Interligand Interactions Research Articles

Thermodynamics and Modeling of Collective Effects in the Organic Ligand Shell of Colloidal Quantum Dots.

ConspectusColloidal nanocrystals are an interesting platform for studying the surface chemistry of materials due to their high surface area/volume ratios, which results in a large fraction of surface atoms. As synthesized, the surfaces of many colloidal nanocrystals are capped by organic ligands that help control their size and shape. While these organic ligands are necessary in synthesis, it is often desirable to replace them with other molecules to enhance their properties or to integrate them into devices. Traditionally, these ligand exchanges have been studied using 1H NMR. Recently, isothermal titration calorimetry has proven itself to be a highly versatile measurement technique, yielding insights into the thermodynamics of the reaction, including the enthalpy and entropy of the reaction, that are inaccessible via 1H NMR. The most common technique for analyzing ligand exchange reactions has been to model these data with one-site and two-site Langmuir isotherm models. Unfortunately, a detailed analysis of 1H NMR and isothermal titration calorimetry data simultaneously demonstrates that these simple models are inadequate for understanding ligand reactions on the surfaces of colloidal nanocrystals.In this Account, we illustrate that the collective effects of the aliphatic chains of the organic ligands on the surfaces of colloidal nanocrystals dictate much of the reaction thermodynamics and how we have manipulated the thermodynamics of ligand exchange reactions by modulating the geometry and length of the organic ligands, the shape of the underlying nanocrystal, and the size of the nanocrystal. One of the main contributions of our body of work is the implementation of a modified Ising model, which accounts for nearest neighbor interactions, or collective effects, between the surface ligands and can be used to fit self-consistent thermodynamic parameters to describe the ligand exchange reactions. Using this model, we reveal the entropic and enthalpic factors of both the head binding group and the tail group that drive exchange reactions. In particular, we demonstrate the significant interligand interactions and the effect that ligand geometry and length have on these interactions. Further, we have shown that as the size of the nanocrystal increases, the interactions between the organic ligands become much stronger, and we have provided evidence that structural differences are present in the solvated ligand shell based on the ligand length. We also demonstrate in the case of ligand exchanges on cadmium selenide quantum dots that the crystal facet has very little impact on the thermodynamics of the ligand exchange using (100) and (111) faceted quantum dots. These findings rely critically on using a composition dependent model. We believe that this model or another accounting for these collective effects is critical for accurately analyzing the thermodynamics of the organic ligand shells for the field moving forward.

Theoretical Investigation of Interconversion Pathways and Intermediates in Hydride/Silyl Exchange of Niobocene Hydride-Silyl Complexes: A DFT Study Incorporating Conformational Search and Interaction Region Indicator (IRI) Analysis.

Niobocene hydride-silyl complexes exhibit intriguing structural characteristics with the potential for direct hydride/silyl exchange, where hydride migration plays a crucial role during conformational interconversion. In this study, quantum chemical calculations were utilized to investigate the transformation pathways involved in hydride/silyl exchange in niobocene trihydride complexes with various dichlorosilanes, including SiCl2Me2, SiCl2iPr2, and SiCl2MePh ligands. The conformational changes and hydride shifts within these niobocene hydride-silyl complexes were examined, and key intermediates were identified. Electronic wavefunction analysis provided insights into the coordination configurations and the nature of inter-ligand interactions. Interaction region indicator (IRI) analysis revealed Van der Waals interactions between chloride atoms and cyclopentadienyl rings, as well as between chloride atoms and Me, iPr, and Ph groups. Notably, distinct interactions between hydride ligands, including those from Si-H moieties and coordinated hydrogen atoms, were observed. Both lateral and central conformations, with respect to silicon coordination to the niobium center, were considered. This study enhances the understanding of intermediate conformations in the hydride/silyl exchange process and provides a detailed characterization of inter-ligand interactions, offering valuable insights for analyzing metallocene complexes with organic ligand coordination.

Evidence and Structural Insights into a Ligand-Mediated Phase Transition in the Solvated Ligand Shell of Quantum Dots.

As synthesized, nanocrystal surfaces are typically covered in coordinating organic ligands, and the degree of packing and order of these ligands are ongoing questions in the field of colloidal nanocrystals, particularly in the solution state. Recently, isothermal titration calorimetry coupled with 1H NMR has been used to probe ligand exchanges on colloidal quantum dots, revealing the importance of the composition of the ligand shell on exchange thermodynamics. Previous work has shown that the geometry and length of a ligand's aliphatic chain can influence the thermodynamics of exchange. This has been attributed to interligand interactions, and the use of a modified Ising model simulation to account for these collective effects has been critical in describing these reactions. In this report, we explore the reaction between indium phosphide quantum dots and zinc chloride on a size series of nanocrystals capped with two different lengths of aliphatic, straight-chain carboxylate ligands to investigate the effect that nanocrystal size has on these interligand interactions. We demonstrate that interligand interactions increase as the nanocrystal size increases, changing the thermodynamics of the ligand exchange reaction. Critically, we show that a self-consistent model of these ligand exchanges does not fit the data without the use of a phase transition term in the model and that the strength of this phase transition depends on the nanocrystal size. Combined with solution state X-ray diffraction, these results provide indirect evidence that ligands are ordered on nanocrystals in the solution state.

Assemble-Disassemble-Reassemble Dynamics in Copper Nanocluster-Based Superstructures.

Assembling metal nanoclusters (MNCs) to form superstructures generates exciting photophysical properties distinct from those of their discrete precursors. Controlling the assembly process of MNCs and understanding the assembly-disassembly dynamics can have implications in achieving the reversible self-assembly of MNCs. The formation of self-assembled copper nanoclusters (CuNCs) as homogeneous superstructures and the underlying mechanisms governing such a process remain unexplored. Smart molecular imprinting of surface ligands can establish the forces necessary for the formation of such superstructures. Herein, we report highly luminescent, ordered superstructures of 4-phenylimidazole-2-thiol (4-PIT)-protected CuNCs with the help of l-ascorbic acid as a secondary ligand. Through a comprehensive spectroscopic analysis, we deciphered the mechanism of the self-assembly process, where the role of interligand H-bonding and C-H-π interactions was established. Notably, efficient reversibility of assembly-disassembly was demonstrated by re-establishing the interligand interactions and regenerating their photophysical and morphological signatures.

Bis-oxazoline derivatives as ancillary ligands for bis-cyclometalated iridium complexes

Organometallic iridium complexes with two cyclometalated ligands (C^N) and one bis-oxazoline derived ancillary ligand (L^X), i.e. (C^N)2Ir(L^X), are reported. The C^N ligands are 1-phenylpyrazoline (ppz), 2-(4,6-difluorophenyl)pyridine (F2ppy), 2-phenylpyridine (ppy), 1-phenylisoquinoline (piq). The box ligand is (4S-+)-phenyl-α-[(4S)-phenyloxazolidin-2-ylidene]-2-oxazoline-2-acetonitrile. The emission of these complexes span across the visible and into the near-ultraviolet region of the electromagnetic spectrum with moderate to high photoluminescence quantum yields (ΦPL = 0.45–1.0). These complexes were found to emit from a metal-ligand to ligand charge transfer (ML'LCT) state and have lifetimes (1.3–2.1 μs), radiative rates (105 s−1), and nonradiative rates (104–105 s−1) comparable to state-of-the-art iridium emitters. The (ppy)2Ir(BOX-CN) complexes were resolved into the Δ- and Λ- diastereomers using differences in their solubility and additionally characterized by x-ray crystallography, stability, and chiroptic studies. The high ΦPL of these isomers results in the best to date brightness for circularly polarized luminescence (CPL) from iridium complexes (7.0 M−1 cm−1), with dissymmetry factors of −0.57 × 10−3 and +1.9 × 10−3 for 3Δ and 3Λ, respectively. The significant difference in CPL magnitude between 3Δ and 3Λ likely arises from interligand interactions (edge-to-face arrangement versus strong π-π interaction) for the pendant phenyl ring of the BOX-CN ligand which differ for the two isomers.

H(N3)dap (Hdap = 2,6-Diaminopurine) Recognition by Cu2(EGTA): Structure, Physical Properties, and Density Functional Theory Calculations of [Cu4(μ-EGTA)2(μ-H(N3)dap)2(H2O)2]·7H2O.

Reactions in water between the Cu2(µ-EGTA) chelate (EGTA = ethylene-bis(oxyethyleneimino)tetraacetate(4-) ion) and Hdap in molar ratios 1:1 and 1:2 yield only blue crystals of the ternary compound [Cu4(μ-EGTA)2(μ-H(N3)dap)2(H2O)2]·7H2O (1), which has been studied via single-crystal X-ray diffraction and various physical methods (thermal stability, spectral and magnetic properties), as well as DFT theoretical calculations. In the crystal, uncoordinated water is disordered. The tetranuclear complex molecule also has some irrelevant disorder in an EGTA-ethylene moiety. In the complex molecule, both bridging organic molecules act as binucleating ligands. There are two distorted five- and two six-coordinated Cu(II) centers. Each half of EGTA acts as a tripodal tetradentate Cu(II) chelator, with a mer-NO2 + O(ether, distal) conformation. Hdap exhibits the tautomer H(N3)dap, with the dissociable H-atom on its less basic N-heterocyclic atom. These features favor the efficient cooperation between Cu-N7 or Cu-N9 bonds with appropriate O-EGTA atoms, as N6-H···O or N3-H···O interligand interactions, respectively. The bridging role of both organics determines the tetranuclear dimensionality of the complex. In this crystal, such molecules associate in zig-zag chains built by alternating π-π interactions between the five- or six-atom rings of Hdap ligands of adjacent molecules. DFT theoretical calculations (using two different theoretical models and characterized by the quantum theory of "atoms in molecules") reveal the importance of these π-π interactions between Hdap ligands, as well as those corresponding to the referred hydrogen bonds in the contributed tetranuclear molecule.

The Copper(II)-Thiodiacetate (tda) Chelate as Efficient Receptor of N9-(2-Hydroxyethyl)Adenine (9heade): Synthesis, Molecular and Crystal Structures, Physical Properties and DFT Calculations of [Cu(tda)(9heade)(H2O)]·2H2O.

Considering that Cu(tda) chelate (tda: dithioacetate) is a receptor for adenine and related 6-aminopurines, this study reports on the synthesis, molecular and crystal structures, thermal stability, spectral properties and DFT calculations related to [Cu(tda)(9heade)(H2O)]·2H2O (1) [9heade: N9-(2-hydroxyethyl)adenine]. Concerning the molecular recognition of (metal chelate)-(adenine synthetic nucleoside), 1 represents an unprecedented metal binding pattern (MBP) for 9heade. However, unprecedentedly, the Cu(tda)-9heade molecular recognition in 1 is essentially featured in the Cu-N1(9heade) bond, without any N6-H⋯O(carboxyl tda) interligand interaction. Nevertheless, N1 being the most basic donor for N9-substituted adenines, this Cu-N1 bond is now assisted by an O2-water-mediated interaction (N6-H⋯O2 and O2⋯Cu weak contact). Also, in the crystal packing, the O-H(ol) of 9heade interacts with its own adenine moiety as a result of an O3-water-mediated interaction (O(ol)-H⋯O3 plus O3-H36⋯π(adenine moiety)). Both water-mediated interactions seem to be responsible for serious alterations in the physical properties of crystalline or grounded samples. Density functional theory calculations were used to evaluate the interactions energetically. Moreover, the quantum theory of atoms-in-molecules (QTAIM), in combination with the noncovalent interaction plot (NCIPlot), was used to analyze the interactions and rationalize the existence and relative importance of hydrogen bonding, chalcogen bonding and π-stacking interactions. The novelty of this work resides in the discovery of a novel binding mode for N9-(2-hydroxyethyl)adenine. Moreover, the investigation of the important role of water in the solid state of 1 is also relevant, along with the chalcogen bonding interactions demonstrated by the density functional theory (DFT) study.

Development of an α-synuclein positron emission tomography tracer for imaging synucleinopathies

Synucleinopathies are characterized by the accumulation of α-synuclein (α-Syn) aggregates in the brain. Positron emission tomography (PET) imaging of synucleinopathies requires radiopharmaceuticals that selectively bind α-Syn deposits. We report the identification of a brain permeable and rapid washout PET tracer [18F]-F0502B, which shows high binding affinity for α-Syn, but not for Aβ or Tau fibrils, and preferential binding to α-Syn aggregates in the brain sections. Employing several cycles of counter screenings with invitro fibrils, intraneuronal aggregates, and neurodegenerative disease brain sections from several mice models and human subjects, [18F]-F0502B images α-Syn deposits in the brains of mouse and non-human primate PD models. We further determined the atomic structure of the α-Syn fibril-F0502B complex by cryo-EM and revealed parallel diagonal stacking of F0502B on the fibril surface through an intense noncovalent bonding network via inter-ligand interactions. Therefore, [18F]-F0502B is a promising lead compound for imaging aggregated α-Syn in synucleinopathies.

Impact of Uniform Facets on the Thermodynamics of Ligand Exchanges on Colloidal Quantum Dots

Nanocrystal surfaces play a critical role in dictating their physical and chemical properties. Colloidal semiconductor nanocrystals, or quantum dots, are generally synthesized with insulating aliphatic ligands, but these ligands can be post-synthetically exchanged with other molecular species for a variety of applications. While previous work has investigated the thermodynamics of ligand exchanges on quasi-spherical quantum dots through sensitive isothermal titration calorimetry and 1H NMR measurements, the influence of well-defined crystal facets on the propensity of these ligand exchanges is yet to be explored using these techniques. We studied the exchange of native cadmium carboxylate ligands for zinc chloride ligands on (111) faceted cadmium selenide tetrahedrons and (100) faceted cadmium selenide cubes. From these measurements, we find the unexpected result that the thermodynamics of this ligand exchange between these facets is nearly identical. Further, a modified Ising model was used to fit both the calorimetric and 1H NMR data to extract thermodynamic parameters for the exchange. These simulations suggest that the observed enthalpic differences can be mostly attributed to varying inter-ligand interactions on the (111) and (100) facets.

Half‐Sandwich Manganese Complex Bearing Fused Oxazoline‐NHC Ligand: Conformational Analysis and Evaluation in Asymmetric Ketone Hydrosilylation

AbstractThe first manganese complex bearing a chiral N‐heterocyclic carbene (NHC) ligand was prepared and studied by spectroscopic methods and X‐ray diffraction. While IR spectroscopy revealed the existence of two isomers in solution with distinct νCO band patterns, DFT calculations indicated that these isomers correspond to rotamers around the Mn−NHC bond and their different spectroscopic properties were rationalized by the occurrence of attractive π(C=C)⋅⋅⋅π*(C≡O) or σ(C−H)⋅⋅⋅π*(C≡O) intramolecular interligand interactions. The evaluation of this complex in catalytic hydrosilylation of acetophenone using Ph2SiH2 under UV irradiation led to the formation of the corresponding (R)‐alcohol with low enantioselectivity.

Spontaneous Patterning of Binary Ligand Mixtures on CdSe Nanocrystals: From Random to Janus Packing.

Binary compositions of surface ligands are known to improve the colloidal stability and fluorescence quantum yield of nanocrystals (NCs), due to ligand-ligand interactions and surface organization. Herein, we follow the thermodynamics of a ligand exchange reaction of CdSe NCs with alkylthiol mixtures. The effects of ligand polarity and length difference on ligand packing were investigated using isothermal titration calorimetry (ITC). The thermodynamic signature of the formation of mixed ligand shells was observed. Correlating the experimental results with thermodynamic mixing models has allowed us to calculate the interchain interactions and to infer the final ligand shell configuration. Our findings demonstrate that, in contrast to macroscopic surfaces, the small dimensions of the NCs and the subsequent increased interfacial region between dissimilar ligands allow the formation of a myriad of clustering patterns, controlled by the interligand interactions. This work provides a fundamental understanding of the parameters determining the ligand shell structure and should help guide smart surface design toward NC-based applications.

Interligand Interactions in Half-Sandwich Nickelacarboranes with Phosphine Ligands: Away from Skeletal Rearrangements

Reactions of nickel(II) phosphine complexes [(dppe)NiCl2], [(MePh2P)2NiCl2] and [(Ph3P)2NiCl2] with C-substituted nido-carboranes [7-R-nido-7,8-C2B9H11]− (R = Me, Ph, C(NHCy)2+) were studied. The reactions with [(dppe)NiCl2] lead to the corresponding nickelacarboranes 3,3-(dppe)-1-R-closo-3,1,2-NiC2B9H10 with absent or negligible steric interactions between the ligands. The reactions of [(MePh2P)2NiCl2] with [7-R-nido-7,8-C2B9H11]− (R = H, Me, Ph) result in nickelacarboranes 3,3-(MePh2P)2-1-R-closo-3,1,2-NiC2B9H10 with noticeable steric loading, while the reaction with [7-(CyNH)2C-nido-7,8-C2B9H11] proceeds with the displacement of one phosphine ligand with the formation of a mixed-ligand phosphine-chloride half-sandwich complex 3-MePh2P-3-Cl-1-(CyNH)2C-closo-3,1,2-NiC2B9H10.

Iron(II) complexes of 2,6-bis(imidazo[1,2-a]pyridin-2-yl)pyridine and related ligands with annelated distal heterocyclic donors.

Following a published synthesis of 2,6-bis(imidazo[1,2-a]pyridin-2-yl)pyridine (L1), treatment of α,α'-dibromo-2,6-diacetylpyridine with 2 equiv. 2-aminopyrimidine or 2-aminoquinoline in refluxing acetonitrile respectively gives 2,6-bis(imidazo[1,2-a]pyrimidin-2-yl)pyridine (L2) and 2,6-bis(imidazo[1,2-a]quinolin-2-yl)pyridine (L3). Solvated crystals of [Fe(L1)2][BF4]2 (1[BF4]2) and [Fe(L2)2][BF4]2 (2[BF4]2) are mostly high-spin, although one solvate of 1[BF4]2 undergoes thermal spin-crossover on cooling. The iron coordination geometry is consistently distorted in crystals of 2[BF4]2 which may reflect the influence of intramolecular, inter-ligand N⋯π interactions on the molecular conformation. Only 1 : 1 Fe : L3 complexes were observed in solution, or isolated in the solid state; a crystal structure of [FeBr(py)2L3]Br·0.5H2O (py = pyridine) is presented. A solvate crystal structure of high-spin [Fe(L4)2][BF4]2 (L4 = 2,6-di{quinolin-2-yl}pyridine; 4[BF4]2) is also described, which exhibits a highly distorted six-coordinate geometry with a helical ligand conformation. The iron(II) complexes are high-spin in solution at room temperature, but 1[BF4]2 and 2[BF4]2 undergo thermal spin-crossover equilibria on cooling. All the compounds exhibit a ligand-based emission in solution at room temperature. Gas phase DFT calculations mostly reproduce the spin state properties of the complexes, but show small anomalies attributed to intramolecular, inter-ligand dispersion interactions in the sterically crowded molecules.

A Tetranuclear Ni(II)-Cubane Cluster Molecule Build by Four µ3-O-Methanolate (MeO) Ligands, Externally Cohesive by Four Unprecedented Bridging µ2-N7,O6-Acyclovirate (acv-H) Anions

Metal ion interactions with nuclei acids and their constituents represent a multi-faceted and growing research field. This contribution deals with molecular recognition between synthetic purine 17 nucleosides and first-row transition metal complexes, with O- and/or N-amino chelators which are able to 18 engage in intra-molecular N-H···(N or O) and O-H···(N or O) interligand interactions. Crystals of these complexes can also display inter-molecular aromatic π-stacking and/or other non-conventional interactions. In this manuscript, we used 2-(2-aminoethoxy)ethanol (2aee) as a potential N,O(e),O(ol)-chelator for nickel(II). However, unexpectedly, the reaction between NiCl2, acyclovir (acv), and 2aee in methanol afforded parallelepiped apple-green crystals of [Ni(acv-H)(MeO)(H2O)]4·8H2O, (1) a tetranuclear molecule with an equimolar Ni(II):µ3-methanolate(1-):µ2-N7,O6-acyclovirate(1-) (acv-H) ratio. The µ2-N7,O6-(acv-H) metal-binding pattern (MBP) is unprecedented in terms of both its anionic and bridging roles. The single-crystal X-ray diffraction structure as well as thermogravimetric analysis and the (FT-IR +Vis-UV) spectra of 1 are reported. Theoretical density functional theory (DFT) calculations are used to analyse the antiparallel π-stacking interactions that govern the formation of self-assembled dimers in the solid state.

Positive Cooperativity Induced by Interstrand Interactions in Silver(I) Complexes with α,α'-Diimine Ligands.

The allosteric positive cooperativity accompanying the formation of compact [CuI(α,α′‐diimine)2]+ building blocks contributed to the historically efficient synthesis of metal‐containing catenates and knotted assemblies. However, its limited magnitude can easily be overcome by the negative chelate cooperativity that controls the overall formation of related polymetallic multistranded helicates and grids. Despite the more abundant use of analogous dioxygen‐resistant [AgI(α,α′‐diimine)2]+ units in modern entangled metallo‐supramolecular assemblies, a related thermodynamic justification was absent. Solid‐state structural characterizations show the successive formation of [AgI(α,α′‐diimine)(CH3CN)][X] and [AgI(α,α′‐diimine)2][X] upon the stepwise reactions of α,α′‐diimine=2,2′‐bipyridine (bpy) or 1,10‐phenanthroline (phen) derivatives with AgX (X=BF4 −, ClO4 −, PF6 −). In room‐temperature, 5–10 mM acetonitrile solutions, these cationic complexes exist as mixtures in fast exchange on the NMR timescale. Spectrophotometric titrations using the unsubstituted bpy and phen ligands point to the statistical (=non‐cooperative) binding of two successive bidentate ligands around AgI, a mechanism probably driven by the formation of hydrophobic belts, that overcomes the unfavorable decrease in the positive charge borne by the metallic cation. Surprisingly, the addition of methyl groups adjacent to the nitrogen donors (6,6′ positions in dmbpy; 2,9 positions in dmphen) induces positive cooperativity for the formation of [Ag(dmbpy)2]+ and [Ag(dmphen)2]+, a trend assigned to additional stabilizing interligand interactions. Adding rigid and polarizable phenyl side arms in [Ag(Brdmbpy)2]+ further reinforces the positively cooperative process, while limiting the overall decrease in metal–ligand affinity.

Computational study of ground-state properties of μ2 -bridged group 14 porphyrinic sandwich complexes.

The structural properties of μ2 -bridged porphyrinic double-decker complexes are investigated and the influence of various ligands, metals, substituents, and bridging atoms on the dominant structural motif is elucidated. A variety of quantum chemical methods including semiempirical (SQM) methods and density functional theory (DFT) is assessed for the calculation of ecliptic and staggered conformational energies. Local coupled cluster (DLPNO-CCSD(T1)) data are generated for reference. The r2 SCAN-3c composite scheme as well as the B2PLYP-D4/def2-QZVPP approach are identified as reliable methods. Energy decomposition analyses (EDA) and localized molecular orbital analyses (LMO) are used to investigate the bonding situation and the nature of the inter-ligand interaction energy underlining the crucial role of attractive London dispersion interactions. Targeted modification of the bridging atom, e.g., by replacing O2- by S2- is shown to drastically change the major structural features of the investigated complexes. Further, the influence of different substituents of varying size at the phthalocyanine ligand regarding the dominant conformation is described.

Self-Assembly of Molecular Trefoil Knots Featuring Pentadecanuclear Homoleptic AuI -, AuI /AgI -, or AuI /CuI -Alkynyl Coordination.

Metal-free and metal-containing molecular trefoil knots are fascinating ensembles that are usually covalently assembled, the latter requiring the rational design of di- or multidentate/multipodal ligands as connectors. In this work, we describe the self-assembly of pentadecanuclear AuI trefoil knots [Au15 (C≡CR)15 ] from monoalkynes HC≡CR (R=9,9-X2 -fluorenyl with X=nBu, n-hexyl) and [AuI (THT)Cl]. Hetero-bimetallic counterparts [Au9 M6 (C≡CR)15 ] (M=Cu/Ag) were self-assembled by reactions of [Au15 (C≡CR)15 ] with [Cu(MeCN)4 ]+ /AgNO3 and HC≡CR. The type of pentadecanuclear trefoil knots described herein is characterized by X-ray crystallography, 2D NMR and HR-ESI-MS. [Au9 Cu6 (C≡CR)15 ] is relatively stable in hexane; its excited state properties were investigated. DFT calculations revealed that non-covalent metal-metal and metal-ligand interactions, together with longer alkyl chain-strengthened inter-ligand dispersion interactions, govern the stability of the trefoil knot structures.

MOFs with 12-Coordinate 5f-Block Metal Centers.

We have constructed an unprecedented MOF platform that accommodates a range of 5f-block metal ions (Th4+, U4+, Np4+, Pu4+) as the primary building block. The isoreticular actinide metal-organic frameworks (An-MOFs) exhibit periodic trends in the 12-coordinate metal environment, ligand configuration, and resulting ultramicroporosity. It holds potential in distinguishing neighboring tetravalent actinides. The metal ionic radius, carboxylate bite angle, anthracene plane twisting, interligand interactions, and countercation templating collectively determine an interplay between solvation, modulation, and complexation, resulting in a coordination saturation of the central actinide, while lanthanide counterparts are stabilized by the formation of a dimer-based motif. Quantum chemical calculations indicate that this large coordination number is only feasible in the high-symmetry environment provided by the An-MOFs. This category of MOFs not only demonstrates autoluminescence (4.16 × 104 counts per second per gram) but also portends a wide-bandgap (2.84 eV) semiconducting property with implications for a multitude of applications such as hard radiation detection.

TADF: Enabling luminescent copper(i) coordination compounds for light-emitting electrochemical cells.

The last decade has seen a surge of interest in the emissive behaviour of copper(i) coordination compounds, both neutral compounds that may have applications in organic light-emitting doides (OLEDs) and copper-based ionic transition metal complexes (Cu-iTMCs) with potential use in light-emitting electrochemical cells (LECs). One of the most exciting features of copper(i) coordination compounds is their possibility to exhibit thermally activated delayed fluorescence (TADF) in which the energy separation of the excited singlet (S1) and excited triplet (T1) states is very small, permitting intersystem crossing (ISC) and reverse intersystem crossing (RISC) to occur at room temperature without the requirement for the large spin–orbit coupling inferred by the presence of a heavy metal such as iridium. In this review, we focus mainly in Cu-iTMCs, and illustrate how the field of luminescent compounds and those exhibiting TADF has developed. Copper(i) coordination compounds that class as Cu-iTMCs include those containing four-coordinate [Cu(P^P)(N^N)]+ (P^P = large-bite angle bisphosphane, and N^N is typically a diimine), [Cu(P)2(N^N)]+ (P = monodentate phosphane ligand), [Cu(P)(tripodal-N3)]+, [Cu(P)(N^N)(N)]+ (N = monodentate N-donor ligand), [Cu(P^P)(N^S)]+ (N^S = chelating N,S-donor ligand), [Cu(P^P)(P^S)]+ (P^S = chelating P,S-donor ligand), [Cu(P^P)(NHC)]+ (NHC = N-heterocyclic carbene) coordination domains, dinuclear complexes with P^P and N^N ligands, three-coordinate [Cu(N^N)(NHC)]+ and two-coordinate [Cu(N)(NHC)]+ complexes. We pay particular attention to solid-state structural features, e.g. π-stacking interactions and other inter-ligand interactions, which may impact on photoluminescence quantum yields. Where emissive Cu-iTMCs have been tested in LECs, we detail the device architectures, and this emphasizes differences which make it difficult to compare LEC performances from different investigations.

Crystal structure of [Rh2(μ-OAc)2(μ-HNOCCF3)2(theophylline)2]·6H2O. Metal bonding to theophylline at the unexpected N(9) site due to the crystal packing effect and a review on intra-molecular interligand interactions affecting metal bonding properties of theophylline

• Crystal structure of a dinuclear Rh 2+ complex of theophylline was determined. • The Rh‒Rh core is occupied at either axial-side by theophylline ligands through N9. • Metal bonding not to expected N7 but to N9 is due to the crystal packing effect. • A discrete, cyclic hexameric water cluster intercalates between theophylline rings. • Metal binding sites of theophylline are reviewed in terms of interligand interaction. Reaction of theophylline with [Rh 2 (μ-OAc) 2 (μ-HNOCCF 3 ) 2 ] gave [Rh 2 (μ-OAc) 2 (μ-HNOCCF 3 ) 2 (theophylline) 2 ]·6H 2 O ( 1 ), whose crystal structure was determined by single-crystal X-ray diffraction. The dirhodium core, where the two different acetato and acetamidato ligands bridging the Rh‒Rh bond are in a trans configuration, is occupied at either axial-side by two theophylline ligands through N(9) with the formation of two kinds of intra-molecular interligand C−H (theophylline)···O hydrogen bonds, one being a bifurcated hydrogen bond between the C(3)-methyl hydrogen as a donor and the acetato and amidato oxygens as acceptors and the other between the C(8) hydrogen and the acetato oxygen. In the crystal lattice, a discrete, hydrogen-bonding, cyclic hexameric water cluster with the flattened chair conformation is sandwiched between theophylline bases, providing the first water hexagon that intercalates between aromatic rings. The participation of the acetamidato NH group in the formation of a hydrogen bond with a water molecule belonging to the water hexagon that governs the crystal packing makes it impossible for the acetamidato ligand to form an intra-molecular hydrogen bond with O(6), causing the failure of the metal bonding to theophylline through N(7). A critical review on metal bonding properties of theophylline observed in so far reported crystal structures is given, emphasizing the significance of intra-molecular interligand interactions (H-bonding, electrostatic repulsion, and steric constraint) as a factor that could affect metal binding sites/modes of theophylline.