Single-crystal X-ray Structural Data Research Articles

A protonated imine-based water-soluble cadmium complex with N, O donor chelating agent: Synthesis, structure, fluorescence efficiency and catecholase activity

A mononuclear air-stable and water soluble six coordinated cadmium (II) complex [Cd(HL)6](ClO4)2 (1) with bi-dentate phenol based ligand [HL = 2-(benzylimino)methyl)phenol] have been synthesized. The complex has been characterized by various spectroscopic techniques. The solid-state structure, by single crystal X-ray diffraction, revealed that Cd(II) complex crystallizes in trigonal space group R-3. Interestingly, single crystal X-ray structure data show that the Schiff base in the complex is present in a zwitterionic form and coordinated through the phenolic oxygen atom only, providing the first example of more than four monodendate Schiff base in zwitterionic form to be coordinated with the central metal ion. Cyclic voltamogram of the cadmium (II) complex (1) exhibits a quasi-reversible oxidation peak in the positive potential region. The redox process occurs due to the generation of phenoxyl radical from the pheolate group of the attached ligand with the central metal ion. Luminescence spectra show a strong emission band around 500 nm. Additionally, the mononuclear cadmium complex (1) shows catechol oxidase activity in methanol under aerobic conditions. The turnover number of the process is 2.766 × 103 h–1. The oxidation process occurs via formation of ligand oriented phenoxyl radical species.

Structural modifications to platinum(II) pincer complexes resulting in changes in their vapochromic and solvatochromic properties.

There is a need to develop rapidly responsive chemical sensors for the detection of low concentrations of volatile organic solvents (VOCs). Platinum pincer complexes have shown promise as sensors because of their colours and vapochromic and solvatochromic properties, that may be related to the non-covalent interactions between the pincer complexes and the guest VOCs. Here we report an investigation into a series of Pt(II) complexes based on the 1,3-di(pyridine)benzene tridentate (N⁁C⁁N) skeleton with the formula [Pt(N⁁C(R)⁁N)(CN)] (R = C(O)Me 2, C(O)OEt 3, C(O)OPh 4) with the fourth coordination site occupied by a cyanide ligand. Solid-state samples of the complexes have been tested with a range of volatiles including methanol, ethanol, acetone, dichloromethane and water, and while 2 displays thermochromism, 3 and 4 display rapidly reversible vapochromism and solvatochromism. These results are correlated with X-ray powder and single crystal X-ray structural data including an assessment of the crystal packing and the void space in the crystalline space. The cyanide ligand and the R substituents are involved in hydrogen bonding that creates the voids within the structures and interact with the solvent molecules that influence the Pt⋯Pt separation in the crystalline state.

A Single Small-Scale Plutonium Redox Reaction System Yields Three Crystallographically-Characterizable Organoplutonium Complexes.

An approach to obtaining substantial amounts of data from a hazardous starting material that can only be obtained and handled in small quantities is demonstrated by the investigation of a single small-scale reaction of cyclooctatetraene, C8H8, with a solution obtained from the reduction of Cp'3Pu (Cp' = C5H4SiMe3) with potassium graphite. This one reaction coupled with oxidation of a product has provided single-crystal X-ray structural data on three organoplutonium compounds as well as information on redox chemistry thereby demonstrating an efficient route to new reactivity and structural information on this highly radioactive element. The crystal structures were obtained from the reduction of C8H8 by a putative Pu(II) complex, (Cp'3PuII)1-, generated in situ, to form the Pu(III) cyclooctatetraenide complex, [K(crypt)][(C8H8)2PuIII], 1-Pu, and the tetra(cyclopentadienyl) Pu(III) complex, [K(crypt)][Cp'4PuIII], 2-Pu. Oxidation of the sample of 1-Pu with Ag(I) afforded a third organoplutonium complex that has been structurally characterized for the first time, (C8H8)2PuIV, 3-Pu. Complexes 1-Pu and 3-Pu contain Pu sandwiched between parallel (C8H8)2- rings. The (Cp'4PuIII)- anion in 2-Pu features three η5-Cp' rings and one η1-Cp' ring, which is a rare example of a formal Pu-C η1-bond. In addition, this study addresses the challenge of small-scale synthesis imparted by radiological and material availability of transuranium isotopes, in particular that of pure metal samples. A route to an anhydrous Pu(III) starting material from the more readily available PuIVO2 was developed to facilitate reproducible syntheses and allow complete spectroscopic analysis of 1-Pu and 2-Pu. PuIVO2 was converted to PuIIIBr3(DME)2 (DME = CH3OCH2CH2OCH3) and subsequently PuIIIBr3(THF)x, which was used to independently synthesize 1-Pu, 2-Pu, and 3-Pu.

Synergistic effect of mixed ligands on the anisotropy axis of two dinuclear dysprosium complexes.

We present the syntheses, crystal structures, magnetic properties and theoretical calculations performed on two dinuclear dysprosium complexes with formulas Dy2(L1)2(L2)2(CH3CH2OH)(CH3OH) (1) and Dy2(L1)2(L3)2(CH3OH)2·1.5CH3OH (2). Single-crystal X-ray structural data analyses showed that both complexes contain two nonequivalent dysprosium ions bridged by two phenolate oxygen atoms. In both complexes, each dysprosium site adopts a N2O6 coordination constitution and triangular dodecahedron (D2d) configuration geometry with different distortion degree. Both complexes display single-molecule magnet behavior manifested by frequency-dependent out-of-phase alternating current susceptibility signal peaks under a zero-applied dc field. The effective energy barrier of the magnetization reversal and relaxation time values are 61 K, 7.1 × 10-6 s (1) and 51 K, 1.9 × 10-6 s (2), respectively. Theoretical calculations revealed a drastic discrepancy between the orientations of the anisotropy axis of the Dy2 ion observed in these two dinuclear complexes, resulting from the different spatial arrangements of the mixed ligands in the core structure.

The molecular structure and vibrational spectra of 4-bromo-2-(((5-methylpyridin-2-yl)imino)methyl)phenol by density functional method

Density Functional Theory methods (BLYP, B3PW91, and B3LYP) with the 6-311G (d,p) basis set were used to calculate the molecular structure, vibrational frequencies and infrared intensities of the title compound. A comparison between the calculated geometric parameters and the corresponding single-crystal X-ray structure data of the title compound was performed. It was observed that the harmonic vibrations, calculated for this compound by the B3LYP/6-311G (d,p) method, are in good agreement with the experimental IR and Raman spectral data (RMSmol = 9.63). Also, the theoretical vibrational spectra of the title compound were evaluated by PEDs, using the SQM 2.0 program. Among the investigated methods, a general better performance of B3LYP was calculated by the aid of PAVF 1.0 program.

Morphology-Independent Stable White-Light Emission from Self-Assembled Two-Dimensional Perovskites Driven by Strong Exciton–Phonon Coupling to the Organic Framework

Hybrid two-dimensional (2D) lead halide perovskites have been employed in optoelectronic applications, including white-light emission for light-emitting diodes (LEDs). However, until now, there have been limited reports about white-light-emitting lead halide perovskites with experimental insights into the mechanism of the broadband emission. Here, we present white-light emission from a 2D hybrid lead chloride perovskite, using the widely known phenethylammonium cation. The single-crystal X-ray structural data, time-resolved photophysical measurements, and density functional theory calculations are consistent with broadband emission arising from strong exciton–phonon coupling with the organic lattice, which is independent of surface defects. The phenethylammonium lead chloride material exhibits a remarkably high color rendering index of 84, a CIE coordinate of (0.37,0.42), a CCT of 4426, and photostability, making it ideal for natural white LED applications.

Synthesis and X-ray Crystal Structure of 2 and 4-Trifluoromethyl Substituted Phenyl Semicarbazone and Thiosemicarbazone

NMR and single crystal X-ray structure data for four structurally similar semicarbazones and thiosemicarbazones were compared. In solution, proton NMR showed considerable variation in their chemical shift values especially for the NH2 protons. In the case of the semicarbazones this peak appeared as a broad singlet with an integration ratio of two while for the thiosemicarbazones the amino group showed two distinct singlets with marked chemical shift differences. This is attributed to the differences in the canonical forms of the thiosemicarbazone amino group and the semicarbazone analogue. Additionally, we provide evidence that the 2-trifluoromethyl phenyl substituted semicarbazone (2) formed an intermolecular hydrogen bond with one of the hydrogens of the NH2 group while this was totally absent in the thiosemicarbazone. We explain this by the restricted rotation of the CN bond in the thiosemicarbazone due to its double bond character compared to the less restricted rotation in semicarbazone compound. NMR and single crystal X-ray structure data for four structurally similar semicarbazones and thiosemicarbazones were compared for their hydrogen bonding characteristics.

Structure-Kinetics Correlations in Isostructural Crystals of α-(ortho-Tolyl)-acetophenones: Pinning Down Electronic Effects Using Laser-Flash Photolysis in the Solid State.

Aqueous suspensions of nanocrystals in the 200-500 nm size range of isostructural α-(ortho-tolyl)-acetophenone (1a) and α-(ortho-tolyl)-para-methylacetophenone (1b) displayed good absorption characteristics for flash photolysis experiments in a flow system, with transient spectra and decay kinetics with a quality that is similar to that recorded in solution. In contrast to solution measurements, reactions in the solid state were characterized by a rate limiting hydrogen transfer reaction from the triplet excited state and a very short-lived biradical intermediate, which does not accumulate. Notably, the rate for δ-hydrogen atom transfer of 1a (2.7 × 10(7) s(-1)) in the crystalline phase is 18-fold larger than that of 1b (1.5 × 10(6) s(-1)). With nearly identical molecular and crystal structures, this decrease in the rate of δ-hydrogen abstraction can be assigned unambiguously to an electronic effect by the para-methyl group in 1b, which increases the contribution of the (3)π,π* configuration relative to the reactive (3)n,π* configuration in the lowest triplet excited state. These results highlight the potential of relating single crystal X-ray structural data with absolute kinetics from laser flash photolysis.

Careful Navigation of the Crystallographic Landscape of MK-8970: A Racemic Acetal Carbonate Prodrug of Raltegravir

MK-8970 is an acetal carbonate prodrug of raltegravir (Isentress). This work presents the Merck team’s investigations into the polymorphism of MK-8970, the thermodynamic relationship between the discovered crystalline forms, and implementation of that knowledge toward solving key processing challenges. MK-8970 was found to exist in two enantiotropic polymorphs, with a crossover temperature of approximately 117 °C, as determined from solubility data. Form 2 of MK-8970, the stable form at ambient temperature, was confirmed to be a true racemic crystal form and not a conglomerate on the basis of single-crystal X-ray structure data. In preparation for scale-up of MK-8970, form control was established by mapping out solubility curves for the relevant crystalline forms in ethyl acetate as a function of temperature. Lastly an investigation of the relative solubilities of MK-8970 and a troublesome imidate impurity identified improved solvent systems for maximizing rejection of this impurity while avoiding signifi...

The promoted Tishchenko reaction and catalytic intermediate by 2-aminopyrrolyl dilithium compounds

The dimerization of aldehydes to the analogous carboxylic esters (Tischenko reaction) has been achieved in impressive yields using the dilithium compounds containing bidentate di-anionic pyrrolyl ligands as initiators. The initiated intermediate {[2-(tBuNCH)C4H3NLi][PhCH2OLi(TMEDA)]}2 was isolated and characterized by satisfactory C, H and N microanalysis, 1H, 13C{1H} and 7Li NMR spectra in pyridine-d5 at ambient temperature, and single crystal X-ray structural data. The processes involve a redox reaction of 2-aminopyrrolyl dilithium compound with aldehyde.

Structure and luminescent investigation of the Ln(III)–β-diketonate complexes containing tertiary amides

The synthesis and photoluminescent properties of Ln(III)–thenoyltrifluoroacetonate and dibenzoylmethanate complexes (Ln=Eu(III) and Gd(III) ions) containing tertiary amides such as dimethylacetamide (DMA), dimethylformamide (DMF), and dimethylbenzamide (DMB) as neutral ligands are reported. The Ln complexes were characterized by elemental analysis, complexometric titration with EDTA, and infrared spectroscopy. Single-crystal X-ray structure data of the [Eu(DBM)3·(DMA)] compound indicates that this complex crystallizes in the triclinic system, space group P1¯ with the following cell parameters: a=10.2580(3)Å, b=10.3843(2)Å, c=22.3517(5)Å, α=78.906(2)°, β=78.049(2)°, λ=63.239(2)°, V=2066.41(9)Å3, and Z=2. The coordination polyhedron for the Eu(III) complex may be described as an approximate C2v distorted monocapped trigonal prism. The optical properties of the Eu(III) complexes were studied based on the intensity parameters and luminescence quantum yield (q). The values of the Ω2 parameter of the Eu–DBM complexes are larger than those for the Eu–TTA complexes, indicating that the Eu(III) ion is in a more polarizable chemical environment in the former case. The geometries of the complexes have been optimized by using the Sparkle Model, and the results have been used to perform theoretical predictions of the ligand-to-metal energy transfer via direct and exchange Coulomb mechanisms.

Tashelgite, CaMgFe2 + Al9O16(OH), a new mineral species from calc-skarnoid in Gorny Shoria

A new mineral species has been discovered at the calc-skarnoid occurrence near the mouth of the Tashelga River, Kuznetsky Alatau, Gorny Shoria, Russia, and named after the locality of its discovery. Associated minerals are calcite, hibonite, grossular, vesuvianite, hercynite, magnetite, corundum, perovskite, scapolite, diopside, and apatite. The new mineral occurs as prismatic or finely fibrous crystals up to 1.5–2.0 mm in length, their parallel intergrowths, and felty aggregates as large as 10 mm across. Tashelgite is bluish green, translucent to transparent, with vitreous luster; D calc = 3.67 g/cm3. The IR spectrum does not contain bands of OH groups. Tashelgite is biaxial (−), with α = 1.736(2), β = 1.746(2), γ = 1.750(2); 2V meas = −20(2)°. Dispersion is strong, r Y (yellowish green) > Z (almost colorless). Chemical composition (electron microprobe, average of five-point analyses, Fe2O3 is estimated from the ratio of intensities \(I(Fe_{K\beta _5 } )/I(Fe_{K\beta _1 } )\) in the X-ray spectrum, H2O was determined as a weight loss on heating in vacuum up to 1000°C), wt %: 7.98 CaO, 6.75 MgO, 0.45 MnO, 11.32 FeO, 1.40 Fe2O3, 70.70 Al2O3, 1.8(2) H2O, 100.40 in total. The empirical formula calculated on the basis of 17 oxygen atoms is H1.27Ca0.90Mg1.06Mn0.04 Fe 1.00 2+ Fe 0.11 3+ Al8.80O17.00. The idealized formula is CaMgFe2+Al9O16(OH). According to single-crystal X-ray structural data, tashelgite is monoclinic, pseudoorthorhombic, space group Pc; unit cell parameters are: a = 5.6973(1), b = 17.1823(4), c = 23.5718(5)A; β = 90.046(3)°; V = 2307.5(1)A3, Z = 8. The crystal structure of tashelgite is unique and characterized by ordering of all cations; Al occupies sites with octahedral and tetrahedral coordination. The cation ordering has also been confirmed by IR spectroscopy. The strongest lines of the X-ray powder diffraction pattern (d, A]-I[hkl] are: 11.79–48 [002], 2.845–43 [061], 2.616–100 [108], 2.584–81 [146], 2.437–44 [163], 2.406–61 [057], 2.202–72 [244]. The type specimen of tashlegite has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia.

2-Methyl-4-phenyl-3,4-dihydroquinazoline

The title compound, C15H14N2, was formed during the lithia­tion of 2-methyl­quinazoline with phenyl­lithium followed by hydrolysis of the inter­mediate lithium 2-methyl-4-phenyl-4H-quinazolin-3-ide. NMR spectra as well as single-crystal X-ray structural data indicate that the reaction product to have the same structure in chloro­form solution as in the crystalline state. The phenyl substituent is twisted out of the plane of the 3,4-dihydro­quinazoline ring system by 86.47 (7)°. In the crystal, inter­molecular N—H⋯N inter­actions connect the mol­ecules into infinite chains.

Metallomacrocycles with a Difference: Macrocyclic Complexes with Exocyclic Ruthenium(II)-Containing Domains

The templated synthesis of organic macrocycles containing rings of up to 96 atoms and three 2,2'-bipyridine (bpy) units is described. Starting with the bpy-centred ligands 5,5'-bis[3-(1,4-dioxahept-6-enylphenyl)]-2,2'-bipyridine and 5,5'-bis[3-(1,4,7-trioxadec-9-enylphenyl)]-2,2'-bipyridine, we have applied Grubbs' methodology to couple the terminal alkene units of the coordinated ligands in [FeL3]2+ complexes. Hydrogenation and demetallation of the iron(II)-containing macrocyclic complexes results in the isolation of large organic macrocycles. The latter bind {Ru(bpy)2} units to give macrocyclic complexes with exocyclic ruthenium(II)-containing domains. The complex [Ru(bpy)2(L)]2+ (isolated as the hexafluorophosphate salt), in which L=5,5'-bis[3-(1,4,7,10-tetraoxatridec-12-enylphenyl)]-2,2'-bipyridine, undergoes intramolecular ring-closing metathesis to yield a macrocycle which retains the exocyclic {Ru(bpy)2} unit. The poly(ethyleneoxy) domains in the latter macrocycle readily scavenge sodium ions, as proven by single-crystal X-ray diffraction and atomic absorption spectroscopy data for the bulk sample. In addition to the new compounds, a series of model complexes have been fully characterized, and representative single-crystal X-ray structural data are presented for iron(II) and ruthenium(II) acyclic and macrocyclic species.

On the Quest for New Mixed-Metal μ-Oxo-bridged Complexes: Synthesis of Compounds Containing Transition Metal−Oxygen−Main Group Metal Motifs M−O−M1 (M = Ti, Zr; M1 = Al, Ga) without Cyclopentadienyl Ligands

The reaction of TiBz4 (Bz = benzyl) with LAlMe(OH), L = (2,6-iPr2C6H3NC(Me))2CH, afforded LAlMe(mu-O)TiBz3 (1) and [LAlMe(mu-O)]2TiBz2 (2), whereas the corresponding reaction with ZrBz4 resulted only in the formation of the trinuclear species [LAlMe(mu-O)]2ZrBz2 (3). The reaction of (Mes 2Ga(OH))2 x THF (Mes = 2,4,6-Me3C6H2) with Ti(NEt2)4 yielded the cluster compound TiGa6O7(NEt2)2(Mes)6 (4). All compounds have been characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Additionally, single crystal X-ray structure data of 1, 3, and 4 are reported. Compounds 1-4 show low catalytic activities in the polymerization of ethylene. Revisiting known mu-oxo-bridged complexes containing the M-O-M(1) (M = Ti, Zr, Hf; M(1) = Al, Ga) skeleton revealed that the application of polynuclear group 13 hydroxides and oxo bridged complexes possesses a potential for the preparation of new polyoxometal clusters.

Reverse Selectivity in m-CPBA Oxidation of Oligothiophenes to Sulfones

Oligothiophene sulfones of up to six rings can be conveniently prepared by the direct oxidation of butyl-substituted thiophene oligomers with m-CPBA in dichloromethane. Reverse selectivity of oxidized rings is observed relative to previously reported systems without beta-substitution. The selectivity in the trimer and hexamer is confirmed with single-crystal X-ray structure data. The sulfones possess red-shifted absorptions and increased electron affinities relative to the parent oligomers.

Supramolecular Self-Assembled Polynuclear Complexes from Tritopic, Tetratopic, and Pentatopic Ligands: Structural, Magnetic and Surface Studies

Polymetallic, highly organized molecular architectures can be created by "bottom-up" self-assembly methods using ligands with appropriately programmed coordination information. Ligands based on 2,6-picolyldihydrazone (tritopic and pentatopic) and 3,6-pyridazinedihydrazone (tetratopic) cores, with tridentate coordination pockets, are highly specific and lead to the efficient self-assembly of square [3 x 3] Mn9, [4 x 4] Mn16, and [5 x 5] Mn25 nanoscale grids. Subtle changes in the tritopic ligand composition to include bulky end groups can lead to a rectangular 3 x [1 x 3] Mn9 grid, while changing the central pyridazine to a more sterically demanding pyrazole leads to simple dinuclear copper complexes, despite the potential for binding four metal ions. The creation of all bidentate sites in a tetratopic pyridazine ligand leads to a dramatically different spiral Mn4 strand. Single-crystal X-ray structural data show metallic connectivity through both mu-O and mu-NN bridges, which leads to dominant intramolecular antiferromagnetic spin exchange in all cases. Surface depositions of the Mn9, Mn16, and Mn25 square grid molecules on graphite (HOPG) have been examined using STM/CITS imagery (scanning tunneling microscopy/current imaging tunneling spectroscopy), where tunneling through the metal d-orbital-based HOMO levels reveals the metal ion positions. CITS imagery of the grids clearly shows the presence of 9, 16, and 25 manganese ions in the expected square grid arrangements, highlighting the importance and power of this technique in establishing the molecular nature of the surface adsorbed species. Nanoscale, electronically functional, polymetallic assemblies of this sort, created by such a bottom-up synthetic approach, constitute important components for advanced molecule-based materials.

Photoluminescence of ortho-bromobenzophenone

Phosphorescence spectra of crystalline ortho-bromobenzophenone (2-bromobenzophenone, 2BrBP) were measured from 1.6K to room temperature. A cardinal emission mechanism crossover occurs within this temperature range. At low temperature the phosphorescence spectrum is a superposition of two similar sets of equidistant bands spaced by the CO stretch frequency. We ascribe these two sets to the emission of two different conformers, one of which is metastable and does not manifest itself above approximately 70K. The presence of two conformers is explained by the fact that the 2BrBP molecule deforms considerably upon excitation. The emission from the stable conformer survives up to approximately 140K or even higher. At roughly 60K and higher, another type of emission reveals itself in the shape of two very broad, partly overlapping bands, which gains in intensity with increasing temperature. Above 150K only this two-hump feature is observed in phosphorescence spectra. Additional phosphorescence experiments were carried out to elucidate the nature of this spectrum, including phosphorescence measurements of 2BrBP in ethanol solutions as well as time-resolved and varying-excitation-intensity measurements from crystals. Based on results of all the experiments reported here and on our own single-crystal x-ray structure data we conclude that the above two-band spectrum recorded near room temperature is due to the emission of single-photon bimolecular triplet excimer formed by the carbonyl groups of two neighboring 2-bromobenzophenone molecules. This is the first time that a bimolecular excimer has been observed and reliably identified in a benzophenone derivative solid.

Observation of triplet excimer emission in 2-bromobenzophenone

Phosphorescence spectra of 2-bromobenzophenone (2Br-BP) crystals were measured from 70 K to room temperature. A capital crossover in the emission mechanism takes place within this temperature range, leaving at room temperature only a broad two-hump feature. Additional phosphorescence experiments, carried out to understand the nature of this spectrum, include measurements from 2Br-BP solutions in ethanol as well as time-resolved and varying-excitation-intensity measurements from crystals. Based on results of these experiments and on our own single-crystal X-ray structure data, we conclude that the above two-band spectrum recorded near room temperature is due to the emission of single-photon bi-molecular triplet excimer formed by the carbonyl groups of two neighbor 2-bromobenzophenone molecules.

Europium(II) and Ytterbium(II) Cyclic Organohydroborates with Agostic Interactions

The divalent lanthanide bis((cyclooctane-1,5-diyl)dihydroborate) complexes {K(THF)4}2{Ln{(mu-H)2BC8H14}4} (Ln = Eu, 3; Yb, 4) were prepared by a metathesis reaction between (THF)(x)LnCl2 and K[H2BC8H14] in THF in a 1:4 molar ratio. Although the reaction ratios were varied between 1:3 and 1:6, complexes 3 and 4 were the only lanthanide 9-BBN hydroborates produced. Because of disorder of THF in crystals of 3 and 4, good single-crystal X-ray structural data could not be obtained. However, when the potassium cation was replaced by the tetramethylammonium cation or when MeTHF (2-methyltetrahydrofuran) was employed in place of THF, good quality crystals were obtained. Complexes [NMe4]2[Ln{(mu-H)2BC8H14}4] (Ln = Eu, 5; Yb, 6) were afforded by metathesis reactions of NMe4Cl with 3 and 4 in situ. On the basis of the single-crystal X-ray diffraction analysis, the four 9-BBN tetrahydroborate ligands are tetrahedrally arranged around the lanthanide cation in 5 and 6. The two structures differ in that one alpha-C-H bond from each of the four {(mu-H)2BC8H14}4 units exhibits an agostic interaction with Eu(II) in 5 but, in complex 6, only two of the alpha-C-H bonds form agostic interactions with Yb(II). Complexes {K(MeTHF)3}2{Ln{(mu-H)2BC8H14}4} (Ln = Eu, 7; Yb, 8) were produced by employing MeTHF in place of THF. The structures of 7 and 8 display connectivity between the anion {Ln{(mu-H)2BC8H14}4}2- and the cation {K(MeTHF)3}+, in which the potassium not only interacts directly with the hydrogens of the Ln-H-B bridged bonds but is also involved in agostic interactions with alpha-C-H bonds. By systematically examining the structures of complexes 3-8 and taking into account the previously reported complexes (THF)4Ln{(mu-H)2BC8H14}2 (Ln = Eu, 1; Yb, 2), it is concluded that Eu(II) appears to have a better ability to form agostic interactions than Yb(II) because of its larger size, even though Yb(II) has a higher positive charge density.