) states of (15)N(2) are recorded at ultrahigh resolution, using a narrow band tunable XUV-laser source. Lifetimes are derived from the linewidths of single rotationally resolved spectral lines after deconvolution of the instrument function. The observed lifetimes depend on the vibrational quantum number and are found to be strongly isotope dependent.     

Darling-Dennison resonance and Coriolis coupling in the bending overtones of the A 1A(u) state of acetylene, C2H2

Rotational analyses have been carried out for the overtones of the nu(4) (torsion) and nu(6) (in-plane cis-bend) vibrations of the A (1)A(u) state of C(2)H(2). The v(4)+v(6)=2 vibrational polyad was observed in high-sensitivity one-photon laser-induced fluorescence spectra and the v(4)+v(6)=3 polyad was observed in IR-UV double resonance spectra via the ground state nu(3) (Sigma(+) (u)) and nu(3)+nu(4) (Pi(u)) vibrational levels. The structures of these polyads are dominated by the effects of vibrational angular momentum: Vibrational levels of different symmetry interact via strong a-and b-axis Coriolis coupling, while levels of the same symmetry interact via Darling-Dennison resonance, where the interaction parameter has the exceptionally large value K(4466)=-51.68 cm(-1). The K-structures of the polyads bear almost no resemblance to the normal asymmetric top patterns, and many local avoided crossings occur between close-lying levels with nominal K-values differing by one or more units. Least squares analysis shows that the coupling parameters change only slightly with vibrational excitation, which has allowed successful predictions of the structures of the higher polyads: A number of weak bands from the v(4)+v(6)=4 and 5 polyads have been identified unambiguously. The state discovered by Scherer et al. [J. Chem. Phys. 85, 6315 (1986)], which appears to interact with the K=1 levels of the 3(3) vibrational state at low J, is identified as the second highest of the five K=1 members of the v(4)+v(6)=4 polyad. After allowing for the Darling-Dennison resonance, the zero-order bending structure can be represented by omega(4)=764.71, omega(6)=772.50, x(44)=0.19, x(66)=-4.23, and x(46)=11.39 cm(-1). The parameters x(46) and K(4466) are both sums of contributions from the vibrational angular momentum and from the anharmonic force field. For x(46) these contributions are 14.12 and -2.73 cm(-1), respectively, while the corresponding values for K(4466) are -28.24 and -23.44 cm(-1). It is remarkable how severely the coupling of nu(4) and nu(6) distorts the overtone polyads, and also how in this case the effects of vibrational angular momentum outweigh those of anharmonicity in causing the distortion.     

Short-range correlations in d-f cyanido-bridged assemblies with XY and XY-Heisenberg anisotropy

Two new d-f cyanido-bridged 1D assemblies [RE(pzam)(3)(H(2)O)Mo(CN)(8)]·H(2)O (RE = Sm(III), Er(III)) were synthesized and their magneto-structural properties have been studied by field-dependent magnetization and specific heat measurements at low temperatures (≥0.3 K). Below ≈ 10 K the ground state of both the Sm(III) and Er(III) ions is found to be a Kramers doublet with effective spin S = 1/2. From analyses of the low-temperature magnetic specific heat and magnetization the exchange coupling between these RE(III) effective spins and the Mo(v) spins S = 1/2 along the structural chains has been determined. It is found to be antiferromagnetic, with J(∥)/k(B) = -2.6 K and Ising-Heisenberg symmetry of the interaction (J(∥)/J(⊥) = 0.3) for RE = Sm(III), whereas the compound with RE = Er(III) behaves as a pure XY chain, with J(⊥)/k(B) = -1.0 K. For the compound [Sm(pzam)(3)(H(2)O)Mo(CN)(8)]·H(2)O a small λ-type anomaly in the specific heat is observed at about 0.6 K, which is ascribed to a transition to long-range magnetic ordering induced by weak interchain interactions of dipolar origin. No evidence for 3D interchain magnetic ordering is found in the Er(III) analogue.     

Preparation and magnetic properties of Mn(hfac)(2)-complexes of 2-(5-pyrimidinyl)- and 2-(3-pyridyl)-substituted nitronyl nitroxides

Mn(hfac)(2) complexes of [2-(5-pyrimidinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazoline-1-oxyl 3-oxide] (1) and its 2-(3-pyridyl) analogue (2) were prepared. Both complexes formed similar dimer structures. However, their packing patterns were considerably different. The pyrimidine dimers were aligned to form a linear chain structure, and each dimer was weakly bound by two sets of O6-C2 short contacts. In the pyridine dimer complex, two structurally similar but independent dimers were alternatively arranged, and two dimer-dimer contacts, O6-C2 (3.13 A) and O6-C3 (3.30 A), were observed. The pyrimidine complex showed strong antiferromagnetic behavior in the high temperature region (150-300 K) and weak ferromagnetic behavior below 100 K. Two models were used to analyze these magnetic properties. One is a quintet-septet thermal equilibrium model with mean-field approximation, which can reproduce the round minimum observed at about 150 K in chi(p)T plots (J(1)/k(B) = -148 +/- 2 K with theta = +2.5 +/- 0.1 K). The other is a ferromagnetic S = 2 chain model to fit the chi(p)T values in the lower temperature region (J(S=2)/k(B) = +0.31 +/- 0.01 K). The pyridine complex showed antiferromagnetic interactions both in the high and low temperature regions. The magnetic behavior was similarly analyzed with the following parameters: J(1)/k(B) = -140 +/- 2 K with theta = -0.55 +/- 0.05 K, and J(S=2)/k(B) = -0.075 +/- 0.003 K. The ligand-ligand interactions for both of the complexes were theoretically analyzed. The calculated results agreed well with the experiments. The stronger antiferromagnetic behavior observed in both the complexes at high temperatures was attributed to the magnetic interaction between the Mn(II) and the coordinating nitroxide oxygen atom. The weaker ferromagnetic interaction, J(S=2)/k(B) = +0.31 +/- 0.01 K, in the pyrimidine complex was attributed to the coulombic O6-C2 contact. Antiferromagnetic interaction J(S=2)/k(B) = -0.075 +/- 0.003 K in the pyridine complex was attributed to the O6-C3 contact.     

Structurally distinct active sites in the copper(II)-substituted aminopeptidases from Aeromonas proteolytica and Escherichia coli

The aminopeptidase from Aeromonas proteolytica (AAP) was titrated with copper, which bound sequentially at two distinct sites. Both the mono- and disubstituted forms of AAP exhibited catalytic hyperactivity relative to the native dizinc enzyme. Monosubstituted AAP exhibited an axial Cu(II) EPR spectrum with slight pH dependence: at pH 6.0 g(parallel) = 2.249, g( perpendicular ) = 2.055, and A(parallel)((63/65)Cu) = 1.77 x 10(-)(2) cm(-)(1), whereas at pH 9.65 g(parallel) = 2.245, g( perpendicular ) = 2.056, and A(parallel)((63/65)Cu) = 1.77 x 10(-)(2) cm(-)(1). These data indicate oxygen and nitrogen ligation of Cu. AAP further substituted with copper exhibited a complex signal with features around g approximately 2 and 4. The features at g approximately 4 were relatively weak in the B(0) perpendicular B(1) (perpendicular) mode EPR spectrum but were intense in the B(0) parallel B(1) (parallel) mode spectrum. The g approximately 2 region of the perpendicular mode spectrum exhibited two components, one corresponding to mononuclear Cu(II) with g(parallel) = 2.218, g( perpendicular ) = 2.023, and A(parallel)((63/65)Cu) = 1.55 x 10(-)(2) cm(-)(1) and likely due to adventitious binding of Cu(II) to a site distant from the active site. Excellent simulations were obtained for the second component of the spectrum assuming that two Cu(II) ions experience dipolar coupling corresponding to an inter-copper distance of 5 A with the two Cu(II) g(z)() directions parallel to each other and at an angle of approximately 17 degrees to the inter-copper vector (H = betaB.g(CuA).S(CuA) + betaB.g(CuB).S(CuB) + [S.A.I](CuA) + [S.A.I](CuB) + [S(CuA).J.S(CuB)]; g(parallel(CuA,CuB)) = 2.218, g( perpendicular )((CuA,CuB)) = 2.060; A(parallel(CuA,CuB))((63/65)Cu) = 1.59 x 10(-)(2) cm(-)(1), J(isotropic) = 50 cm(-)(1), r(Cu)(-)(Cu) = 4.93 A, and chi = 17 degrees ). The exchange coupling between the two copper ions was found to be ferromagnetic as the signals exhibited Curie law temperature dependence. The Cu-Cu distance of approximately 5 A indicated by EPR was significantly higher than the inter-zinc distance of 3.5 A in the native enzyme, and the dicopper species therefore represents a novel dinuclear site capable of catalysis of hydrolysis. In contrast to AAP, the related methionyl aminopeptidase from Escherichia coli (EcMetAP) was found to bind only one Cu(II) ion despite possessing a dinuclear binding site motif. A further difference was the marked pH dependence of the signal in EcMetAP, suggestive of a change in ligation. The structural motifs of these two Cu(II)-substituted aminopeptidases provide important insight into the observed catalytic activity.     

Formation and stability of molybdenum-tellurium oxides MoTeO5, Mo2TeO8, Mo3TeO11 and MoTe2O7 in the gas phase. Quantum chemical and mass spectrometry determination of standard enthalpy of formation

The formation of mixed molybdenum-tellurium oxides MoTeO5, Mo2TeO8, Mo3TeO11, MoTe2O7 in the gas phase has been studied by mass spectrometry (MS) experiments at temperatures of about 938 K and studied theoretically by quantum chemical (QC) methods. Structural and thermodynamic data for the molecules was calculated. The mixed oxides MoTeO5, Mo2TeO8, Mo3TeO11 and MoTe2O7 in the gas phase have been reported for the first time. Experimental thermodynamic data have been determined by means of MS and confirmed theoretically by DFT and ab initio (MP2) calculations. Adiabatic ionisation potentials (IPs) were obtained experimentally and compared with theoretical vertical ionisation potentials. The following values are given: Δ(f)H(298)(0) (MoTeO5) = ?730.2 kJ mol(?1) (MS), Δ(f)H(298)(0) (MoTeO5) = ?735.4 kJ mol(?1) (DFT), ?717.3 kJ mol(?1) (MP2), S(298)(0) (MoTeO5) = 389.5 J mol(?1) K(?1) (DFT), c(p)(0)(T)(MoTeO5) = 141.71 + 13.54 × 10(?3)T ? 2.53 × 10(6)T(?2) J mol(?1) K(?1) (298 < T < 940 K) (DFT), Δ(f)H(298)(0) (Mo2TeO8) = ?1436.3 kJ mol(?1) (MS), Δ(f)H(298)(0) (Mo2TeO8) = ?1436.1 kJ mol(?1) (DFT), ?1455.9 kJ mol(?1) (MP2), S(298)(0) (Mo2TeO8) = 517.1 J mol(?1) K(?1) (DFT), c(p)(0)(T)(Mo2TeO8) = 228.64 + 24.15 × 10(?3)T ? 4.09 × 10(6)T(?2) J mol(?1) K(?1) (298 < T < 940 K) (DFT), Δ(f)H(298)(0) (Mo3TeO11) = ?2132.7 kJ mol(?1) (MS), Δ(f)H(298)(0) (Mo3TeO11) = ?2110.7 kJ mol(?1) (DFT), ?2163.2 kJ mol(?1) (MP2), S(298)(0) (Mo3TeO11) = 629.3 J mol(?1) K(?1) (DFT), c(p)(0)(T)(Mo3TeO11) = 316.40 + 34.10 × 10(?3)T ? 5.74 × 10(6)T(?2) J mol(?1) K(?1) (298 < T < 940 K) (DFT), Δ(f)H(298)(0) (MoTe2O7) = ?999.7 kJ mol(?1) (MS), Δ(f)H(298)(0) (MoTe2O7) = ?1002.7 kJ mol(?1) (DFT), ?1000.9 kJ mol(?1) (MP2), S(298)(0) (MoTe2O7) = 504.8 J mol(?1) K(?1) (DFT), c(p)(0)(T)(MoTe2O7) = 211.19 + 18.02 × 10(?3)T ? 3.53 × 10(6)T(?2) J mol(?1) K(?1) (298 < T < 940 K) (DFT), IP(MoTeO5) = 10.68 eV (DFT), IP(Mo2TeO8) = 10.4 ± 0.5 eV (MS), IP(Mo2TeO8) = 10.41 eV (DFT), IP(Mo3TeO11) = 10.7 ± 0.5 eV (MS), IP(Mo3TeO11) = 10.18 eV (DFT), IP(MoTe2O7) = 9.91 eV (DFT).     

Ultrafast decay of superexcited c 4Σu- nlσg v=0,1 states of O2 probed with femtosecond photoelectron spectroscopy

Neutral superexcited states in molecular oxygen converging to the O(2)(+) c (4)Σ(u)(-) ion state are excited and probed with femtosecond time-resolved photoelectron spectroscopy to investigate predissociation and autoionization relaxation channels as the superexcited states decay. The c (4)Σ(u)(-) 4sσ(g) v=0, c (4)Σ(u)(-) 4sσ(g) v=1, and c (4)Σ(u)(-) 3dσ(g) v=1 superexcited states are prepared with pulsed high-harmonic radiation centered at 23.10 eV. A time-delayed 805 nm laser pulse is used to probe the excited molecular states and neutral atomic fragments by ionization; the ejected photoelectrons from these states are spectrally resolved with a velocity map imaging spectrometer. Three excited neutral O* atom products are identified in the photoelectron spectrum as 4d(1)?(3)D(J)°, 4p(1) (5)P(J)° and 3d(1) (3)D(J)° fragments. Additionally, several features in the photoelectron spectrum are assigned to photoionization of the transiently populated superexcited states. Using principles of the ion core dissociation model, the atomic fragments measured are correlated with the molecular superexcited states from which they originate. The 4d(1) (3)D(J)° fragment is observed to be formed on a timescale of 65 ± 5 fs and is likely a photoproduct of the 4sσ(g) v = 1 state. The 4p(1) (5)P(J)° fragment is formed on a timescale of 427 ± 75 fs and correlated with the neutral predissociation of the 4sσ(g) v = 0 state. The timescales represent the sum of predissociation and autoionization decay rates for the respective superexcited state. The production of the 3d(1) (3)D(J)° fragment is not unambiguously resolved in time due to an overlapping decay of a v = 1 superexcited state photoelectron signal. The observed 65 fs timescale is in good agreement with previous experiments and theory on the predissociation lifetimes of the v = 1 ion state, suggesting that predissociation may dominate the decay dynamics from the v = 1 superexcited states. An unidentified molecular state is inferred by the detection of a long-lived depletion signal (reduction in autoionization) associated with the B (2)Σ(g)(-) ion state that persists up to time delays of 105 ps.     

Photoassociation spectroscopy of ultracold metastable 3He dimers

The bound states of the fermionic (3)He(2 (3)S(1)) + (3)He(2 (3)P(j)) system, where j = 0, 1, 2, are investigated using the recently available ab initio short-range (1,3,5)Σ(+)(g,u) and (1,3,5)Π(g,u) potentials computed by Deguilhem et al. (J. Phys. B: At., Mol. Opt. Phys., 2009, 42, 015102). Single-channel and multichannel calculations have been undertaken in order to investigate the effects of Coriolis and non-adiabatic couplings. The possible experimental observability of the theoretical levels is assessed using criteria based upon the short-range character of each level and their coupling to metastable ground states. Purely long-range levels have been identified and 30 short-range levels near five asymptotes are suggested for experimental investigation.     

On the nature of the trigonal fields in hexaaquachromium(III) in guanidinium aluminum sulfate hexahydrate

Zeeman and site selective luminescence and excitation spectra in the region of the 2E<--4A2 transition are reported for the hexaaquachromium(III) complex in the trigonal ferroelectric guanidinium aluminum sulfate hexahydrate. The two prominent transitions are due to the R1 lines of the two sites of C3 and C3v point symmetry. The two R1 lines display g parallel = -3.1 and g parallel = -3.2, respectively, and show no measurable Zeeman shift or splitting with B perpendicular c. This behavior is consistent with the presence of a very large trigonal field. A peculiar feature of the present system is the conspicuous absence of any prominent R2 line. From the Zeeman data with B perpendicular c and a comparison of vibrational sidelines in excitation and luminescence it is concluded that the R2 level strongly interacts with vibrational levels.     

Ferromagnetic coupling in a 1D coordination polymer containing a symmetric [Cu(mu1,1-N3)2Cu(mu1,1-N3)2Cu]2+ core and based on an organic ligand obtained from the solid state

Addition of rctt-tetrakis(2-pyridyl)cyclobutane (2,2'-tpcb) in a Cu(II)/N(3)- solution afforded the 1D coordination polymer [Cu(3)(N(3))(6)(2,2'-tpcb)(DMF)(2)](n) (1). The ligand 2,2'-tpcb serves as a tetradentate bis-chelating ligand by linking linear [(DMF)Cu(mu(1,1)-N(3))(2)Cu(N(3))(2)(mu(1,1)-N(3))(2)Cu(DMF)] trinuclear units to produce a zigzag chain. Within each centrosymmetric trinuclear unit there exist two irregularly asymmetric end-on double azido-bridged [Cu(mu(1,1)-N(3))(2)Cu](2+) cores, while one of the largest Cu-Nazide-Cu angles is observed. Magnetic susceptibility data, measured from 2 to 300 K, show bulk moderate ferromagnetic coupling within the magnetically isolated trinuclear units. These data were fitted to the appropriate equation derived from the Hamiltonian H = -J(1)(S(A1)S(B) + S(A2)S(B)) - J(2)S(A1)S(A2), giving the parameters J1 = +70(3) cm(-1), J2 = -3(2) cm(-1), g = 2.12(1), with an intertrimer interaction parameter theta = -0.74(2) K. The coupling constants were correlated with the structural parameters. Density functional calculations reproduce very well the experimental J values and show that ferromagnetism for this complex is mainly due to the topology of the magnetic orbitals and the different coordination spheres of two neighboring Cu(II) atoms, resulting in a small overlap of the orbitals possessing the unpaired electrons.     

Molecular paramagnetic semiconductor: crystal structures and magnetic and conducting properties of the Ni(dmit)(2) salts of 6-oxoverdazyl radical cations (dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

Four kinds of 1:1 and 1:3 salts of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation ([1](+)) and its mono- and dimethyl derivatives ([2](+) and [3](+)) with Ni(dmit)(2) anions (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) ([1](+)[Ni(dmit)(2)](-) (4), [2](+)[Ni(dmit)(2)](-) (5), [3](+)[Ni(dmit)(2)](-) (6), and [1](+)[Ni(dmit)(2)](3)(-) (7)) have been prepared, and the magnetic susceptibilities (chi(M)) have been measured between 1.8 and 300 K. The chi(M) values of salts 5 and 7 can be well reproduced by the sum of the contributions from (i). a Curie-Weiss system with a Curie constant of 0.376 (K emu)/mol and negative Weiss constants (THETAV;) of -0.4 and -1.7 K and (ii). a dimer system with strong negative exchange interactions of 2J/k(B) = -354 and -258 K, respectively. The dimer formations in Ni(dmit)(2) anions have been ascertained by the crystal structure analyses of salts 4-6. In salts 4 and 6, Ni(dmit)(2) dimer molecules are sandwiched between two verdazyl cations, indicating the formation of a linear tetramer in 4 and 6. The magnetic susceptibility data for salts 4 and 6 have been fitted to a linear tetramer model using an end exchange interaction of 2J(1)/k(B) = -600 K and a central interaction of 2J(2)/k(B) = -280 K for 4 and 2J(1)/k(B) = -30 K and 2J(2)/k(B) = -580 K for 6, respectively. The results of the temperature dependence of the g(T) value in salts 4-6 obtained by ESR measurement also support the above analyses. The 1:1 salts 4-6 are insulators. On the other hand, the conductivity of the 1:3 salt 7 at 20 degrees C was sigma = 0.10 S cm(-)(1) with an activation energy E(A) = 0.099 eV, showing the semiconductor property. Salt 7 is a new molecular paramagnetic semiconductor.     

High-frequency, high-field EPR; magnetic susceptibility; and X-ray studies on a ferromagnetic heterometallic complex of diethanolamine (H2L), [Cu4(NH3)4(HL)4][CdBr4]Br2.3dmf.H2O

The novel heterometallic complex [Cu(4)(NH(3))(4)(HL)(4)][CdBr(4)]Br(2).3dmf.H(2)O has been prepared in the reaction of zerovalent copper with cadmium oxide in the air-exposed solution of ammonium bromide and diethanolamine (H(2)L) in dimethylformamide (dmf). The compound is monoclinic, with space group P2(1)/c, a = 14.876(3) A, b = 33.018(6) A, c = 11.437(2) A, beta = 108.182(3)(o), and Z = 4. The crystal lattice consists of [Cu(4)(NH(3))(4)(HL)(4)](4+) cations, [CdBr(4)](2)(-), Br(-) anions, and uncoordinated dmf and water molecules. In the cation, four independent Cu atoms occupy vertexes of a distorted tetrahedron with bridged Cu...Cu distances in the range 3.127(2)-3.333(3) A and other Cu...Cu separations being 3.445(3)-3.503(2) A. The magnetic susceptibility and the EPR spectra were measured over the temperature ranges 1.8-300 and 3-300 K, respectively. The magnetic moment was found to increase with decreasing temperature to reach a maximum of 2.60 muB per one copper atom at ca. 10 K and was found, subsequently, to diminish slightly at lower temperatures owing to zero-field and Zeeman splitting of the S = 2 ground state. The temperature dependence of the magnetic susceptibility was fitted to the spin Hamiltonian H = J(ab)S(a)S(b) + J(bc)S(b)S(c) + J(cd)S(c)S(d) + J(ad)S(a)S(d) + J(ac)S(a)S(c) + J(bd)S(b)S(d) with the exchange integrals J(ab) = J(bc) = J(cd) = J(ad) = -65(3) cm(-1) and J(ac) = J(bd) = +1(3) cm(-1). High-field, high-frequency (95-380 GHz) EPR spectra due to an S = 2 ground state were simulated with g(x) = 2.138(1), g(y)) = 2.142(1), g(z) = 2.067(1), D = -0.3529(3) cm(-1), and E = -0.0469(8) cm(-1). Calculations based on the X-ray structure indicate a negligible contribution of the magnetic dipole-dipole interactions to the zfs parameters D and E. A discussion of the isotropic and anisotropic exchange interactions and their effect on the zfs parameters is also given.     

Structure and magnetism of the tetra-copper(II)-substituted heteropolyanion [Cu(4)K(2)(H(2)O)(8)(alpha-AsW(9)O(33))(2)](8-)

The novel heteropolyanion [Cu(4)K(2)(H(2)O)(8)(alpha-AsW(9)O(33))(2)](8)(-) (1) has been synthesized and characterized by IR spectroscopy, elemental analysis, and magnetic studies. Single-crystal X-ray analysis was carried out on [K(7)Na[Cu(4)K(2)(H(2)O)(6)(alpha-AsW(9)O(33))(2)].5.5H(2)O](n)(K(7)Na-1), which crystallizes in the tetragonal system, space group P42(1)m, with a = 16.705(4) A, b = 16.705(4) A, c = 13.956(5) A, and Z = 2. Interaction of the lacunary [alpha-AsW(9)O(33)](9)(-) with Cu(2+) ions in neutral, aqueous medium leads to the formation of the dimeric polyoxoanion 1 in high yield. Polyanion 1 consists of two alpha-AsW(9)O(33) units joined by a cyclic arrangement of four Cu(2+) and two K(+) ions, resulting in a structure with C(2)(v)() symmetry. All copper ions have one terminal water molecule, resulting in square-pyramidal coordination geometry. Three of the copper ions are adjacent to each other and connected via two micro(3)-oxo bridges. EPR studies on K(7)Na-1 and also on Na(9)[Cu(3)Na(3)(H(2)O)(9)(alpha-AsW(9)O(33))(2)].26H(2)O (Na(9)-2) over 2-300 K yielded g values that are consistent with a square-pyramidal coordination around the copper(II) ions in 1 and 2. No hyperfine structure was observed due to the presence of strong spin exchange, but fine structure was observed for the excited (S(T) = 3/2) state of Na(9)-2 and the ground state (S(T) = 1) of K(7)Na-1. The zero-field (D) parameters have also been determined for these states, constituting a rare case wherein one observes EPR from both the ground and the excited states. Magnetic susceptibility data show that Na(9)-2 has antiferromagnetically coupled Cu(2+) ions, with J = -1.36 +/- 0.01 cm(-)(1), while K(7)Na-1 has both ferromagnetically and antiferromagnetically coupled Cu(2+) ions (J(1) = 2.78 +/- 0.13 cm(-)(1), J(2) = -1.35 +/- 0.02 cm(-)(1), and J(3) = -2.24 +/- 0.06 cm(-)(1)), and the ground-state total spins are S(T) = 1/2 in Na(9)-2 and S(T) = 1 in K(7)Na-1.     

Accurate potential energy curve for B2. Ab initio elucidation of the experimentally elusive ground state rotation-vibration spectrum

The electron-deficient diatomic boron molecule has long puzzled scientists. As yet, the complete set of bound vibrational energy levels is far from being known, experimentally as well as theoretically. In the present ab initio study, all rotational-vibrational levels of the X (3)Σ(g)(-) ground state are determined up to the dissociation limit with near-spectroscopic accuracy (<10 cm(-1)). Two complete sets of bound vibrational levels for the (11)B(2) and (11)B-(10)B isotopomers, containing 38 and 37 levels, respectively, are reported. The results are based on a highly accurate potential energy curve, which also includes relativistic effects. The calculated set of all vibrational levels of the (11)B(2) isotopomer is compared with the few results derived from experiment [Bredohl, H.; Dubois, I.; and Nzohabonayo, P. J. Mol. Spectrosc. 1982, 93, 281; Bredohl, H.; Dubois, I.; and Melen, F. J. Mol. Spectrosc. 1987, 121, 128]. Theory agrees with experiment within 4.5 cm(-1) on average for the four vibrational level spacings that are so far known empirically. In addition, the present theoretical analysis suggests, however, that the transitions from higher electronic states to the ground state vibrational levels v = 12-15 deserve to be reanalyzed. Whereas previous experimental investigators considered them to originate from the v' = 0 vibrational level of the upper state (2)(3)Σ(u)(-), the present results make it likely that these transitions originate from a different upper state, namely the v' = 16 or the v' = 17 vibrational level of the (1)(3)Σ(u)(-) state. The ground state dissociation energy D(0) is predicted to be 23164 cm(-1).     

Optical Zeeman spectroscopy of the (0,0) B(4)Γ - X(4)Φ band systems of titanium monohydride, TiH, and titanium monodeuteride, TiD

The Zeeman effect in the (0,0) bands of the B(4)Γ(5∕2) - X(4)Φ(3∕2) system of titanium monohydride, TiH, and titanium monodeuteride, TiD, has been recorded and analyzed. Magnetic tuning of the spectral features recorded at high resolution (full width at half maximum ? 35 MHz) and at a field strength of 4.5 kG is accurately modeled using an effective Zeeman Hamiltonian. The determined magnetic g-factors for the X(4)Φ(3∕2) (v = 0) state deviate only slightly from those expected for an isolated (4)Φ(3∕2) state whereas those for the B(4)Γ(5∕2)(v = 0) deviate significantly from those of an isolated (4)Γ(5∕2) state. The rotational dependence of the magnetic tuning in the B(4)Γ(5∕2)(v = 0) state is attributed to perturbations from a nearby (4)Φ state.