Pseudo Trigonal Planar Research Articles

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 80[1] Gelingt die Identifizierung der Streck‐ und Kippschwingungen des pseudo‐trigonal‐planaren La(η5‐C5H5)3‐Fragments in den Schwingungsspektren von [La(η5‐C5H5)3­(NCCH3)2] ohne die Hilfe von Modellrechnungen auf der Basis der Dichtefunktionaltheorie?

AbstractIn order to reliably assign the four previously observed coincidences in the range 210–260 cm–1 in the low temperature vibrational spectra of [LaCp3(NCCH3)2] (Cp = η5‐C5H5–) (1) to the expected stretching and tilting modes of the pseudo trigonal planar LaCp3 moiety, additionally the “polarized“ Raman spectra of an oriented single crystal of 1 were recorded. By this means, the signal of the tilting vibration of the irreducible representation (irrep) E′' could be separated from the remaining skeletal vibrations consisting of the irreps A1′, E' and E′. The bands of the two latter could be identified by applying the less common method of the “symmetry allowed vibronic couplings of electronic zero point transitions“ to the vibronic sidebands of the purely electronic transition 1Γ1(3H4)→8Γ1(3P0) of [LaCp3(NCCH3)2]:Pr3+ (2). Hence, the remaining band corresponds to the symmetric stretching of A1′ symmetry.

Electronic structures of organometallic complexes of f elements LXXIX: Truncated crystal field splitting patterns of monomeric pseudo trigonal planar Yb(η5-C5H4R)3 (R = Me, Et, tBu, SiMe3) complexes and polymeric [(η5-C5H5)2Yb(μ-η5:η1-C5H5)] as well as selected mono adducts

The absorption spectra of pseudo (ψ) trigonal planar tris(methylcyclopentadienyl)ytterbium(III) (Yb(C5H4Me)3) have been recorded at room temperature and circa 77 K. The vibronic transitions were separated from the expected three purely electronic ones by correlating the transition energies with observed and assigned vibrational transition frequencies in the infrared spectrum. With this knowledge, the zero-phonon transitions in the absorption spectra of Yb(C5H4R)3 (R = Et, tBu, SiMe3) and [(η5-C5H5)2Yb(μ-η5:η1-C5H5)] (YbCp3), the latter being known since 1967, could be separated from phonon-assisted ones. The first low temperature luminescence measurements of an organometallic YbIII compound were performed by means of powdered YbCp3•THF and YbCp3•CNC6H11, respectively, and in both cases purely electronic and vibronic transitions were separated. The wavefunctions resulting from a fit of the truncated crystal field splitting pattern of YbCp3•THF allowed interpretation of the spectroscopic splitting factors g||/g⊥ and the temperature dependence of the paramagnetic susceptibility of this compound as well as the susceptibility anisotropy χ|| − χ⊥ of YbCp3•B (B = CNnBu, γ-picoline) and Yb(C5H4Me)3•B (B = CNtBu).

Self-Assembly of Thiacalix[4]arene-Supported Nickel(II)/Cobalt(II) Complexes Sustained by in Situ Generated 5-Methyltetrazolate Ligand

Solvothermal reactions of thiacalix[4]arene, NaN3, and acetonitrile in the presence of nickel(II)/cobalt(II) salts yielded four discrete complexes sustained by the in situ generated 5-methyltetrazolate ligand, [NiII12(PTC4A)3(μ6-CO3)2(μ-Mtta)2(μ-Mtta)4 (μ4-Mtta)2(Py)4]·7DMF·2Py·dma (1), [CoII12(PTC4A)3(HCOO)3(μ6-CO3)2 (μ-Mtta)(μ-Mtta)2(μ4-Mtta)2(Py)4]·5DMF·dma (2), [CoII12(BTC4A)3(HCOO)2 (μ6-CO3)2(μ-Mtta)4(μ4-Mtta)2(dma)2(Pz)2]·2DMF·3dma (3), and [CoII16(BTC4A)4(μ4-Cl)4 (HCOO)2(μ-Mtta)6(μ-Mtta)8]·10DMF·6CH3CN·4Hdma (4) (H4PTC4A = p-phenylthiacalix[4]arene; H4BTC4A = p-tert-butylthiacalix[4]arene; HMtta = 5-methyl tetrazolate). Crystal structural analyses revealed that complexes 1–3 are stacked by pseudotrigonal planar entities, which consist of three metalII4-thiacalix[4]arene subunits including two shuttlecock-like and one cylinder-like ones. These subunits are connected in an up-to-down-to-up fashion through six different 5-methyl tetrazolate anions. Both the in situ generated 5-methyl tetrazolate anion and carbonato anion play an important role in constructing these high-nuclearity clusters. When the corresponding chloride salt was used as precursors in the synthesis, complex 4 was obtained, which is stacked by wheel-like entities possessing four shuttlecock-like building blocks linked by eight in situ generated 5-methyl tetrazolate ligands in an up-to-up fashion. The differences in the structures of complexes 3 and 4 indicate that the geometry and size of the corresponding anions together with their coordinating properties are essential in determining the final structures. The magnetic properties of complexes 1–4 were examined, indicating strong antiferromagnetic interactions between the nickel(II)/cobalt(II) ions in the temperature range of 50–300 K.

Electronic structures of organometallic complexes of f elements LXXIII: Parametric analysis of the crystal field splitting pattern of tris(η 5-pentamethylcyclopentadienyl)cerium(III)

By comparing the far infrared (polyethylene pellets, room temperature) and mid-infrared spectra (KBr pellets, room temperature and ca. 90 K) of pseudo trigonal planar Ce(η 5-C 5Me 5) 3 ( 1) with the corresponding ones of La(η 5-C 5Me 5) 3 ( 2) and considering the low temperature paramagnetic susceptibility data of 1 the crystal field (CF) splitting pattern of 1 could be derived. The free parameters of a phenomenological Hamiltonian were fitted to this pattern achieving an r.m.s. deviation of 8.9 cm −1 for seven assignments. The fact that the difference of the experimental energies of the barycenters of CF levels of the multiplets 2F 7/2 and 2F 5/2 is larger than in the gaseous free Ce 3+ ion (experimental “anti”-relativistic nephelauxetic effect) could be explained by coupling effects of these multiplets via the CF, resulting in a lower spin–orbit coupling parameter than in the case of the free gaseous Ce 3+ ion. The experimental CF splitting pattern of 1 is compared to the results of a relativistic DV-Xα calculation on the pseudo trigonal planar model compound Ce(η 5-C 5H 5) 3. In addition, the prediction of the energies of f → d and charge transfer transitions of Ce(η 5-C 5H 5) 3 are compared to the absorption and luminescence spectra of complex 1.

Parametric Analysis of the Crystal Field Splitting Pattern of Sm(η5-C5Me5)3Derived on the Basis of Absorption Spectra of Pellets or Solutions and Electronic Raman Spectra of Oriented Single Crystals

By comparing the absorption spectrum of pseudo trigonal planar Sm(eta(5)-C(5)Me(5))(3) (1) (KBr pellet, methylcyclohexane solution) with the previously assigned one of Sm(eta(5)-C(5)Me(4)H)(3) (2) a truncated experimental crystal field (CF) splitting pattern of the former compound could be derived in the NIR range. Because of its dark brown color, fluorescence is not observed from complex 1, and thus the CF splitting pattern in the low energy range could not be determined on the basis of luminescence measurements. However, comparing the FIR and MIR spectra (pellets) as well as the Raman spectra of oriented single crystals of 1 with those of La(eta(5)-C(5)Me(5))(3) (3) at least two additional CF levels could be detected. The free parameters of a phenomenological Hamiltonian were fitted to the thus extended CF splitting pattern of 1, leading to a reduced rms deviation of 15.0 cm(-1) for 21 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Sm(3+) central ion was estimated, and seems to be the third largest one ever encountered in Sm(III) chemistry. The obtained Slater parameter F(2) and the spin-orbit coupling parameter zeta(4f) allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively, of Sm(III) compounds. With its low F(2) value, complex 1 is the most covalent Sm(III) compound (considering only f electrons) found to date. The experimentally based non-relativistic molecular orbital scheme (in the f range) of complex 1 was set up and compared with the results of a previous Xalpha-SW calculation on the pseudo trigonal planar model compound Sm(eta(5)-C(5)H(5))(3). In the frame of the search for f-f and electronic Raman transitions, the vibrational spectra (FIR/MIR of pellets, Raman spectra of oriented single crystals) of compound 1 were recorded too, and partly assigned on the basis of the observed coincidences and polarizations.

Synthesis and Structural Characterization of [Ag(H-dpa) (η2-styrene)]BF4: Comparing Silver and Copper for Olefin Binding

The molecular structure of the complex bis-(2-pyridyl)amine(η2-styrene)silver(I) tetrafluoroborate has been determined. The geometry about the Ag+ ion is pseudo-trigonal planar, with coordination sites occupied by the two pyridyl nitrogen atoms and the midpoint of the alkene double bond. Crystal packing of the molecule is influenced by hydrogen bonding of the amine with the tetrafluoroborate anion, in addition to intermolecular Ag+···aromatic contacts. 1H NMR confirms crystallographic data that suggest weak metal to olefin π-backbonding. Crystal data: space group P21/n, a = 12.764(3), b = 10.590(2), c = 13.624(3) A, β = 91.17(3)°, V = 1841.3(7) A3, Z = 4, R = 0.0453, wR 2 = 0.1098. The geometry about the Ag+ ion in [Ag(H-dpa)(η2-styrene)]BF4 is pseudo-trigonal planar, with coordination sites occupied by the two pyridyl nitrogen atoms and the midpoint of the alkene double bond. Crystal packing of the molecule is influenced by hydrogen bonding of the amine with the tetrafluoroborate anion, in addition to intermolecular Ag+···aromatic contacts.

Synthesis and Reactivity of [(silox)2MoNR]2Hg (R = tBu, tAmyl; silox = OSitBu3): Unusual Thermal Stability and Ready Nucleophilic Cleavage Rationalized by Electronic Factors

Treatment of (DME)Cl2Mo(=NR)2 (R=tBu, (1-tBu), tAmyl (1-tAmyl)) with 2 equiv of tBu3SiOH (siloxH) and 1 equiv of HCl produced (silox)2Cl2Mo=NR (R=tBu, (3-tBu), tAmyl (3-tAmyl)); subsequent reduction by Na/Hg afforded the Mo(V) chloride, (silox)2ClMo=NtBu (4-tBu), and the Mo(IV) mercury derivatives, [(silox)2Mo=NR]2Hg (R=tBu ((5-tBu)2Hg), tAmyl ((5-tAmyl)2Hg)). Reductions of 3-tBu and 3-tAmyl in the presence of L (L=PMe3, pyridine, 4-picoline) led to the isolation of adducts (silox)2(Me3P)Mo=NR (R=tBu (6-tBu), tAmyl (6-tAmyl)) and (silox)2L2Mo=NtBu (L=py (7-py), 4-pic (7-4-pic)). Single-crystal X-ray structural investigations of pseudo-tetrahedral 4-tBu, Hg-capped, pseudo-trigonal planar (5-tBu)2Hg, pseudo-tetrahedral 6-tBu, and trigonal bipyramidal 7-4-pic reveal that all possess a closed O-Mo-O angle when compared to the N=Mo-O angles. A molecular orbital rationale and supporting calculations suggest that this is a manifestation of the greater pi-donating ability of the imido relative to that of the siloxides. While the D(Mo-Hg) of [(HO)2Mo=NH]2Hg ((5')2Hg) was calculated to be 22.4 kcal/mol, (5-R)2Hg (R=tBu, tAmyl) are remarkably stable; (5-tBu)2Hg degraded in a first-order fashion with DeltaG=31.9(1) kcal/mol. In the presence of strong (L=PMe, pyridine, S8) or weak (L=2-butyne, ethylene, N2O, 1,4,7,10-tetrathiacyclododecane, 1,4,7,10,13,16-hexathiacyclooctadecane) nucleophiles, an enhanced rate of Mo-Hg bond cleavage was noted, with some of the former group generating adducts in <5 min; the products were 6-tBu, 7-py, (silox)2(S)Mo=NtBu (10-tBu), (silox)2Mo=NtBu(C2Me2) (8-tBu), (silox)2(C2H4)Mo=NtBu (11-tBu), (silox)2(O)Mo=NtBu (9-tBu), and a mixture of 10-tBu and 11-tBu, respectively. Some of these were independently prepared via substitution of 6-tBu. According to calculations and a molecular orbital rationale, dissociation of the Mo-Hg bond in (5-R)2Hg (R=tBu, tAmyl) is orbitally forbidden, and the addition of a nucleophile to the terminus of the Mo-Hg-Mo linkage mitigates the symmetry requirements. The mechanism of thermal degradation was studied with mixed success. NMR spectroscopy revealed imido exchange between (5-tBu)2Hg and (5-tAmyl)2Hg during an initial induction period and a subsequent rapid exchange period that implicated free 5-R (R=tBu, tAmyl). Further crossover studies revealed siloxide exchange as an additional complication.

Electronic Structures of Organometallic Complexes of f Elements. 62 Parametric Analysis of the Crystal Field Splitting Pattern of Pseudo Trigonal Planar Nd(η5‐C5Me4H)3

Abstract The absorption spectrum of pseudo (Ψ) trigonal planar Nd(η5‐C5Me4H)3 (1) has been measured at room and low temperatures. From the spectra obtained, a truncated crystal field (CF) splitting pattern could be derived, and simulated by fitting the parameters of a phenomenological Hamiltonian. For 38 assignments, a reduced r.m.s. deviation of 30.7 cm−1 was achieved. On the basis of the CF parameters used, the global CF strength experienced by the Nd3+ central ion is estimated. The obtained Slater parameter F2 and the spin‐orbit coupling parameter ξ4f allow the insertion of compound 1 into truncated nephelauxetic and relativistic nephelauxetic series. Besides, the experimentally based non‐relativistic molecular orbital scheme (in the f range) of complex 1 is set up and compared with the results of an SW‐Xα calculation on the fictive trigonal planar model complex NdCp3.

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 63 Parametrische Analyse des Kristallfeld‐Aufspaltungsmusters von pseudo trigonal‐planarem Er(η5‐C5H4tBu)3

AbstractElectronic Structures of Organometallic Compounds of f Elements. 63 Parametric Analysis of the Crystal Field Splitting Pattern of Pseudo Trigonal Planar Er(η5‐C5H4tBu)3The absorption spectrum of presumably pseudo trigonal planar Er(η5‐C5H4tBu)3 (1) has been measured at room and low temperatures. From the spectra obtained, a truncated crystal field (CF) splitting pattern could be derived, and simulated by fitting the parameters of a phenomenological Hamiltonian. For 34 assignments, a reduced r.m.s. deviation of 24.8 cm−1 was achieved. On the basis of the CF parameters used, the global CF strength experienced by the Er3+ central ion is estimated, and the experimentally based non‐relativistic molecular orbital scheme (in the f range) is set up and compared with the result of an SW‐Xα calculation on the fictive trigonal planar model complex Dy(η5‐C5H5)3.

Copper Complexes with the Ligand [Cp2MoH2

The reaction of CuCl with [CP2MoH2] yields the complex [Cu(Cp2MoH2)2Cl]. An X-ray structure analysis shows that the coordination of the copper(I) ion by two [CP2MoH2] ligands and the chloride ion is pseudo-trigonal planar. The hydride ligands were located by using difference Fourier methods. A manifold of reactions took place when an aqueous solution of CUSO4 was treated with a solution of [Cp2MoH2] in dichloromethane in a 1:2 molar ratio. The X-ray structure analysis established a polymeric structure of the complex [Cu(Cp2MoH2)2Cu(Cp2MoH2)SO4]n with two different copper centers.

The electronic structure of organometallic complexes of the f elements: XL. Crystal field strength of η5-cyclopentadienyl ligand estimated on the basis of the crystal field parameters of (Me3SiC5H4)3PrIII

The absorption, magnetic circular dichroism and luminescence spectra of monomeric pseudo trigonal planar (η5-Me3SiC5H4)3PrIII (Cp′Pr) have been measured at room and at low temperatures. Applying the selection rules for molecular D3h symmetry, a truncated crystal field (CF) splitting pattern (which comprises essentially excited Γ4 and Γ6 states) could be derived. The parameters of an empirical Hamiltonian were fitted to the energies of 24 levels to give an r.m.s. deviation of 21.4 cm−1. On the basis of the CF parameters obtained, the CF strength of one Cp ligand was estimated.

Molybdenum–copper–sulphur-containing cage system and its bioinorganic relevance. Preparation and X-ray crystal structure of (Cu3MoS3Cl)(PPh3)3S with an interesting stereochemistry of non-equivalent Cu atoms

The preparation and structural characterization of (Cu3MoS3Cl)(PPh3)3S, which has a molybdenum–copper–sulphur-containing pseudo-cubane type cage structure and which is a model for Cu–Mo–S interactions in biochemical processes, is reported; the stereochemistry of the three non-equivalent Cu atoms is unusual with the co-ordination of copper ranging from strongly distorted tetrahedral to pseudo-trigonal planar.