DFT-UX3LYP studies on the coordination chemistry of Ni2+. Part 1: Six coordinate [Ni(NH3)n(H2O)(6-n)]2+ complexes

DFT calculations with the UX3LYP hybrid functional and a medium-sized 6-311++G(d,p) basis set were performed to examine the gas-phase structure of paramagnetic (S = 1) six-coordinate complexes [Ni(NH3)n(H2O)(6-n)](2+), 0 < or = n < or = 6. Significant interligand hydrogen bonding was found in [Ni(H2O)6](2+), but this becomes much less significant as NH3 replaces H2O in the coordination sphere of the metal. Bond angles and bond lengths obtained from these calculations compare reasonably well with available crystallographic data. The mean calculated Ni-O bond length in [Ni(H2O)6](2+) is 2.093 A, which is 0.038 A longer than the mean of the crystallographically observed values (2.056(22) A, 108 structures) but within 2sigma of the experimental values. The mean calculated Ni-N bond length in [Ni(NH3)6](2+) is 2.205(3) A, also longer (by 0.070 A) than the crystallographically observed mean (2.135(18) A, 7 structures). Valence bond angles are reproduced within 1 degree. The successive replacement of H2O by NH3 as ligands results in an increase in the stabilization energy by 7 +/- 2 kcal mol(-1) per additional NH3 ligand. The experimentally observed increase in the lability of H2O in Ni(II) as NH3 replaces H2O in the coordination sphere is explained by an increase in the Ni-OH2 bond length. It was found from a natural population analysis that complexes with the highest stabilization energies are associated with the greatest extent of ligand-to-metal charge transfer, and the transferred electron density is largely accommodated in the metal 4s and 3d orbitals. An examination of the charge density rho bcp and the Laplacian of the charge density nabla(2)rho(bcp) at the metal-ligand bond critical points (bcp) in the series show a linear correlation with the charge transferred to the metal. Values of nabla(2)rho(bcp) are positive, indicative of a predominantly closed-shell interaction. The charge transferred to the metal increases as n, the number of NH3 ligands in the complex, increases. This lowers the polarizing ability of the metal on the ligand donors and the average metal-ligand bond length increases, resulting in a direct correlation between the dissociation energy of the complexes and the reciprocal of the average metal-ligand bond length. There is a strong correlation between the charge transferred to the metal and experimental DeltaH values for successive replacement of H2O by NH3, but a correlation with stability constants (log beta values) breaks when n = 5 and 6, probably because of entropic effects in solution. Nevertheless, DFT calculations may be a useful way of estimating the stability constants of metal-ligand systems.     

Synthesis and characterization of copper-, zinc-, manganese-, and cobalt-substituted dimeric heteropolyanions, [(alpha-XW9O33)2M3(H2O)3](n-) (n = 12, X =As(III), Sb(III), M = Cu(2+), Zn(2+); n = 10, X = Se(IV), Te(IV), M = Cu(2+) and [(alpha-AsW9O33)2WO(H2O)M2(H2O)2](10-) (M = Zn(2+), Mn(2+), Co(2+)

Interaction of the lacunary [alpha-XW9O33](9-) (X = As(III), Sb(III)) with Cu(2+) and Zn(2+) ions in neutral, aqueous medium leads to the formation of dimeric polyoxoanions, [(alpha-XW9O33)2M3(H2O)3](12-) (M = Cu(2+), Zn(2+); X = As(III), Sb(III)), in high yield. The selenium and tellurium analogues of the copper-containing heteropolyanions are also reported: [(alpha-XW9O33)2Cu3(H2O)3](10-) (X = Se(IV), Te(IV)). The polyanions consist of two [alpha-XW9O33] units joined by three equivalent Cu(2+) (X = As, Sb, Se, Te) or Zn(2+) (X = As, Sb) ions. All copper and zinc ions have one terminal water molecule resulting in square-pyramidal coordination geometry. Therefore, the title anions have idealized D3h symmetry. The space between the three transition metal ions is occupied by three sodium ions (M = Cu(2+), Zn(2+); X = As(III), Sb(III)) or potassium ions (M = Cu(2+); X = Se(IV), Te(IV)) leading to a central belt of six metal atoms alternating in position. Reaction of [alpha-AsW9O33](9-) with Zn(2+), Co(2+), and Mn(2+) ions in acidic medium (pH = 4-5) results in the same structural type but with a lower degree of transition-metal substitution, [(alpha-AsW9O33)2WO(H2O)M2(H2O)2](10-) (M = Zn(2+), Co(2+), Mn(2+)). All nine compounds are characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analysis. The solution properties of [(alpha-XW9O33)2Zn3(H2O)3](12-) (X = As(III), Sb(III)) were also studied by 183W-NMR spectroscopy.     

3,6-bis(2'-pyridyl)pyridazine (L) and its deprotonated form (L - H+)- as ligands for {(acac)2Ru(n+)} or {(bpy)2Ru(m+)}: investigation of mixed valency in [{(acac)2Ru}2(mu-L - H+)]0 and [{(bpy)2Ru}2(mu-L - H+)]4+ by spectroelectrochemistry and EPR

Crystallographically characterised 3,6-bis(2'-pyridyl)pyridazine (L) forms complexes with {(acac)2Ru} or {(bpy)2Ru2+}via one pyridyl-N/pyridazyl-N chelate site in mononuclear Ru(II) complexes (acac)2Ru(L), 1, and [(bpy)2Ru(L)](ClO4)2, [3](ClO4)2. Coordination of a second metal complex fragment is accompanied by deprotonation at the pyridazyl-C5 carbon {L --> (L - H+)-} to yield cyclometallated, asymmetrically bridged dinuclear complexes [(acac)2Ru(III)(mu-L - H+)Ru(III)(acac)2](ClO4), [2](ClO4), and [(bpy)2Ru(II)(mu-L - H+)Ru(II)(bpy)2](ClO4)3, [4](ClO4)3. The different electronic characteristics of the co-ligands, sigma donating acac- and pi accepting bpy, cause a wide variation in metal redox potentials which facilitates the isolation of the diruthenium(III) form in [2](ClO4) with antiferromagnetically coupled Ru(III) centres (J = -11.5 cm(-1)) and of a luminescent diruthenium(II) species in [4](ClO4)3. The electrogenerated mixed-valent Ru(II)Ru(III) states 2 and [4]4+ with comproportionation constants Kc > 10(8) are assumed to be localised with the Ru(III) ion bonded via the negatively charged pyridyl-N/pyridazyl-C5 chelate site of the bridging (L - H+)- ligand. In spectroelectrochemical experiments they show similar intervalence charge transfer bands of moderate intensity around 1300 nm and comparable g anisotropies (g1-g3 approximatly 0.5) in the EPR spectra. However, the individual g tensor components are distinctly higher for the pi acceptor ligated system [4]4+, signifying stabilised metal d orbitals.     

Electronic structure of linear thiophenolate-bridged heteronuclear complexes [LFeMFeL](n)(+) (M = Cr, Co, Fe; n = 1-3): a combination of kinetic exchange interaction and electron delocalization

The electronic properties of the isostructural series of heterotrinuclear thiophenolate-bridged complexes of the general formula [LFeMFeL](n)(+) with M = Cr, Co and Fe where L represents the trianionic form of the ligand 1,4,7-tris(4-tertbutyl-2-mercaptobenzyl)-1,4,7-triazacyclononane, synthesized and investigated by a number of experimental techniques in the previous work(1), are subjected now to a theoretical analysis. The low-lying electronic excitations in these compounds are described within a minimal model supported by experiment and quantum chemistry calculations. It was found indeed that various experimental data concerning the magnetism and electron delocalization in the lowest states of all seven compounds are completely reproduced within a model which includes the electron transfer between magnetic orbitals at different metal centers and the electron repulsion in these orbitals (the Hubbard model). Moreover, due to the trigonal symmetry of the complexes, only the electron transfer between nondegenerate orbital, a(1), originating from the t(2g) shell of each metal ion in a pseudo-octahedral coordination, is relevant for the lowest states. An essential feature resulting from quantum chemistry calculations, allowing to explain the unusual magnetic properties of these compounds, is the surprisingly large value and, especially, the negative sign of the electron transfer between terminal iron ions, beta'. According to their electronic properties the series of complexes can be divided as follows: (1). The complexes [LFeFeFeL](3+) and [LFeCrFeL](3+) show localized valences in the ground electronic configuration. The strong antiferromagnetic exchange interaction and the resulting spin 1/2 of the ground-state arise from large values of the transfer parameters. (2). In the complex [LFeCrFeL](+), due to a higher energy of the magnetic orbital on the central Cr ion than on the terminal Fe ones, the spin 3/2 and the single unpaired a(1) electron are almost localized at the chromium center in the ground state. (3). The complex [LFeCoFeL](3+) has one ground electronic configuration in which two unpaired electrons are localized at terminal iron ions. The ground-state spin S = 1 arises from a kinetic mechanism involving the electron transfer between terminal iron ions as one of the steps. Such a mechanism, leading to a strong ferromagnetic interaction between distant spins, apparently has not been discussed before. (4). The complex [LFeFeFeL](2+) is characterized by both spin and charge degrees of freedom in the ground manifold. The stabilization of the total spin zero or one of the itinerant electrons depends on beta', i.e., corresponds to the observed S = 1 for its negative sign. This behavior does not fit into the double exchange model. (5). In [LFeCrFeL](2+) the delocalization of two itinerant holes in a(1) orbitals takes place over the magnetic core of chromium ion. Although the origin of the ground-state spin S = 2 is the spin dependent delocalization, the spectrum of the low-lying electronic states is again not of a double exchange type. (6). Finally, the complex [LFeCoFeL](2+) has the ground configuration corresponding to the electron delocalization between terminal iron atoms. The estimated magnitude of the corresponding electron transfer is smaller than the relaxation energy of the nuclear distortions induced by the electron localization at one of the centers, leading to vibronic valence trapping observed in this compound.     

Metal complexes with a new N(4)O(3) amine pendant-armed macrocyclic ligand: synthesis, characterization, crystal structures, and fluorescence studies

The synthesis of a new oxaaza macrocyclic ligand, L, derived from O(1),O(7)-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren containing an amine terminal pendant arm, and its metal complexation with alkaline earth (M = Ca(2+), Sr(2+), Ba(2+)), transition (M = Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+)), post-transition (M = Pb(2+)), and Y(3+) and lanthanide (M = La(3+), Er(3+)) metal ions are reported. Crystal structures of [H(2)L](ClO(4))(2).3H(2)O, [PbL](ClO(4))(2), and [ZnLCl](ClO(4)).H(2)O are also reported. In the [PbL] complex, the metal ion is located inside the macrocyclic cavity coordinated by all N(4)O(3) donor atoms while, in the [ZnLCl] complex, the metal ion is encapsulated only by the nitrogen atoms present in the ligand. pi-pi interactions in the [H(2)L](ClO(4))(2).3H(2)O and [PbL](ClO(4))(2) structures are observed. Protonation and Zn(2+), Cd(2+), and Cu(2+) complexation were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. The 10-fold fluorescence emission increase observed in the pH range 7-9 in the presence of Zn(2+) leads to L as a good sensor for this biological metal in water solution.     

Cyanide-bridged iron(II,III) cube with multistepped redox behavior

A building unit of Prussian blue was isolated as a cyanide-bridged iron cube of [Fe(II)4Fe(III)4(CN)12(tp)8] x 12 DMF x 2 Et2O x 4 H2O [tp(-) = hydrotris(pyrazolyl)borate]. A cyclic voltammogram showed quasi-reversible four-stepped redox waves, which correspond to [Fe(III)4Fe(II)4]/[Fe(III)5Fe(II)3](+), [Fe(III)5Fe(II)3](+)/[Fe(III)6Fe(II)2](2+), [Fe(III)6Fe(II)2](2+)/[Fe(III)7Fe(II)1](3+), and [Fe(III)7Fe(II)1](3+)/[Fe(III)8](4+) processes. Controlled potential absorption spectral measurements revealed two intervalence charge-transfer bands at 816 and 1000 nm, which were assigned to charge transfers from Fe(II) ions to adjacent and remote Fe(III) ions, respectively, in the cube.     

Structural tuning of charge,orbital, and spin ordering in double-cell perovskite series between NdBaFe(2)O(5) and HoBaFe(2)O(5)

Charge, orbital, and magnetic ordering of NdBaFe(2)O(5) and HoBaFe(2)O(5), the two end-members of the double-cell perovskite series RBaFe(2)O(5), have been characterized over the temperature range 2-450 K, using differential scanning calorimetry, neutron thermodiffractometry and high-resolution neutron powder diffraction. Upon cooling, both compounds transform from a class-III mixed valence (MV) compound, where all iron atoms exist as equivalent MV Fe(2.5+) ions, through a "premonitory" charge ordering into a class-II MV compound, and finally to a class-I MV phase at low-temperature. The latter phase is characterized by Fe(2+)/Fe(3+) charge ordering as well as orbital ordering of the doubly occupied Fe(2+) d(xz) orbitals. The relative simplicity of the crystal and magnetic structure of the low-temperature charge-ordered state provide an unusual opportunity to fully characterize the classical Verwey transition, first observed in magnetite, Fe(3)O(4). Despite isotypism of the title compounds at high temperature, neutron diffraction analysis reveals striking differences in their phase transitions. In HoBaFe(2)O(5), the Verwey transition is accompanied by a reversal of the direct Fe-Fe magnetic coupling across the rare earth layer, from ferromagnetic in the class-II and -III MV phases to antiferromagnetic in the low-temperature class-I MV phase. In NdBaFe(2)O(5), the larger Nd(3+) ion increases the Fe-Fe distance, thereby weakening the Fe-Fe magnetic interaction. This decouples the charge and magnetic ordering so that the Fe-Fe interaction remains ferromagnetic to low temperature. Furthermore, the symmetry of the charge-ordered class-I MV phase is reduced from Pmma to P2(1)()ma and the magnitude of the orbital ordering is diminished. These changes destabilize the charge-ordered state and suppress the temperature at which the Verwey transition occurs. A comparison of the magnetic and structural features of RBaFe(2)O(5) compounds is included in order to illustrate how structural tuning, via changes in the radius of the rare-earth ion, can be used to alter the physical properties of these double-cell perovskites.     

DFT-B3LYP, NPA-, and QTAIM-based study of the physical properties of [M(II)(H2O)2(15-crown-5)] (M = Mn, Fe, Co, Ni, Cu, Zn) complexes

A density functional theory study of the structure of the title compounds with the divalent metal ions in their high-spin ground state, obtained using B3LYP/6-311++G(d,p) in vacuo and in aqueous solution simulated using a polarized continuum medium, is reported for the first time. The modeling reproduces the pseudo pentagonal bipyramidal crystallographic structures very well, including some asymmetry in the equatorial bonds lengths to the crown ether O donors. The very marked asymmetry in the Ni(2+) structure due to a Jahn-Teller distortion of a d(8) system in a D(5h) ligand field is also well reproduced. The gas phase binding energies of the complexes follow the order Mn(2+) < Fe(2+) < Co(2+) < Ni(2+) < Cu(2+) > Zn(2+), in precise agreement with the Irving-William series. Both the NPA and Bader charges show there is ligand-to-metal charge transfer; however, the values obtained from the NPA procedure, unlike those obtained from Bader's quantum theory of molecules approach, do not correlate with the electronegativity of the metal ions, the stabilization energies of the solvated complexes or the ionic radii of the metal ions, and so appear to be less reliable. The nature of the bonding between the ligands and the metal ions has been explored using the topological properties of the electron charge density. The metal-ligand bond distances were found to be exponentially correlated with the electron charge density, its Laplacian, and with its curvature in the direction of the bond path at M-O bond critical points. While the bonding with coordinated H(2)O is predominantly ionic, that to the crown ether donor atoms has some covalent character the extent of which increases across the first transition series. The delocalization indices of M-O bonds in these complexes correlate reasonably well with the electron density and its Laplacian at the bond critical points; this therefore provides a rapid and computationally very efficient way of determining these properties, from which insight into the nature of the bonding can be obtained, obviating the need for time-consuming integration over atomic basins.     

Binding of the two-valence-electron metal ions Sc(+), Ti(2+), and V(3+) to the second-row hydrides BeH(2), BH(3), NH(3), OH(2), and FH: a computational study

We report results from a computational study of the binding in complexes formed from one of the transition-metal ions Sc(+), Ti(2+), or V(3+), each of which has two valence electrons outside an argon core, and one of the second-row hydrides FH, OH(2), NH(3), BH(3), or BeH(2). The complexes that involve the electron-rich ligands FH, OH(2), and NH(3) have strong ion-dipole components to their binding. There are large stabilization energies for sigma-interactions that transfer charge from occupied lone-pair natural bond orbitals on the F, O, or N atom of the (idealized) Lewis structure into empty non-Lewis orbitals on the metal ions; these interactions effectively increase electron density in the bonding region between the metal ion and liganded atom, and the metal ions in these complexes act in the capacity of Lewis acids. The complexes formed from the electron-poor hydrides BH(3) and BeH(2) consistently incorporate bridging hydrogen atoms to support binding, and there are large stabilization energies for interactions that transfer charge from the Be-H or B-H bonds into the region between the metal ion and liganded atom. The metal ions in Sc(+)-BeH(2), Ti(2+)-BeH(2), Ti(2+)-BH(3), and V(3+)-BH(3) act in the capacity of Lewis acids, whereas the scandium ion in Sc(+)-BH(3) acts as a Lewis base.     

Competing interactions in the tetranuclear spin cluster [Ni[(OH)(2)Cr(bispictn)](3)]I(5).5H(2)O. An inelastic neutron scattering and magnetic study

The properties of the spin state manifold of the tetranuclear cluster Ni[(OH)(2)Cr(bispictn)](3)]I(5).5H(2)O (bispictn = N,N'-bis(2-pyridylmethyl)-1,3-propanediamine) are investigated by combining magnetic susceptibility and magnetization measurements with an inelastic neutron scattering (INS) study on an undeuterated sample of Ni[(OH)(2)Cr(bispictn)](3)]I(5).5H(2)O. The temperature dependence of the magnetic susceptibility indicates an S = (1)/(2) ground state, which requires antiferromagnetic interactions both between Cr(3+) and Ni(2+) ions and among the Cr(3+) ions. INS reveals potential single-ion anisotropies to be negligibly small and enables an accurate determination of the exchange parameters. The best fit to the experimental energy level diagram is obtained by an isotropic spin Hamiltonian H = J(CrNi)(S(1)().S(4)() + S(2)().S(4)() + S(3)().S(4)()) + J(CrCr)(S(1)().S(2)() + S(1)().S(3)() + S(2)().S(3)()) with J(CrNi) = 1.47 cm(-)(1) and J(CrCr) = 1.25 cm(-)(1). With this model, the experimental intensities of the observed INS transitions as well as the temperature dependence of the magnetic data are reproduced. The resulting overall antiferromagnetic exchange is rationalized in terms of orbital exchange pathways and compared to the situation in oxalato-bridged clusters.     

Crystallographic, electrochemical, and electronic structure studies of the mononuclear complexes of Au(I)/(II)/(III) with [9]aneS2O ([9]aneS2O = 1-oxa-4,7-dithiacyclononane)

The mononuclear macrocyclic complexes [Au(I)([9]aneS2O)2]BF4 x MeCN 1a, [Au(II)([9]aneS2O)2](BF4)2 x 2 MeCN 2a, and [Au(III)([9]aneS2O)2](ClO4)6(H5O2)(H3O)2 3 ([9]aneS2O = 1-oxa-4,7-dithiacyclononane) have been prepared and structurally characterized by single crystal X-ray crystallography. The oxidation of [Au([9]aneS2O)2](+) to [Au([9]aneS2O)2](2+) involves a significant reorganization of the co-ordination sphere from a distorted tetrahedral geometry in [Au([9]aneS2O)2](+) [Au-S 2.3363(12), 2.3877(12), 2.6630(11), 2.7597(13) A] to a distorted square-planar co-ordination geometry in [Au([9]aneS2O)2](2+). The O-donors in [Au([9]aneS2O)2](2+) occupy the axial positions about the Au(II) center [Au...O = 2.718(2) A] with the S-donors occupying the equatorial plane [Au-S 2.428(8) and 2.484(8) A]. [Au([9]aneS2O)2](3+) shows a co-ordination sphere similar to that of [Au([9]aneS2O)2](2+) but with significantly shorter axial Au...O interactions [2.688(2) A] and equatorial Au-S bond lengths [2.340(4) and 2.355(6) A]. The cyclic voltammogram of 1 in MeCN (0.2 M NBu4PF6, 253 K) at a scan rate of 100 mV s(-1) shows an oxidation process at E(p)(a) = +0.74 V and a reduction process at E(p)(c) = +0.41 V versus Fc(+)/Fc assigned to the two-electron Au(III/I) couple and a second reduction process at E(p)(c) = +0.19 V assigned to the Au(I/0) couple. This electrochemical assignment is confirmed by coulometric and UV-vis spectroelectrochemical measurements. Multifrequency EPR studies of the mononuclear Au(II) complex [Au([9]aneS2O)2](2+) in a fluid solution at X-band and as frozen solutions at L-, S-, X-, K-, and Q-band reveal g(iso) = 2.0182 and A(iso) = -44 x 10(-4) cm(-1); g(xx) = 2.010, g(yy) = 2.006, g(zz) = 2.037; A(xx) = -47 x 10(-4) cm(-1), A(yy) = -47 x 10(-4) cm(-1), A(zz) = -47 x 10(-4) cm(-1); P(xx) = -18 x 10(-4) cm(-1), P(yy) = -10 x 10(-4) cm(-1), and P(zz) = 28 x 10(-4) cm(-1). DFT calculations predict a singly occupied molecular orbital (SOMO) with 27.2% Au 5d(xy) character, consistent with the upper limit derived from the uncertainties in the (197)Au hyperfine parameters. Comparison with [Au([9]aneS3)2](2+) reveals that the nuclear quadrupole parameters, P(ii) (i = x, y, z) are very sensitive to the nature of the Au(II) co-ordination sphere in these macrocyclic complexes. The observed geometries and bond lengths for the cations [Au([9]aneS2O)2](+/2+/3+) reflect the preferred stereochemistries of d(10), d(9), and d(8) metal ions, respectively, with the higher oxidation state centers being generated at higher anodic potentials compared to the related complexes [Au([9]aneS3)2](+/2+/3+).     

Copper-complex-linked polytungsto-bismuthate (-antimonite) chain containing sandwich Cu(II) ions partially modified with imidazole ligand

Two sandwich-type complexes Na9n(Cu(im)4(H2O)2)1.5n(Cu(im)4(H2O))n[{Cu(im)4}{Na(H2O)2}3{Cu3(im)2(H2O)}(XW9O33)2]2n .(xH2O)n (im=imidazole, X=Bi (1), Sb(2), x=42.5 (1), 40 (2)) have been synthesized and structurally characterized. Basic frameworks of 1 and 2 are built from sandwich-type [{Na(H2O) 2} 3{Cu3(im)2(H2O)}(XW9O33)2](9-) (X=Bi or Sb) anions and [Cu(im) 4](2+) cations. The Cu(2+) and Na(+) ions in the central belt are coordinated by alpha-[XW9O33](9-) units, im, and water molecules to form {CuO4(im)}, {CuO4(H2O)}, and {NaO4(H2O)2} groups in which Cu (2+) ions are partially modified with im ligands. These groups connect alternately forming a six-membered ring including six alpha-[XW9O 33](9-) units. Neighboring anions are further linked by [Cu(im) 4](2+) cations to display an unprecedented anionic chain, which is first observed in sandwich-type tungsto-bismuthate (-antimonite) system. Two kinds of isolated copper complexes and sodium ions are located as counterions, which cause three-dimensional packings of 1 and 2 to present interesting cage structures. The magnetic properties for 1 and 2 both indicate dominant antiferromagnetic interactions among trinuclear Cu(II) clusters.     

Computational study of analogues of the uranyl ion containing the -N=U=N- unit: density functional theory calculations on UO2(2+), UON+, UN2, UO(NPH3)3+, U(NPH3)2(4+), [UCl4[NPR3]2] (R = H, Me), and [UOCl4[NP(C6H5)3]

The electronic and geometric structures of the title species have been studied computationally using quasi-relativistic gradient-corrected density functional theory. The valence molecular orbital ordering of UO2(2+) is found to be pi g < pi u < sigma g < sigma u (highest occupied orbital), in agreement with previous experimental conclusions. The significant energy gap between the sigma g and sigma u orbitals is traced to the "pushing from below" mechanism: a filled-filled interaction between the semi-core uranium 6p atomic orbitals and the sigma u valence level. The U-N bonding in UON+ and UN2 is significantly more covalent than the U-O bonding in UON+ and UO2(2+). UO(NPH3)3+ and U(NPH3)2(4+) are similar to UO2(2+), UON+, and UN2 in having two valence molecular orbitals of metal-ligand sigma character and two of pi character, although they have additional orbitals not present in the triatomic systems, and the U-N sigma levels are more stable than the U-N pi orbitals. The inversion of U-N sigma/pi orbital ordering is traced to significant N-P (and P-H) sigma character in the U-N sigma levels. The pushing from below mechanism is found to destabilize the U-N f sigma molecular orbital with respect to the U-N d sigma level in U(NPH3)2(4+). The uranium f atomic orbitals play a greater role in metal-ligand bonding in UO2(2+), UN2, and U(NPH3)2(4+) than do the d atomic orbitals, although, while the relative roles of the uranium d and f atomic orbitals are similar in UO2(2+) and U(NPH3)2(4+), the metal d atomic orbitals have a more important role in the bonding in UN2. The preferred UNP angle in [UCl4(NPR3)2] (R = H, Me) and [UOCl4(NP(C6H5)3)]- is found to be close to 180 degrees in all cases. This preference for linearity decreases in the order R = Ph > R = Me > R = H and is traced to steric effects which in all cases overcome an electronic preference for bending at the nitrogen atom. Comparison of the present iminato (UNPR3) calculations with previous extended Hückel work on d block imido (MNR) systems reveals that in all cases there is little or no preference for linearity over bending at the nitrogen when R is (a) only sigma-bound to the nitrogen and (b) sterically unhindered. The U/N bond order in iminato complexes is best described as 3.     

Density functional theory study of trans-dioxo complexes of iron, ruthenium, and osmium with saturated amine ligands, trans-[M(O)2(NH3)2(NMeH2)2]2+ (M=Fe, Ru, Os), and detection of [Fe(qpy)(O)2]n+ (n=1, 2) by high-resolution ESI mass spectrometry

Density functional theory (DFT) calculations on trans-dioxo metal complexes containing saturated amine ligands, trans-[M(O)2(NH3)2(NMeH2)2]2+ (M=Fe, Ru, Os), were performed with different types of density functionals (DFs): 1) pure generalized gradient approximations (pure GGAs): PW91, BP86, and OLYP; 2) meta-GGAs: VSXC and HCTH407; and 3) hybrid DFs: B3LYP and PBE1PBE. With pure GGAs and meta-GGAs, a singlet d2 ground state for trans-[Fe(O)2(NH3)2(NMeH2)2]2+ was obtained, but a quintet ground state was predicted by the hybrid DFs B3LYP and PBE1PBE. The lowest transition energies in water were calculated to be at lambda approximately 509 and 515 nm in the respective ground-state geometries from PW91 and B3LYP calculations. The nature of this transition is dependent on the DFs used: a ligand-to-metal charge-transfer (LMCT) transition with PW91, but a pi(Fe-O)-->pi*(Fe-O) transition with B3LYP, in which pi and pi* are the bonding and antibonding combinations between the dpi(Fe) and ppi(O(2-)) orbitals. The FeVI/V reduction potential of trans-[Fe(O)2(NH3)2NMeH2)2]2+ was estimated to be +1.30 V versus NHE based on PW91 results. The [Fe(qpy)(O)2](n+) (qpy=2,2':6',2':6',2':6',2'-quinquepyridine; n=1 and 2) ions, tentatively assigned to dioxo iron(V) and dioxo iron(VI), respectively, were detected in the gas phase by high-resolution ESI-MS spectroscopy.     

Electrochemical Properties and ESR Characterization of Mixed Valence alpha-[XMo(3)(-)(x)()V(x)()W(9)O(40)](n)()(-) Heteropolyanions with X = P(V) and Si(IV), x = 1, 2, or 3

Electrochemical behavior of the alpha-[SiMo(3)(-)(x)()V(x)()W(9)O(40)]((4+)(x)()())(-) and alpha-[PMo(3)(-)(x)()V(x)()W(9)O(40)]((3+)(x)()())(-) anions with x = 1, 2, or 3 were studied. Electrochemical reduction of each compounds was consistent with its Mo/V ratio, reduction of vanadium and molybdenum atoms occurring in the +0.6 to -0.6 V potential range. The one-electron-reduced species were prepared by electrolysis and then characterized by ESR spectroscopy. The g and A values for V(4+)ions appeared to depend on the nature of the surrounding atoms (Mo(VI), W(VI), and V(V)). In solution at 330 K, the ESR spectrum of the protonated alpha-H[SiMoV(IV)VW(9)O(40)](6)(-) anion displayed 29 superhyperfine lines which were related to the partial localization of the electron on one vanadium nucleus. The ESR spectra at room temperature for the divanadium-substituted anions showed a strong anisotropy of the A tensor which would be related to the electron transfer along a preferential axis. An isolated V(4+) signal was not observed, even at 12 K, indicating that the electron is never firmly trapped on one single vanadium atom.     

Electronic structure of the [MNH2]+ (M = Sc-Cu) complexes

B3LYP geometry optimizations for the [MNH2]+ complexes of the first-row transition metal cations (Sc+-Cu+) were performed. Without any exception the ground states of these unsaturated amide complexes were calculated to possess planar geometries. CASPT2 binding energies that were corrected for zero-point energies and including relativistic effects show a qualitative trend across the series that closely resembles the experimental observations. The electronic structures for the complexes of the early and middle transition metal cations (Sc+-Co+) differ from the electronic structures derived for the complexes of the late transition metal cations (Ni+ and Cu+). For the former complexes the relative higher position of the 3d orbitals above the singly occupied 2p(pi) HOMO of the uncoordinated NH2 induces an electron transfer from the 3d shell to 2p(pi). The stabilization of the 3d orbitals from the left to the right along the first-row transition metal series causes these orbitals to become situated below the HOMO of the NH2 ligand for Ni+ and Cu+, preventing a transfer from occurring in the [MNH2]+ complexes of these metal cations. Analysis of the low-lying states of the amide complexes revealed a rather unique characteristic of their electronic structures that was found across the entire series. Rather exceptionally for the whole of chemistry, pi-type interactions were calculated to be stronger than the corresponding sigma-type interactions. The origin of this extraordinary behavior can be ascribed to the low-lying sp2 lone pair orbital of the NH2 ligand with respect to the 3d level.     

First 3D Pr(III)-Ni(II)-Na(I) polymer and a 3D Pr(III) open network based on pyridine-2,4,6-tricarboxylic acid

The self-assembly of pyridine-2,4,6-tricarboxylic acid (H(3)ptc) with metal salts under hydrothermal conditions gave two novel coordination polymers, {[Pr(mu(5)-ptc)(H(2)O)(2)].1.5H(2)O}(n)() (1) and {Na(2)NiPr(mu(4)-ClO(4))(mu(2)-HOCH(2)CH(2)OH)(mu(4)-ptc)(2)(H(2)O)(8)}.4.5H(2)O}(n)() (2). 1 is a 3D open network with five ptc ligands coordinating with one metal center and carboxylate groups linking metal centers to form a (4,6) net. 2 is the first Pr/Ni/Na heterotrimetallic complex, a unique 3D framework containing four different bridged ligands in the system.     

Binding Patterns in Single-Ligand Complexes of NH(3), H(2)O, OH(-), and F(-) with First Series Transition Metals

Single-ligand complexes of first series transition metals with ammonia, water, hydroxide, and fluoride, many known in the gas phase, have been studied in calculations covering the 20 mono- and divalent cations and some very unusual binding patterns have been found. Binding energies and binding geometries were calculated at MP2 level, using a basis with a (6d/4d) contraction in the metal d space and 6-311+G sets for the ligands. The results were used to distinguish the effect of steadily increasing nuclear charge across the series from the varying effects of d shell occupation. Even with only one ligand, the M(2+) adducts displayed the familiar ligand field effects, d shell repulsion in the expected d(delta) < d(pi) < d(sigma) order being superimposed on a regular progression to stronger binding and shorter bonds; that progression was disturbed only at the d(5) and d(10) positions, when the d(sigma) orbital was occupied. Monovalent metal adducts behaved in strikingly different fashion, with irregular changes across early and late series metals in both bond length and bond strength. The irregularities are only partly attributable to the presence of both d(n)()(-)(1)s and d(n)() ground states in the series. The other part of the explanation is the binding of anionic ligands inside the radial maximum of the 4s orbital. At these distances the normal binding preference shown by H(2)O and NH(3) for d(n)() over sd(n)()(-)(1) cations is reversed. In contrast to steeply rising binding energies across the divalent metal ion adducts, the trend lines for the monovalent series are flat, the increments in nuclear charge being insufficent to offset the extra repulsion of electrons added to the d shell.     

Complex formation reactions of lanthanum(III), cerium(III), thorium(IV), dioxouranyl(IV) complexes with tricine

Equilibrium studies for the heavy metal ions La(III), Ce(III), Th(IV) and UO2(IV) (M) complexes of the zwitterionic buffer tricine (L) in aqueous solution are investigated. Stoichiometry and stability constants for the different complexes formed as well as hydrolysis products of the metal cations are determined at 25 degrees C and ionic strength 0.1 M NaNO3. The stability of the formed complexes are discussed in terms of the nature of the heavy metal cation. The solid complexes are synthesized and characterized by means of elemental analysis, FTIR, and TG analysis. The general molecular formulae of the obtained complexes is suggested to be [M(L)2](NO3)n-2(H2O)x, where n = the charge of the metal cation, x = no. of water molecules.