Co₁₁Li[(OH)₅O][(PO₃OH)(PO₄)₅], a Lithium-Stabilized, Mixed-Valent Cobalt(II,III) Hydroxide Phosphate Framework

Abstract

A new metastable phase, featuring a lithium-stabilized mixed-valence cobalt(II,III) hydroxide phosphate framework, CoLi[(OH)O][(POOH)(PO)], corresponding to the simplified composition CoLi(OH)PO, is prepared by hydrothermal synthesis. Because the pH-dependent formation of other phases such as Co(OH)(POOH) and olivine-type LiCoPO competes in the process, a pH value of 5.0 is crucial for obtaining a single-phase material. The crystals with dimensions of 15 μm × 30 μm exhibit a unique elongated triangular pyramid morphology with a lamellar fine structure. Powder X-ray diffraction experiments reveal that the phase is isostructural with the natural phosphate minerals holtedahlite and satterlyite, and crystallizes in the trigonal space group P31m (a = 11.2533(4) Å, c = 4.9940(2) Å, V = 547.70(3) Å, Z = 1). The three-dimensional network structure is characterized by partially Li-substituted, octahedral [MO(OH)] (M = Co, Li) dimer units which form double chains that run along the [001] direction and are connected by [PO] and [PO(OH)] tetrahedra. Because no Li-free P31m-type Co(OH)PO phase could be prepared, it can be assumed that the Li ions are crucial for the stabilization of the framework. Co L-edge X-ray absorption spectroscopy demonstrates that the cobalt ions adopt the oxidation states +2 and +3 and hence provides further evidence for the incorporation of Li in the charge-balanced framework. The presence of three independent hydroxyl groups is further confirmed by infrared spectroscopy. Magnetization measurements imply a paramagnetic to antiferromagnetic transition at around T = 25 K as well as a second transition at around 9-12 K with a ferromagnetic component below this temperature. The metastable character of the phase is demonstrated by thermogravimetric analysis and differential scanning calorimetry, which above 558 °C reveal a two-step decomposition to CoO, Co(PO), and olivine-type LiCoPO with release of water and oxygen.

Cobalt Release from a Nanoscale Multiphase Lithiated Cobalt Phosphate Dominates Interaction with Shewanella oneidensis MR-1 and Bacillus subtilis SB491

“…This question is an important one given the high likelihood of increased production, use, and disposal of nanoscale metal phosphates and the dearth of research looking at the impact of metal phosphate ENMs on organisms and specifically bacteria. Past works show that release of transition metal ions from metal oxide ENMs can play a major role in interactions with organisms. ,, This is in line with the mechanism of interaction between the mLCP and the two bacteria in this work. In other cases, ROS generation drives metal oxide toxicity.…”

“…Liu and Lal show that a FePO 4 dietary supplement reduces the metabolic activity of human colonic epithelial cells . Melby et al show that lithiated cobalt phosphate nanoparticles, synthesized in the same manner as the ENMs used in this work, induce minimal toxicity in trout gill epithelial cells when compared to a cobalt-containing metal oxide. , Previous work by members of our group demonstrates that copper phosphate nanoparticles increase resistance of watermelon plants to disease and increase fruit yields . However, there is the unanswered question of whether nanoscale metal phosphates generally follow the same rules of interaction understood for other classes of metal-based ENMs …”

“…We employed a polyol synthetic approach using cobalt acetate, ammonium phosphate, and lithium precursors with the goal of synthesizing nanoscale LiCoPO 4 . Previous studies have reported that synthesis of LiCoPO 4 frequently forms multiple chemical phases and structural polymorphs. ,,,, Similarly, analysis of the X-ray diffraction (XRD) trace for the synthesized material (Figure ) shows that the product is a multiphase material with putative peak assignments to [Co­(H 2 O) 6 ]­(H 2 PO 2 ) 2 (Crystallography Open Database (COD) code: 2012913), NH 4 [CoPO 4 (H 2 O)] (COD code: 2008122), and LiC 2 H 3 O 2 (COD code: 7206368). On the basis of the sharpness of peaks within the XRD trace, these phases appear to be crystalline.…”

“…One complication with metal phosphates, as with metal oxides, is the possibility of Co­(II) and Co­(III) metal centers, which has implications for ROS production. A differentiator between phosphate nanomaterials compared with oxide analogues is that phosphates have more complex crystal structures and frequently form mixtures of closely related hydroxy–phosphate structures. − Despite their structural complexity and the frequent presence of multiple phases, the widespread emergence of transition-metal-based nanomaterials warrants the study of the potential environmental impacts of these materials. Yet, within the field of nanotoxicology, there has been little exploration of the interactions of nanoscale metal phosphates with organisms.…”