Isostructural Host Research Articles

Cage Match: Comparing the Anion Binding Ability of Isostructural Versus Isofunctional Pairs of Metal-Organic Nanocages.

Affinities of six anions (mesylate, acetate, trifluoroacetate, p-toluenecarboxylate, p-toluenesulfonate, and perfluorooctanoate) for three related Pt2+ -linked porphyrin nanocages were measured to probe the influence of different noncovalent recognition motifs (e. g., hydrogen bonding, electrostatics, π bonding) on anion binding. Two new hosts of M6 L3 12+ (1b) and M4 L2 8+ (2) composition (M=(en)Pt2+ , L=(3-py)4 porphyrin) were prepared in a one-pot synthesis and allowed comparison of hosts that differ in structure while maintaining similar N-H hydrogen-bond donor ability. Comparisons of isostructural hosts that differ in hydrogen-bonding ability were made between 1b and a related M6 L3 12+ nanoprism (1a, M=(tmeda)Pt2+ ) that lacks N-H groups. Considerable variation in association constants (K1 =1.6×103 M-1 to 1.3×108 M-1 ) and binding mode (exo vs. endo) were found for different host-guest combinations. Strongest binding was seen between p-toluenecarboxylate and 1b, but surprisingly, association of this guest with 1a was only slightly weaker despite the absence of NH⋅⋅⋅O interactions. The high affinity between p-toluenecarboxylate and 1a could be turned off by protonation, and this behavior was used to toggle between the binding of this guest and the environmental pollutant perfluorooctanoate, which otherwise has a lower affinity for the host.

Enhancing Spin Coherence in Optically Addressable Molecular Qubits through Host-Matrix Control

Optically addressable spins are a promising platform for quantum information science due to their combination of a long-lived qubit with a spin-optical interface for external qubit control and readout. The ability to chemically synthesize such systems—to generate optically addressable molecular spins—offers a modular qubit architecture which can be transported across different environments and atomistically tailored for targeted applications through bottom-up design and synthesis. Here, we demonstrate how the spin coherence in such optically addressable molecular qubits can be controlled through engineering their host environment. By inserting chromium (IV)-based molecular qubits into a nonisostructural host matrix, we generate noise-insensitive clock transitions, through a transverse zero-field splitting, that are not present when using an isostructural host. This host-matrix engineering leads to spin-coherence times of more than 10 μs for optically addressable molecular spin qubits in a nuclear and electron-spin-rich environment. We model the dependence of spin coherence on transverse zero-field splitting from first principles and experimentally verify the theoretical predictions with four distinct molecular systems. Finally, we explore how to further enhance optical-spin interfaces in molecular qubits by investigating the key parameters of optical linewidth and spin-lattice relaxation time. Our results demonstrate the ability to test qubit structure-function relationships through a tunable molecular platform and highlight opportunities for using molecular qubits for nanoscale quantum sensing in noisy environments.Received 18 March 2022Revised 16 June 2022Accepted 1 July 2022DOI:https://doi.org/10.1103/PhysRevX.12.031028Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasChemical Physics & Physical ChemistryQuantum engineeringQuantum information processingSpintronicsQuantum InformationCondensed Matter, Materials & Applied Physics

Application of Judd–Ofelt theory in analyzing Nd3+ doped SrF2 and CaF2 transparent ceramics

Nd3+ doped SrF2 and CaF2 transparent ceramics were fabricated by vacuum hot-press sintering and the absorption spectra, emission spectra as well as luminescence decays of the samples were measured. Judd-Ofelt (J–O) theory was used to analyze the optical performance of Nd3+ in these two isostructural hosts. The Nd: SrF2 transparent ceramic was found to have smaller line strength, larger radiative lifetime and smaller Ω2 value (corresponding to more ionic Nd3+-ligand bonding and more symmetry of Nd3+ environment). These features made it easier for Nd: SrF2 to realize population inversion and strong emission, thus doing good to laser performance. The strong emission of 4F3/2 → 4I9/2 transition in Nd: SrF2, which was predicted by J–O theory and demonstrated by luminescence spectrum, made it possible to achieve effective laser output around 900 nm. The intensity parameters and radiative lifetimes of ceramics were found comparable with their corresponding single crystals.

A highly selective host based on the pamoate ion

Five isostructural host–guest complexes based on the pamoate ion have been identified and characterised. The host framework is made up of hydrogen-bonded units of pamoate and 4-phenylpyridinium ions, held together by weak C–H⋯π and stacking interactions, and in each complex the guest molecules reside in cavities within this framework. Although the host is not porous, it is thermally stable and also highly selective, encapsulating 1,4-dioxane preferentially over various other solvents.

Coherent electron spin manipulation in a dilute oriented ensemble of molecular nanomagnets: pulsed EPR on doped single crystals

Doping a Cr7Zn molecular nanomagnet into a diamagnetic and isostructural host allows pulsed X-band EPR on single crystals, including relaxation and nutation experiments on the S = 3/2 ground state.

1,10-Phenanthroline-dithiolate mixed ligand transition metal complexes. Synthesis, characterization and EPR spectroscopy

Abstract A series of new N2S2 mixed ligand transition metal complexes, where N2 is phenanthroline and S2 is 1,2-dithiooxalate (dto) or 1,2-dithiosquarate (dtsq), has been synthesized and characterized. IR spectra reveal that the 1,2-dithiolate ligands are coordinated via the sulfur atoms forming a N2S2 coordination sphere. The copper(II) complex [Cu(phen)(dto)] was studied by EPR spectroscopy as a diamagnetically diluted powder. The diamagnetic dilution resulted from doping of the copper complex into the isostructural host lattice of the nickel complex [Ni(phen)(dto)]. The electronic situation in the frontier orbitals of the copper complex calculated from the experimental data is compared to the results of EHT and DFT calculations. Furthermore, one side product, chlorobis(1,10-phenanthroline)copper(I) ethanol solvate hydrate [(phen)2CuCl]·C2H5OH·H2O, was formed by a reduction process and characterized by X-ray diffraction. In the crystal packing one-dimensional columns of dimers are formed, stabilized by significant π–π interactions.

Theoretical investigation of a single erbium center in hexagonal gallium nitride

A theoretical energy-level analysis was based on parametric Hamiltonian for the 4f 11 electronic configuration of Er 3+ ions in C 3 v center, and it permitted a phenomenological characterization of crystal-field (CF) Hamiltonian parameters. This characterization allowed us to calculate the energy of the missing stark levels of the 4I 15/2 and 4I 13/2 states and to confirm the presence of a single emission center with C 3 v symmetry. The calculated CF and strength parameters are compared with those obtained for Sm 3+, Pr 3+ and Yb 3+ ions in the same host and with Er 3+ in other isostructural hosts.

Ethynyl Group as a Supramolecular Halogen and C≡C−H···C≡C Trimer Synthon in 2,4,6-Tris(4-ethynylphenoxy)-1,3,5-triazine

Halogen−ethynyl interaction mimicry and the role of halogen trimer synthon (X···X)3 in crystal packing have been discussed in several papers. However, the ethynyl trimer motif (C⋮C−H···C⋮C)3 has not been systematically studied in crystal engineering. The (C⋮C−H···C⋮C)3 synthon is reproduced in 10 isostructural host−guest crystalline adducts in the R3 space group. Not only are the ethynyl structures (4-EPOT) identical to the iodo series (4-IPOT) because of deliberate design but they also show tighter guest inclusion due to the stronger C⋮C−H···π hydrogen bond compared to the I···I interaction. 4-EPOT−guest inclusion adducts are more stable than 4-IPOT inclusion compounds on the basis of Cerius2 lattice energy computations (ΔE = ∼8 kcal mol-1). The temperature for guest release in thermal gravimetric analysis from the 4-EPOT−host framework is higher than the solvent boiling point (Tonset − Tbp) by as much as 123 °C for CH2Cl2, 103 °C for C6F6, and 83 °C for Et2O. The guest molecules are included in the hos...

Potassium beryllium sulfate dihydrate, K 2Be(SO 4) 2·2H 2O: Crystal structure and infrared spectroscopy

The crystal and molecular structure of the title compound, K 2Be(SO 4) 2·2H 2O, as determined by single crystal X-ray diffraction and infrared spectroscopy is reported and discussed. K 2Be(SO 4) 2·2H 2O crystallizes in the monoclinic space group P2 1/ c ( a=11.143(2), b=11.515(2), c=7.314(1) Å, β=95.08(1)°, V=934.8 Å 3, Z=4, R1=0.034 for 3524 F o>4 σ( F o) and 153 variables). The structure is characterized by tetrahedral chain fragments consisting of a BeO 2(H 2O) 2 group sharing corners with two SO 4 tetrahedra. These [Be(SO 4) 2(H 2O) 2] 2− units are interlinked by irregular KO 7 polyhedra and hydrogen bonds. Generally, the observed bond lengths and angles comply well with crystal chemical experience. Most of the infrared and Raman bands corresponding to the internal vibrations of the SO 4 2 − ions appear as doublets, thus reflecting the existence of two crystallographically different [SO 4]-tetrahedra in agreement with the structural data. The strengths of the hydrogen bonds as deduced from the infrared wavenumbers of the uncoupled OD modes of matrix-isolated HDO molecules (bands at 2278, 2352 and 2388 cm −1, liquid nitrogen temperature) are discussed in terms of the the O w⋯O bond distances, the different hydrogen bond acceptor capabilities of the oxygen atoms and the Be–OH 2 interactions. The intramolecular OH bond lengths are derived from the ν OD vs. r OH correlation curve [J. Mol Struct. 404 (1997) 63]. The water librations couple intensively with the translatory modes of the Be 2+ ions (BeO 4 skeleton vibrations) and the normal modes of SO 4 2 − ions, thus producing small isotopic shifts. The SO 4 2 − guest ions matrix-isolated in the isostructural host lattice K 2Be(SeO 4) 2·2H 2O exhibit doublet bands in the region of the stretching modes (the bands corresponding to the bending modes could not be recognized well), thus indicating a statistical distribution of the guest ions over the two available crystallographic positions. The distortion of the SO 4 2 − guest ions in the host selenate lattice is weaker than that of the same ions in the neat sulfate owing to the larger unit-cell volume of the host compound, i.e. to the smaller repulsion potential of the host lattice.

Crystal Engineering Involving C−H···N Weak Hydrogen Bonds: Penannular Enclosure of Organic Guests by a Diquinoline Host

The preparation and properties of the racemic lattice inclusion host 6α,13α-dibromo-5bα,6,12bα,13-tetrahydropentaleno[1,2-b:4,5-b′]diquinoline (8) are described. Strong hydrogen bonding interactions are not possible for this versatile host compound. Instead, weaker interactions (such as aryl offset face-face, aryl edge-face, halogen-halogen, halogen-π, and C−H···N synthons) compete against each other to generate the inclusion structure of lowest energy. The guests are contained within molecular pens formed by two hosts enclosing each guest. These host molecules are not directly linked at the corners of the pen, but rather assemble with their neighbours into layers of pens by means of aryl offset face-face interactions. The C−H···N weak hydrogen bond plays a dominant role in these structures by linking adjacent layers edge-edge through two distinct types of double motifs. One is the previously recognised aryl C−H···N dimer, while the other is a new bifurcated Ar−H···N···H−CBr−Ar interaction. The X-ray structures of nine inclusion compounds formed by 8 are reported. Seven of these in space group P21/c have isostructural host lattices where the layers of pens are stacked to produce guest channels. Several different guest arrangements are observed. In contrast, (8)2·(CH3CCl3) in space group C2/c and (8)2·(CF3C6H5) in P212121 have the pen layers stacked so as to enclose their guests in cages. The structure of the nonbrominated precursor 7, which undergoes self-resolution on crystallisation, is also described in crystal engineering terms. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Gadolinium in lutetium fluoride—an electron paramagnetic resonance study

Gadolinium (Gd 3+) in Czochralski-grown lutetium fluoride (LuF 3) has been investigated by electron paramagnetic resonance (EPR). Detailed analysis of the EPR angular dependencies reveals that Gd 3+ entered substitutionally for Lu 3+ in monoclinic C s site symmetry. The Lu site seems to be more distorted by the Gd ion as compared to the Y site in YF 3. The zero-field splitting of the ground state b 2 0 is −1.8372 GHz which is more than twice compared to that of Gd 3+ in host crystals of LaF 3, in which gadolinium has the same co-ordination number. The results of the fine structure analysis are compared to a similar study in the iso-structural host YF 3. The obtained results seem to be in contrast to the superposition model.

Intercalation of Ketones in Vanadyl Phosphate and Isostructural Hosts

The intercalation of acetone and butan-2-one in vanadyl and niobyl phosphates and niobyl arsenate is reported. All intercalates prepared are tetragonal and their basal spacings are close to each other. The intercalates contain one molecule of the ketone per formula unit. The existence of keto-enol tautomerism of guest molecules in interlayer space is assumed.

Photoisomerization of (2-cyanoethyl)(isonicotinic acid)cobaloxime complex in a series of isostructural host–guest complex crystals

A series of host–guest complex crystals has been formed between (2-cyanoethyl)(isonicotinic acid)cobaloxime as a guest and dicyclohexylamine, cycloheptylcyclohexylamine and cyclohexylcyclooctylamine as hosts. The X-ray analyses revealed that the three crystals are isostructural to each other. There are two crystallographically independent molecules in an asymmetric unit of each crystal. One of the cobaloxime molecules, A, has the 2-cyanoethyl group with gauche conformation around the central C–C bond while that of the B molecule has the trans conformation. When the powdered samples of the crystals were irradiated with a xenon lamp, the 2-cyanoethyl groups were isomerized to the 1-cyanoethyl group. The reaction rate was estimated from the change in the FT-IR spectra of the stretching vibration mode of the C–N triple bond. The reaction rates of the 2-cyanoethyl groups with gauche and trans conformations were estimated separately from the spectra. The rate constant of the 2-cyanoethyl group with the gauche conformation is significantly greater than that with the trans conformation in each crystal. The isomerization rate was accelerated as the size of the cycloalkane ring increased. The reaction cavity for the 2-cyanoethyl group expands as the ring size increases. This suggests that it is possible to control the reaction rate if a series of the host–guest complexes are formed and the size of the host molecule is systematically changed.

Inclusion compounds with the drug 5-Methoxysulphadiazine: Structures, thermodynamics of decomposition and relationship to polymorphism of the sulphonamide

Abstract The structures and thermal decompositions of the solvates of 5-methoxysulphadiazine with dioxane, chloroform and tetrahydrofuran have been investigated by X-ray analysis, differential scanning calorimetry and thermogravimetry. These species are clathrates with 1:1 host-guest stoichiometry crystallizing in space group P21/c with very similar unit cell parameters. Their structures are based on a common isostructural host framework in which the guest molecules occupy channels with the narrowest constriction being 2 A. The unusual stability of these species and their decomposition to a common polymorph (Form I) of 5-methoxysulphadiazine are rationalized on the basis of crystal packing analysis, potential energy calculations and estimates of the activation energy for desolvation. Hydrogen bonding patterns between host molecules in the clathrates are compared with those occurring in two polymorphic forms of the parent sulphonamide.

Electron spin resonance studies of low symmetry oxomolybdenum(V) ions diluted in the pseudo-isostructural chlorotin(IV) moiety

The results of a single crystal ESR study of LMoOCl2 diluted in the isostructural host LSnCl3 are reported. These results confirm the monoclinic ESR symmetry deduced previously from frozen solution measurements giving the rotation angle between the tensor axes as 35° compared with 33° in previous study. The single crystal data show that none of the principal g- or A-tensor axes coincide with metal-ligand directions.

Electron spin resonance of Gd3+ in triacetate tetrahydrates of Sm, Nd, Er, Y, Yb, and Dy

An EPR study of Gd3+-doped single crystals of triacetate tetrahydrates of Sm, Nd, Er, Y, Yb, and Dy has been made in order to study the systematics of EPR spectra in these homologous isostructural hosts at various temperatures. The absolute signs of the spin Hamiltonian parameters are determined from intensities of lines at liquid helium temperatures. The parameters are evaluated using a rigorous least-squares fitting procedure. As far as the systematics of the parameters are concerned, it is found that while the parameter b22 varies linearly, the parameter b02 varies approximately linearly with the atomic radius of the host rare-earth ion. The EPR studies presented here suggest a monoclinic symmetry at the site of the rare-earth ions in the rare-earth triacetate tetrahydrate crystals investigated. As well, all rare-earth sites are found to be magnetically equivalent. The EPR data also suggest that the Nd host undergoes some structural change at about 238 K.

Host‐Lattice Effects in the EPR Spectra of Gd3+ Doped Hydrated Single Crystals of Rare‐Earth Chlorides, Nitrates, and Sulphates

AbstractLarge amount of X‐band EPR data, for external field orientations in both, the zx and xy planes, are obtained for Gd3+ ion doped rare‐earth trichloride hexahydrate (RCH), rare‐earth trisulfate octahydrate (RSO), and rare‐earth trinitrate hexahydrate (RNH) single crystals. A rigorous least‐squares fitting procedure is used to evaluate the spin Hamiltonian parameters g‖, g⊥ and b (including those with negative m values). Approximate linear dependences upon the host rare‐earth ion radius is found on both, the parameters b and b within each family of the isostructural hosts investigated.

Electron spin resonance of Gd3+ in trifluorides of La, Ce, Pr, and Nd

An EPR study of Gd3+-doped single crystals of CeF3, LaF3, PrF3, and NdF3 has been made in order to study the systematics of spectra in these homologous isostructural hosts. The method of preparation of samples is presented. The measurements are carried out at all three—room, liquid nitrogen, and liquid helium—temperatures. Thus, the absolute signs of all the spin Hamiltonian parameters are determined from intensities of lines at liquid helium temperatures. The parameters are evaluated from a simultaneous fitting of all lines observed in the zx and xy planes in a rigorous least-squares fitting procedure, which utilizes numerical diagonalization of the spin Hamiltonian matrix. As far as the systematics of the parameters are concerned, it is found that the parameter b02 varies linearly with the atomic radius of the host rare-earth ion, while the parameter b22 does not show any such behavior. It it hoped that the experimental results presented in this paper would be helpful in further theoretical understanding of the interaction of the Gd3+ ion with its environment due to simplicity of the rare-earth trifluoride crystal structure, in that in these crystals there are no water molecules present.