A hybrid vanadium fluoride with structurally isolated S = 1 kagome layers

Abstract

A new organically-templated vanadium (III) fluoride, (NH 4 ) 2 (C 2 H 8 N)[V 3 F 12 ], has been prepared using an ionothermal approach. This compound has a unique layered structure featuring distorted S = 1 kagome planes separated by the cationic species. The compound exhibits magnetic frustration, with a canted antiferromagnetic ground state. On further cooling within the ground state a pronounced change in magnetisation kinetics is observed.The kagome lattice antiferromagnet is perhaps the most famous example of a geometrically-frustrated magnetic system 1,2 . The ideal kagome antiferromagnet consists of layers of corner-sharing equilateral triangles, with antiferromagnetically-coupled magnetic cations at each node. The inherent magnetic frustration in this system can be seen when one attempts to place 'spins' on each node of the triangles such that all near-neighbour interactions satisfy antiparallel (ie. antiferromagnetic, AFM) alignment. Not all preferred interactions can be satisfied simultaneously, leading to a vastly-increased number of compromise spin configurations of equally low energy. This frustration can result in various states that lie beyond the standard notions of long-range magnetic ordering (LRO) and spontaneous symmetry breaking, leading to either spin glass, spin ice and spin liquid states 3,4 . The inhibition of LRO is particularly acute in systems with 'quantum spins' (ie. J = S = ½ for the magnetic cations) for which quantum fluctuations combine with frustration to suppress LRO down to the lowest-accessible temperatures, in favour of quantum spin liquid ground states (QSLs).There is now growing evidence that these long-sought QSL states exist in recently studied S = ½ kagome antiferromagnets including herbertsmithite 5,6 and kapellasite 7 (both polymorphs of the composition ZnCu 3 (OH) 6 Cl 2 ) and the vanadium oxyfluoride [NH 4 8,9 . Analogous systems with S = 1 spins usually freeze into LRO states [10][11][12][13][14][15][16] (full details are given in ESI, Table S1) because here quantum fluctuations play a diminished role and probably more importantly, due to single ion anisotropy effects, which start to play a role for S > ½. Nevertheless, the diverse range of behaviour exhibited by the few examples so far, and the various theoretically proposed states for the related S = 1 triangular lattices 17,18 , demonstrates that further, chemically different, examples of S = 1 kagome magnets are of significant interest.In this paper we report a novel example of this family, in the compound (NH 4 ) 2 (C 2 H 8 N)[V 3 F 12 ] 1. This study forms part of our ongoing efforts to explore and understand the complex solvothermal/ionothermal chemistry of vanadium fluoride-based systems 8,[19][20][21] . Specifically, compound 1 was isolated by using identical chemistry ¶ to that in the preparation of the QSL compound DQ-VOF, except that the temperature of the reaction was increased from 170 to 210 C and the time was increased from 1 day to 5 days. Remarkably, this adjustment in reaction conditions pro...

Synthesis of a d2 kagome lattice antiferromagnet, (CH3NH3)2NaV3F12

“…The weaker antiferromagnetic coupling in 1-V could originate from additional, competing, ferromagnetic exchange interaction due to the extra d electron in either d xz or d yz orbitals for V 3+ in comparison to Ti 3+ . 37 Similar phenomenon has been observed in the jarosites with V 3+ , Cr 3+ and Fe 3+ . 4,20 Therefore, we cannot rule out the contribution from the potential competing ferromagnetic exchange interaction to the spin glass state in 1-V despite of the dominant antiferromagnetic interactions between spins.…”

“…31 The effective magnetic moment of m eff ¼ 2.361(23) m B /V 3+ deviates from the theoretical value of 2.83 m B for S ¼ 1 spin but is close to the value observed for several A 2 BV 3 F 12 compounds. 31,37 A change in slope around 8 K in the temperature-dependence of inverse susceptibility can be observed. This change in slope could be due to several effects including the formation of short-range magnetic ordering or the single-ion anisotropy of V 3+ in the tetragonal environment.…”

“…2a) indicates that 1-V has dominantly antiferromagnetic interactions, which is similar to the other A 2 BV 3 F 12 compounds. 31,37 Therefore, the 1-V, with a non-distorted kagome lattice and dominantly antiferromagnetic interactions is a candidate material to study theground state of S ¼ 1 KLAFs. The frustration parameter f ¼ |q cw /T c | (T c represents any cooperative-ordering transition temperature) is an empirical measurement of frustration.…”

Kagome-type isostructural 3D-transition metal fluorosulfates with spin 3/2 and 1: synthesis, structure and characterization

“…[5][6][7][8][9][10][11][12] Thus, halide anions have been explored to generate a kagome type lattice, which is also advantageous in terms of minimizing the ambiguity of hydrox-ide composition. 13 To expand the area of synthesizing kagome structures, various other anions like azides 14,15 and organic templates [16][17][18][19][20] have also been used which gave aesthetically pleasing structures with remarkable magnetic properties.…”

Crystal structure of guanidinium hexafluoridovanadate(III), (CN3H6)3[VF6]: an unusual hybrid compound related to perovskite

“…In some of our recent work we have prepared vanadium fluorides and oxyfluorides exhibiting vanadium in oxidation state +3, +4 and +5 and also mixed valence systems, with vanadium typically in octahedral coordination. The VF 6 or VOF 5 octahedral units may be linked into structures of varying dimensionality, for example oligomeric units, chains or layer structures (Aldous et al, 2007;Aidoudi et al, 2014a;Aidoudi et al, 2014b). Here we present a novel vanadium(III) fluoride, [CN 3 H 6 ] 3 [VF 6 ], containing discrete VF 6 octahedral units, linked via hydrogen-bonded guanidinium moieties into a cubic supramolecular array which has similarities to the perovskite structural family.…”