Ionothermal Synthesis Enables Access to 3D Open Framework Manganese Phosphates Containing Extra-Large 18-Ring Channels

Abstract

An ionothermal synthesis study of transition metal phosphates using the ionic liquid 1-butyl-4-methylpyridinium hexafluorophosphate [C4mpy]­[PF6] yielded four new, different open framework manganese compounds, that is, K2Mn3(HPO4)2(PO3F)­F2 (1), (NH4)2Mn3(HPO4)2(PO3F)­F2 (2), KMn3(H2PO4)­(HPO4)2F2 (3), and (NH4)­Mn3(H2PO4)­(PO3F)2F2 (4). The obtained products not only feature new framework topologies unprecedented in the family of phosphates but also interesting properties as the transition metal gives rise to both luminescent (rendering them potential nonrare earth containing red emitting phosphors) and unconventional magnetic properties governed by geometric frustrations. Aside from the structural analysis (powder and single-crystal X-ray diffraction, infrared spectroscopy), a variety of characterization methods (photoluminescence spectroscopy and magnetic measurements) were applied to study the material’s properties. Single crystal X-ray studies reveal that 1 (P21/c with a = 5.501(1), b = 14.203(3), c = 16.905(4) Å, β = 108.65(3)°, V = 1251.4 Å3, and Z = 4) and 2 (P2 1 /c with a = 5.587(1), b = 14.507(3), c = 17.364(3) Å, β = 108.75(3)°, V = 1332.6(5) Å3, and Z = 4) feature S-shaped 18-ring channels along [100], which are formed by trimer-Mn3O9F2 chains parallel to [100] and interconnecting PO3(OH) and PO3F tetrahedra. The structure of compounds 3 (C2/c with a = 20.307(4), b = 7.635(1), c = 7.834(2) Å, β = 103.26(3)°, V = 1182.2(4) Å3, and Z = 4) and 4 (C2/c with a = 20.402(4), b = 7.673(1), c = 7.845(2) Å, β = 103.56(3)°, V = 1193.8(4) Å3, and Z = 4) are characterized by layers, which are built of Mn3O8F4 octahedra trimers, with Kagomé topology parallel to the bc plane featuring 3,6-ring channels. The layers are stacked according to a sequence of AA i along the a axis. Taking into account the [P(2)­O3(OH)/P­(2)­O3F] tetrahedra, the Kagomé layers are replenished to a Mn3O2(HPO4)/Mn3O2(PO3F) composition, which are interlinked by [P(1)­O2(OH)2] forming 10-ring channels parallel to [001]. Charge compensation of the macroanions is achieved by K+ (1 and 3) and (NH4)+ (2 and 4) cations. At room temperature, compounds 1–4 demonstrate a reddish orange emission ascribed to the spin-forbidden 4T1g(4G) → 6A1g(6S) transition of the Mn2+ ions. Upon lowering the temperature to 77 K, the emission of each compound is red-shifted and becomes pure red. Compounds 1 and 2 contain spin trimers with a presumable doubled ground state. The intertrimer magnetic coupling is relatively weak, and small ferrimagnetic domains are possible in 1. The magnetic behavior of 3 and 4 can be considered as antiferromagnetic. This can be understood as their staircase Kagomé lattices are distorted, meaning that the intrinsic geometrical frustration is lifted.

Synthesis of a three-dimensional cross-linked Ni–V2O5 nanomaterial in an ionic liquid for lithium-ion batteries

“…This method has many advantages over traditional hydrothermal synthesis and organic solvothermal synthesis, including mild conditions, simple operation, reaction under normal pressure and the elimination of potential safety hazards. 35,36 In addition, because of the role of ionic liquids as templates, ionothermal preparation can effectively improve the specic surface area of materials synthesized. There are many types of ionic liquid.…”

“…To gain an insight into the mechanism underlying the formation of the 3D cross-linked coralline morphology, the effects of the reaction time (12,24,36,48,60, and 72 h) at a synthesis temperature of 180 C were studied. The results are shown in Fig.…”

From a Dense Structure to Open Frameworks: The Structural Plethora of Alkali Metal Iron Fluorophosphates

“…Porous materials, such as zeolites, 1 open-framework metal phosphates, 2 metal–organic frameworks, 3 covalent organic frameworks, 4 and so on, are attracting considerable attention in both fundamental and applied research. 5 , 6 Open-framework materials not only offer substantial structural diversity with spectacular architecture but also allow easy incorporation of additional components such as transition metal cations making it possible to further tune material properties such as magnetism, 7 electrical transport, 8 and electronic 9 and optical 10 properties. Furthermore, it is possible to combine different properties in one material and yield multifunctional materials with interesting property combinations.…”

“… 12 In this context, particularly with transition metal phosphates, 17 , 18 multifunctional materials can be realized, which combine porosity with magnetism, luminescence, or catalytic properties originating from a specific transition metal. 7 , 19 , 20 …”

Ionothermal Synthesis, Structures, and Magnetism of Three New Open Framework Iron Halide-Phosphates

“…In 2004, Morris coined the term ionothermal synthesis when he applied ionic liquids (ILs) in the synthesis of open-framework aluminum phosphates . Ionothermal synthesis is currently receiving great interest because of the tunable chemical and physicochemical solvent properties that ionic liquids have as compared to traditional solvents such as water or organic solvents. , Using ILs in syntheses result in novel open-framework compounds, such as metal-, boro-, alumino-, and silicoaluminophosphates and organic–inorganic hybrid materials with interesting structural architectures, new compositions, and attractive properties. − However, ILs are mainly discussed as being templates and solvents, much less as task-specific mineralizers.…”