Coordination Of Nitrogen Atom Research Articles

Synthesis, Structure, and Magnetic Characterization of a C3-Symmetric MnIII3CrIII Assembly: Molecular Recognition Between a Trinuclear MnIII Triplesalen Complex and a fac-Triscyano CrIII Complex

The reaction of the tris(tetradentate) triplesalen ligand H(6)talen(t-Bu(2)), which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with Mn(II) salts under aerobic conditions, affords, in situ, the trinuclear Mn(III) triplesalen complex [(talen(t-Bu(2))){Mn(III)(solv)(n)}(3)](3+). This species then reacts with [(Me(3)tacn)Cr(CN)(3)] to form the tetranuclear complex [{(talen(t-Bu(2)))Mn(III)(3)}{(Me(3)tacn)Cr(CN)(3)}](3+) ([Mn(III)(3)Cr(III)](3+)). The regular ligand folding observed in the trinuclear triplesalen complex preorganizes the three metal ions for the reaction with three facially coordinated nitrogen atoms of [(Me(3)tacn)Cr(CN)(3)]. [{(talen(t-Bu(2)))(Mn(III)(MeOH))(3)}{(Me(3)tacn)Cr(CN)(3)}](ClO(4))(3) (1) was characterized by infrared spectroscopy, elemental analysis, mass spectrometry, electron absorption spectroscopy, and magnetic measurements. The molecular structure was established for the acetate-substituted derivative [{(talen(t-Bu(2)))(Mn(III)(MeOH))(2)(Mn(III)(OAc))}{(Me(3)tacn)Cr(CN)(3)}](ClO(4))(2) (2) by single-crystal X-ray diffraction. Variable-temperature-variable-field and mu(eff) versus T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian, consisting of isotropic exchange, zero-field splitting, and Zeeman interaction components. Satisfactory reproduction of the experimental data has been obtained for the parameters J(Mn-Cr) = -0.12 +/- 0.04 cm(-1), J(Mn-Mn) = -0.70 +/- 0.03 cm(-1), and D(Mn) = -3.0 +/- 0.4 cm(-1). These generate a triply degenerate pseudo S(t) = 7/2 spin manifold, which cannot be appropriately described by a giant spin model and which exhibits a weak easy-axis magnetic anisotropy. This is corroborated by the onset of a frequency-dependent chi'' signal at low temperatures, demonstrating a slow relaxation of the magnetization indicative of 1 being a single-molecule magnet. Comparing the properties to those of the heptanuclear analogue [{(talen(t-Bu(2)))Mn(III)(3)}(2){Cr(III)(CN)(6)}](3+) ([Mn(III)(6)Cr(III)](3+)) formed by the reaction of 2 equiv of [(talen(t-Bu(2))){Mn(III)(solv)(n)}(3)](3+) with 1 equiv of [Cr(CN)(6)](3-) [Glaser, T.; Heidemeier, M.; Weyhermüller, T.; Hoffmann, R.-D.; Rupp, H.; Müller, P. Angew. Chem. Int. Ed., 2006, 45, 6033-6037] demonstrates a lower driving force for formation, a strongly reduced J(Mn-Cr) exchange, a slightly reduced J(Mn-Mn) exchange, and a significantly longer Mn-N(N[triple bond]C) bond length in [Mn(III)(3)Cr(III)](3+). Taking into account magneto-structural correlations establishes a supramolecular interaction between the two [(talen(t-Bu(2)))Mn(III)(3)](3+) subunits in [Mn(III)(6)Cr(III)](3+) responsible for the structural distortion and the short Mn-N(N[triple bond]C) distance which results in a strong J(Mn-Cr) exchange and thus [Mn(III)(6)Cr(III)](3+) being a single-molecule magnet with a relatively high effective anisotropy barrier of 25.4 K.

New Insight into the Nature of Catalytic Activity of Pyrolysed Iron Porphyrin Based Electro-Catalysts for the Oxygen Reduction Reaction (ORR) in Acidic Media

In this contribution, catalysts, prepared by an impregnation technique have been characterized structurally and chemically via 57Fe Mößbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and by elemental analysis, respectively. On the basis of the structural characterization it was concluded that those FeN4 centres in which iron is mesomericly bonded to four nitrogen atoms, are catalyzing the ORR. Furthermore, XPS as well as Mößbauer spectroscopy revealed that with increasing pyrolysis temperature the electron density at iron atoms was increased while that of the coordinating nitrogen atoms was reduced. This behaviour was connected with a decreased electric field gradient(EFG) as estimated by quadrupole splitting. EFG is interpreted in terms of a larger iron-nitrogen-bond distance and/or a slight movement of iron out of plane. We propose that this characteristic of the centres within the graphene planes, in which the centres are incorporated, enables the higher turn-over frequency during ORR of pyrolysed porphyrins.

Synthesis and Functional Group Transformations of Tris(pyrazol-1-yl)meth­ane (Tpm) and -ethane (Tpe) Derivatives for the Preparation of Sterically Hindered Chelating Macrobicycles

Tris(pyrazol-1-yl)methane (Tpm) and -ethane (Tpe) chelate derivatives bearing meta-benzonitrile groups in the position ortho to the coordinating nitrogen atom have been prepared from 3-(1H-pyrazol-3-yl)benzonitrile, and subjected to functional group transformations leading to the corresponding benzylthiol-substituted derivatives. The Tpe analogue was reacted with 1,3,5-tribromomethylbenzene in basic conditions to afford the Tpe-incorporating macrobicycle 2 in 40% yield.

Iron(II) Tris-[N4-substituted-3,5-di(2-pyridyl)-1,2,4-triazole] Complexes: Structural, Magnetic, NMR, and Density Functional Theory Studies

Eight mononuclear iron(II) complexes of N(4)-3,5-di(2-pyridyl)-1,2,4-triazole (Rdpt) ligands have been prepared and characterized. In all cases the iron(II)/ligand ratio used is 1:3, giving red complexes of the general formula [Fe(II)(Rdpt)(3)](BF(4))(2) x solvents, in 55-89% yield. The ligands differ only in the nature of the N(4)-substituent (amino, pyrrolyl, iso-butyl, methyl, phenyl, para-tolyl, 3,5-dichlorophenyl, and 4-pyridyl; for ligands adpt, pldpt, ibdpt, medpt, phdpt, ptdpt, Cldpt, and pydpt, respectively) allowing substituent effects on the properties of the resulting iron(II) complexes to be probed. The low temperature crystal structures of seven of the complexes reveal low spin iron(II) environments. Packing analyses reveal anion-pi and acetonitrile-pi interactions involving the tetrafluoroborate counteranions and interstitial acetonitrile molecules, respectively. Both "pi-pockets" and "pi-sandwiches" are observed. Solid state magnetic susceptibility measurements (4-300 K) indicate the iron(II) is low spin (LS) in all complexes at all temperatures studied, except for [Fe(II)(pldpt)(3)](BF(4))(2) x 1 1/2 H(2)O which has the beginnings of spin crossover (SCO) at elevated temperatures. Downfield shifts and peak broadening observed in the variable temperature (1)H NMR studies indicate that in d(3)-nitromethane solution the LS [Fe(II)(Rdpt)(3)](2+) complexes are in equilibrium with a trace of a high spin (HS) species. (15)N NMR spectra (measured and calculated) of the ligands reveal that altering the N(4)-substituent changes the chemical shift of the N(1) triazole and pyridine nitrogen atoms, allowing probing of the relationship between ligand substituent and the nature of the coordinating nitrogen atoms.

Insight into the copper coordination environment in the prion protein through density functional theory calculations of EPR parameters

Density functional theory (DFT) calculations of Cu(II) electron paramagnetic resonance (EPR) parameters for the octarepeat unit of the prion protein were conducted. Model complexes were constructed and optimized using the crystal structure of the octarepeat unit of the prion protein. Copper g and A tensors and nitrogen hyperfine and quadrupole coupling constants were calculated using DFT. Solvent effects were incorporated using the conductor-like screening model as well as through the inclusion of explicit water molecules. Calculations using the model with an additional axial water molecule added to the coordination sphere of the Cu(II) metal center give the best qualitative agreement for the copper g and A tensors. The S-band experimental EPR spectra were interpreted in light of the DFT calculations of the directly coordinated nitrogen hyperfine coupling constants which indicate that the three directly coordinated nitrogen atoms in the octarepeat unit are not equivalent. These results demonstrate that DFT calculations of EPR parameters can provide important insight with respect to the structural interpretation of experimental EPR data.

DFT Calculations of Space Structures of MII Complexes with (N,N,N,N)-Coordinating Macroheterocyclic Ligand – 1,8-Dioxa-3,6,10,13-tetraazacyclotetradecanetetrathione-4,5,11,12

Geometric parameters of MnII, CoII, NiII and CuII complexes with 1,8-dioxa-3,6,10,13-tetraazacyclotetradecanetetrathione-4,5,11,12 macrohetrocyclic ligand with N,N,N,N-coordination mode, which can be formed as a result of template processes in MII – ethanedithioamide-1,2 – methanal triple systems, were calculated using DFT B3LYP method with 6-31G(d) basic set. Additional 6-membered metal chelate cycles formed as a result of template “stitching” are not planar and considerably tilted in respect to two 5-membered cycles. In addition, in VIV complex, both these cycles are on one side from the mean N,N,N,N-plane formed by coordinating nitrogen atoms, in all other complexes – on different sides of this plane.

Syntheses, structures, and magnetic properties of heterometallic coordination polymers with carboxyphosphonate linkers

Five heterometallic coordination polymers were synthesized utilizing the multifunctional carboxyphosphonate ligand N-(phosphonomethyl)iminodiacetic acid (H4PMIDA), N(CH2PO(OH)2)(CH2COOH)2, with a coordinating nitrogen atom and two carboxylate and one phosphonate groups. The compounds were characterized structurally and magnetically. [Cu2M2(PMIDA)2(H2O)6]·3H2O for M = Mn (1-CuMn), Co (2-CuCo), and Cd (3-CuCd) are isostructural (space groupP21/n) and made of honeycomb-like 2D layers which, in turn, are made of unusual double-stranded meso-helices. [Cu2Ln2(PMIDA)2(C2O4)(H2O)6]·3.5H2O for Ln = La (4-CuLa) and Nd (5-CuNd)) are also isostructural (P21/c) but with open 3D framework structures. They contain dinuclear CuLn(PMIDA) secondary building units that are bridged by phosphonate tetrahedra and form infinite chains along the c axis. The chains are interconnected via carboxylic groups and form double-decker layers which, in turn, are connected by the oxalate linkers to form the open three-dimensional framework. The magnetic properties of the compounds were measured and analyzed in detail.

Reactivity of 1,3-bis(2-pyridyl)benzene, N⁁CH⁁N, with gold(iii) chlorides: salts, adducts and cyclometalated pincer derivatives. Crystal and molecular structures of [HN⁁CH⁁N][AuCl4], [Au(N⁁C⁁N)Cl][PF6] and [Au(N⁁C⁁N)Cl(PPh3)2][PF6

The reaction of 1,3-bis(2-pyridyl)benzene, N--CH--N, with H[AuCl(4)] has been studied under different conditions. Mono- ([N--CH--NH][AuCl(4)]) and di-protonated salts ([HN--CH--NH][AuCl(4)](2)), as well as an adduct, [(N--CH--N)(AuCl(3))(2)], have been isolated. Very rare cyclometalated pincer derivatives, [Au(N--C--N)Cl](+) have been obtained as different salts, either by transmetallation from the corresponding mercury(ii) derivative, [Hg(N--C--N)Cl], or by direct C-H activation. The structures in the solid state of [N--CH--NH][AuCl(4)] and [Au(N--C--N)Cl][PF(6)] have been solved by X-ray diffraction. Reaction of the pincer derivatives with PPh(3), dppm (bis(diphenylphosphino)methane) and dppe (1,2-bis(diphenylphosphino)ethane) occurs with displacement of the coordinated nitrogen atoms to afford [Au(N--C--N)(Cl)(PPh(3))(2)](+), [Au(N--C--N)(Cl)(dppm)(2)](+) and [Au(N--C--N)(Cl)(dppe)](+), respectively. The X-ray structure of [Au(N--C--N)(Cl)(PPh(3))(2)][PF(6)] confirms that the ligand N--C--N is only sigma-carbon bonded and the PPh(3) molecules are in a trans-arrangement. The pattern of the (31)P{(1)H}NMR spectrum of [Au(N--C--N)(Cl)(dppm)(2)](+), a pair of "triplets", deserves comments: the spectrum is not of the A(2)X(2) type but a case of a deceptively simple AA'XX' spin system.

Exchange Interactions and Zero-Field Splittings in C3-Symmetric MnIII6FeIII: Using Molecular Recognition for the Construction of a Series of High Spin Complexes Based on the Triplesalen Ligand

The reaction of the tris(tetradentate) triplesalen ligand H6talen(t-Bu2), which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with Mn(II) salts under aerobic conditions affords, in situ, the trinuclear Mn(III) triplesalen complexes [(talen(t-Bu2)){Mn(III)(solv)n}3]3+. These can be used as molecular building blocks in the reaction with [Fe(CN)6]3- as a hexaconnector to form the heptanuclear complex [{(talen(t-Bu2)){Mn(III)(solv)n}3}2{Fe(III)(CN)6}]3+ ([Mn(III)6Fe(III)]3+). The regular ligand folding observed in the trinuclear triplesalen complexes preorganizes the three metal ions for the reaction of three facially coordinated nitrogen atoms of a hexacyanometallate and provides a driving force for the formation of the heptanuclear complexes [M(t)6M(c)]n+ (M(t), terminal metal ion of the triplesalen building block; M(c), central metal ion of the hexacyanometallate) by molecular recognition, as has already been demonstrated for the single-molecule magnet [Mn(III)6Cr(III)]3+. [{(talen(t-Bu2))(Mn(III)(MeOH))3}2{Fe(III)(CN)6}][Fe(III)(CN)6] (1) was characterized by single-crystal X-ray diffraction, FTIR, ESI- and MALDI-TOF-MS, Mössbauer spectroscopy, and magnetic measurements. The molecular structure of [Mn(III)6Fe(III)]3+ is overall identical to that of [Mn(III)6Cr(III)]3+ but exhibits a different ligand folding of the Mn(III) salen subunits with a helical distortion. The Mössbauer spectra demonstrate a stronger distortion from octahedral symmetry for the central [Fe(CN)6]3- in comparison to the ionic [Fe(CN)6]3-. At low temperatures in zero magnetic fields, the Mössbauer spectra show magnetic splittings indicative of slow relaxation of the magnetization on the Mössbauer time scale. Variable-temperature-variable-field and mu(eff) versus T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian, consisting of isotropic exchange, zero-field splitting, and Zeeman interaction taking into account the relative orientation of the D tensors. Satisfactory reproduction of the experimental data has been obtained for parameters sets J(Mn-Mn) = -(0.85 +/- 0.15) cm(-1), J(Fe-Mn) = +(0.70 +/- 0.30) cm(-1), and D(Mn) = -(3.0 +/- 0.7) cm(-1). Comparing these values to those of [Mn(III)6Cr(III)]3+ provides insight into why [Mn(III)6Fe(III)]3+ is not a single-molecule magnet.

Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

Flash photolysis and K-edge x-ray absorption spectroscopy (XAS) were used to investigate the functional and structural effects of pH on the oxygen affinity of three homologous arthropod hemocyanins (Hcs). Flash photolysis measurements showed that the well-characterized pH dependence of oxygen affinity (Bohr effect) is attributable to changes in the oxygen binding rate constant, k(on), rather than changes in k(off). In parallel, coordination geometry of copper in Hc was evaluated as a function of pH by XAS. It was found that the geometry of copper in the oxygenated protein is unchanged at all pH values investigated, while significant changes were observed for the deoxygenated protein as a function of pH. The interpretation of these changes was based on previously described correlations between spectral lineshape and coordination geometry obtained for model compounds of known structure (Blackburn, N. J., Strange, R. W., Reedijk, J., Volbeda, A., Farooq, A., Karlin, K. D., and Zubieta, J. (1989) Inorg. Chem., 28, 1349-1357). A pH-dependent change in the geometry of cuprous copper in the active site of deoxyHc, from pseudotetrahedral toward trigonal was assigned from the observed intensity dependence of the 1s --> 4p(z) transition in x-ray absorption near edge structure (XANES) spectra. The structural alteration correlated well with increase in oxygen affinity at alkaline pH determined in flash photolysis experiments. These results suggest that the oxygen binding rate in deoxyHc depends on the coordination geometry of Cu(I) and suggest a structural origin for the Bohr effect in arthropod Hcs.

Ligation of Aza bases to the AgF2 molecule: a theoretical study

We have analyzed the electronic structure and chemical bonding for molecular adducts of the Ag(II)F2 molecule with various aza Lewis bases including ammonia, nitriles, secondary amines, and their derivatives exhibiting various degrees of fluorination. Density functional theory calculations indicate that a progressive shift occurs of the spin density from the Ag center towards the coordinating nitrogen atoms of aza ligands, as the ligation energy increases. Chemistry of Ag(II) might be extended with little effort beyond the known aza connections, to include nitriles, perfluorinated nitriles and perfluorinated amines.

Toward a Better Understanding of the Reactivity of Titanium and Zirconium Complexes with an Aryl-Substituted Tripodal Triamido Ligand Derived from cis,cis-1,3,5-Triaminocyclohexane: A Density Functional Study

Tilley and co-workers have shown that titanium and zirconium hydride complexes containing the triamido [cis,cis-1,3,5-(3,5-tBu2C6H3N)3C6H9]3− ligand (L) do not polymerize ethene. To get insight in this observation we have studied these systems and various modifications thereof using density functional theory. The reactivity toward ethene was investigated by computing the energy barriers for ethene insertion in the metal−hydride and metal−alkyl bonds of these compounds with the alkyl chain represented by a methyl or ethyl group. For titanium and zirconium complexes of L, the computational results agree with the experimental observation that insertion is possible in metal−hydride but not in metal−alkyl bonds. The energy barrier for insertion in the metal−alkyl bond can be lowered somewhat by reducing the steric bulk of the triamido ligand; however, even in the absence of any steric hindrance this barrier remains very high and no polymerization activity is expected. The ethene insertion barriers increase when reducing the rigidity of the triamido ligand by the introduction of methylene bridges between the coordinating nitrogen atoms and the cyclohexane backbone or replacing the cyclohexane-based ligand by three NH2 groups. The effect of changing the four-coordinate ligand environment of titanium to a five-coordinate one by adding an additional donor molecule (NH3) was found to be small. A significant lowering of the ethene insertion barriers in the metal−alkyl bonds was found only when creating a much more unsaturated metal center by removal of one of the −NR groups or replacement of one of these groups by a much weaker coordinating −OR group. Both the cationic d0 and neutral d1 variants of the latter compounds may be active polymerization catalysts. The calculated ease of ethene insertion is shown to be dominated by the electrophilicity of the metal center, quantified as the binding energy of the probe molecule ammonia, and roughly parallels the complexation energy of the ethene monomer.

Unprecedented twofold intramolecular hydroamination in diam(m)ine-dicarboxylatodichloridoplatinum(iv) complexes – ethane-1,2-diaminevs.ammine ligands

Reaction of (OC-6-13)-bis(2Z-3-carboxyacrylato)dichlorido(ethane-1,2-diamine)platinum(IV) and (OC-6-13)-diamminebis(2Z-3-carboxyacrylato)dichloridoplatinum(IV) with propylamine in the presence of 1,1'-carbonyl diimidazole afforded not the expected amides; instead, beside amide formation, a twofold intramolecular attack of the am(m)ine ligand at the C[double bond, length as m-dash]C bonds was observed involving either both (ethane-1,2-diamine) or only one (ammine) coordinated nitrogen atom(s).

Spectroscopy of Eu3+ and Tb3+ pyridine- and pyrazine-2-carboxylates

Abstract The luminescence excitation, luminescence and vibrational spectra of europium and terbium pyridine- and pyrazine-2-carboxylates were investigated. A special attention was paid to spectroscopic characterization of tetrakis-compounds, MLn(Lig) 4 ·H 2 O, where M = NH 4 , Na; Ln = Eu, Tb; Lig = pyridine-2-carboxylate and pyrazine-2-carboxylate anions. The features of the spectra indicated a decrease of the interaction of carboxylic groups and an increase of the donor–acceptor interaction of coordinated nitrogen atoms with the lanthanide ions in different tetrakis-salts in comparison with the tris-salts. This is accompanied by clear manifestation of the 4f–5d electronic transitions in the excitation spectra of terbium salts.

Bonding Properties Related with Chiral Discrimination in Dinuclear Metal Complexes of Group 10

AbstractA series of neutral dinuclear homo‐ and heterochiral complexes formed by hydrazine (a molecule with axial chirality), a metal atom of group 10 (Ni, Pd, Pt), and halogen atoms (F, Cl, Br, I) was studied by computational methods including density functional theory. In the optimized structures the heterochiral complexes were always found to be energetically favored. The chiral discrimination depends on the contributions coming from the metal atoms and the halogen anions attached to them. Moreover, the relative energies of the optimized complexes are correlated with the electronegativity of the metals and the halogens as well as with the relative distances of the bond critical points in the metal–nitrogen bonds. Also the smaller deviation of the ligand–metal–ligand angles from the ideal value of 90° corresponds to the heterochiral complexes. An analysis of the bonding properties reveals a complex mechanism for the behavior of the electron lone pairs of the nitrogen and halogen atoms. The electronic properties of the optimized complexes were studied by NBO (Natural Bond Orbital) and QTAIM (Quantum Theory of Atoms in Molecules) methods. An NBO analysis of the energy differences between the stabilizing energies related to the interactions between an electron lone pair of the coordinated nitrogen atom and the opposite M–X antibonding orbital explain the differences of the total energies between the diastereomeric heterochiral and homochiral complexes. The stabilizing energies have systematically more negative values in the heterochiral complexes; this can be interpreteted as a measure of the trans influence. Small energy values related to the cis influence were found mainly in the nickel complexes. The M–N bonds in the heterochiral complexes are more polar with a higher bond order than that in the homochiral ones, as shown by QTAIM methods. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Synthesis, lead lability and ring deformation of three 1,4,8,11,15,18,22,25-octasubstituted phthalocyaninato lead derivatives

The syntheses and attempted syntheses of some non-peripherally (1,4,8,11,15,18,22,25) octasubstituted lead phthalocyanines from their corresponding metal-free derivatives are described. Some compounds exhibited lability of the lead ion during work-up to regenerate the starting material. The results of single crystal X-ray diffraction analyses of 1,4,8,11,15,18,22,25-octahexyl-, 1,4,8,11,15,18,22,25-octa-iso-pentyl- and 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanines are reported and cast some light on the greater stability of 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine, in terms of ease of loss of the lead ion, over the other two substituted lead phthalocyanines studied. The phthalocyanine cores of all three derivatives adopt a saddle-shaped geometry rather than the saucer-shaped conformation exhibited by unsubstituted lead phthalocyanine. The saddle-shaped conformation would appear to offer a means of relieving steric interactions between the substituents on adjacent benzene rings. That steric interactions are a feature of these molecules is perhaps reflected in the different distortions of the saddle conformations. This is greatest for compound 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanine bearing the isopentyl groups, expected to introduce the most interactions, and least for compound 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine where S atoms rather than methylene groups are adjacent to the benzene ring. The molecules of 1,4,8,11,15,18,22,25-octahexyl- and 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine pack together in pairs with their nearest neighbouring molecule; their lead atoms, displaced from the core and directed towards each other. The presence of the S atoms in 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine leads to close Pb … S contacts between the molecules. Attractive Pb … S interactions in this compound may also account for the larger displacement of the Pb from the mean-plane of the four coordinated nitrogen atoms at the centre of the phthalocyanine core than is found for 1,4,8,11,15,18,22,25-octahexyl- and 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanines. The molecular packing of 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanine is more complex because of the presence of tetrahydrofuran molecules (the solvent of recrystallisation) within the crystal, offering additional interactions with the Pb atoms.

Solvation structure of metal ions in nitrogen-donating solvents

The solvation structure of the Mn(II), Fe(II), Co(II), Ni(II), and Zn(II) ions has been determined in various nitrogen-donating solvents of n-propylamine (PA), trimethylenediamine (TA), ethylenediamine (EN), pyridine (PY), 2-methylpyridine (2MPY), 4-methylpyridine (4MPY), and acetonitrile (AN) by the X-ray absorption spectroscopy. The 6-coordinate octahedral structure has been observed for all the ions except for the species of Zn(II) in PA and 2MPY. The mixed formation of 4- and 6-coordinate species is found for Zn(II) in TA, of which the electron donicity is compared with that of PA. A similar mixed formation of solvated species has been observed for the Co(II) ion in PA. The M–N bond distances vary in the order Mn(II) > Fe(II) > Co(II) > Ni(II) < Zn(II) as expected from the ligand field theory. There are systematic shifts in the series of the M–N bond distances in the aliphatic amines, pyridines, and nitriles, which may be related to the electronic structure of the coordinating nitrogen atoms.

Actinide(III) and lanthanide(III) complexes with nitrogen ligands: Counterions and ligand substituent effects on the metal–ligand bond

Relativistic density functional theory calculations are reported for actinide(III) (An=U, Am, Cm) and lanthanide(III) (Ln=La, Nd) complexes with tridentate aromatic nitrogen ligands. Calculations have been performed on 2,2′:6′,2″-terpyridine (Terpy) complexes with various species in the first coordination sphere of the metal ion besides one Terpy ligand (H 2O, Cl − and NO 3 − ) and on bis(1,2-4-triazin-3-yl)pyridine (Btp) complexes with various susbtituents attached to the triazine rings (CH 3, OCH 3 and CN). Metal–ligand bonds in trivalent lanthanum, neodynium, americium and curium complexes are predominantly ionic, and significant variations are found in metal–nitrogen bond lengths when the total charge of the complexes is changed by the number of counterions or when the charges on the coordinating nitrogen atoms are altered by substituents. Uranium–ligand bonds are more covalent and smaller variations are found in uranium–nitrogen bond distances. The most remarkable effect on uranium–ligand bonds is obtained by attaching CN groups to the Btp, uranium(5f)-to-Btp(π*) back-bonding is enhanced and uranium–nitrogen bonds are shortened.

Counteranion‐Induced Formation of cis and trans Singly and Doubly H2biim‐Bridged Di‐, Hexa‐, and Polymeric Ag–H2biim Complexes

AbstractA series of cis and trans singly and doubly H2biim‐bridged di‐, hexa‐, and polymeric complexes of silver(I) (H2biim = 2,2′‐biimidazole), namely [Ag2(μ‐H2biim)2]SO4·2H2O (1),[Ag2(μ‐H2biim)2(μ‐ox)]n (2), [Ag6(μ‐H2biim)5(H2biim)2](ClO4)4(CH3CO2)2·2H2O (3), and [Ag(μ‐H2biim)(nicotinate)]n (4) have been synthesized and characterized by X‐ray crystallography and IR and photoluminescence spectroscopy. The structural topology of the Ag–H2biim system is determined by the charge of the counteranions. Thus, dianionic counterions facilitate the formation of dimeric structures driven by the charge‐balance requirement, whereas a monoanionic counterion favors the formation of helical structures. Counteranions of larger size lead to either finite helical structures or a trans arrangement of the coordinating nitrogen atoms because of steric requirements. Organic counteranions with a strong coordination ability bind to the Ag+ ions while inorganic counteranions are uncoordinated. The argentophilic attraction is not dominant in this system. Examination of the luminescent properties of H2biim and compounds 1–4 indicates that the fluorescence emission of H2biim is effectively shifted upon metal coordination. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)

Room-temperature NIR phosphorescence of new iridium (III) complexes with ligands derived from benzoquinoxaline

A new series of new iridium (III) complexes (1–5) bearing ligands derived from benzoquinoxaline were designed and synthesized. X-ray structural analyses of 1 reveal a distorted octahedral geometry around the Ir atom in which the pyrazolate chelate is located opposite to the cis-oriented carbon donor atoms of benzoquinoxaline, while the benzoquinoxaline ligands adopt an eclipse configuration and their coordinated nitrogen atoms and carbon adopt trans- and cis-orientation, respectively. Complexes 1–5 exhibit moderate NIR phosphorescence with peak maxima located at around 910–930 nm. As supported by the TDDFT approach, the transition mainly involves benzoquinoxaline 3π–π* intraligand charge transfer (ILCT) and metal (Ir) to benzoquinoxaline charge transfer (MLCT) of which the spectroscopy and dynamics of relaxation have been thoroughly investigated. The relatively weak NIR emission can be tentatively rationalized by the low energy gap of which the radiationless deactivation may be governed by nearly temperature-independent, weak-bonding motions in combination with a minor channel incorporating small torsional motions associated with phenyl ring in the benzoquinoxaline sites.Key words: phosphorescence, NIR, iridium, benzoquinoxaline, isoquinoline, bipyridine, pyrazolate, acetylacetonate.