Pseudo-tetrahedral Arrangement Research Articles

Magnetic Anisotropy and Relaxation of Pseudotetrahedral [N2 O2 ] Bis-Chelate Cobalt(II) Single-Ion Magnets Controlled by Dihedral Twist Through Solvomorphism.

The methanol solvomorph 1 ⋅ 2MeOH of the cobalt(II) complex [Co(LSal,2-Ph )2 ] (1) with the sterically demanding Schiff-base ligand 2-(([1,1'-biphenyl]-2-ylimino)methyl)phenol (HLSal,2-Ph ) shows the thus far largest dihedral twist distortion between the two chelate planes compared to an ideal pseudotetrahedral arrangement. The cobalt(II) ion in 1 ⋅ 2MeOH exhibits an easy-axis anisotropy leading to a spin-reversal barrier of 55.3 cm-1 , which corresponds to an increase of about 17 % induced by the larger dihedral twist compared to the solvent-free complex 1. The magnetic relaxation for 1 ⋅ 2MeOH is significantly slower compared to 1. An in-depth frequency-domain Fourier-transform (FD-FT) THz-EPR study not only allowed the direct measurement of the magnetic transition between the two lowest Kramers doublets for the cobalt(II) complexes, but also revealed the presence of spin-phonon coupling. Interestingly, a similar dihedral twist correlation is also observed for a second pair of cobalt(II)-based solvomorphs, which could be benchmarked by FD-FT THz-EPR.

Kink distortion of the pseudo-S4 axis in pseudotetrahedral [N2O2] bis-chelate cobalt(II) single-ion magnets leads to increased magnetic anisotropy.

Two new mononuclear cobalt(II) complexes with the general formula [Co(L1,2)2] (1 and 2) were synthesized using bidentate Schiff base ligands with NO donor set, namely, 2-(benzothiazole-2-ylimino)methyl-5-(diethylamino)phenol (HL1) and its methyl substituted derivative 2-(6-methylbenzothiazole-2-ylimino)methyl-5-(diethylamino)phenol (HL2). X-ray structure analysis reveals a distorted pseudotetrahedral coordination sphere at the cobalt(II) ion, that cannot be described by a simple twisting of the two ligand chelate planes with respect to each other, which would imply a rotation about the pseudo-S4 axis of the complex. Such a pseudo-rotation axis would approximately be colinear with the two vectors defined by the cobalt ion and the two centroids of the chelate ligands, where the angle κ between the two vectors would be 180° in an ideal pseudotetrahedral arrangement. For complexes 1 and 2, the observed distortion can be characterized by a significant bending at the cobalt ion with angles κ of 163.2° and 167.4°, respectively. Magnetic susceptibility and FD-FT THz-EPR measurements together with ab initio calculations reveal an easy-axis type of anisotropy for both complexes 1 and 2, with a spin-reversal barrier of 58.9 and 60.5 cm-1, respectively. For both compounds, frequency-dependent ac susceptibility measurements show an out-of-phase susceptibility under applied static fields of 40 and 100 mT, which can be analyzed in terms of Orbach and Raman processes within the observed temperature range.

Trans-Dichloridotetrakis(pyridine-κN)rhodium(III) chloride methanol tetrasolvate

In the solvated title salt, [RhCl2(C5H5N)4]Cl·4CH3OH, the RhIIIatom lies on a special position of 2.22 site symmetry. Consequently, the cationic complex has molecularD2symmetry with atransdisposition for two equivalent Cl−and four equivalent pyridine ligands. The Rh—Cl and Rh—N bond lengths are 2.3452 (7) and 2.064 (2) Å, respectively. The planes of the coordinating pyridine ligands are tilted synchronously, with a dihedral angle of 40.76 (9)° between the least-squares pyridine plane and the coordination plane defined by the RhIIIand four pyridine N atoms. The chloride counter-anion is located on a crystallographic \overline{4}.. site, and is surrounded by four methanol molecules to which it is bound in a pseudo-tetrahedral arrangement by O—H...Cl hydrogen bonds.

Photophysical Properties of Pt(II) Polypyridines with Five- versus Six-Membered Chelate Rings: Trade-Offs in Angle Strain.

This report describes the synthesis and characterization of a series of eight [Pt(NNN)X]+ complexes where the tridentate NNN ligand is (2,2'-bipyrid-6-yl)(pyrid-2-yl)sulfide (btp) or methyl(2,2'-bipyrid-6-yl)(pyrid-2-yl)amine (bmap) and X is OMe, Cl, phenylethynyl (C2Ph), or cyclohexylethynyl (C2Cy). The expectation was that inserting a heteroatom into the backbone of 2,2':6',2″-terpyridine (trpy) would expand the overall intraligand bite angle, introduce ILCT character into the excited states, and improve the photophysical properties. Crystal structures of [Pt(bmap)C2Ph]+ and [Pt(btp)Cl]+ reveal that atom insertion into the trpy backbone successfully expands the bite angle of the ligand by 8-10°. However, the impact on the photophysics is minimal. Indeed, of the eight systems investigated, only the [Pt(bmap)C2Ph]+ and [Pt(btp)C2Ph]+ complexes display appreciable emission in fluid solution, and they exhibit shorter emission lifetimes than [Pt(trpy)C2Ph]+. One reason is that the bond angle preferences of platinum and the inserted heteroatom induce the six-membered rings to deviate from planarity and adopt a boat-like conformation, impairing charge delocalization within the ligand. In addition, angle strain induces the donor atoms about platinum to assume a pseudotetrahedral arrangement, which offsets any benefit due to the increase in overall bite angle by promoting deactivation via d-d excited states. The results reveal that, in order to improve the luminescence of a [Pt(NNN)X]+ system, one must take care to avoid trading one kind of angle strain for another.

Synthesis and characterization of new tetraalkylaminophosphonium chlorides

GRAPHICAL ABSTRACT

Assembly of a coordination cage with four aromatic channel receptors on the outside.

Silver salts and triphosphine ligands with biphenyl substituents assemble to give coordination cages with four external aromatic channel receptors in a pseudo-tetrahedral arrangement.

P,P-Di-tert-butyl-N-trimethylsilyl-P-(trimethylsilylamino)phosphine imidato-kappa2N,N']bis(pyridine-kappaN)lithium(I).

In the title compound, [Li(C(14)H(36)N(2)PSi(2))(C(5)H(5)N)(2)], the bulky chelating monoanionic P,P-di-tert-butyl-N-trimethylsilyl-P-(trimethylsilylamino)phosphine imidate ligand and two pyridine ligands bind to Li in a pseudo-tetrahedral arrangement with twofold symmetry. The Li-N(phosphine) distance is 2.048 (5) A, while the Li.P distance is 2.520 (6) A.

Crystal structure of bis[dihydrobis(3,5-dimethy-1-pyrazolyl)borato]cadmium(II)

The structure of [H2B(3,5-Me2pz)2]2Cd shows the four nitrogen donor atoms form a pseudotetrahedral arrangement about the cadmium(II). The intraligand N—Cd—N angles are restricted to an average of 91.4° by the chelate rings forcing the interligand N—Cd—N bond angles to average 119.4°. The Cd—N bond distances average 2.21 A with a range of 0.04 A. The crystal is in the triclinic space group, P\(\overline 1\) with a = 7.6793(2) A, b = 8.5992(2) A, c = 25.0874(4) A, α = 91.0791(2)°, β = 97.9769(4)°, γ = 110.2344(6)°, and Z = 2.

Synthesis and characterization of oxo- and thiophosphorylcyclopentadienyl Ti(IV) thiolate complexes. Crystal structures of [( η5-C 5H 4P(S)Ph 2)( η5-C 5H 4SiMe 3)TiCl 2] and [( η5-C 5H 4P(S)Ph 2) 2Ti(SPh) 2]·C 4H 10O

New titanium (IV) complexes containing diphenyloxo- or diphenylthiophosphorylcyclopentadienyl ligands are obtained by reaction of diphenylphosphinocyclopentadienyl derivatives with the appropriate oxidizer (S 8 or H 2O 2). The crystal structures of [( η 5-C 5H 4P(S)Ph 2)( η 5-C 5H 4SiMe 3)TiCl 2] 3 and [( η 5-C 5H 4P(S)Ph 2) 2Ti(SPh) 2]·C 4H 10O 7 indicate in both cases, a pseudo-tetrahedral arrangement around the titanium atom. The two SPh ligands in compound 7 are orientated in opposite sites of the TiS 2 plane, which suggests an anti conformation for this molecule.

Hexafluoropentanedionatosilver(I) complexes stabilised by multidentate N-donor ligands: crystal structure of a charge-separated salt species soluble in supercritical carbon dioxide

A tetrahydrofuran suspension of silver(I) oxide reacted with Hhfpd (1,1,1,5,5,5-hexafluoropentane-2,4-dione) to give in situ ‘[Ag(hfpd)]’ after removal of the solvent in vacuo. Addition of equimolar ratios of multidentate amines to toluene solutions of the ‘[Ag(hfpd)]’ led to the isolation of several hexafluoropentanedionatosilver(I) complexes, [Ag(hfpd)(L–L)] [L–L = Me 2 NCH 2 CH 2 NHMe (trimen) 1, Me 2 N(CH 2 ) 2 NMe(CH 2 ) 2 NMe 2 (pmdien) 2 or Me 2 N(CH 2 ) 2 NMe(CH 2 ) 2 NMe(CH 2 ) 2 NMe 2 (hmten) 3]. Addition of only half a molar equivalent of hmten to a toluene solution of ‘[Ag(hfpd)]’ led to the synthesis of [Ag(hmten)][Ag(hfpd) 2 ] 4. The products have been characterised by a variety of methods including microanalysis, IR, 1 H and 13 C NMR spectroscopy and mass spectrometry and all complexes dissolve readily in supercritical carbon dioxide. Complexes 2 and 4 have been further characterised by X-ray crystallography. The structure of 2 contains a monomeric five-co-ordinate silver(I) cation in which the two chelating oxygens and two of the three amine nitrogens are in an almost planar arrangement. In comparison, the structure of 4 reveals a charge-separated salt; one of the silver atoms is exclusively co-ordinated to two hfpd ligands in a pseudo-tetrahedral arrangement, whilst the other is encapsulated by an hmten molecule.

The synthesis, fluctionality and structural characterization of ReMo 3H 4(CO) 123−

The reaction of ReH 9 2− with Mo(diglyme)(CO) 3 leads to the formation of the mixed metal cluster trianion, ReMo 3H 4(CO) 12 3−. This species has been characterized analytically, spectroscopically and through X-ray diffraction analysis. A pseudo-tetrahedral arrangement of M(CO) 3 fragments is adopted, such that each set of three carbonyl ligands eclipses the adjacent three tetrahedral edges, an apparent result of the location of the hydride ligands on the tetrahedral faces. Variable temperature NMR studies revealed a fluctional process for some of the carbonyl ligands, but not for the hydrides. Crystal data for [Me 4N] 3[ReMo 3H 4(CO) 12]·THF; space group P2 1/ n, a = 12.157(2), b = 21.480(4), c = 15.964(3) A ̊ , β = 98.26(1)°, Z = 4, R = 0.067 and R w = 0.076 .

Synthesis, characterization, and structures of New Titanocene Isoselenocyanato Complexes

AbstractThe complexes [Ti(η5‐C5H4R)2(NCSe)2] [R = Me (1), SiMe3 (2), or SiEt3 (3)] were prepared from the corresponding dichlorides with KSeCN in acetone; the oxygen‐bridged complex [Ti(η5‐C5H4Me)2(NCSe)]2O (4) was formed by air oxidation of (1). All complexes were characterized by elemental microanalysis and by IR, 1H NMR, and mass spectroscopies. An X‐ray analysis of (1) and (4) confirms the results of IR studies that these complexes contain N‐bonded selenocyanate ligands. In molecules (1) and (4) there is a pseudotetrahedral arrangement about each titanium. The NCSe chains are linear with normal NC and CSe bond distances. The dimer (4) contains an approximately linear TiOTi bridge (angle 173.4º) with a TiO bond distance of 1.838 Å. The structural results are compared with those in related compounds.

General Method for the Preparation of Alkyne-Functionalized Oligopyridine Building Blocks.

A large series of alkyne-substituted oligopyridines based on 2,2'-bipyridine, 1,10-phenanthroline, 2,2':6',2"-terpyridine, or 1,8-naphthyridine substrates has been synthesized and fully characterized. The palladium(0)-catalyzed coupling of bromo- or chloro-substituted derivatives with (trimethylsilyl)acetylene proceeds readily in diisopropylamine under ambient conditions giving good yields of the corresponding alkyne-substituted substrates oligoPy(C&tbd1;C)SiMe(3). The terminal monoynes oligoPyC&tbd1;CH become available upon treatment with K(2)CO(3) in methanol. Stepwise homologation of the acetylene function by Cadiot-Chodkiewicz coupling of oligoPyC&tbd1;CH with (bromoethynyl)triethylsilane (BrC&tbd1;CSiEt(3)) affords, in good yield, the silylated diynes oligoPy(C&tbd1;C)(2)SiEt(3), from which the terminal diynes oligoPy(C&tbd1;C)(2)H are formed by treatment with aqueous methanolic alkali. Reaction of oligoPy(C&tbd1;C)(2)H with BrC&tbd1;CSiEt(3) yields the silylated triynes oligoPy(C&tbd1;C)(3)SiEt(3) in modest yield. Further homologation is limited by nucleophilic attack of n-propylamine at the C-2 carbon of the alkyne chain, giving rise to a mixture of cis/cis (48%), cis/trans (33%), and trans/trans (19%) enaminediyne compounds 21a-c. Glaser oxidative self-coupling of the terminal diynes provides access to ditopic bipyridine or terpyridine ligands oligoPy(C&tbd1;C)(4)oligoPy comprising a tetrayne spacer. Quantitative formation of air-stable copper(I) complexes is described for the 6,6'-substituted ligands. A single crystal X-ray structure of complex 22a shows that the two ligands are interlocked around the copper(I) center in a pseudotetrahedral arrangement, similar to the structure deduced from NMR and FAB(+) data. The synthetic methods reported herein represent a valuable approach to the large-scale preparation of alkyne-functionalized oligopyridines.

Synthesis and X-ray structure of an organolanthanum complex [(Bu tCp) 3LaClLi(THF) 3

LaCl 3·2LiCl reacts with two equivalents of Bu t CpNa in THF to give the complex [(Bu t Cp) 3LaClLi(THF) 3]. The crystal structure was determined by X-ray diffraction at room temperature. Two units, (Bu t Cp) 3La and Li(THF) 3, are connected by a single chlorine bridge. The 10-coordinated lanthanum atom was bonded to three Bu t Cp groups and one chlorine atom to form a distorted pseudo-tetrahedral arrangement.

Synthesis and characterization of thiolate derivatives of bis(trimethylsilylcyclopentadienyl)titanium(IV). The crystal and molecular structure of [η 5-C 5H 4SiMe 3) 2Ti(SC 6F 5) 2

A series of new compounds [(η 5-C 5H 4SiMe 3) 2Ti(SR) 2] [R = C 6F 5 ( 1), C 6H 5 ( 2), CH 2C 6H 5 ( 3), or C 2H 5 ( 4)] and [(η 5-C 5H 4SiMe 3) 2TiCl(SC 6H 11)] ( 5) has been obtained. The 1H NMR spectra in the cyclopentadienyl region show different patterns depending on the nature of the thiol group. The 13C NMR spectra of the [(η) 5-C 5H 4SiMe 3) 2Ti(SR) 2] compounds show three resonances, whereas the spectrum of the complex [(η 5-C 5H 4SiMe 3) 2TiCl(SC 6H 11)] exhibits five. The crystal structure of compound 1 has been determined by X-ray diffraction. There is a pseudotetrahedral arrangement about the titanium atom. The molecule adopts an “ endo” ( anti) conformation of the cyclopentadienyl rings.

Organolanthanoids. XVII. The Synthesis of Bis(diphenylphosphinocyclopentadienyl)ytterbium(II) and Derived Heterobimetallic Complexes [Yb(thf)n(C5H4PPh2)2Z] [Z=Ni(CO)2, Mo(CO)4 or PtMe2; n = 1 or 2; thf = Tetrahydrofuran]. The X-Ray Crystal-Structure of [Yb(thf)2(C5H4PPh2)2Ni(CO)2

Reaction of diphenylphosphinocyclopentadiene with Yb (C6F5)2 or with ytterbium metal and Hg(C6F5)2 in tetrahydrofuran ( thf ) gives, after workup with toluene, the phosphinoytter-bocene , [Yb (C5H4PPh2)2( thf )]. Treatment with thf or with N,N,N′,N′- tetramethylethane-1,2-diamine ( tmen ) yields [ Yb (C5H4PPh2)2L2] (L = thf or L2 = tmen ). Redox trans- metallation between ytterbium metal and Tl (C5H4PPh2) in l,2-dimethoxyethane ( dme ) gives thallium metal and [ Yb (C5H4PPh2)2(dme )]. The ytterbium-transition metal hetero-bimetallics [ Yb ( thf ) (C2H4PPh2)2Z]. nPhMe [Z = Ni(CO)2, Mo(CO)4 or PtMe2, n = 2/3 or 1] have been prepared by reaction of [ Yb ( thf )(C5H4PPh2)2] with Ni(CO)2(PPh3)2, Mo(CO)4( nbd ) ( nbd = norbornadiene ) or PtMe2(cod) (cod = cycloocta-1,5-diene) in toluene. Treatment of the heterobimetallics with tetrahydrofuran [Z = PtMe2 or Mo(CO)4] or a preparation in thf /toluene [Z = Ni(CO)2] yields [ Yb ( thf )2(C5H4PPh2)2PtMe2]. thf, [ Yb ( thf )2(C2H4PPh2)2Mo(CO)4]. thf and [ Yb ( thf )2 (C5H4PPh2)2Ni(CO)2]. The X-ray crystal structure of the last compound (triclinic, space group Pi, a 14.514(5), b 13.565(1), c 10.866(5) 93.11(2), β 104.65(3), γ 97.25(2)�, U 2045 � 3 , Z 2, 5141 data refined to R 0.031) reveals eight-coordinate ytterbium with a pseudo-tetrahedral arrangement of two thf ligands and the cyclopentadienyl ring centroids of two ή5 -diphenylphosphinocyclopentadienide ligands . The latter are also bonded through phosphorus to the Ni(CO)2 group, resulting in tetrahedral stereochemistry for nickel. Infrared spectroscopy suggests the presence of ytterbium- isocarbonyl bonding in solid [ Yb ( thf )(C2H4PPh2)2Z] [Z = Ni(CO)2 or Mo(CO)4].

Some substitution reactions of ligands coordinated to the bis(cyclopentadienyl)titanium moiety, the X-ray crystal structure of Ti(η 5-C 5H 5) 2(OPh) 2 and an assessment of the anti-tumour activity of some cyclopentadienyl titanium compounds

The new complexes Ti(η 5-C 5H 5)Cl(OC 6H 4NH 2-3) 2, Ti(η 5-C 5H 5)Cl(O 2CPh) 2, Ti(η 5-C 5H 5) 2(O 2C(S)C 6H 4-1,2), Ti(η 5-C 5H 5) 2Cl(SC 6H 4OH-4), Ti(η 5-C 5H 5) 2(OC 6H 4NH 2-3) 2 and Ti(η 5-C 5H 5) 2Cl(OC 6H 4Z) (Z = NO 2-2, NO 2-3, NO 2-4, NH 2-3) have been synthesized. The free amine group in Ti(η 5-C 5H 5) 2Cl(OC 6H 4NH 2-3) reacts with RCl [R = MeCO, PhCO, (OCCO) 1/2, Br(CH 2) 3CO] in the presence of base to give Ti(η 5-C 5H 5) 2Cl(R) but, in the absence of base, PhCOCl reacts to give PhCONHC 6H 4OH-3 and Ti(η 5-C 5H 5) 2Cl 2. The X-ray crystal structure of Ti(η 5-C 5H 5) 2(OPh) 2 has been determined and reveals a pseudo-tetrahedral arrangement of the two η 5-cyclopentadienyl and two phenoxide ligands around titanium. The Ti—O(Ph) distances are 1.907(3) Å and O—Ti—O is 98.1(2)°. The anti-tumour activities of Ti(η 5-C 5H 5)Cl(OC 6H 4NH 2-3) 2, Ti(η 5-C 5H 5)Cl(O 2CPh) 2 and Ti(η 5-C 5H 5) 2(O 2C(S)C 6H 4-1,2) have been assessed in vitro using a panel of seven human tumour cell lines.

Structural, vibrational and solid-state NMR studies of the halogenocuprate(I) complexes [(PPh3)2CuI2]- and [(PPh3)CuI3Cu(PPh3)

Single-crystal X-ray diffraction, vibrational spectroscopy, and solid state NMR spectroscopy have been used to characterize two new types of ionic copper(1) complexes. The anion in [PPh3Me]+[(PPh3)2Cu12]c-o ntains two PPh, ligands coordinated to the copper atom of a Cu12 unit in a pseudotetrahedral arrangement, with Cu-P = 2.292 (2), 2.288 (2) A, Cu-I = 2.692 (I), 2.702 ( I ) A, P-Cu-P = 121.24 (9), and I-Cu-I = 108.62 (4)' (monoclinic, P21/c, a = 12.138 (5) A, b = 14.776 (6) A, c = 28.197 (14) A, 0 = 103.76 (4)O, Z = 4, R = 0.040 for 4490 'observed (I > 3 4 ) ) reflections). The far-IR spectrum shows a strong band at 118 cm-l that is assigned to the antisymmetric Cu-I stretching mode of the CUI, unit. The CPMAS ,*P NMR spectrum shows a strong singlet at 18.1 ppm (relative to 85% H3Po4) due to the cation and a weaker quartet centered at -16.7 ppm due to the coordinated PPh, in the anion, with line spacings due to Cu-P coupling of 1.08, 1.20, and 1.23 kHz. The anion in [PPh,Me]+[ (PPh,)CuI,Cu(PPh,)]- consists of an approximately D,h Cu213 unit with three iodine atoms bridging the two copper atoms and with one PPh, molecule completing a pseudotetrahedral arrangement around each copper atom. The crystallographically imposed symmetry of the ion is C,,, with the 3-fold axis passing through the P-Cu bonds. The core structural parameters are (5)O, and Cu-I-Cu = 54.88 (4)' (cubic, P2,3, a = 17.744 (IO) A, Z = 4, R = 0.036 for 1390 observed reflections). This is the first reported example of a binuclear copper(1) complex with three bridging ligands and is an example of an unusual bonding situation in which two coordination tetrahedra are linked by sharing a common face. This has the effect of producing an unusually short Cu-- -Cu separation of 2.50 A. The far-IR spectrum shows a band at 127 cm-' that is assigned to the doubly degenerate perpendicular Cu-I stretching mode of the CutIl unit. The CPMAS NMR spectrum shows a strong singlet at 20.1 ppm due to the cation and a broad quartet centered at -15.8 ppm due to the coordinated PPh, in the anion. The splitting pattern for this quartet does not conform to expectations for an AX spin system involving coupling between I = I / , and I = ,/, nuclei. The assignments of the ~(CU-I)I R bands in both complexes are supported by approximate normal-wordinate analyses, and the resulting Cu-I force constants are compared with the values obtained in similar analyses of related iodocopper(1) complexes.

Synthesis and characterization of copper(I)-pyrazole complexes. X-Ray crystal structure of [Cu(pzH) 2Cl] 2 and NMR investigation of the fluxional behaviour of [Cu(pzH) 2(CO)Cl

The product of the reduction of [Cu(pzH) 4Cl 2] (pzH = pyrazole, C 3H 4N 2) with Cu powder has been shown by single crystal X-ray analysis to the dimeric species [Cu(pzH) 2Cl] 2. The crystals are monoclinic, space group P2 1/ n, with a 6.327(1), b 9.610(1), c 15.066(1) Å, β 96.91(1), and Z = 2. The refinements performed by full-matrix least-squares methods, for 1417 independent significant reflexions, gave a final R value of 0.030. Each dimeric unit, located on a crystallographic inversion centre, contains two Cu atoms (Cu…Cu′ 3.401(1) Å), each surrounded by two bridging C1 atoms and two pzH ligands, in a pseudo-tetrahedral arrangement. The reaction of carbon monoxide with [Cu(pzH) 2Cl] 2 gave the new species [Cu(pzH) 2(CO)Cl], which was characterized by IR and NMR spectroscopy. Fluxional behaviour of the pyrazole ligands, equalizing their 3 and 5 positions, was revealed by both 1H and 13C NMR spectra. Variable temperature 13C NMR experiments in different conditions (solvent or concentrations) lead to different E a values, indicating that the exchange process is not intramolecular, and is favoured in donor solvents, at temperatures above 250 K. In concentrated solutions in CD 2Cl 2 a double-slope Arrhenius plot was obtained, suggesting the occurrence of two different processes, whose natures are discussed.

Organolanthanides—XVI. Preparation and structure of bis(η 5-cyclopentadienyl)bis(triphenylphosphine oxide)ytterbium(II)—the first X-ray crystal structure of a phosphine oxideorganolanthanide(II) complex

Reaction of Cp 2Yb(DME) (Cp = cyclopentadienyl; DME = 1,2-dimethoxyethane) with triphenylphosphine oxide yields Cp 2Yb(OPPh 3) 2. The X-ray crystal structure shows eight-coordinate ytterbium with a pseudo-tetrahedral arrangement of two oxygen donor atoms and the centroids of two eclipsed η 5-cyclopentadienyl rings. Surprisingly short Yb—O distances (2.30(2); 2.33(2) Å) and the absence of major inter-ligand contacts indicate an uncrowded arrangement.