A biphenyl-spaced bis-pyrazolylpyridine ligand interacts with ferrous ions to engender a dimetallic helical coordination cage that encapsulates an Fe³⁺ tris-anilate complex. The host-guest interaction breaks the symmetry of the Fe²⁺ centers causing a differential spin crossover behavior in them that can be followed in great detail crystallographically.

Luminescent metal-organic frameworks (LMOFs) are among the fastest growing solid-state optical materials and have been studied for a wide variety of applications. However, when developing a new LMOF, it can be challenging to balance a strong luminescence quantum yield with all other important properties required by the intended application (appropriate excitation/emission wavelengths, chemical and physical stability, low toxicity, etc.). Being able to post-synthetically improve a LMOF's quantum yield is valuable, as it offers additional tunability in materials design and modification. As framework flexibility can limit quantum yield, post-synthetic methods of rigidifying an LMOF have the potential to improve its performance. This paper discusses a pair of nearly identical isoreticular LMOFs, and uses them as a model system to investigate how framework flexibility affects quantum yield. Introducing optically-inactive guests into a LMOF pore is shown to be an effective method for rigidifying the framework, improving the quantum yield of a flexible LMOF from 12.2% to 59.3% - an improvement of nearly 400%.

A series of copper halide based inorganic-organic hybrid semiconductors have been synthesized. Structural analysis confirms that all compounds are composed of one-dimensional Cu4X62- anionic chains that coordinate to cationic ligands via Cu-N dative bonds. Different coordination affinities of the ligands lead to two types of ligand arrangements with various structural distortions. All compounds are highly resistant to heat and moisture as a result of the combination of coordinate and ionic bonds. Low energy emission with high efficiency is achieved for these compounds and the emission energy (∼552-615 nm) and color (yellow-orange) can be tuned by varying the ligand and halogen element. The electronic structure and luminescence mechanism are examined by both experimental and theoretical methods. More importantly, all compounds demonstrate good solubility in polar aprotic solvents, a desired property that is absent in all other CuX hybrid families of extended structures, which is attributed primarily to the ionic nature of this material class. The good solution-processability, and cost effective and easily scalable synthesis coupled with high quantum efficiencies and framework stability make these hybrid materials promising phosphors for general lighting applications.

Electron paramagnetic resonance and crystallographic studies on copper-doped cadmium creatininium sulfate (CdCrnS) were undertaken to study the characteristics of a copper-hexahydrate complex in an organic analogue of Tutton's salt. X-ray diffraction experiments determined the crystal structure of CdCrnS at both 100 and 298 K. CdCrnS, like Tutton salt, crystallizes in the monoclinic space group P2₁/n. The unit cell contains two cadmium hexahydrate complexes, four creatininium ions, four sulfates, and four additional solvation waters. Both crystallography and EPR find that the doped copper replaces the cadmium in the structure. Single-crystal EPR measurements at room temperature determined the g and copper hyperfine (A^Cu) tensors (principal values: g = 2.437, 2.134, and 2.080 and A^Cu = -327, -84.8, and 7.33 MHz). EPR spectra of the powder at room temperature gave g = 2.448, 2.125, and 2.085 and A^Cu = -315, -75.0, and 35.0 MHz and at 110 K gave g = 2.462, 2.116, and 2.077 and A^Cu = -340, -30.0, and 35.0 MHz. The room-temperature tensors are close to the "rigid lattice limit" values found in copper-doped Tutton salts but with a higher g_min and weaker A^Cu_x coupling than average. A small but measurable temperature dependency of the tensors indicated the presence of a dynamic Jahn-Teller (JT) effect. In addition, the EPR line width changed dramatically with temperature, which is like that found in all copper-doped Tutton crystals. Utilizing the model of Silver-Getz for the g-value variation gave an estimate for the energy difference (δ₁₂ = 640 cm^-1) between the ground and next highest JT configurations. An empirical correlation appears to exist between δ₁₂ and g_min and A^Cu_x for the copper hexahydrates studied in similar crystals. This suggests a relationship between the amount of unpaired spins in the copper d-orbital x lobe and the gap between wells of the adiabatic potential surface.

A new bis(pyrazolylpyridine) ligand (H2 L) has been prepared to form functional [Fe2 (H2 L)3 ](4+) metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe2 (H2 L)3 ]X(PF6 )2 ⋅xCH3 OH (1, x=5.7 and X=Cl; 2, x=4 and X=Br), X@[Fe2 (H2 L)3 ]X(PF6 )2 ⋅yCH3 OH⋅H2 O (1 a, y=3 and X=Cl; 2 a, y=1 and X=Br) and X@[Fe2 (H2 L)3 ](I3 )2 ⋅3 Et2 O (1 b, X=Cl; 2 b, X=Br). Their structure and functional properties are described in detail by single-crystal X-ray diffraction experiments at several temperatures. Helicates 1 a and 2 a are obtained from 1 and 2, respectively, by a single-crystal-to-single-crystal mechanism. The three possible magnetic states, [LS-LS], [LS-HS], and [HS-HS] can be accessed over large temperature ranges as a result of the structural nonequivalence of the Fe(II) centers. The nature of the guest (Cl(-) vs. Br(-) ) shifts the spin crossover (SCO) temperature by roughly 40 K. Also, metastable [LS-HS] or [HS-HS] states are generated through irradiation. All helicates (X@[Fe2 (H2 L)3 ])(3+) persist in solution.

Abstract: The synthesis of conjugated polymers with ionic substituents directly bound to their main chain repeat units is a strategy for generating strongly electron‐accepting conjugated polyelectrolytes, as demonstrated through the synthesis of a series of ionic azaquinodimethane (iAQM) compounds. The introduction of cationic substituents onto the quinoidal para‐azaquinodimethane (AQM) core gives rise to a strongly electron‐accepting building block, which can be employed in the synthesis of ionic small molecules and conjugated polyelectrolytes (CPEs). Electrochemical measurements alongside theoretical calculations indicate notably low‐lying LUMO values for the iAQMs. The optical band gaps measured for these compounds are highly tunable based on structure, ranging from 2.30 eV in small molecules down to 1.22 eV in polymers. The iAQM small molecules and CPEs showcase the band gap reduction effects of combining the donor‐acceptor strategy with the bond‐length alternation reduction strategy. As a demonstration of their utility, the iAQM CPEs so generated were used as active agents in photothermal therapy.

Herein we introduce fully modular synthesis leading to three representative examples of rigid molecular rods that are intended to form sturdy monolayers on various surfaces. These molecules contain two triptycene units that are designed to interlock into a compact "double-decker" structure. Two of the three final products provided suitable crystals for X-ray diffraction (analyzed on synchrotron), allowing deeper insight into packing in the 3-D crystal lattice. The acidity of all three compounds were determined by capillary electrophoresis, and the pK_a values ranged between 2.06-2.53. All three rigid rods easily formed Langmuir-Blodgett monolayers (LBMs) on the water-air interfaces, with the area per molecule equal to 55-59 Ų /molecule, suggesting tight intermolecular packing. The thickness of all three films reached ∼19 Å after transfer to a gold (111) surface, meaning that individual molecules are tilted maximally 38° from the axis perpendicular to the surface. The structure of one of these films on a gold (111) surface was visualized by AFM. These geometrically unique molecules represent promising platforms with a wide scope of applicability in the supramolecular architecture.

The synthesis of bimetallic molecular silicide complexes is reported, based on the use of multiple Si-H bond activations in SiH₄ at the metal centers of 14-electron LCo^I fragments (L = Tp″, HB(3,5-diisopropylpyrazolyl)₃^-; [BP₂^tBuPz], PhB(CH₂P^tBu₂)₂(pyrazolyl)). Upon exposure of (Tp″Co)₂(μ-N₂) (1) to SiH₄, a mixture of (Tp″Co)₂(μ-H) (2) and (Tp″Co)₂(μ-H)₂ (3) was formed and no evidence for Si-H oxidative addition products was observed. In contrast, [BP₂^tBuPz]-supported Co complexes led to Si-H oxidative additions with the generation of silylene and silicide complexes as products. Notably, the reaction of ([BP₂^tBuPz]Co)₂(μ-N₂) (5) with SiH₄ gave the dicobalt silicide complex [BP₂^tBuPz](H)₂Co═Si═Co(H)₂[BP₂^tBuPz] (8) in high yield, representing the first direct route to a symmetrical bimetallic silicide. The effect of the [BP₂^tBuPz] ligand on Co-Si bonding in 7 and 8 was explored by analysis of solid-state molecular structures and density functional theory (DFT) investigations. Upon exposure to CO or DMAP (DMAP = 4-dimethylaminopyridine), 8 converted to the corresponding [BP₂^tBuPz]Co(L)_x adducts (L = CO, x = 2; L = DMAP, x = 1) with concomitant loss of SiH₄, despite the lack of significant Si-H interactions in the starting complex. On heating to 60 °C, 8 underwent reaction with MeCl to produce small quantities of Me_xSiH_4-x (x = 1-3), demonstrating functionalization of the μ-silicon atom in a molecular silicide to form organosilanes.