Allan Jacobson

Assembling macroscopic helices with controllable chirality and understanding their formation mechanism are highly desirable but challenging tasks for artificial systems, especially coordination polymers. Here, we utilize solvents as an effective tool to induce the formation of macroscopic helices of chiral coordination polymers (CPs) and manipulate their helical sense. We chose the Ni/R-,S-BrpempH₂ system with a one-dimensional tubular structure, where R-,S-BrpempH₂ stands for R-,S-(1-(4-bromophenyl)ethylaminomethylphosphonic acid). The morphology of the self-assemblies can be controlled by varying the cosolvent in water, resulting in the formation of twisted ribbons of R-,S-Ni(Brpemp)(H₂O)·H₂O (R-,S-2T) in pure H₂O; needle-like crystals of R-,S-Ni(Brpemp)(H₂O)₂·1/3CH₃CN (R-,S-1C) in 20 vol % CH₃CN/H₂O; nanofibers of R-,S-Ni(Brpemp)(H₂O)·H₂O (R-,S-3F) in 20-40 vol % methanol/H₂O or ethanol/H₂O; and superhelices of R-,S-Ni(Brpemp)(H₂O)·H₂O (R-,S-4H or 5H) in 40 vol % propanol/H₂O. Interestingly, the helicity of the superhelix can be controlled by using a propanol isomer in water. For the Ni/R-BrpempH₂ system, a left-handed superhelix of R-4H(M) was obtained in 40 vol % NPA/H₂O, while a right-handed superhelix of R-5H(P) was isolated in 40 vol % IPA/H₂O. These results were rationalized by theoretical calculations. Adsorption studies revealed the chiral recognition behavior of these compounds. This work may contribute to the development of chiral CPs with a macroscopic helical morphology and interesting functionalities.

Nanotubular materials have garnered considerable attention since the discovery of carbon nanotubes. Although the layer-to-tube rolling up mechanism has been well recognized in explaining the formation of many inorganic nanotubes, it has not been generally applied to coordination polymers (CPs). To uncover the key factors that determine the rolling-up of layered CPs, we have chosen the Co/R-, S-Xpemp [Xpemp = (4-X-1-phenylethylamino)methylphosphonic acid, X = H, F, Cl, Br] systems and study how the weak interactions influence the formation of layered or tubular structures. Four pairs of homochiral isostructural compounds R-, S-Co(Xpemp)(H₂O)₂ [X = H (1H), F (2F), Cl (3Cl), Br (4Br)] were obtained with tubular structures. The inclusion of 3,3′-azobipyridine (ABP) guest molecules led to compounds R-, S-[Co(Xpemp)(H₂O)₂]₄·ABP·H₂O with layered structures when X was Cl (5Cl) and Br (6Br), but tubular compounds 1H and 2F when X was H and F. Layered structures were also obtained for racemic compounds meso-Co(Xpemp)(H₂O)₂ [X = F (7F), Cl (8Cl), Br (9Br)] using racemic XpempH₂ as the reaction precursor, but not when X = H. A detailed study on R-6Br revealed that layer-to-tube transformation occurred upon removal of ABP under hydrothermal conditions, forming R-4Br with a tubular structure. Similar layer-to-tube conversion did not occur in organic solvents. The results demonstrate that weak interlayer interactions are a prerequisite but not sufficient for the rolling-up of the layers. In the present cases, water also provides a driving force in the layer-to-tube transformation. The experimental results were rationalized by theoretical calculations.

This paper reports the synthesis and study of doped metal oxides as the shell in core-shell nanoparticle architectures. Specifically, the manuscript describes the synthesis of gold nanoparticles (Au NPs) and gold-silver nanoshells (GS-NSs) coated with antimony-doped and zinc-doped tin oxide shells (i.e., [email protected], [email protected], [email protected], and [email protected]) with comparison to the undoped SnO2-coated analogs [email protected] and [email protected] The doped tin oxide core-shell nanoparticles prepared here were thoroughly characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Separately, their optical properties were evaluated by UV-vis and photoluminescence spectroscopy. The results demonstrate that noble metal nanoparticles such as Au NPs and GS-NSs, which exhibit strong surface plasmon resonances at visible to near-infrared wavelengths, can be activated across a broader region of the solar spectrum when used in conjunction with wide bandgap semiconductors. In particular, utilization of a GS-NS core induces a near-complete suppression in the electron-hole recombination processes in the tin oxide materials. Potential impacts on sensing and photonic applications are highlighted.

Materials with two-dimensional, geometrically frustrated, spin-½ lattices offer a fertile playground for the study of intriguing magnetic phenomena such as quantum spin liquid behavior, but their prepara-tion has been a challenge. In particular, the long-sought, exotic spin-½ star structure has not been experimentally realized to date. Here, we report the synthesis of [(CH3)2(NH2)]3[CuII3(μ3-OH)3(μ3-SO4)(μ3-SO4)3]∙0.24H2O with a S = ½ star structure. Based on the magnetic susceptibility and heat capacity measurements, the Cu-based compound exhibits antiferromagnetic interactions but no magnetic ordering or spin freezing down to 2 K. The spin-frustrated material appears to be a promising quantum spin liquid candidate.

The geometrically frustrated diamond spin chain system has yielded materials with a diversity of interesting magnetic properties but is predominantly limited to compounds with single-spin components. Here, we report the compound [(CH₃)₂NH₂]₆[Fe^III₄Fe^II₂(μ₃-O)₂(μ₃-OH)₂(μ₃-SO₄)₈] (1), which features the mixed-valent iron(II/III) diamond chain: ^∞[Fe^III–(Fe^III)₂–Fe^III–(Fe^II)₂]. ⁵⁷Fe Mössbauer spectroscopy shows that two-thirds of the total spins in the ^∞[Fe^III₄Fe^II₂] diamond chain are spin-5/2 (high-spin Fe^III), while the remaining one-third are spin-2 (high-spin Fe^II). To date, 1 is the only diamond-chain compound composed of more than one type of dimer, namely, (Fe^III)₂ and (Fe^II)₂. On the basis of temperature-dependent ⁵⁷Fe Mössbauer spectroscopy data, an alternating noncollinear 90° magnetic structure is proposed. Both the (Fe^III)₂ and (Fe^II)₂ dimers are antiferromagnetically coupled and align in the direction along the chain axis ≈ [010], whereas the moments of the bridging Fe^III monomers are oriented orthogonally. The spin canting, arising from the anisotropy of the Fe^II ions, leads to ferrimagnetic ordering at low temperatures.