Our recent observations of an unexpected Ce(III) hydrolysis product from the reaction of 4-amino-1,2,4-triazole (4-NH₂-1,2,4-Triaz) with CeCl₃·7H₂O, [Ce₆(μ₃-O)₄(μ₃-OH)₂(μ₃-Cl)₂(Cl)₆(μ₂-4-NH₂-1,2,4-Triaz)₁₂]·7H₂O, the first high-nuclearity lanthanide complex where all Ln atoms are connected pairwise through 12 N-donor ligands or 12 neutral bridging ligands of any type, prompted us to explore the utility of this ligand in trapping additional f-element examples. Reactions of LnCl₃·6H₂O (Ln = Nd, Eu, Ho) with a large excess of 4-NH₂-1,2,4-Triaz (20 equiv) and with the addition of small amounts of water to help solubilize the metal salts led to the isolation of the unique hydrolysis products [Nd₆(μ₃-OH)₈Cl₆(μ₂-4-NH₂-1,2,4-Triaz)₁₂][Cl₄]·2H₂O, [Eu₆(μ₆-Cl)_0.23(μ₃-O_0.77)4(μ₃-O)_2.6(μ₃-Cl)_0.4Cl₆(μ₂-4-NH₂-1,2,4-Triaz)₁₂], and [Ho₆(μ₆-Cl)_0.21(μ₃-O_0.79)₄(μ₃-OH)₂Cl₆(μ₂-4-NH₂-1,2,4-Triaz)₁₂][Cl]_3.4. We also report a Ce(III) analogue prepared in glassware contaminated with Pb(OAc)₂, namely, [Ce₆(μ₃-OH)₈(BrPbBr₅)(μ₂-4-NH₂-1,2,4-Triaz)_11.5(OH₂)₆][Pb_0.84Br_4.2][Br]_3.8·2(4-NH₂-1,2,4-Triaz)·3.6H₂O. The Nd(III) complex is the structurally most ordered with a clear [Nd₆(μ₃-OH)₈] cluster core, while the Eu(III) and Ho(III) compounds contain partial occupancy of a μ6 position and thus result in an incomplete Ln₆O₉ cluster core formation. The crystallographic results suggest that the 4-NH₂-1,2,4-Triaz ligand brings Ln(III) ions together, followed by the formation of an Ln₆O₈ or Ln₆O₉ core with whatever remaining anions or ligands can be incorporated. Given the complexity of the hydrolysis products of nuclear waste, we expect to continue to find a myriad of closely related complex structures of these types for the f-elements. 

In search of ionic liquids (ILs) with multiple types of soft donor atoms capable of preferentially complexing a range of soft metal ions over harder ions, we investigated structural clues to the role of hydrogen bonding in IL behavior through a series of salts with anions containing both N- and S-donor atoms based on azole thiolates. Reaction of equimolar amounts of triethylamine (Et₃N) or diisobutylamine (DBA) with 1-phenyl-1H-tetrazole-5-thiol (PhTzSH), 1-methyl-1H-tetrazole-5-thiol (MeTzSH), or 5-methyl-1,3,4-dithiazole-2-thiol (MeDiTSH) yielded [Et₃NH][MeTzS] (1), a yellow liquid, and the low melting yellow solids [DBAH][MeTzS] (2), [Et₃NH][PhTzS] (3), [DBAH][PhTzS] (4), [Et₃NH][MeDiTS] (5), and [DBAH][MeDiTS] (6). Thermal analysis revealed that all of them qualify as ILs with melting points below 100 °C. Single crystal X-ray structure analysis of 2–6 revealed the presence of an extensive H-bonding network that includes the rare N–H⋯S hydrogen bonds in 3, 4, and 6. These weaker interactions appear to significantly influence thermal behavior, where strong bonding leads to higher melting temperatures and lower decomposition points.

Albeit tris(8-hydroxyquinolinato) aluminum (Alq₃) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as π-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S₁ level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq₃ and related materials, both as solids and thin films with quantum yields (QYs) up to 40–50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C.

Using Ce(III) as both a representative lanthanide and actinide analog, the ability of mixtures of acidic and basic azoles to allow direct access to homoleptic N-donor f-element complexes in one pot reactions from hydrated salts as starting materials was examined by reacting mixtures of 4-amino-1,2,4-triazole (4-NH2-1,2,4-Triaz), 5-amino-tetrazole (5-NH2-HTetaz), and 1,2,3-triazole (1,2,3-HTriaz) in 1:1 and 1:3 ratios with CeCl3 center dot 7H(2)O, [C(2)mim](3)[CeCl6] ([C(2)mim](+) = 1-ethyl-2-methylimidazolium), and Ce(NO3)(3)center dot 6H(2)O. Although unsuccessful in our goal, structural analysis revealed that neutral 4-NH2-1,2,4-Triaz is structure directing via eta(2)mu(2)kappa(2) bridging, with the formation of the dinuclear complexes [Ce2Cl2(mu(2)-4-NH2-1,2,4-Triaz)(4)(H2O)(8)]Cl-4 center dot 4H(2)O, [Ce-2(mu(2)-4-NH2-1,2,4-Triaz)(4)(4-NH2-1,2,4-Triaz)(2)(Cl)(6)], and [4-NH2-1,2,4-HTriaz][Ce-2(mu(2)-4-NH2-1,2,4-Triaz)(2)(mu(2)-NO3)(NO3)(6)(H2O)(2)]. When the synthetic conditions favored hydrolysis, the hexanuclear Ce(III) complex [Ce-6(mu(3)-O)(4)(mu(3)-OH)(2)(mu(3)-Cl)(2)(Cl)(6)(mu(2)-4-NH2-1,2,4-Triaz)(12)]center dot 7H(2)O was isolated. This unexpected hydrolysis product represents the first example of a high nuclearity lanthanide complex where all Ln atoms are pairwise connected through 12 N-donor ligands or 12 neutral bridging ligands of any type, a rare example of incorporation of non-oxo coordinating anions in the M6X8 core, and the first reported Ce(III) hexanuclear complex of this type.

Continuing our investigations of ionic liquid (IL) based routes to a library of f-element/soft donor complexes which could be studied crystallographically, we have explored the dissolution of f-element salts in protic imidazole-based ILs containing only soft donors at high temperatures to drive off volatiles, including water and carboxylic or mineral acids. Here we present our results, reacting acidic and basic azoles in 1:3 or 1:1 stoichiometric compositions at elevated temperature, followed by saturation with Nd(OAc)(3)center dot xH(2)O or Ce(OAc)(3)center dot xH(2)O, which led to 13 new metal-acetate polymeric complexes identified by single-crystal X-ray diffraction. We found that the diversity in coordination modes of the simple acetate ligand that interfere with substitution of the softer N donors led to several readily crystallizable complexes forming two distinct groups with respect to f-element interaction with the ionic liquid precursors. When the acidic/basic azole ratio was 1:3, acetate and a neutral basic azole were found to be coordinated to the metal centers but no water, although in one case (2) water was observed in the secondary coordination sphere: [Ce(mu(2)-OAc)(3)(C(1)im)](n) (1, C(1)im = 1-methylimidazole), [Nd(mu(2)-(OAc)(3)(C(1)im)](n)center dot nH(2)O (2), [Ce(mu(2)-OAc)(3)(C(2)im)](n) (3, C(2)im = 1-ethylimidazole), [Ln(mu(2)-OAc)(3)DMF](n) (Ln = Nd (4), Ce (5); dimethylformamide (DMF) was substituted for the azole mixture), and [Nd(mu(2)-OAc)(3)(C(4)im)](n) (6, C(4)im = 1-butylimidazole). However, when the stoichiometric ratio was 1:1, water was always observed coordinated to the metal ions with the acidic azole included in the structure as a solvate or cocrystal, despite a higher reaction temperature: [Nd(mu(2)-OAc)(3)(OH2)](n)center dot n(1,2,3-Taz) (7,1,2,3-Taz = 1,2,3-triazole), [Ln(mu(2)-OAc)(3)(OH2)](n)center dot n(4,5-DCim) (Ln = Nd (8), Ce (9), 4,5-DCim = 4,5-dicyanoimidazole), [Ln(mu(2)-OAc)(3)(OH2)](n)center dot n(3,5-diNH(2)-1,2,4-Taz) (Ln = Nd (10), Ce (11), 3,5diNH(2)-1,2,4-Taz = 3,5-diamino-1,2,4-triazole), [Ce(mu(2)-OAc)(3)(OH2)](n)center dot n(3-NH2-1,2,4-Taz) (12, 3-NH2-1,2,4-Taz = 3-amino-1,2,4-triazole), and [Nd(mu(2)-OAc)(3)(OH2)](n)center dot n(5-NH2-Tz) (13, 5-NH2-Tz = 5-aminotetrazole). All of the compounds retain the Ln:OAc- ratio of 1:3 and form 1D polymeric chains; however, they exhibit a variety of coordination modes affecting the degree of chain condensation. The isolation of both hydrated and anhydrous products revealed different abilities of the investigated soft N-donors to compete with O-donors finding their place in the coordination sphere of the lanthanide or in the crystal lattice.

Access to lanthanide acetate coordination compounds is challenged by the tendency of lanthanides to coordinate water and the plethora of acetate coordination modes. A straightforward, reproducible synthetic procedure by treating lanthanide chloride hydrates with defined ratios of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C(2)mim][OAc]) has been developed. This reaction pathway leads to two isostructural crystalline anhydrous coordination complexes, the polymeric [C(2)mim](n)[{Ln(2)(OAc)(7)}(n)] and the dimeric [C(2)mim](2)[Ln(2)(OAc)(8)], based on the ion size and the ratio of IL used. A reaction with an IL : Ln-salt ratio of 5 : 1, where Ln=Nd, Sm, and Gd, led exclusively to the polymer, whilst for the heaviest lanthanides (Dy-Lu) the dimer was observed. Reaction with Eu and Tb resulted in a mixture of both polymeric and dimeric forms. When the amount of IL and/or the size of the cation was increased, the reaction led to only the dimeric compound for all the lanthanide series. Crystallographic analyses of the resulting salts revealed three different types of metal-acetate coordination modes where eta(2)mu kappa(2) is the most represented in both structure types.

The metal-organic material (UO)-O-V((UO2)-O-VI)(2)(OH)(5)-(Triaz)(2) (Triaz = 1,2,4-triazolate) has been isolated from the reaction of UO2(NO3)(2)center dot 6H(2)O with 1,2,4-triazole in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C(2)mim][OAc]). The compound's crystal structure is comprised of planar inorganic layers interconnected by organic linkers into a 3D framework. These layers represent a uranium-based coordination polymer with a Kagome topology that to the best of our knowledge has never been recognized in f-element coordination chemistry.

Many crystalline materials form polymorphs and undergo solid–solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)2 which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms.

Four mono-substituted N-butylpyridinium salts, 1-butyl-4-dimethylaminopyridinium chloride [b4dmapy]Cl, 1-butyl-4-methylpyridinium bromide [b4mpy]Br, 1-butyl-4-methylpyridinium hexafluorophosphate [b4mpy][PF₆], and 1-butyl-3-methylpyridinium hexafluorophosphate [b3mpy][PF₆] were synthesized and characterized using single crystal X-ray diffraction. The crystal structures were examined with the intent of identifying ion interactions leading to higher melting points of the halide salts with respect to the [PF₆]^– salts. The changes in hydrogen bonding, C–H⋅⋅⋅π, and van der Waals interactions have been analyzed with respect to anion, functional groups, and the symmetry of the cation to establish interdependence with the compound’s physicochemical properties. It has been observed that the cation–anion interactions are represented by highly directional hydrogen bonds and show strong preference to positions of interaction depending on the anion. The cations of the halide salts show strong tendency towards higher dimensional formations, while those of the [PF₆]^– salts prefer low dimensional assemblies both being based mainly on the weaker van der Waals interactions. These interactions depend on the shape of the cation but may offer certain structure-ordering rigidity accommodating variable anions.

Aperiodic formations continue to focus interest in areas ranging from advanced scientific theories to practical everyday applications. Starting from diverse and tightly bonded intermetallic compounds, this world showed an important breakthrough toward the so-called soft systems of meso/macroscale: liquid crystals, thin films, polymers, proteins, etc. This work opens a route for making bulk quasicrystals (QC) in an unprecedented but very common area, with molecular ligands. Since these systems are, to a large extent, transparent, they extend the possible areas of QC application to previously unreachable corners, e.g., photonics. We combined efficient bridging ligands with uranyl pentagonal bonding centers and, unexpectedly, brought the unique attributes of f-element coordination chemistry to an interdisciplinary area of aperiodic formations. Taking advantage of the planar coordination of uranyl ions, we were able to direct the structure expansion solely in two directions with a characteristic snub square tiling, a predicted but previously unobtainable dodecagonal approximant.