Tunable valence tautomerism in lanthanide-organic alloys

The inimitable electronic structures of the lanthanide (Ln) ions are key to advanced materials and technologies involving these elements. The trivalent ions are ubiquitous and are used much more widely than the divalent and tetravalent analogues, which possess vastly different optical and magnetic properties. Hence, alteration of the valence electron count by external stimuli can lead to dramatic changes in materials properties. Compounds exhibiting a temperature-induced complete Ln(III) ⇄ Ln(II) switch, referred to as a valence tautomeric (VT) transition, are rare. Here we present an abrupt and hysteretic VT transition in a lanthanide-based coordination polymer, SmI2(pyrazine)3, driven by the interconversion of Sm(II)-pyrazine(0) and Sm(III)-pyrazine(·-) redox pairs. Alloying SmI2(pyrazine)3 with Yb(II) yields isomorphous Sm1-xYbxI2(pyrazine)3 solid solutions with VT transition critical temperatures ranging widely from 200 K to ∼50 K at ambient pressure. These findings demonstrate a simple strategy to realize thermally switchable magnetic materials with chemically tunable transition temperatures.

A zero-valent palladium cluster-organic framework

Acquiring spatial control of nanoscopic metal clusters is central to their function as efficient multi-electron catalysts. However, dispersing metal clusters on surfaces or in porous hosts is accompanied by an intrinsic heterogeneity that hampers detailed understanding of the chemical structure and its relation to reactivities. Tethering pre-assembled molecular metal clusters into polymeric, crystalline 2D or 3D networks constitutes an unproven approach to realizing ordered arrays of chemically well-defined metal clusters. Herein, we report the facile synthesis of a {Pd3} cluster-based organometallic framework from a molecular triangulo-Pd3(CNXyl)6 (Xyl = xylyl; Pd3) cluster under chemically mild conditions. The formally zero-valent Pd3 cluster readily engages in a complete ligand exchange when exposed to a similar, ditopic isocyanide ligand, resulting in polymerization into a 2D coordination network (Pd3-MOF). The structure of Pd3-MOF could be unambiguously determined by continuous rotation 3D electron diffraction (3D-ED) experiments to a resolution of ~1.0 Å (>99% completeness), showcasing the applicability of 3D-ED to nanocrystalline, organometallic polymers. Pd3-MOF displays Pd03 cluster nodes, which possess significant thermal and aerobic stability, and activity towards hydrogenation catalysis. Importantly, the realization of Pd3-MOF paves the way for the exploitation of metal clusters as building blocks for rigidly interlocked metal nanoparticles at the molecular limit.

Reactive Solubilization of Heterometallic Clusters by Treatment of (TrBi3 )2- Anions (Tr=Ga, In, Tl) with [Mn{N(SiMe3 )2 }2 ]

Lowering the charge of Zintl anions by (element-)organic substituents allows their use as sources of (semi)metal nanostructures in common organic solvents, as realized for group 15 anions or Ge₉ ^4- and Sn₉ ^4- . We developed a new strategy for other anions, using low-coordinate 3d metal complexes as electrophiles. [K(crypt-222)]⁺ salts of (TrBi₃ )^2- anions dissolved in situ in Et₂ O and/or THF when reacted with [Mn(hmds)₂ ]. Work-up afforded soluble [K(crypt-222)]⁺ salts of [{(hmds)₂ Mn}₂ (TlBi₃ )]^2- (in 1), [{(hmds)₂ Mn}₂ (Bi₂ )]^2- (in 2), and [{(hmds)Mn}₄ (Bi₂ )₂ ]^2- (in 3) (crypt-222=4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane; Tr=Ga, In, Tl; hmds=N(SiMe₃ )₂ ), representing rare cases of Zintl clusters with open-shell metal atoms. 1 comprises the first coordination compound of the (TlBi₃ )^2- anion, 2 features a diamond-shaped {Pn₂ M₂ } unit, and 3 is a mixed-valent Mn^I /Mn^II compound. The uncommon electronic structures in 1-3 and magnetic coupling were studied by comprehensive DFT calculations.

Developing and Comparing 2,6-Anthracene Derivatives: Optical, Electrochemical, Thermal, and Their Use in Organic Thin Film Transistors

Anthracene-based semiconductors have attracted great interest due to their molecular planarity, ambient and thermal stability, tunable frontier molecular orbitals and strong intermolecular interactions that can lead to good device field-effect transistor performance. In this study, we report the synthesis of six anthracene derivatives which were di-substituted at the 2,6-positions, their optical, electrochemical and thermal properties, and their single crystal structures. It was found that 2,6-functionalization with various fluorinated phenyl derivatives led to negligible changes in the optical behaviour while influencing the electrochemical properties. Furthermore, the choice of fluorinated phenyl moiety had noticeable effects on melting point and thermal stability (ΔTm < 55 °C and ΔTd < 65 °C). Bottom-gate top-contact (BGTC) organic thin transistors (OTFTs) were fabricated and characterized using the 2,6-anthracene derivatives as the semiconducting layer. The addition of fluorine groups on the phenyl groups led to a transition from p-type behaviour to n-type behaviour in BGBC OTFTs.

Developing 9,10-anthracene Derivatives: Optical, Electrochemical, Thermal, and Electrical Characterization

Anthracene-based semiconductors are a class of molecules that have attracted interest due to their air stability, planarity, potential for strong intermolecular interactions, and favorable frontier molecular orbital energy levels. In this study seven novel 9,10-anthracene-based molecules were synthesized and their optical, electrochemical, and thermal properties were characterized, along with their single crystal arrangement. We found that functionalization of the 9,10-positions with different phenyl derivatives resulted in negligible variation in the optical properties with minor (±0.10 eV) changes in electrochemical behavior, while the choice of phenyl derivative greatly affected the thermal stability (Td > 258 °C). Preliminary organic thin film transistors (OTFTs) were fabricated and characterized using the 9,10-anthracene-based molecules as the semiconductor layer. These findings suggest that functionalization of the 9,10-position of anthracene leads to an effective handle for tuning of the thermal stability, while having little to no effect on the optical properties and the solid-state arrangement.

Three-Dimensional Magnetic Exchange Networks in Trigonal Bisdithiazolyl Radicals

The N-methyl-4-phenyl-pyridine-bridged bisdithiazolyl radical PhBPMe is polymorphic, crystallizing from cold acetonitrile in a trigonal α-phase, space group P3₁21, and from hot dichloroethane in an orthorhombic β-phase, space group Pca2₁. The crystal structures of both phases consist of slipped π-stacks of undimerized radicals aligned laterally into herringbone arrays. In the β-phase, there are two independent radicals in the asymmetric unit, and the resulting π-stacks form corrugated layers interspersed by methyl and phenyl groups which block the approach of neighboring radicals. In the α-phase, the methyl/phenyl groups and the radical π-stacks separately form spirals about 3₁ axes, the latter giving rise to a 3D network of close radical/radical contacts. Variable temperature magnetic susceptibility measurements on the β-phase indicate strong antiferromagnetic coupling. Weaker but predominantly antiferromagnetic interactions (θ = -20.7 K) are observed in the α-phase. A high temperature series expansion analysis of the magnetic data for the α-phase affords antiferromagnetic exchange energies for the one- and two-step radical/radical interactions about the 3₁ spirals ( J₁ = -1.2 K, J₂ = -10.9 K, respectively), with weak ferromagnetic interactions along the π-stacks ( J_π = +1.8 K). Despite the presence of a 3D network based on the dominant J₂ interactions, which affords two independent bipartite sublattices, no evidence of bulk antiferromagnetic order has been observed above T = 2 K. The magnetic results are discussed in light of exchange energies calculated using density functional theory broken symmetry methods.

S-Functionalization of 3,5-bis(2-pyridyl)-1,2,4,6-thiatriazine: probing the effect of alkyl chain length in the development of tethered materials

The preference of S-alkyl-thiatriazines towards intra vs. intermolecular addition is dependent on alkyl chain length, as demonstrated experimentally and computationally.

Boratriazines: inducing luminescence through boron incorporation into a terpy-type framework

The synthesis and physicochemical properties of pyridyl and pyrimidyl functionalized 1,3,5,2-triazaborinines are reported, along with the Lewis acid–base adduct pyrimidine-2-carboximidamide trifluoroborane, which forms as a side product in the reaction with the pyrimidyl substituents.

Alkyl-functionalization of 3,5-bis(2-pyridyl)-1,2,4,6-thiatriazine

S-Alkyl-1,2,4,6-thiatriazines, which can be preparedviatwo pathways, are described. The regioselectivity and photophysical properties are rationalized through computational studies.

Connecting mononuclear dysprosium single-molecule magnets to form dinuclear complexes via in situ ligand oxidation

A Dy₂ complex, exhibiting SMM behaviour, and its Y analogue were prepared via in situ oxidation of Py₂TTA, a pincer type ligand, followed by dimerisation.