The role of d orbitals in tetrahedral hybrid orbitals of oxy-ions

The hybrid orbitals of tetrahedral oxy-ions containing some d character have been calculated by maximum overlap method. The d characters of hybrid orbitals increase in the order of SiO, PO, SO, ClO, and decrease in order of GeO, AsO, SeO, BrO. The bond strengths are also obtained for these ions. The hybrid Orbital of VO, CrO, and MnO are of the type d³s as the result of calculation.     

Ferromagnetic versus antiferromagnetic exchange interactions in tetrathiafulvalene-based 3d/4f heterobimetallic complexes

(TTF-salphen)M compounds (TTF-salphen(2-)=4,5-bis(propylthio)tetrathiafulvalene-N,N'-phenylenebis(salicylideneimine) dianion; M=Cu(II) and Ni(II)) have been treated with Ln(hfac)(3)·2H(2)O precursors (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion; Ln=Gd(III), Tb(III), and Dy(III)) to elaborate unprecedented 3d/4f TTF-based heterobimetallic complexes of formula [(TTF-salphen)MLn(hfac)(3)]. All the structures of these compounds have been resolved by X-ray diffraction on single crystals. The structures of these complexes are formed by a TTF-salphen(2-) ligand coordinated to the 3d metal ions in the inert tetradentate N(2)O(2) site. The Ln(hfac)(3) fragment is coordinated to the (TTF-salphen)M one through the two phenolate bridges. Even if the complexes are similar in both Cu(II) and Ni(II) families, the crystal packing is different. In the first case, dimers of TTF-salphen(2-) donors constitute the organic network. In the other case, a reminiscent organic network is observed with S···S contacts. The photophysical properties of [(TTF-salphen)CuDy(hfac)(3)] (3) in chloroform solution highlight the redshift of the TTF→salphen charge transfer (400 cm(-1)) relative to the analogue excitations in (TTF-salphen)Cu, which attest to the stability of these structures in solution. Static magnetic measurements have allowed us to quantify the ferromagnetic interactions (J=+1.29 cm(-1)) between Cu(II) and Gd(III) in the [(TTF-salphen)CuGd(hfac)(3)] complex. Finally, an empirical method that consists of the comparisons of the magnetic properties of [(TTF-salphen)CuTb(hfac)(3)] with [(TTF-salphen)NiTb(hfac)(3)] and [(TTF-salphen)CuDy(hfac)(3)] with [(TTF-salphen)NiDy(hfac)(3)] has established that ferromagnetic interactions take place between Cu(II) and Tb(III) ions, whereas unusual antiferromagnetic interactions have been identified between Cu(II) and Dy(III) ions.     

Rationalization of the lanthanide-ion-driven magnetic properties in a series of 4f-5d cyano-bridged chains

Magnetic properties of new d-f cyanido-bridged 1D assemblies [RE(pzam)(3)(H(2)O)W(CN)(8)]·H(2)O (RE(III) = Gd, 1, Tb, 2, Dy, 3; pzam = pyrazine-2-carboxamide) were studied by temperature- and field-dependent magnetization measurements. No evidence for 3D interchain magnetic ordering is found above 2 K. Multiconfiguration ab initio calculations and subsequent modeling afforded simulation of the weak zero-field splitting effect in 1 and discussion of magnetic anisotropy in the f units of compounds 2 and 3. A semiquantitative corroboration with the experimental magnetic measurements is presented, performing the simulation of magnetic susceptibility vs temperature and magnetization vs field variation. The association into molecular and supramolecular architectures is analyzed by means of energy decomposition subsequent to the DFT calculations on idealized molecular models extracted from the experimental chain structure.     

The role of 3d orbitals in the bonding of phosphorus compounds

Ab initio LCAO-MO-SCF calculations for several typical molecules containing phosphorushave been undertaken to study the role of phosphorus 3d orbitals in the bonding.It is emphasizedthat the discussion about the 3d orbital participation in bonding should be based on a reasonable choiceof basis sets and it seems suitable to choose the atomic orbitals in proper molecular environment asthe basis set.As an approximation,the optimized minimal STO-NG basis sets have been adoptedin the present paper.The results obtained well exhibit the model of 3d orbital participation in bonding.It is shown that under the influence of highly electronegative ligands the phosphorus 3d orbitals con-tract greatly,their energy levels drop considerably,and thus they can effectively participate in bond-ing.The presence of highly electronegative ligands seems necessary.The contribution of 3d orbitalsto bonding is achieved mainly through the concertedformation of σ bonds and p-d backbonds,thoughthe contribution to σ bonding is minor.The three-center,four-electron bond modelis only approxi-mately correct.The results of the present paper demonstrate that the model of 3d orbital participationin bonding favoured by experimental chemists is reasonable and possesses sound ground.     

磷的d轨道在H~3PO分子中的作用

用分子片轨道在分子环境中发生极化的概念研究d轨道在H~3PO分子中的作用。H~3PO分子被分为两个分子片---H~3P和O.在RHF/6-31G^*水平上计算出分子环境中的极化了的分子片轨道(FOM)。再剔除d函数为主的FOM,用剩余的FOM为基进行构型优化,得到与RHF/6-31G^*相近的结果。这一结果说明磷原子的d函数在H~3PO分子中仅仅起一个极化函数的作用,而不是起价轨道作用。     

J-dependence of the isotope shift in Gd I 4f 7 5d 2 6s(a 11 F)

TheJ-dependence of the isotope shift in the terma ¹¹ F of 4f ⁷ 5d ² 6s between six stable Gd isotopes was found to be represented by these parameter values (in MHz):z _5d (160?158)=19.4(1.8),z _5d (160?157)=37.2(1.0),z _5d (160?156)=42.4(1.7),z _5d (160?155)=49.1(2.0),z _5d (160?154)=59.0(2.0). The normalization with the corresponding changes in the mean-square nuclear charge-radiiδ〈r ²〉 yields values which are almost constant, mean value:z _5d /δ〈r ²〉=134(14) MHZ/fm². This indicates a second order IS interaction of the magnetic and the field shift operator.     

Hyperfine structure and core polarization in Nd I 4f 4f 4 5d6s

The high resolution laser-atomic-beam technique was used to investigate the hyperfine structure in Nd I 4f ⁴ 5d6s ⁷ L, ⁷ K, ⁷ I, ⁷ H, ⁷ G, ⁵ L, ⁵ K, and ⁵ I for both of the stable odd isotopes. The metastable states were populated by an arc discharge burning in the atomic beam, and 31 transitions to higher odd levels have been studied. Knowledge of the hyperfine constants of 34 levels of 4f ⁴ 5d6s allowed a comprehensive parametric analysis to be performed, using the effective tensor operator formalism. Compared to earlier analyses, a significant reduction of errors has been achieved for all the parameters. The contact parameter a _4f ¹⁰ has been fitted freely, thus providing an experimental value for the core-polarization effects. They are about six times larger than the relativistic effects.     

The role of the 5f orbitals in bonding, aromaticity, and reactivity of planar isocyclic and heterocyclic uranium clusters

The molecular and electronic structures, stabilities, bonding features and magnetic properties of prototypical planar isocyclic cyclo-U n X n ( n = 3, 4; X = O, NH) and heterocyclic cyclo-U n (mu 2-X) n ( n = 3, 4; X = C, CH, NH) clusters as well as the E@[ c-U 4(mu 2-C) 4], (E = H (+), C, Si, Ge) and U@[ c-U 5(mu 2-C) 5] molecules including a planar tetracoordinate element E (ptE) and pentacoordinate U (ppU) at the ring centers, respectively, have been thoroughly investigated by means of electronic structure calculation methods at the DFT level. It was shown that 5f orbitals play a key role in the bonding of these f-block metal systems significantly contributing to the cyclic electron delocalization and the associated magnetic diatropic (magnetic aromaticity) response. The aromaticity of the perfectly planar cyclo-U n X n ( n = 3, 4; X = O, NH), cyclo-U n (mu 2-X) n ( n = 3, 4; X = C, CH, NH), E@[ c-U 4(mu 2-C) 4], (E = H (+), C, Si, Ge) and U@[ c-U 5(mu 2-C) 5] clusters was verified by an efficient and simple criterion in probing the aromaticity/antiaromaticity of a molecule, that of the nucleus-independent chemical shift, NICS(0), NICS(1), NICS zz (0) and the most refined NICS zz (1) index in conjunction with the NICS scan profiles. Natural bond orbital analyses provided a clear picture of the bonding pattern in the planar isocyclic and heterocyclic uranium clusters and revealed the features that stabilize the ptE's inside the six- and eight-member uranacycle rings. The ptE's benefit from a considerable electron transfer from the surrounding uranium atoms in the E@[ c-U 4(mu 2-C) 4], (E = H (+), C, Si, Ge) and U@[ c-U 5(mu 2-C) 5] clusters justifying the high occupancy of the np orbitals of the central atom E.     

The role of the sulfur 3d orbitals in bond formation in sulfur-containing compounds

The role of the sulfur 3d orbitals in bond formation is discussed by taking into account the influence of the environment on the orbitals of the sulfur atom in the molecules. The calculation results of a series of prototype molecules containing sulfur such as SF₂ SF₄, NSF₃, SF₀, H₂S are reported. It is convincingly shown that in highly electronegative environment the energy levels of the sulfur 3d orbitals are reduced to the vicinity of those of the ligand valence orbitals and their spatial distributions are contracted to the bonding area, and therefore they can participate in bond formation to a certain extent, which is enhanced by the formation of the d-p π back bonds. It seems that the result reported in this paper is helpful for the solution of the long-standing debate about the sulfur 3d orbital participation in bond formation.     

Hyperfine structure in the configurations4f 4 6s 2 and4f 4 5d 6s of Nd I

The high resolution laser-atomic-beam technique was used to investigate the hyperfine structure in Nd I 4f ⁴6s ^{2 5} I,⁵ F,⁵ S and 4f ⁴5d6s ⁷ L,⁷ K,⁷ I,⁷ H. The metastable states were populated by an arc discharge burning in the atomic beam. The measured hyperfine constantsA andB of the levels of 4f ⁴6s ² and 4f ⁴5d6s allow a parametric analysis to be performed using the effective tensor operator formalism. The experimental radial integrals of the 4f and 5d electrons fit with those of the other lanthanides. The 4f radial integrals are in agreement with values of optimized Hartree-Fock-Slater calculations. The spectroscopic quadrupole moments of¹⁴³Nd and¹⁴⁵Nd are deduced from the 4f parameters:Q _I =?0.610(21) b and ?0.314(12) b, respectively. TheQ _I resulting from the 5d parameter are in satisfactory agreement with these values. The hyperfine anomaly due to thes electron in 4f ⁴5d 6s amounts to about 1%.     

Tensor polarizabilities of the 4f 7(8 S)5d6s 2 9 D 2,3,4,5,6 levels in Gd I

The optical pumping method with rf detection and the nonlinear level crossing technique were used in parallel electric and magnetic fields to investigate the Stark splitting of all the fine structure levels of the ground multiplet 4f ⁷ (⁸ S) 5d6s ^{2 9} D in Gd I. The tensor polarizabilities were deduced from the level crossing and the rf signals. The variation of the tensor polarizabilities is well reproduced by the LS coupling approximation, except for the small value of the⁹ D ₅ level. A value of the tensor polarizability of the 5d electron is evaluated from the experimental results, ₂(5d)=2.00(6) kHz(kV/cm)². It is shown that the ratio between the electric quadrupole constant and the tensor polarizability is constant, except for the⁹ D ₅ ratio, which is caused by a breakdown of the central field model.     

Comparison of the Chemical Properties of 4f, 5f,and 6d Elements

Similarities and differences in the chemical properties of lanthanides, actinides, and transactinides are analyzed. The general tendency of the change in the thermodynamic properties of trivalent lanthanides and actinides is established. The validity of the hypothesis of the pair analogy of trivalent lanthanides and actinides is revised. The oxidation-reduction properties of actinides and transactinides Pu–Hs and Np–Bh are compared.     

Enhancing the blocking temperature in single-molecule magnets by incorporating 3d-5d exchange interactions

We report the first single-molecule magnet (SMM) to incorporate the [Os(CN)(6)](3-) moiety. The compound (1) has a trimeric, cyanide-bridged Mn(III)-Os(III)-Mn(III) skeleton in which Mn(III) designates a [Mn(5-Brsalen)(MeOH)](+) unit (5-Brsalen=N,N'-ethylenebis(5-bromosalicylideneiminato)). X-ray crystallographic experiments reveal that 1 is isostructural with the Mn(III)-Fe(III)-Mn(III) analogue (2). Both compounds exhibit a frequency-dependent out-of-phase χ'(T) alternating current (ac) susceptibility signal that is suggestive of SMM behaviour. From the Arrhenius expression, the effective barrier for 1 is found to be Δ(eff)/k(B)=19 K (τ(0)=5.0×10(-7) s; k(B)=Boltzmann constant), whereas only the onset (1.5 kHz, 1.8 K) of χ'(T) is observed for 2, thus indicating a higher blocking temperature for 1. The strong spin-orbit coupling present in Os(III) isolates the E'(1g(1/2))(O(h)*) Kramers doublet that exhibits orbital contributions to the single-ion anisotropy. Magnetic susceptibility and inelastic neutron-scattering measurements reveal that substitution of [Fe(CN)(6)](3-) by the [Os(CN)(6)](3-) anion results in larger ferromagnetic, anisotropic exchange interactions going from quasi-Ising exchange interactions in 2 to pure Ising exchange for 1 with J(parallel)(MnOs)=-30.6 cm(-1). The combination of diffuse magnetic orbitals and the Ising-type exchange interaction effectively contributes to a higher blocking temperature. This result is in accordance with theoretical predictions and paves the way for the design of a new generation of SMMs with enhanced SMM properties.     

Experimental evidence and DFT studies of next-nearest-neighbor magnetic interactions through diamagnetic 3d and 4d ions

The copper template effect allows the preparation of tridentate ligands that chelate copper ions, leaving unoccupied the fourth basal coordination position and at least one axial position of the copper coordination polyhedron. Two such cationic complexes, [LCu](+) and [L(1)Cu](+) (L(-) = 2-{(E)-[(2-aminoethyl)imino]methyl}phenoxo] and L(1-) = 2-{(E)-[(2-aminopropyl)imino]methyl}phenoxo), react with diamagnetic polycyanometalate tectons such as Ni(CN)(4)(2-) or Ag(CN)(2)(-) to yield different neutral 1D complexes. In {[(LCu)(2)Ni(CN)(4)]}(n) (1) the four cyano nitrogen atoms are involved in coordination with copper ions in such a manner that each copper atom is pentacoordinated and linked to two cyano functions that occupy axial and equatorial coordination positions. Two L(1)Cu(+) cationic entities are linked, through their equatorial plane, to two trans cyano groups of the Ni(CN)(4)(2-) tecton in complex [(L(1)Cu)(2)Ni(CN)(4)] (2), the two uncoordinated cyano groups being involved in hydrogen bonds. 2 is a racemate, a S stereoisomer being associated with a R one in each [(L(1)Cu)(2)Ni(CN)(4)] unit. Zigzag Cu-Ag chains are present in [(LCu)Ag(CN)(2)] (3), where the copper centers are pentacoordinated and connected to the cyano groups in an alternate axial-equatorial coordination scheme. A bidimensional structure is developed by interchain argentophilic interactions. In complex 4, {(L(1)CuMeOH)(L(1)Cu)[Ag(CN)(2)](2)}, two L(1)Cu units are connected by a NC-Ag-CN bridge in an equatorial position. These resulting units exhibit argentophilic interactions with [Ag(CN(2))](-) entities that are monocoordinated in the equatorial position to the next unit, ultimately leading to a chain. Weak Cu-Cu magnetic interactions are detected in the four compounds, antiferromagnetic in the case of equatorial-equatorial copper interactions, ferromagnetic for orthogonal interacting copper orbitals (axial-equatorial interactions), while axial-axial bridges are characterized by an absence of interaction. The presence of weak ferromagnetic interactions through large NC-Ni-CN or NC-Ag-CN bridges (Cu···Cu distances larger than 10 ?) furnishes experimental evidence for the existence of next-nearest-neighbor interactions through diamagnetic centers. DFT calculations do confirm the existence of these magnetic transmission pathways through the diamagnetic metal bridge.     

On the hyperfine structure in the configurations 4f n 6s 2, 4f n 5d6s, 4f n 6s6p,and 4f n−15d6s 2 of the lanthanides

A survey of hyperfine analyses in the low-lying configurations 4f ⁿ 6s ², 4f ⁿ 5d6s, 4f ⁿ 6s6p, and 4f ^n?1 5d6s ² of the lanthanides is given. Experimental hf radial integrals 〈r ^?3〉 _nl ^kj are indicated for the configurations under investigation. From a comparison of experimental and theoretical hf radial integrals configuration-interaction contributions Δ _nl ^kj to the hfs have been evaluated for the configurations for which corresponding integrals were available. With nuclear electric quadrupole moments from muonic x-ray investigations and radial integrals 〈r ^?3〉 _nl ⁰¹ and 〈r ^?3〉 _nl ⁰² from experimental hfs quadrupole shielding correctionsR _nl ⁰¹ have been obtained. The variation of hyperfine radial integrals, configuration-interaction contributions and quadrupole shielding corrections over the 4f shell in the configurations under study is discussed. Trends of these quantities in different configurations are compared.     

Study of 3d – 4f and 3d – 5f quartet and doublet transitions of doubly excited three-electron ions

We present the first observation of optical transitions between doubly excited doublet states in the term systems N V, O VI and F VII. The spectra were produced by foil excitation of fast ion beams. The assignment of the spectral lines was made by comparison with the results of MCDF calculations along the isoelectronic sequence. The same method also led to the identification of two 3d – 4f quartet transitions in Mg X.     

J-dependence of the isotope shift in Gd I 4f 75d6s 2(a 9 D)

The angular distribution of electrons resulting from off-resonant ionisation of atomic hydrogen has been measured recently [1]. Here we report calculations of these angular distributions using the method of implicit summation [2] to calculate the n-photon absorption probabilities in the nth order of perturbation theory.     

The role of cation-pi interactions in biomolecular association. Design of peptides favoring interactions between cationic and aromatic amino acid side chains.

Cation-pi interactions between amino acid side chains are increasingly being recognized as important structural and functional features of proteins and other biomolecules. Although these interactions have been found in static protein structures, they have not yet been detected in dynamic biomolecular systems. We determined, by (1)H NMR spectroscopic titrations, the energies of cation-pi interactions of the amino acid derivative AcLysOMe (1) with AcPheOEt (2) and with AcTyrOEt (3) in aqueous and three organic solvents. The interaction energy is substantial; it ranges from -2.1 to -3.4 kcal/mol and depends only slightly on the dielectric constant of the solvent. To assess the effects of auxiliary interactions and structural preorganization on formation of cation-pi interactions, we studied these interactions in the association of pentapeptides. Upon binding of the positively-charged peptide AcLysLysLysLysLysNH(2) (5) to the negatively-charged partner AcAspAspXAspAspNH(2) (6), in which X is Leu (6a), Tyr (6b), and Phe (6c), multiple interactions occur. Association of the two pentapeptides is dynamic. Free peptides and their complex are in fast exchange on the NMR time-scale, and 2D (1)H ROESY spectra of the complex of the two pentapeptides do not show intermolecular ROESY peaks. Perturbations of the chemical shifts indicated that the aromatic groups in peptides 6b and 6c were affected by the association with 5. The association constants K(A) for 5 with 6a and with 6b are nearly equal, (4.0 +/- 0.7) x 10(3) and (5.0 +/- 1.0) x 10(3) M(-)(1), respectively, while K(A) for 5 with 6c is larger, (8.3 +/- 1.3) x 10(3) M(-)(1). Molecular-dynamics (MD) simulations of the pentapeptide pairs confirmed that their association is dynamic and showed that cation-pi contacts between the two peptides are stereochemically possible. A transient complex between 5 and 6 with a prominent cation-pi interaction, obtained from MD simulations, was used as a template to design cyclic peptides C(X) featuring persistent cation-pi interactions. The cyclic peptide C(X) had a sequence in which X is Tyr, Phe, and Leu. The first two peptides do, but the third does not, contain the aromatic residue capable of interacting with a cationic Lys residue. This covalent construct offered conformational stability over the noncovalent complexes and allowed thorough studies by 2D NMR spectroscopy. Multiple conformations of the cyclic peptides C(Tyr) and C(Phe) are in slow exchange on the NMR time-scale. In one of these conformations, cation-pi interaction between Lys3 and Tyr9/Phe9 is clearly evident. Multiple NOEs between the side chains of residues 3 and 9 are observed; chemical-shift changes are consistent with the placement of the side chain of Lys3 over the aromatic ring. In contrast, the cyclic peptide C(Leu) showed no evidence for close approach of the side chains of Lys3 and Leu9. The cation-pi interaction persists in both DMSO and aqueous solvents. When the disulfide bond in the cyclic peptide C(Phe) was removed, the cation-pi interaction in the acyclic peptide AC(Phe) remained. To test the reliability of the pK(a) criterion for the existence of cation-pi interactions, we determined residue-specific pK(a) values of all four Lys side chains in all three cyclic peptides C(X). While NOE cross-peaks and perturbations of the chemical shifts clearly show the existence of the cation-pi interaction, pK(a) values of Lys3 in C(Tyr) and in C(Phe) differ only marginally from those values of other lysines in these dynamic peptides. Our experimental results with dynamic peptide systems highlight the role of cation-pi interactions in both intermolecular recognition at the protein-protein interface and intramolecular processes such as protein folding.     

The role of antiferromagnetic exchange interactions in dinuclear Cr(III) dithiocarbamates and a stepwise behavior of magnetic moment

In this study the role of the antiferromagnetic interactions in recently synthesized dinuclear Cr(III) complex has been investigated. Since there was not enough structural information for the characterization of the synthesis, we claim that there should be antiferromagnetic interactions between the dinuclear Fe(III) ions, if the proposed structure is the real structure. A new experiment is proposed to test the predictions of this theoretical investigation.