Putting ScTGa₅ (T = Fe, Co, Ni) on the Map: How Electron Counts and Chemical Pressure Shape the Stability Range of the HoCoGa₅ Type

We explore the factors stabilizing one member of the diverse structures encountered in Ln–T–E systems (Ln = lanthanide or similar early d-block element, T = transition metal, E = p-block element): the HoCoGa₅ type, an arrangement of atoms associated with unconventional superconductivity. We first probe the boundaries of its stability range through the growth and characterization of ScTGa₅ crystals (T = Fe, Co, Ni). After confirming that these compounds adopt the HoCoGa₅ type, we analyze their electronic structure using density functional theory (DFT) and DFT-calibrated Hückel calculations. The observed valence electron count range of the HoCoGa₅ type is explained in terms of the 18-<i>n</i> rule, with <i>n</i> = 6 for the Ln atoms and <i>n</i> = 2 for the T sites. The role of atomic sizes is investigated with DFT-chemical pressure (DFT-CP) analysis of ScNiGa₅, which reveals negative pressures within the Ga sublattice as it stretches to accommodate the Sc and T atoms. This CP scheme is consistent with HoCoGa₅-type gallides only being observed for relatively small Ln and T atoms. These conclusions account for the relative positions of the HoCoGa₅, BaMg₄Si₃, and Ce₂NiGa₁₀ types in a structure map, demonstrating how combining the 18-<i>n</i> and CP schemes can guide our understanding of Ln–T–E systems

Eutectoid Flux Growth and Physical Properties of Single Crystal Ln₁₁₇Ni_{54–<i>y</i>}Sn_{112–<i>z</i>} (Ln = Gd–Dy)

Ln₁₁₇Ni_{53–<i>y</i>}Sn_{112–<i>z</i>} (Ln = Gd–Dy) have been grown via the eutectoid flux growth method, characterized using single crystal X-ray diffraction, and determined to have a face centered cubic unit cell with lattice parameters of <i>a</i> = 30.070(4), 29.862(5), and 29.823(4) Å for the Gd, Dy, and Tb analogues. The compounds contain over 1100 atoms per unit cell with a complex bonding network and multiple magnetic sublattices. In addition, disorder is prevalent throughout the structure. These physical characteristics are ideal when searching for ultralow thermal conductivity materials. Magnetic susceptibility and electrical properties are presented, and all analogues exhibit positive Curie–Weiss constants, suggesting ferromagnetic interactions in each compound, in addition to a spin-glass component to the magnetic behavior

Eutectoid Flux Growth and Physical Properties of Single Crystal Ln₁₁₇Ni_{54–<i>y</i>}Sn_{112–<i>z</i>} (Ln = Gd–Dy)

Ln₁₁₇Ni_{53–<i>y</i>}Sn_{112–<i>z</i>} (Ln = Gd–Dy) have been grown via the eutectoid flux growth method, characterized using single crystal X-ray diffraction, and determined to have a face centered cubic unit cell with lattice parameters of <i>a</i> = 30.070(4), 29.862(5), and 29.823(4) Å for the Gd, Dy, and Tb analogues. The compounds contain over 1100 atoms per unit cell with a complex bonding network and multiple magnetic sublattices. In addition, disorder is prevalent throughout the structure. These physical characteristics are ideal when searching for ultralow thermal conductivity materials. Magnetic susceptibility and electrical properties are presented, and all analogues exhibit positive Curie–Weiss constants, suggesting ferromagnetic interactions in each compound, in addition to a spin-glass component to the magnetic behavior

Polymorphic, Porous, and Host–Guest Nanostructures Directed by Monolayer–Substrate Interactions: Epitaxial Self-Assembly Study of Cyclic Trinuclear Au(I) Complexes on HOPG at the Solution–Solid Interface

Synthesis, crystallographic characterization, and molecular self-assembly of two novel cyclotrimeric gold­(I) complexes, Au₃[3,5-(COOEt)₂Pz]₃ (Au₃Pz₃) and Au₃[(<i>n</i>-Pr–O)­CN­(Me)]₃ (Au₃Cb₃) was studied. Single crystal X-ray crystallography data reveal that both gold­(I) complexes have one-dimensional stacking patterns caused by intermolecular Au­(I)···Au­(I) aurophilic interactions. The Au₃Pz₃ trimer units stack with two alternate and symmetrical Au­(I)···Au­(I) interactions while the Au₃Cb₃ units have three alternating and nonsymmetrical Au­(I)···Au­(I) interactions. Molecular self-assembly of the gold­(I) complexes on the 1-phenyloctane/highly ordered pyrolytic graphite (HOPG) (0001) solution–solid interface is studied with scanning tunneling microscopy (STM). The gold­(I) cyclotrimers form epitaxial nanostructures on the HOPG surface. At a concentration of ∼1 × 10^–4 M, Au₃Pz₃ complexes exhibit a single morphology, while Au₃Cb₃ complexes exhibit polymorphology. Two polymorphs, one nonporous and the other porous, are observed at 22.0 ± 2.0 °C for Au₃Cb₃ complexes. A nonporous, low-surface-density (0.82 molecules/nm²) Au₃Cb₃ nanostructure forms first and then transforms into a high-density (1.43 molecules/nm²) porous nanostructure. This is the first time any porous surface nanostructure is reported for an organometallic system. The porous structure is thought to be stabilized by a combination of hydrogen bonding and monolayer–substrate interactions. These pores are utilized to incorporate pyrene into the film, rendering this the first organometallic host–guest system imaged at the solid–solution interface. Molecular and periodic density functional theory (DFT) calculations shed light on the two-dimensional topography and polymorphic self-assembly revealed by STM; these calculations suggest significant electronic hybridization of the Au₃ trimer orbitals and HOPG. The multiple-technique approach used herein provides insights concerning molecule–substrate and molecule–molecule interactions

Molecular and Electronic Structure of Cyclic Trinuclear Gold(I) Carbeniate Complexes: Insights for Structure/Luminescence/Conductivity Relationships

An experimental and computational study of correlations between solid-state structure and optical/electronic properties of cyclotrimeric gold­(I) carbeniates, [Au₃(RNCOR′)₃] (R, R′ = H, Me, ⁿBu, or ^cPe), is reported. Synthesis and structural and photophysical characterization of novel complexes [Au₃(MeNCOⁿBu)₃], [Au₃(ⁿBuNCOMe)₃], [Au₃(ⁿBuNCOⁿBu)₃], and [Au₃(^cPeNCOMe)₃] are presented. Changes in R and R′ lead to distinctive variations in solid-state stacking, luminescence spectra, and conductive properties. Solid-state emission and excitation spectra for each complex display a remarkable dependence on the solid-state packing of the cyclotrimers. The electronic structure of [Au₃(RNCOR′)₃] was investigated via molecular and solid-state simulations. Calculations on [Au₃(HNCOH)₃] models indicate that the infinitely extended chain of eclipsed structures with equidistant Au--Au intertrimer aurophilic bonding can have lower band gaps, smaller Stokes shifts, and reduced reorganization energies (λ). The action of one cyclotrimer as a molecular nanowire is demonstrated via fabrication of an organic field effect transistor and shown to produce a p-type field effect. Hole transport for the same cyclotrimerdoped within a poly­(9-vinylcarbazole) hostproduced a colossal increase in current density from ∼1 to ∼1000 mA/cm². Computations and experiments thus delineate the complex relationships between solid-state morphologies, electronic structures, and optoelectronic properties of gold­(I) carbeniates

Rigidifying Fluorescent Linkers by Metal–Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal–organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 ± 0.5%) under Ar, representing ca. 3600 cm^–1 blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity

Synthesis, Spectroscopic Properties, and Photoconductivity of Black Absorbers Consisting of Pt(Bipyridine)(Dithiolate) Charge Transfer Complexes in the Presence and Absence of Nitrofluorenone Acceptors

The diimine–dithiolato ambipolar complexes Pt­(dbbpy)­(tdt) and Pt­(dmecb)­(bdt) (dbbpy = 4,4′-di-<i>tert</i>-butyl-2,2′-bipyridine; tdt^2– = 3,4-toluenedithiolate; dmecb = 4,4′-dimethoxyester-2,2′-bipyridine; bdt^2– = benzene-1,2-dithiolate) are prepared herein. Pt­(dmecb)­(bdt) exhibits photoconductivity that remains constant (photocurrent density of 1.6 mA/cm² from a 20 nm thin film) <i>across the entire visible region of the solar spectrum</i> in a Schottky diode device structure. Pt­(dbbpy)­(tdt) acts as donor when combined with the strong nitrofluorenone acceptors 2,7-dinitro-9-fluorenone (DNF), 2,4,7-trinitro-9-fluorenone (TRNF), or 2,4,5,7-tetranitro-9-fluorenone (TENF). Supramolecular charge transfer stacks form and exhibit various donor–acceptor stacking patterns. The crystalline solids are “black absorbers” that exhibit continuous absorptions spanning the entire visible region and significant ultraviolet and near-infrared wavelengths, the latter including long wavelengths that the donor or acceptor molecules alone do not absorb. Absorption spectra reveal the persistence of donor–acceptor interactions in solution, as characterized by low-energy donor/acceptor charge transfer (DACT) bands. Crystal structures show closely packed stacks with distances that underscore intermolecular DACT. ¹H NMR provides further evidence of DACT, as manifested by upfield shifts of aromatic protons in the binary adducts versus their free components, whereas 2D nuclear Overhauser effect spectroscopy (NOESY) spectra suggest coupling between dithiolate donor protons with nitrofluorenone acceptor protons, in correlation with the solid-state stacking. The NMR spectra also show significant peak broadening, indicating some paramagnetism verified by magnetic susceptibility data. Solid-state absorption spectra reveal further red shifts and increased relative intensities of DACT bands for the solid adducts vs solution, suggesting cooperativity of the DACT phenomenon in the solid state, as further substantiated by ν_C–O and ν_N–O IR bands and solid-state tight-binding computational analysis