Basal Ligands Research Articles

Effect of Reaction Time on Lanthanide Borate Perrhenate Complexes.

Six new trivalent lanthanide borate perrhenate structures─the isostructural series Ln[B8O11(OH)4(H2O)(ReO4)] (Ln = Ce-Nd, Sm, Eu; 1) and La[B6O9(OH)2(H2O)(ReO4)] (2)─have been prepared and structurally characterized. Single-crystal X-ray diffraction analysis reveals that both structures crystallize in the P21/n space group, contain 10-coordinated trivalent lanthanides in a capped triangular cupola geometry, are 3D borate framework materials, and contain either terminal (1) or bridging (2) perrhenate moieties. The presence or lack of a bridging perrhenate, along with the identity of the basal ligands, dictates how the layers are tethered together, ultimately leading to the different structures. Furthermore, the formation of 1 is sensitive to the reaction time employed. Herein, the synthesis, structural descriptions, and spectroscopy of these trivalent lanthanide perrhenate borate complexes are presented.

Theoretical Investigations of the Spin Hamiltonian Parameters for the Mononuclear Square Pyramidal [CuO5] Groups in Two Paddle Wheel Copper Complexes

The spin Hamiltonian parameters (SHPs) (g factors and hyperfine structure constants) for the mononuclear square pyramidal [CuO5] groups in two paddle wheel copper complexes {Cu2(μ2–O2CCH3)4}(OCNH2CH3) and \({}_{\infty }^{3} [{\text{Cu}}_{ 2}^{\text{I}} {\text{Cu}}_{ 2}^{\text{II}} ( {\text{H}}_{ 2} {\text{O)}}_{ 2} {\text{L}}_{ 2} {\text{Cl}}_{ 2} ]\) are theoretically investigated from the perturbation calculations of these parameters for a rhombically elongated octahedral 3d 9 group. The slightly larger anisotropy Δg (≈ g // − g⊥) of complex 1 than complex 2 is attributed to the slightly bigger deviations of the polar angles related to the ideal value 90° and relative differences between the axial and basal Cu–O distances in the former. The axiality of the EPR signals for both systems can be illustrated as the fact that the perpendicular anisotropic contributions to X and Y components of the SHPs arising from the four basal ligands with slightly distinct bond lengths and bond angles may roughly cancel one another. The signs of hyperfine structure constants are also theoretically determined for both complexes.

Reactivity of Cyclopentadienyl Molybdenum Compounds towards Formic Acid: Structural Characterization of CpMo(PMe3)(CO)2H, CpMo(PMe3)2(CO)H, [CpMo(μ-O)(μ-O2CH)]2, and [Cp*Mo(μ-O)(μ-O2CH)]2.

The molecular structures of CpMo(PMe3)(CO)2H and CpMo(PMe3)2(CO)H have been determined by X-ray diffraction, thereby revealing four-legged piano-stool structures in which the hydride ligand is trans to CO. However, in view of the different nature of the four basal ligands, the geometries of CpMo(PMe3)(CO)2H and CpMo(PMe3)2(CO)H deviate from that of an idealized four-legged piano stool, such that the two ligands that are orthogonal to the trans H-Mo-CO moiety are displaced towards the hydride ligand. While CpRMo(PMe3)3-x(CO)xH (CpR = Cp, Cp*; x = 1, 2, 3) are catalysts for the release of H2 from formic acid, the carbonyl derivatives, CpRMo(CO)3H, are also observed to form dinuclear formate compounds, namely, [CpRMo(μ-O)(μ-O2CH)]2. The nature of the Mo···Mo interactions in [CpMo(μ-O)(μ-O2CH)]2 and [Cp*Mo(μ-O)(μ-O2CH)]2 have been addressed computationally. In this regard, the two highest occupied molecular orbitals of [CpMo(μ-O)(μ-O2CH)]2 correspond to metal-based δ* (HOMO) and σ (HOMO-1) orbitals. The σ2δ*2 configuration thus corresponds to a formal direct Mo-Mo bond order of zero. The preferential occupation of the δ* orbital rather than the δ orbital is a consequence of the interaction of the latter orbital with p orbitals of the bridging oxo ligands. In essence, lone-pair donation from oxygen increases the electron count so that the molybdenum centers can achieve an 18-electron configuration without the existence of a Mo-Mo bond, whereas a Mo═Mo double bond is required in the absence of lone-pair donation.

Ionic Cocrystals of Pharmaceutical Compounds: Sodium Complexes of Carbamazepine

Three inorganic cocrystal (ICC) forms of carbamazepine (CBZ) have been synthesized, and their crystal structures are described. [Na(CBZ)4(MeOH)][I]·H2O, [Na(CBZ)5][I3], and [Na(CBZ)5][C13H10N][IBr2]2 are the first CBZ structures that contain metal cations, and the latter example also contains acridinium, which is a known metabolite of CBZ. All three Na complexes have distorted square pyramidal NaO5 coordination geometries but different conformations of the four basal ligands and different hydrogen bonding interactions for the apical ligand. The hydrogen bonded synthons that have been identified for other species that contain neutral CBZ molecules are absent in all these Na containing ICC phases and are replaced by Na–O dative bonds. However, previously identified nonpolar supramolecular constructs in the form of stacks and dimers are shared with other CBZ containing structures.

A structural study of [CpM(CO)3H] (M = Cr, Mo and W) by single-crystal X-ray diffraction and DFT calculations: sterically crowded yet surprisingly flexible molecules

The single-crystal X-ray structures of the complexes [CpCr(CO)3H] 1, [CpMo(CO)3H] 2 and [CpW(CO)3H] 3 are reported. The results indicate that 1 adopts a structure close to a distorted three-legged piano stool geometry, whereas a conventional four-legged piano stool arrangement is observed for 2 and 3. Further insight into the equilibrium geometries and potential energy surfaces of all three complexes was obtained by DFT calculations. These show that in the gas phase complex 1 also prefers a geometry close to a four-legged piano stool in line with its heavier congeners, and implying strong packing forces at work for 1 in the solid state. Comparison with their isolelectronic group 7 tricarbonyl counterparts [CpM(CO)3] (M = Mn 4 and Re 5) illustrates that 1, 2 and 3 are sterically crowded complexes. However, a surprisingly soft bending potential is evident for the M-H moiety, whose order (1 approximately = 2 < 3) correlates with the M-H bond strength rather than with the degree of congestion at the metal centre, indicating electronic rather than steric control of the potential. The calculations also reveal cooperative motions of the hydride and carbonyl ligands in the M(CO)3H unit, which allow the M-H moiety to move freely, in spite of the closeness of the four basal ligands, helping to explain the surprising flexibility of the crowded coordination sphere observed for this family of high CN complexes.

Dicarbonyl(η5-cyclopentadienyl)bis(trimethylphosphine)molybdenum(II) trifluoromethanesulfonate

In the title compound, [Mo(C5H5)(CO)2(C3H9P)2]CF3SO3, the cationic complex displays a classical four-legged piano-stool square-pyramidal geometry with a trans configuration of the basal ligands around the Mo atom. The cyclo­penta­dienyl (Cp) ligand occupies the apical position of the piano-stool configuration. The average Mo—P bond length of the two trans PMe3 ligands is 2.474 (5) Å and the Mo—Cp centroid distance is 2.003 (2) Å.

Structural and EPR Studies on Single-Crystal and Polycrystalline Samples of Copper(II) and Cobalt(II) Complexes with N2S2-Based Macrocyclic Ligands

The properties of Cu(II) and Co(II) complexes with oxygen- or nitrogen-containing macrocycles have been extensively studied; however, less attention has been paid to the study of complexes containing sulfur atoms in the first coordination sphere. Herein we present the interaction between these two metal ions and two macrocyclic ligands with N2S2 donor sets. Cu(II) and Co(II) complexes with the pyridine-containing 14-membered macrocycles 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L) and 7-(9-anthracenylmethyl)-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) have been synthesized. The X-ray structural analysis of {[Co(ClO4)(H2O)(L)][Co(H2O)2(L)]}(ClO4)3 shows two different metal sites in octahedral coordination. The EPR spectra of powdered samples of this compound are typical of distorted six-coordinated Co(II) ions in a high-spin (S=3/2) configuration, with the ground state being S=1/2 (g1=5.20, g2=3.20, g3=1.95). The EPR spectrum of [Cu(ClO4)(L)](ClO4) was simulated assuming an axial g tensor (g1=g2=2.043, g3=2.145), while that of [Cu(ClO4)(L1)](ClO4) slightly differs from an axial symmetry (g1=2.025, g2=2.060, g3=2.155). These results are compatible with a Cu(II) ion in square-pyramidal coordination with N2S2 as basal ligands. Single-crystal EPR experiment performed on [Cu(ClO4)(L1)](ClO4) allowed determining the eigenvalues of the molecular g tensor associated with the copper site, as well as the two possible orientations for the tensor. On the basis of symmetry arguments, an assignment in which the eigenvectors are nearly along the Cu(II)-ligand bonds is chosen.

Trans-Bis[2-(aminomethyl)-1H-benzimidazole-κ2N2,N3]aquacopper(II) dichloride dihydrate

In the title compound, [Cu(C8H9N3)2(H2O)]Cl2·2H2O, the CuII ion is coordinated in a square-pyramidal geometry, with four N atoms as basal ligands and one water O atom as an apical ligand. The complex mol­ecule is situated on a crystallographic twofold rotation axis. The mol­ecules are bonded to their neighbours by N—H⋯O, O—H⋯Cl and N—H⋯Cl hydogen bonds. The packing is further stabilized by π–π inter­actions between the substituted imidazole mol­ecules.

Ab Initio Calculations of Co Shielding in Model Complexes

Recent ab initio calculations of cobalt NMR shielding show that DFT-GIAO calculations using hybrid functionals are found to reproduce experimental values well. This method is used to calculate the variation of the cobalt NMR shielding tensor of sqaure pyramidal nitrosyl complexes with respect to the CoNO geometry and to differing basal ligands. The isotropic shielding is shown to have a large negative derivative with respect to CoX distance where X is a ligating atom.; the derivative with respect to NO distance is smaller but still significant. The zz component where z is along the CoN(NO) bond is more sensitive to the basal ligands but the other two principal components are sensitive to the CoNO geometry.

Synthesis, spectroscopic studies and molecular structure of original halogeno-[ S-methyl 3-(2-hydroxyphenylethylidene)dithiocarbazato]oxo–rhenium(V) complexes

A new neutral rhenium(V)–oxo complex with tridentate Schiff base (SNO-CH 3), derived from the condensation of 2-hydroxyacetophenone with dithiocarbazic acid methyl ester (H 2N–NH–C(S)SCH 3) was prepared by a substitution reaction on the square pyramidal ionic complex [ReOCl 4][NBu 4]. Reacting the rhenium complex [Re VO(SNO-CH 3)Cl] 1 with lithium iodide (LiI) allows the formation of the iodo homologous rhenium(V)–oxo complex [Re VO(SNO-CH 3)I] 2. Compounds 1 and 2 were characterized by elemental analysis, IR, NMR spectra and mass spectrometry (FAB). The structure of [ReO(SNO-CH 3)I] 2 was determined by single X-ray diffraction methods. The coordination around rhenium is distorted square pyramidal with an apical double bonded oxo atom [ReO: 1.660 Å] and the basal ligands bend away from the oxo group.

Nephelauxetic series of in-plane ligands for square-pyramidal nitridochromium(V) complexes as studied by means of ESR spectroscopy

The crystal structure of the nitridochromium(V) complex [CrN(salophen)]·MeCN [H 2salophen= N, N′-bis(salicylidene)- o-phenylenediamine] has been determined. The coordination geometry of this complex, similar to those of all the nitridochromium(V) complexes investigated so far, is square pyramidal with the nitride ion occupying the apex. The ESR parameters of the nitridochromium(V) complexes isolated so far were compared with one another to show an enormous expansion of the 3d electron cloud due to the strong CrN triple bonding. Moderate covalency in the in-plane bonds was also concluded. The nephelauxetic series of three types of the basal ligands is deduced to be salen≈salophen>bpb≈mebpb≈dmebpb>oep≈ttp (in nephlauxetic ratio) for the high-oxidation nitridochromium(V), H 2salen= N, N′-bis(salicylidene)ethane-1,2-diamine, H 2bpb=1,2-bis(pyridine-2-carboxamido)benzene, H 2mebpb=1,2-bis(pyridine-2-carboxamido)-4-methylbenzene, H 2dmbpb=1,2-bis(pyridine-2-carboxamido-4,5-dimethylbenzene, H 2oep=2,3,7,8,12,13,17,18-octaethylporphyrin and H 2ttp=5,10,15,20-tetra- p-tolylporphyrin.

Synthesis and15N nuclear magnetic resonance shift tensors of bent nitrosyl complexes with N-substituted salicylideneiminate coligands; the shift tensor as a criterion of MNO bond angle

A series of nitrosylcobalt–Schiff base complexes [Co(NO)(asal)2][asal =N-alkyl- or N-aryl-salicylideneiminate, o-OC6H4CHNR, R = Me(msal), Et(esal), Bun(bsal), Ph(phsal) or CH2Ph(bzsal)] has been prepared. Single-crystal X-ray structure analysis of the esal derivative shows the molecule to be pyramidal with a bent apical nitrosyl group [Co–N 1.738(12), N–O 1.16(2)A, Co–N–O 129(1)°] and a trans arrangement of the basal ligands [Co–O 1.833(6), Co–N 1.950(6)A]. The crystals are orthorhombic, space group Pbca, a= 9.544(3), b= 17.000(3), c= 11.359(3)A, Z= 4; the structure was refined to R= 0.059 for 822 observed reflections. The compounds are not very stable in solution, but high-resolution cross-polarisation magic-angle spinning 15N NMR spectroscopy of the [Co(15NO)(asal)2] solids, and also of [Co(15NO)(ketox)2]( ketox =o-OC6H4CMeNOH), shows large isotropic shifts (ca. 730 ppm relative to nitromethane) characteristic of bent nitrosyls. Also characteristic are the nitrogen shift tensors, with one very large component (1100–1960 ppm) reflecting the low energy of the n(N)→π*(NO) circulation. The large ranges of the shielding anisotropy Δ(540–1150 ppm) and the asymmetry parameter η(1.25–2.40) reflect the sensitivity (because of the low excitation energies) of the tensor components to relatively small changes in the geometry of the MNO group, and its relation to the ligands in the basal plane.

Trans-chloroacetatonitrosylbis(triphenylphosphine)rhodium

The synthesis and structural characterization of the tetragonal pyramidal complex [Rh(O 2CCH 3)Cl(NO)(PPh 3) 2] are reported. This complex has a trans arrangement of basal ligands with a bent apical nitrosyl group inclined towards the acetato ligand.

Facile oxidation of a bound nitrosyl group to a nitrato ligand: Preparation and structures of cis-dibromonitrosylbis(dicyclohexyl-phosphine)rhodium, [RhBr 2(NO){P(C 6H 11) 2H} 2] and trans-dibromonitratobis (dicyclohexylphosphine)rhodium, [RhBr 2(NO 3){P(C 6H 11) 2H} 2

The synthesis and structure of the tetragonal pyramidal complex [RhBr 2(NO) {P(C 6H 11) 2H} 2] are reported. This complex has a cis-disposition of basal ligands with an apical nitrosyl group inclined towards the bromide ligands. [RhBr 2(NO){P(C 6H 11) 2H} 2] readily and irreversibly takes up atmospheric dioxygen to form the nitrato complex [RhBr 2(NO 3){P(C 6H 11) 2H} 2], whose structure is also described. In this complex the bromide and phosphine ligands are trans- and cis-disposed, respectively.

Pseudorotation in pentacoordinated phosphorus compounds. The influence of the conformational transmission effect on the barriers to pseudorotation in cyclic alkoxyphosphoranes

A variable-temp. 13C NMR study on a series of monocyclic oxyphosphoranes I (R1 = H, Me; R2 = Me, Ph; R3 = Me, OEt; R4 = Me, cyclopentylmethyl, etc.) is used to examine the influence of the conformational transmission effect on the barriers to pseudorotation in pentacoordinated P compds. The pseudorotation rates of monocyclic oxyphosphoranes exhibiting the conformational transmission effect is 2-4 times faster as compared to their counterparts in which the effect is absent. The conformational change in the basal ligands of the intermediate square planar structures, due to the conformational transmission effect, is responsible for the lowering of the activation barriers by 2-3 kJ mol-1.

Technetium(V)–nitrido complexes of dithiocarbazic acid derivatives. Reactivity of [TcN]2+core towards Schiff bases derived from S-methyl dithiocarbazate. Crystal structures of [S-methyl 3-(2-hydroxyphenylmethylene)dithiocarbazato]nitrido(triphenylphosphine)technetium(V) and bis(S-methyl 3-isopropylidenedithiocarbazato)nitridotechnetium(V)

New technetium(V)–nitrido complexes with bi- and tri-dentate Schiff bases, derived from the condensation of various aldehydes and acetone with the methyl ester of dithiocarbazic acid, NH2NHC(S)SCH3, were prepared by substitution or substitution–reduction reactions on the square-pyramidal complexes [TcVNCl2(PPh3)2] and [TcVINCl4]–. The final complexes all maintain the square-pyramidal geometry of the starting compounds with the TcN group in an apical position. The bidentate ligands give rise to mono- and di-substituted complexes, in which they are co-ordinated to the metal through the β-nitrogen atom and the thiol sulphur atom; in monosubstituted complexes, the remaining two positions in the plane of the square pyramid are occupied by triphenylphosphine (PPh3) and Cl– groups. The tridentate Schiff bases co-ordinate to the metal, in the basal plane, as doubly negatively charged ligands through the phenolic oxygen atom, the β-nitrogen atom, and the thiol sulphur atom, the fourth position being occupied by the phosphorus atom of a PPh3 group. The crystal structures of [TcNL1(PPh3)](1)[H2L1=S-methyl 3-(2-hydroxyphenylmethylene)dithiocarbazate] and [TcN(L12)2](2)(HL12=S-methyl 3-isopropylidenedithiocarbazate) have been determined. Relevant crystal data for (1) are: refined from 5 008 reflections with I 3σ(I) to a final R of 0.029, crystals are triclinic, space group P, with unit-cell dimensions a= 8.309(1), b= 12.294(1), c= 13.308(3)A, α= 96.22(1), β= 95.07(1), γ= 101.34(1), and Z= 2; for (2): refined from 1 756 reflections with I 3σ(I) to a final R of 0.023, crystals are monoclinic, space group I2/a, with unit-cell dimensions a= 16.707(3), b= 8.838(1), c= 12.514(2)A, β= 106.85(1)°, and Z= 4. In both complexes, the co-ordination around Tc is distorted square pyramidal with an apical multiply bonded nitrogen atom [TcN 1.611(3)A in (1) and 1.613(3)A in (2)] and the basal ligands bent away from the nitrido group.

Ligand field effects in the nuclear magnetic shielding of nitrogen-15 and cobalt-59 in bent nitrosyl complexes of cobalt(III)

A range of square-pyramidal complexes of cobalt(III) with a bent apical nitrosyl ligand has been prepared and examined by VN and VZCo NMR spectroscopy, in a study of nephelauxetic and spectrochemical effects at the metal and nitrogen nuclei in the bent Co-NO chromophore. The basal ligands in this comparison include dithiocarbamate, quadridentate Schiff base or porphine, and bis-chelating diamine or oximate, so as to give S4, S2N2, N4, OONN, or ONON coordination in the plane and a range of substituents in the chelate and phenylene rings. The shielding of both cobalt and nitrogen tends to decrease with decrease in the M(d) *(NO) back-bonding, as indicated by the MN and NO bond distances, the MNO angle and the NO stretching frequency. The shieldings decrease from sulfur to nitrogen to oxygen coligators and also with electron withdrawal by ring substituents (and vice versa), i.e. with decrease in the ligand field splitting and in the nephelauxetism of the coligands. These parallelisms of the cobalt and nitrogen shielding accord with the orbital theory that was developed to explain the bending of the MNO ligand and influences of the metal and coligands. Significant interdependence of spectrochemical and nephelauxetic effects at cobalt and nitrogen arises frommore » the degree of overlap and similarity in energies of the frontier orbitals for the paramagnetic circulation at nitrogen (n(N) * (NO)) and at cobalt (d-d). 43 references, 5 figures, 2 tables.« less

Ring contraction and double α-addition of cationic (C 5H 5)Mo(CO) 2 (Schiff Base Chelate) complexes: The crystal and molecular structures of (η- 5C 5H 5)Mo(CO)[η 2-NH(CH 3)C(NC 5H 4)C 6H 5] [η 2-OCH(C 6H 5

The structure of racemic [η 5-C 5H 5)]Mo(CO)[η 2-NH(CH 3)C(NC 5H 4)C 6H 5] [η 2-OCH 6H 5] was determined from single crystal X-ray diffraction data. The compound crystallizes in space group P 1 (z = 2) with a = 9.035(6), b = 12.314(6), c = 13.220(5) Å, α = 65.91(4), β = 71.40(4), γ = 72.42(4)°; cell volume 1246.97 Å 3. The Mo atom sits at the center of a Cp-capped trigonal pyramid with a terminal carbonyl group, an η 2-aminomethylene and an η 2-benzaldehyde moiety as basal ligands. Structural features indicate that both η 2-ligands act as π-acids, accepting Mo electron density through their hetero atoms.

Structure and magnetism in the chloro-bridged copper(II) complex Di-μ-chloro-bis[chlorobis(4-methyloxazole)copper(II)

The dimeric complex bis[dichlorobis(4-methyloxazole)copper(II)], [Cu(4-Meox) 2Cl 2] 2 or [CuC 4H 5NO) 2Cl 2] 2 has been synthesized and its structure has been determined from three-dimensional counter X-ray data. The complex crystallizes in the monoclinic space group P2 1/n with two dimeric formula units in a cell of dimensions a= 8.177(2), b = 12.866(5), c = 11.063(6) Å,β = 98.31(3)°. The structure has been refined by least-squares techniques to a value of the conventional R-factor (on F) of 0.033 based on 2071 independent data. The geometry at each copper center is severely distorted tetragonal pyramidal, the basal ligands being two trans nitrogen atoms from the 4-Meox ligands and two trans chloride ligands while the apical site is occupied by an inversion-related chloride ion. Thus, the dimeric entity is of the axial-equatorial type in which the inversion-related bridging chloride ligands are each axial to one copper and equatorial to the other. The CuCu separation in the dimer is 3.507(1) Å and the bridging CuClCu′ angle (φ) is 89.46(2)°. The magnetic susceptibility of the complex exhibits a maximum near 2 K, and the data have been fitted to the magnetization expression yielding g = 2.118 and a singlet-triplet separation of 2.6 cm −1 with the singlet as the ground state.

Nitrido-azido-Komplexe des Molybdäns(VI) Synthese und Kristallstruktur von MoN(N3)3(NC5H5) / Nitrido Azido Complexes of Molybdenum (VI) Synthesis and Crystal Structure of MoN(N3)3(NC5H5)

Abstract The explosive nitrido azido complexes MoN(N3)Cl2 · py and MoN(N3)3py are prepared by the reaction of MoCl4(py)2 with (CH3)3SiN3 in 1,2-dichloroethane. Both compounds hydrolyze quickly in moist air. After separation of the insoluble, black MoN(N3)Cl2 · py from the solution of MoN(N3)3py, the latter can be obtained in form of monoclinic, red crystals of the space group C2/c. Its structure consists of monomeric complexes, wherein the Mo atom has a square pyramidal coordination. The nitrido ligand occupies the apex and forms a strong multiple bond of 163.4 pm to the Mo atom. σ-Bonds of different strength exist between the Mo atom and the basal ligands: MO-N3 - 204.3 pm; Mo-py = 225.8 pm. The α-N atoms of the azido groups are sp2 hybridized, with their lone pair pointing away from the nitrido ligand. The pyridine ligand forms an angle of 61.6° to the basal plane of the coordination polyhedron.