Preparation, First Structure Analysis, and Magnetism of the Long‐Known Nickel Benzoate Trihydrate – A Linear Ni···Ni···Ni Polymer and Its Parallels with the Active Site of Urease

Synthesis, crystal structure, infrared spectrum, and thermal properties of [Ni(1,10-phenanthroline)3](fumarate)·9H2O complex with hydrogen bonded supramolecular layers involving fumarate anions

From the aqueous-ethanolic system Ni(OH)2—H2 fum—phen (H2fum = fumaric acid, phen = 1,10-phenanthroline), novel complex [Ni(phen)3](fum)·9H2O (1) was isolated and characterized by chemical analyses and FT-IR spectroscopy. Results of single crystal X-ray structure analysis have shown that the ionic crystal structure of 1 is built of [Ni(phen)3]2+ complex cations, fumarate dianions and nine crystallographically independent water molecules of crystallization. The Ni(II) atom exhibits hexa-coordination by three phen ligands with mean Ni-N bond length of 2.090 Å. Water molecules form hydrophilic supramolecular layers with fumarate dianions via extended network of O—H···O type hydrogen bonds with O···O distances from the range of 2.676(2)—2. 916(2) Å; hydrophobic complex cations are embedded between these layers. Thermal study of 1 has shown that endothermic dehydration in the temperature range of 95—195 °C takes at least two steps of the process.

Graphical Abstract

Crystal structure of [Ni(phen)3]fum·9H2O (phen = 1,10-phenanthroline; H2 fum = fumaric acid) which is built of supramolecular layers formed by hydrogen bonded water solvate molecules and fum dianions and between the supramolecular layers embedded [Ni(phen)3]2+ complex cations is described here.

Influence of Metal-Ligand Coordination on the Elemental Growth and Alloying Composition of Pt-Ni Octahedral Nanoparticles for Oxygen Reduction Electrocatalysis

Understanding the role of surfactants or ligands on the growth mechanism of metal/alloy nanoparticles (NPs) is important for controlled synthesis of functional metallic NPs with tailored structures and properties. There have been a number of works showing the significant impact of surfactants/ligands on the shape-controlled synthesis of nanocrystals with well-defined surfaces. Beyond the morphological shape control, impact of the surfactants/ligands on the alloying structure of bimetallic nanocrystals, however, still remains largely unaddressed. We reveal here a significant effect of benzoic acid ligand on the elemental growth and alloying phase structure of octahedral Pt-Ni NPs, a class of highly active electrocatalyst for oxygen reduction reaction in fuel cells. Contrary to previous reports showing the critical role of benzoic acid in directing the growth of octahedral Pt-Ni NPs, we found that benzoic acid played a minor role in forming the octahedral shape; instead, it can strongly coordinate with Ni cation and significantly slows down its reduction rate, leading to a phase separation in the Pt-Ni NP products (a mixture of Pt-rich octahedral NPs and nearly pure Ni NPs). Such phase separation further resulted in a lower catalytic activity and stability. These results help us comprehensively understand the effect of metal-ligand coordination chemistry on the elemental growth mechanism and alloying phase structure of bimetallic NPs, complementing previous emphasis on the role of surfactants in purely morphological shape control.

Exceptionally slow magnetic relaxation in cobalt(ii) benzoate trihydrate

Cobalt(ii) benzoate trihydrate prepared by the reaction of CoCO₃ with benzoic acid (HBz) in boiling water followed by crystallization has been structurally characterized as a chain-like system with the formula unit [Co(Bz)(H₂O)₂]Bz·H₂O where the Co(ii) atoms are triply linked by one bridging syn-syn benzoato (Bz) and two aqua ligands; additional benzoate counter ions and solvate water molecules are present in the crystal structure. DC magnetic measurements reveal a sizable exchange coupling of a ferromagnetic nature between the Co(ii) atoms. At T_N = 5.5 K the paramagnetic phase switches to the antiferromagnetic phase. Though the remnant magnetization is zero, the magnetization curve shows two lobes of a hysteresis loop and the DC relaxation experiments confirm a long relaxation time at T = 2.0 K. AC susceptibility data confirm a slow relaxation of magnetization even in the antiferromagnetic phase. In the absence of the magnetic field, two relaxation channels exist. The relaxation time for the low frequency channel is as slow as τ_LF > 1.6 s and data fitting yields τ_LF (2.1 K) = 14 s. The high-frequency relaxation time obeys the Orbach process at a higher temperature whereas the Raman process dominates the low-temperature region. Three slow relaxation channels are evidenced at the applied magnetic field B_DC = 0.1 T.