Single-crystal X-ray Diffraction Characterization Research Articles

Bismuth Coordination Polymers with Fluorinated Linkers: Aqueous Stability, Bivolatility, and Adsorptive Behavior.

Bismuth metal-organic frameworks and coordination polymers (CP) are challenging to synthesize, given the poor solubility of bismuth precursors and asymmetric and labile ligation of Bi3+ due to its intrinsic lone pair. Here, we synthesize and structurally characterize three Bi3+-CPs, exploiting a tetrafluoroterephtalate (F4BDC) linker to determine the effect of high acidity on these synthesis and coordination challenges. Single-crystal X-ray diffraction characterization showed that pi-pi stacking of linkers directs framework arrangement and generally deters open porosity in the three structures, respectively featuring Bi chains (Bi chain -F 4 BDC), Bi dimers (Bi 2 -F 4 BDC) linked into chains, and Bi tetramers (Bi 4 -F 4 BDC). Powder X-ray diffraction and microscopic imaging show the high purity and stability of these compounds in water. Naphthalenedisulfonate (NDS) was used as a mineralizer in the synthesis of (Bi chain -F 4 BDC) and (Bi 4 -F 4 BDC), and studies of its role in assembly pathways yielded two additional structures featuring mixed NDS and F4BDC, respectively, linking monomer and octamer Bi nodes, and confirmed that F4BDC is the preferred (less labile) linker. Methylene blue (MB) adsorption studies show differing efficacies of the three Bi-F4BDC phases, attributed to surface characteristics of the preferential growth facets, while generally most effective adsorption is attributed to the hydrophobicity of fluorinated ligands. Finally, thermogravimetric analysis of all three Bi-F4BDC phases indicates simultaneous ligand degradation and in situ formation of volatile Bi compounds, which could be exploited in the chemical vapor deposition of Bi-containing thin films.

Capturing the Long-Sought Dy@C2v(5)-C80 via Benzyl Radical Stabilization.

Endohedral metallofullerenes (EMFs) are one type of intriguing metal/carbon hybrid molecule with the molecule configuration of sphere cavity-encapsulating metal ions/metal clusters due to their unique physicochemical properties and corresponding application in the fields of biological materials, single molecule magnet materials and energy conversion materials. Although the EMF family is growing, and versatile EMFs have been successfully synthesized and confirmed using crystal structures, some expected EMF members have not been observed using the conventional fullerene separation and purify strategy. These missing EMFs raise an interesting scientific issue as to whether this is due to the difficulty in separating them from the in situ formed carbon soot. Herein, we successfully captured a long-sought dysprosium-based EMF bearing a C2v(5)-C80 cage (Dy@C2v(5)-C80) in the form of Dy@C2v(5)-C80(CH2Ph)(Ph = −C6H5) from carbon soot containing versatile EMFs using simple benzyl radical functionalization and unambiguously confirmed the molecule structure using single crystal X-ray diffraction characterization. Meanwhile, the crystal structure of Dy@C2v(5)-C80(CH2Ph) showed that a single benzyl group was grafted onto the (5,6,6)-carbon, suggesting the open-shell electronic configuration of Dy@C2v(5)-C80. The theoretical calculations unveiled that the benzyl radical addition enables the modulation of the electronic configuration of Dy@C2v(5)-C80 and the corresponding stabilization of Dy@C2v(5)-C80 in conventional organic solvents. This facile stabilization strategy via benzyl radical addition exhibits the considerable capability to capture these missing EMFs, with the benefit of enriching the endohedral fullerene family.

Heteroleptic Crown-Substituted Tris(phthalocyaninates) as Dynamic Supramolecular Scaffolds with Switchable Rotational States and Tunable Magnetic Properties.

Herein we report single-crystal X-ray diffraction characterization and complementary solution studies of supramolecular interaction between potassium salts and heteroleptic homo- and heteronuclear triple-decker crown phthalocyaninates [(15C5)4Pc]M*[(15C5)4Pc]M(Pc) or [M*,M], where M* and M = Y and/or Tb. Our results evidence that, in contrast to the previously studied crown-substituted phthalocyanines, the interaction of K+ cations with [M*,M] does not induce their intermolecular aggregation. Instead, the cations reversibly intercalate between the crown-substituted phthalocyanine ligands, resulting in switching of the coordination polyhedron of the metal center M* from square-antiprismatic to square-prismatic. In the case of terbium(III) complexes, such a switching alters their magnetic properties, which can be read-out by 1H NMR spectroscopy. For [Tb*,Y], such a switching causes an almost 25% increase in the axial component of the magnetic susceptibility tensor. Even though the polyhedron of the paramagnetic center in [Y*,Tb] is not switched, minor structural perturbations associated with the overall reorganization of the receptor also cause smaller, but nevertheless appreciable, growth of the axial anisotropy. The observed effects render the studied complexes as molecular switches with tunable magnetic properties.

Cation-Induced Dimerization of Crown-Substituted Gallium Phthalocyanine by Complexing with Alkali Metals: The Crucial Role of a Central Metal.

The single-crystal X-ray diffraction characterization of cation-induced supramolecular assembly of the gallium(III) tetra(15-crown-5)phthalocyaninate [(HO)Ga(15C5)4Pc] (1Ga) is reported. The structures of two crystalline dimers, {[(1Ga)2Rb4]4+(iNic-)4}·10CDCl3 and {[(2Ga)2Rb4]4+(OH-)2(Piv-)2}·16CDCl3 (2Ga-[(Piv)Ga(15C5)4Pc]), as well as UV-vis and NMR studies of the soluble supramolecular dimers formed by 1Ga and K+, Rb+, and Cs+ salts are provided. In contrast to the previously reported aluminum complex where the Al-O-Al bond was formed, no μ-oxo bridge was observed between the gallium atoms in the supramolecular dimers under similar conditions, despite the fact that aluminum and gallium belong to the same group of the periodic table. The detailed investigation of the cation-induced dimers of 1Ga confirms the uniformity of their structure for all large alkali cations, where two molecules of crown-substituted gallium phthalocyaninate are 4-fold bound by K+, Rb+, or Cs+. The gallium(III) coordination sphere is labile, and the nature of the solvent during supramolecular dimerization has an effect on the axial ligand exchange: Piv- in nonpolar CHCl3 replaces the initial OH- in 1Ga, while such a process is not observed in CHCl3/CH3OH media.

Intramolecular sp2-sp3 Disequalization of Chemically Identical Sulfonamide Nitrogen Atoms: Single Crystal X-Ray Diffraction Characterization, Hirshfeld Surface Analysis and DFT Calculations of N-Substituted Hexahydro-1,3,5-Triazines

In this manuscript, the synthesis and single crystal X-ray diffraction characterization of four N-substituted 1,3,5-triazinanes are reported along with a detailed analysis of the noncovalent interactions observed in the solid state architecture to these compounds, focusing on C–H···π and C–H···O H-bonding interactions. These noncovalent contacts have been characterized energetically by using DFT calculations and also by Hirshfeld surface analysis. In addition, the supramolecular assemblies have been characterized using the quantum theory of “atoms-in-molecules” (QTAIM) and molecular electrostatic potential (MEP) calculations. The XRD analysis revealed a never before observed feature of the crystalline structure of some molecules: symmetrically substituted 1,3,5-triazacyclohexanes possess two chemically identical sulfonamide nitrogen atoms in different sp2 and sp3-hybridizations.

Air-Stable Half-Sandwich Iridium Complexes as Aerobic Oxidation Catalysts for Imine Synthesis.

Several N,O-coordinate half-sandwich iridium complexes, 1-5, containing constrained bulky β-enaminoketonato ligands were prepared and clearly characterized. Single-crystal X-ray diffraction characterization of these complexes indicates that the iridium center adopts a distorted octahedral geometry. Complexes 1-5 showed good catalytic efficiency in the oxidative homocoupling of primary amines, dehydrogenation of secondary amines, and the oxidative cross-coupling of amines and alcohols, which furnished various types of imines in good yields and high selectivities using O2 as an oxidant under mild conditions. No distinctive substituent effects of the iridium catalysts were observed in these reactions. The diverse catalytic activity, broad substrate scope, mild reaction conditions, and high yields of the products made this catalytic system attractive in industrial processes.

Kinetically Stable Single Crystals of Perovskite-Phase CsPbI3.

We use asolid-state method to synthesize single crystals of perovskite-phase cesium lead iodide (γ-CsPbI3) that are kinetically stable at room temperature. Single crystal X-ray diffraction characterization shows the compound is orthorhombic with the GdFeO3 structure at room temperature. Unlike conventional semiconductors, the optical absorption and joint density-of-states of bulk γ-CsPbI3 is greatest near the band edge and decreases beyond the Eg for at least 1.9 eV. Bulk γ-CsPbI3 does not show an excitonic resonance and has an optical band gap of 1.63(3) eV, ∼90 meV smaller than has been reported in thin films; these and other differences indicate that previously measured thin film γ-CsPbI3 shows signatures of quantum confinement. By flowing gases in situ during powder X-ray diffraction measurements, we confirm that γ-CsPbI3 is stable to oxygen but rapidly and catalytically converts to non-perovskite δ-CsPbI3 in the presence of moisture. Our results provide vital parameters for theoretical and experimental investigations into perovskite-phase CsPbI3 that will the guide the design and synthesis of atmospherically stable inorganic halide perovskites.

Supramolecular Assemblies in Pb(II) Complexes with Hydrazido-Based Ligands

Herein, we describe the synthesis and single crystal X-ray diffraction characterization of several Pb(II) complexes using Schiff base hydrazido-based ligands and different counterions (NO3−, I– and ClO4). In the three complexes reported in this work, the lead(II) metal exhibits a high coordination number (n > 8) and thus it is apparently not involved in tetrel bonding interactions. Moreover, the aromatic ligands participate in noncovalent interactions that play an important role in the formation of several supramolecular assemblies in the solid state of the three Pb(II) complexes. These assemblies have been analyzed by means of Hirshfeld surface analysis and DFT calculations.

Synthesis of two platinum(II) complexes with 2-methyl-8-quinolinol derivatives as ligands and study of their antitumor activities

Two platinum(II) complexes, [Pt(ClQ)(DMSO)Cl] (ClQ-Pt) and [Pt(BrQ)(DMSO)Cl] (BrQ-Pt), with 5,7-dichloro-2-methyl-8-quinolinol (H-ClQ) and 5,7-dibromo-2-methyl-8-quinolinol (H-BrQ) as ligands, respectively, have been synthesized and characterized. The single-crystal X-ray diffraction characterization as well as other spectroscopic and analytical studies of ClQ-Pt and BrQ-Pt revealed that the coordination geometry of Pt(II) can be described as a four-coordinated square planar geometry. By MTT assay, ClQ-Pt displayed the most potent activity, with IC50 values of 5.02–34.38 μM against MGC80-3, T-24, Hep-G2 and BEL-7402 tumor cells. Among them, the T-24 cells the highest sensitivity to ClQ-Pt and BrQ-Pt with IC50 value of 5.02 ± 0.62 μM and 18.02 ± 1.05 μM, respectively. In addition, ClQ-Pt caused a higher percentage of apoptotic T-24 cells (ca. 33.75%) than that of BrQ-Pt (ca. 23.85%) and cisplatin (ca. 12.82%). Mechanistic studies revealed that ClQ-Pt and BrQ-Pt caused T-24 cell cycle arrest at the S phase, as shown by the down-regulation of cyclin A and CDK2 expression levels. In addition, ClQ-Pt and BrQ-Pt also caused mitochondrial dysfunction. Interestingly, the in vitro anticancer activity of ClQ-Pt was higher than those of BrQ-Pt and cisplatin, more selective for T-24 tumor cells than for normal HL-7702 cells. Taken together, we concluded that the 5- and 7-substitution groups of the ClQ ligands play an important role in determining the anti-proliferation activity of the corresponding Pt(II) complexes.

Superconducting SrSnP with Strong Sn–P Antibonding Interaction: Is the Sn Atom Single or Mixed Valent?

The large single crystals of SrSnP were prepared using Sn self-flux method. The superconductivity in the tetragonal SrSnP is observed with the critical temperature of ∼2.3 K. The results of a crystallographic analysis, superconducting characterization, and theoretical assessment of tetragonal SrSnP are presented. The SrSnP crystallizes in the CaGaN structure type with space group P4/nmm (S.G. 129, Pearson symbol tP6) according to the single-crystal X-ray diffraction characterization. A combination of magnetic susceptibility, resistivity, and heat capacity measurements confirms the bulk superconductivity with Tc = 2.3(1) K in SrSnP. According to the X-ray photoelectron spectroscopy measurement, the assignments of Sr2+ and P3– are consistent with the chemical valence electron balance principles. Moreover, it is highly likely that Sn atom has only one unusual oxidation state. First-principles calculations indicate the bands around Fermi level are hybridized among Sr d, Sn p, and P p orbitals. The strong Sn–P and Sr–P interactions pose as keys to stabilize the crystallographic structure and induce the superconductivity, respectively. The physics-based electronic and phononic calculations are consistent with the molecular viewpoint. After inclusion of the spin–orbit coupling into the calculation, the band degeneracies at Γ-point in the first Brillouin zone split into two bands, which yield to the van Hove singularities around Fermi level.

The dinuclear scandium(III) cyclooctatetraenyl chloride complex di-μ-chlorido-bis[(η8-cyclooctatetraene)(tetrahydrofuran-κO)scandium(III)

Only a few cyclooctatetraene dianion (COT) π-complexes of lanthanides have been crystallographically characterized. This first single-crystal X-ray diffraction characterization of a scandium(III) COT chloride complex, namely di-μ-chlorido-bis[(η8-cyclooctatetraene)(tetrahydrofuran-κO)scandium(III)], [Sc2(C8H8)2Cl2(C4H8O)2] or [Sc(COT)Cl(THF)]2 (THF is tetrahydrofuran), (1), reveals a dimeric molecular structure with symmetric chloride bridges [average Sc-Cl = 2.5972 (7) Å] and a η8-bound COT ligand. The COT ring is planar, with an average C-C bond length of 1.399 (3) Å. The Sc-C bond lengths range from 2.417 (2) to 2.438 (2) Å [average 2.427 (2) Å]. Direct comparison of (1) with the known lanthanide (Ln) analogues (La, Ce, Pr, Nd, and Sm) illustrates the effect of metal-ion (M) size on molecular structure. Overall, the M-Cl, M-O, and M-C bond lengths in (1) are the shortest in the series. In addition, only one THF molecule completes the coordination environment of the small ScIII ion, in contrast to the previously reported dinuclear Ln-COT-Cl complexes, which all have two bound THF molecules per metal atom.

NMR crystallography for structural characterization of oxovanadium(V) complexes: deriving coordination geometry and detecting weakly coordinated ligands at atomic resolution in the solid state.

NMR crystallography is an emerging method for atomic-resolution structural analysis of ubiquitous vanadium(V) sites in inorganic and bioinorganic complexes as well as vanadium-containing proteins. NMR crystallography allows for characterization of vanadium(V) containing solids, based on the simultaneous measurement of (51)V-(15)N internuclear distances and anisotropic spin interactions, described by (13)C, (15)N, and (51)V chemical shift anisotropy and (51)V electric field gradient tensors. We show that the experimental (51)V, (13)C, and (15)N NMR parameters are essential for inferring correct coordination numbers and deriving correct geometries in density functional theory (DFT) calculations, particularly in the absence of single-crystal X-ray structures. We first validate this approach on a structurally known vanadium(V) complex, ((15)N-salicylideneglycinate)-(benzhydroxamate)oxovanadium(V), VO(15)NGlySalbz. We then apply this approach to derive the three-dimensional structure of (methoxo)((15)N-salicylidene-glycinato)oxovanadium(V) with solvated methanol, [VO((15)NGlySal)(OCH3)]·(CH3OH). This is a representative complex with potentially variable coordination geometry depending on the solvation level of the solid. The solid material containing molecules of CH3OH, formally expressed as [VO((15)NGlySal)(OCH3)]·(CH3OH), is found to have one molecule of CH3OH weakly coordinated to the vanadium. The material is therefore best described as [VO((15)NGlySal)(OCH3)(CH3OH)] as deduced by the combination of multinuclear solid-state NMR experiments and DFT calculations. The approach reported here can be used for structural analysis of systems that are not amenable to single-crystal X-ray diffraction characterization and which can contain weakly associated solvents.

Synthesis and characterization of trianionic pincer-type complexes of tantalum(V) including solid (X-ray) and solution (NMR) state assignment of an intraligand N–H—F hydrogen bonding interaction

Tanatalum(V) complexes ligated with a trianionic ONO3− pincer-type ligand were synthesized and characterized. Using the ONO trianionic pincer ligand precursor 2,2′-(azanediylbis(3-methyl-6,1-phenylene))bis(1,1,1,3,3,3-hexafluoropropan-2-ol) [CF3-ONO]H3 (1) and various sources of Ta(V), the following pincer complexes were synthesized: (I) anionic trichloride complex {[CF3-ONO]TaCl3}{HNEt3}·(HNEt3Cl)x (2), (II) diamido-amine complex [CF3-ONO]Ta(NMe2)2(HNMe2) (3-NHMe2) and its amine free version [CF3-ONO]Ta(NMe2)2 (3), (III) the neutral trichloride [CF3-ONHO]TaCl3 (4), (IV) the neutral dichloride [CF3-ONO]TaCl2(THF) (5), and (V) the dibenzyl complex [CF3-ONO]TaBn2 (6). Characterization methods include the complete assignment (where possible) for 1H, 13C, 19F, and 15N NMR spectra for complexes 2–6, and single crystal X-ray diffraction characterization for complexes 2, 3, and 4. Interesting aspects regarding the interplay of the ligand in its dianionic form versus its trianionic form, and an unusual H⋯F hydrogen bonding interaction within complex 4 were discovered from these synthetic pursuits.

Sampling rifamycin conformational variety by cruising through crystal forms: implications for polymorph screening and for biological models

In this work, we report on a non-solvate and on a new solvate forms of rifamycin S, demonstrating that another stable conformation of the active molecule exists and it may be isolated by planning the crystallization conditions. In fact, in these structures rifamycin S has a previously uncharacterised, bent conformation: implications of these findings on the models used to explain rifamycin activity are discussed. Polymorphism has also been reported for the rifamycin-based antibiotic rifaximin, but without single-crystal X-ray diffraction characterization. Here the structure of a tetrahydrate form of rifaximin is discussed; confirming the flexibility of the drug, the two independent molecules in the unit cell are an example of conformational isomorphism.

Further errors in polymorph identification: furosemide and finasteride

Reassessment of the reported single-crystal X-ray diffraction characterization of polymorphs of furosemide and finasteride shows that, in each case, incomplete data collections have resulted in the mistaken identification of two forms that are, in fact, identical.

Structural analysis of products from the C 60-piperazine reaction. Consistent geometric distortions of the fullerene core upon adduct formation

The reaction of C 60 with piperazine yields the single addition product, C 60N 2C 2H 4 2, and six double addition products which can be chromatographically separated. Of these, single crystal X-ray diffraction characterization has produced structural data for the identification of (C 2H 4) 2N 2C 60 and three isomeric forms of the double addition product, (C 2H 4) 2N 2 2C 60. Addition of the N 2(C 2H 4) 2 units produces local distortions of the fullerene core which involve marked elongation of the CC bond at the 6:6 ring junction that is involved in the addition and outward displacement of these carbons from their usual positions by ca 0.33–0.40 Å. The combined effects of double addition can produce local distortions that appear visually more severe but which retain the structural features found in the single addition product.