Universal Single-Ion Physics in Spin–Orbit-Coupled d5 and d4 Ions

Nov 5, 2018 - Synopsis. Six new 4d4 and 4d5 compounds with isolated RuCl6 octahedra have been synthesized to study single-ion physics in the presence ...
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Universal Single-Ion Physics in Spin−Orbit-Coupled d5 and d4 Ions Hongcheng Lu,† Juan R. Chamorro,†,‡ Cheng Wan,‡ and Tyrel M. McQueen*,†,‡,§ †

Institute for Quantum Matter and Department of Physics and Astronomy, ‡Department of Chemistry, and §Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, United States

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ABSTRACT: We have identified six new 4d4 and 4d5 compounds with isolated RuCl6 octahedra, with formulas (HMA)4RuCl6·Cl (1; MA = methylamine), (HGly)4RuCl6·Cl (2; gly = glycine), (HGly)3RuCl6·2H2O (3), (NH4)2RuCl6 (4), (HPy)2RuCl6 (5; py = pyridine), and H2(4,4′bpy)RuCl6 (6; 4,4′-bpy = 4,4′-bipyridine). We find that the temperaturedependent magnetization is well described by single-ion physics in the presence of spin−orbit coupling and negligible superexchange interactions. Further, we find that many compounds in the literature are also well described by single-ion physics, and our results demonstrate the importance of considering single-ion physics when evaluating candidate geometric frustrated magnets in the presence of spin−orbit coupling.

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present data on three new Ru3+ (4d5) and three Ru4+ (4d4) materials whose structures contain isolated RuCl6 octahedra. Magnetization measurements indicate that the d5 compounds show effective magnetic moments comparable to the expected moment for a J = 1/2 system, whereas the d4 compounds show temperature-independent magnetic susceptibilities indicative of a J = 0 singlet ground state, both of which can be attributed to the significant strength of SOC. We find that these compounds very closely match the theoretical Kotani curves for isolated magnetic units20−24 and that such behavior is nearly universal in d4 and d5 systems.

INTRODUCTION Geometric magnetic frustration can lead to a variety of exotic states of matter, such as the quantum spin liquid (QSL), where magnetic moments fluctuate to absolute zero without establishing long-range magnetic order. Although most studies involving QSLs have involved 3d transition metals, such as ZnCu3(OH)6Cl2, Cu3V2O7(OH)2·2H2O, PbCuTe2O6, and κ(BEDT-TTF)2Cu2(CN)3,1−4 there has been much recent interest in 4d and 5d systems owing to their comparatively larger spin−orbit coupling (SOC), which considerably modifies the electronic states and can result in bonddirection-dependent exchange interactions and unexpected insulating ground states, such as in Sr2IrO45,6 and other systems.7,8 Specific subtypes of QSLs can also be stabilized through strong SOC, such as Kitaev spin liquids in twodimensional honeycomb lattices such as α-RuCl3 and A2IrO3 (A = Li, Na),9−13 which, despite the emergence of magnetic ordering at finite temperatures due to interlayer interactions,10−18 present the opportunity to explore novel physics. To clearly investigate the importance and effect of SOC on the magnetic behavior, it is best to study systems with isolated magnetic ions for negligible magnetic superexchange interactions, so as to probe true single-ion physics. An example of the effect that SOC can have on the magnetic behavior is the La11−xSrxIr4O24 system, where strongly spin−orbit-coupled Ir4+ can be fully oxidized to Ir5+.19 Despite the two unpaired electrons expected in Ir5+ 5d4 octahedra, where an effective magnetic moment peff = 2.83 μB is expected based on peff = [g2S(S + 1)]1/2, a peff = 0 μB is observed,19 confirming the effect that SOC can have on the magnetic ground state of this system. Although much work has been performed on understanding iridate systems, less work has been performed to understand the role of SOC for other 4d and 5d materials. In this work, we © XXXX American Chemical Society

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EXPERIMENTAL SECTION

Synthesis. Ruthenium chloride hydrate (RuCl3·3H2O; Oakwood Chemical), 2,2′-bipyridine (C10H8N2; >99%, Alfa Aesar), 4,4′bipyridine (C10H8N2; 98%, Alfa Aesar), oxalic acid dihydrate (H2C2O4·2H2O; 98%, Alfa Aesar), glycine (NH3CH2COO; >99.5%, Alfa Aesar), aqueous methylamine (CH3NH2; 40 wt %, Alfa Aesar), pyridine (C5H5N; 99.5%, Acros Organics), and aqueous hydrochloric acid (HCl; 36.5−38 wt %, EMD Millipore) were all used as received. Brown single crystals of (HMA)4RuCl6·Cl (1; MA = methylamine) were synthesized by adding 0.130 g of RuCl3·3H2O, 0.126 g of H2C2O4·2H2O, 0.5 mL of aqueous methylamine, and 0.5 mL of aqueous HCl to a 23 mL Teflon-lined Parr autoclave. The autoclave was quickly heated to 150 °C, held for 72 h, and then cooled to ambient temperature at 2 °C/h. The brown single crystals (up to 2 mm) were recovered in air after vacuum filtration by easy separation from a byproduct of green crystals [nonmagnetic phase of (HMA)2RuCl4(CO)·H2O]. Orange single crystals of (HGly)4RuCl6·Cl (2; gly = glycine) were synthesized by adding 0.390 g of RuCl3·3H2O, 0.195 g of glycine, and 1.0 mL of aqueous HCl to a 23 mL Teflon-lined Parr autoclave. The autoclave was quickly heated to 120 °C, held for 48 h, and then Received: September 23, 2018

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DOI: 10.1021/acs.inorgchem.8b02718 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Crystal Data, Structure Solutions, and Refinements for Compounds 1−6 formula weight (g/mol) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z λ(Kα) (Å) T (K) maximum θ (deg) ρcalc (g/cm3) R1 (Rp) wR2 (Rwp) GOF(χ2) formula weight (g/mol) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z λ(Kα) (Å) T (K) maximum θ (deg) ρcalc (g/cm3) R1 (Rp) wR2 (Rwp) GOF(χ2)

1

2

3

(CH6N)4RuCl6·Cl 477.49 monoclinic P2/n 15.8512(3) 7.2067(1) 15.8853(3) 90 103.34(1) 90 1765.72(5) 4 0.71073 110(2) 33.1 1.796 0.029 0.071 1.12 4

(C2H6NO2)4RuCl6·Cl 653.53 triclinic P1̅ 9.3786(2) 10.8350(2) 12.0872(2) 66.39(1) 87.29(1) 89.27(1) 1124.18(4) 2 0.71073 110(2) 33.1 1.931 0.018 0.044 1.11 5

(C2H6NO2)3RuCl6·2H2O 578.04 orthorhombic Pna21 12.4495(2) 7.5314(1) 20.7120(3) 90 90 90 1942.00(5) 4 0.71073 110(2) 33.1 1.977 0.015 0.035 1.05 6

(NH4)2RuCl6 349.86 cubic Fm3̅m 9.7628(1) 9.7628(1) 9.7628(1) 90 90 90 930.52(3) 4 0.71073 110(2) 33.0 2.497 0.0008 0.017 1.29

(C5H6N)2RuCl6 473.99 triclinic P1̅ 7.0620(2) 7.8861(2) 7.9031(2) 83.05(1) 84.54(1) 64.87(1) 395.09(2) 1 0.71073 110(2) 30.5 1.992 0.025 0.065 1.08

cooled to ambient temperature at 2 °C/h. The orange single crystals were recovered in air after vacuum filtration by easy separation from a small amount of a byproduct of dark-red cube crystals. Dark-orange plate single crystals of (HGly)3RuCl6·2H2O (3) were synthesized by adding 0.520 g of RuCl3·3H2O, 0.260 g of glycine, and 1.0 mL of aqueous HCl to a 23 mL Teflon-lined Parr autoclave. The autoclave was quickly heated to 120 °C, held for 48 h, and then cooled to ambient temperature at 2 °C/h. The dark-orange plate single crystals were recovered in air after vacuum filtration by easy separation from a small amount of a byproduct of dark-red cube crystals. Dark-red cube single crystals of (NH4)2RuCl6 (4) were synthesized by adding 0.260 g of RuCl3·3H2O, 0.065 g of glycine (as a NH4+ source after decomposition), and 2 mL of aqueous HCl to a 23 mL Teflon-lined Parr autoclave. The autoclave was quickly heated to 120 °C, held for 48 h, and then cooled to ambient temperature at 2 °C/h. The dark-red single crystals were recovered in air after vacuum filtration. The dark-red cube single crystals of compound 4 are also a byproduct in the syntheses of both compounds 2 and 3. Dark-green single crystals of (HPy)2RuCl6 (5; py = pyridine) were synthesized by adding 0.130 g of RuCl3·3H2O, 0.2 mL of pyridine, and 0.8 mL of aqueous HCl to a 23 mL Teflon-lined Parr autoclave.

(C10H10N2)RuCl6 471.97 orthorhombic Ibam 7.2800(2) 12.7473(3) 15.6102(3) 90 90 90 1448.64(5) 4 0.71073 110(2) 30.5 2.164 0.019 0.049 1.13

The autoclave was quickly heated to 150 °C, held for 72 h, and then cooled to ambient temperature at 2 °C/h. The dark-green single crystals were recovered in air after vacuum filtration. Dark-red single crystals of H2(4,4′-bpy)RuCl6 (6; 4,4′-bpy = 4,4′bipyridine) were synthesized by adding 0.13 g of RuCl3·3H2O, 0.156 g of 4,4′-bipyridine, and 1.0 mL of aqueous HCl to a 23 mL Teflonlined Parr autoclave. The autoclave was quickly heated to 150 °C, held for 72 h, and then cooled to ambient temperature at 2 °C/h. The dark-green single crystals were recovered in air after vacuum filtration. The phase purities of all samples for further measurements were confirmed by powder X-ray diffraction (XRD). Crystallographic Determination. Powder XRD patterns were collected on a Bruker D8 Focus X-ray diffractometer using Cu Kα radiation (λ = 1.54184 Å) and a LynxEye detector. The single-crystal XRD experiments for 1−6 were conducted at T = 110(2) K on a SuperNova diffractometer (equipped with an Atlas detector) with Mo Kα radiation (λ′ = 0.71073 Å) and run by the program CrysAlisPro (version 1.171.36.32; Agilent Technologies, 2013). The same program was used to refine the cell dimensions and for data reduction. The structures were determined by direct methods, completed by Fourier difference syntheses with SIR97,25 and refined using SHELXL-2014.26 Analytical numeric absorption corrections B

DOI: 10.1021/acs.inorgchem.8b02718 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Crystal structures of (a) 1, (b) 2, (c) 3, (d) 4, (e) 5, and (f) 6 with isolated ruthenium octahedra. based on the multifaceted crystal model were applied using the same program, CrysAlisPro. H atoms of organic and water molecules were included in the refinement model in calculated positions [C−H = 0.93 Å, N−H = 0.86 Å, O−H = 0.82 Å; Uiso(H) = 1.5Ueq(C,N); Uiso(H) = 1.2Ueq(O)] if they were not observed by XRD, or unstable refinement was caused by weak diffraction. Additional symmetry elements were checked using the program PLATON.27 Crystallographic data are reported in Tables 1 and S1. Magnetometer. A Quantum Design physical property measurement system with the ACMS option was used to study the temperature dependence of magnetization M at T = 2−300 K under μ0H = 1 T of all six compounds and the field dependence of M under magnetic fields between −7 and +7 T at T = 2 K. Magnetic susceptibilities were approximated by χ ≈ M/H with subtraction of the sample container background and diamagnetic correction derived from Pascal’s constants.28 Calculations. The calculations for molecular orbitals were performed on Gaussian09 using restricted spin-density functional theory with the Becke three-parameter hybrid functional “B3LYP”29 and basis set “def2-SVP” [improved default (TURBOMOLE) basis set “def2” with split-valence (SV) basis set plus smaller polarization function “P”].30,31 The models of input files for calculation with all atoms frozen except for added H atoms are simplified as neutral molecules of H3RuCl6 (doublet state) for 1−3 and H2RuCl6 (singlet and triplet states) for 4−6, respectively, which were generated from each structural model of 1−6 by replacing each organic molecule with H atoms around the RuCl6 octahedron. All calculations exclude the SOC effects.

shortest Ru−Ru distances of 7.2, 7.1, and 7.2 Å, respectively. Locally, some very small distortions can be observed within the RuCl6 octahedra, with bond lengths varying up to a maximum of 1.40% (Figure S1 and Table 2). Compounds 4−6, containing Ru4+ (4d4), crystallize in the space groups P1̅, Ibam, and Fm3̅m, respectively. These systems also show highly isolated RuCl6 separated by large organic units with Ru−Ru distances of 6.9, 7.1, and 7.3 Å, respectively. Slight distortions are also observed in these systems, with a maximum difference in the intraoctahedral bond lengths of Table 2. Selected Bond Lengths for Compounds 1−6 bond Ru1−Cl1 (×2) Ru1−Cl2 (×2) Ru1−Cl3 (×2) Ru1−Cl1 (×2) Ru1−Cl2 (×2) Ru1−Cl3 (×2) Ru−Cl1 Ru−Cl2 Ru−Cl3

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RESULTS Structural Descriptions. The crystal structures of 1−6 contain isolated RuCl6 octahedra, as well as isolated organic cations and chloride anions, as shown in Figure 1. Compounds 1−3, with Ru3+ (4d5), crystallize in the space groups P2/n, P1̅, and Pna21, respectively. RuCl6 octahedra are isolated from one another in all three compounds, separated by a complex network of organic, chloride, and hydrogen ions, with the

Ru−Cl (×6) Ru−Cl1 (×2) Ru−Cl2 (×2) Ru−Cl1 (×2) Ru−Cl2 (×2) C

bond Length (Å)

bond

Compound 1 2.3829(6) Ru2−Cl4 (×2) 2.3693(8) Ru2−Cl5 (×2) 2.3694(6) Ru2−Cl6 (×2) Compound 2 2.3718(3) Ru2−Cl4 (×2) 2.3752(3) Ru2−Cl5 (×2) 2.3752(2) Ru2−Cl6 (×2) Compound 3 2.3881(4) Ru−Cl4 2.3802(4) Ru−Cl5 2.3574(4) Ru−Cl6 Compound 4 2.3266(3) Compound 5 2.3223(7) Ru−Cl3 (×2) 2.3197(11) Compound 6 2.2948(7) Ru−Cl3 (×2) 2.3477(7)

bond Length (Å) 2.3749(6) 2.3711(8) 2.3749(6) 2.3904(3) 2.3699(3) 2.3580(3) 2.3663(4) 2.3692(4) 2.3903(4)

2.3519(6)

2.3266(6)

DOI: 10.1021/acs.inorgchem.8b02718 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

both shape and scale.40,41 As expected, no long-range magnetic order is observed above T = 2 K for any of these compounds. Also, in contrast to compounds 1−3, the magnetization of compounds 4−6 as a function of the field shows very small magnetic moments at μ0H = 7 T at T = 2 K (Figure S3b), with values of M7 T = 0.058(1), 0.051(1), and 0.054(1) μB, respectively, which are much smaller than the expected spinonly saturation value of Msat = 1 μB. This serves to demonstrate the nonmagnetic nature of 4d4 systems compared to 4d5. In the limit of a single ion in the presence of octahedral coordination, it is possible to analytically compute the expected temperature dependence of the effective magnetic moment per ion, peff. This analysis was first done in 1949 by Kotani, who showed that a plot of peff versus kT/λ (k is the Boltzmann constant, T is the temperature, and λ is the systemdependent SOC constant) follows a universal curve. Such Kotani plots for compounds 1−6, as well as a variety of other d4 and d5 compounds in the literature, are shown in Figure 3. The λ values used were 610 cm−1 for Ru3+,22 1400 cm−1 for Ru4+,23 2050 cm−1 for Ir4+,42 and 5500 cm−1 for Ir5+.23 As seen, the data for compounds 1−3 (d5) and 4−6 (d4) follow the expected theoretical results given by Kotani.

2.31% (Figure S1). All Ru−Cl bond lengths (as shown in Table 2) are consistent with the bond lengths observed in other systems containing the same elements.32−36 Also, some isostructures for 1,37 5,38 and 639 have been reported. Magnetic Properties. Polycrystalline samples, obtained by grinding single crystals, were used to investigate the magnetic properties of these materials. Compounds 1−3 with Ru3+ 4d5 show paramagnetic behavior down to 2 K with no signs of long-range magnetic order (Figure S2a). As shown in Figure 2a, a Curie−Weiss analysis of the data between 50 and 300 K

Figure 2. Temperature dependence of (χ − χ0)−1 at μ0H = 1 T: (a) for 1−3; (b) for 4−6. The magnetic susceptibility is approximated as χ ≈ Μ/Η.

yields effective moments peff = 1.74(1), 1.76(1), and 1.74(1) μB, respectively, which are all in excellent agreement with the expected value peff = 1.73 for a spin-only J = 1/2 magnet. The very small Weiss temperatures for the compounds of θ = 0.9(12), 0.0(5), and 0.9(3) K, respectively, are indicative of very weak and negligible magnetic interactions between Ru3+ ions for all three compounds as expected. As shown in Figure S3a, magnetization as a function of the field for these compounds shows near-complete saturation at μ0H = 7 T at T = 2 K with M7 T = 0.91(2), 0.92(1), and 0.92(1) μB, respectively, which are close to the calculated spin-only value of Msat = 1 μB for Ru3+ 4d5 in the doublet state. In contrast to compounds 1−3 with Ru3+ 4d5, the magnetic susceptibilities of compounds 4−6 with Ru4+ 4d4 show almost temperature-independent behavior, particularly in the lowtemperature range, as shown in Figure S2b. Interestingly, the magnetic susceptibility curves for these compounds look similar to those of one-dimensional chain antiferromagnets with broad maxima indicative of short-range correlations in

Figure 3. Theoretical Kotani curve with only single-ion physics effects on strongly spin−orbit-coupled (a) d5 ions in 1−3 in this work and αRuCl3,46 [Ru(NH3)5Cl]Cl2·H2O,47 [Hbpy][Ru(bpy)Cl4]·H2O,47 [Ru(NH3)6]Cl3,47 and SrLa10Ir4O2419 and (b) d4 ions in 4−6 in this work and Ag3LiRu2O6,48 NaIrO3,46 Sr2YIrO6-(1),50 Sr2YIrO6(2),51 Sr 2 YIrO 6-(3),52 Ba 2 YIrO 6, 52 Ba 2 ScIrO6 ,53 Sr 2 ScIrO6 , 53 Sr3CaIr2O9,49 Ba3ZnIr2O9,54 and Sr5La6Ir4O24.19 The effective magnetic moment peff per mole of ruthenium ions is calculated by peff = [8(χ − χ0)T]1/2. D

DOI: 10.1021/acs.inorgchem.8b02718 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Molecular Orbital Calculations. The calculated electronic structures for compounds 1−3 without considering SOC are similar to those of compounds 4−6 due to distortions so small in the octahedra with Oh symmetry that they remain nearly unchanged. As shown in Table S2, the octahedral crystal-field splitting and on-site electron−electron repulsion (Hubbard U) are around 4.1 and 2.6 eV, respectively, for the doublet state of compounds 1−3 and 4.4 and 2.6 eV for the triplet state, respectively, for compounds 4−6.

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DISCUSSION There are many factors that influence the magnetic ground state of a material, including the magnitude of the spins, spin anisotropy, exchange and superexchange interactions, structural distortions, SOC, and others. To clearly investigate the effect of SOC on the magnetic properties, a material containing truly isolated magnetic units that are not participating in exchange or superexchange interactions is desirable. Compounds 1−6 fulfill this requirement (with Ru−Ru distances around 7.0 Å and no chemical bonds between ruthenium octahedra except for hydrogen bonds) and concomitantly show no signs of long-range magnetic order down to at least T = 2 K. Figure S1 shows the distortions in the ruthenium octahedra in compounds 1−6, which are very small and thus virtually retain Oh symmetry. The large octahedral crystal-field splitting in 4d and 5d transition-metal halides between eg and t2g orbitals and the largely reduced interelectronic repulsion usually yields low-spin configurations with mostly paired spins, as shown in Figure 4, in contrast to the high-spin configurations observed in 3d transition-metal halides, such as in (4,4′-bpy)FeCl3.40 In order to fully understand the magnetic ground states of compounds 1−6, we must first take symmetries into consideration. In an octahedral crystal field, the five d orbitals are split into eg and t2g manifolds. In the case of d5, as shown in Figure 4a, placing five electrons into these manifolds gives rise to many multielectron states (2T2, 4T1, 6A1, 4T2, ...), of which the spin and orbital triplet 2T2 is the ground state. When subjected to SOC, the 6-fold degenerate 2T2 is further split into two sublevels, Γ7 and Γ8,43 and the ground state becomes a doublet with J = 1/2. In contrast, when four electrons are placed in the t2g manifold, as is the case for d4, as shown in Figure 4b, a manifold containing many states (3T1, 5E, 1T2, 1E, ...) emerges with the spin and orbital triplet 3T1 as the ground state. SOC then splits this ground state into multiple states (Γ1, Γ4, Γ3, and Γ5),44,45 with the lowest in energy being a single-ion spin orbital singlet (J = 0). Thus, for compounds 1−6, despite all containing isolated RuCl6 octahedra, compounds 1−3 with Ru3+ (4d5; J = 1/2) and compounds 4−6 with Ru4+ (4d4; J = 0) exhibit completely distinct magnetic behavior. In compounds 1−3, the behaviors of the magnetic susceptibility χ(T) and near-complete saturation at μ0H = 7 T at T = 2 K with M7 T/Ms ≈ 93% in magnetization M(H) curves are observed, whereas nearly temperature-independent magnetic susceptibility curves are observed in compounds 4−6, and the magnetization at 7 T at 2 K is very small. Thus, as shown in Figure 3a, peff values at 2 K for 1−3 are all very close to the theoretical value of 1.732 μB for a doublet ground state with J = 1/2, whereas they are close to zero in 4−6 as expected for a J = 0 singlet ground state. It should be noted that the sudden decrease in peff at the lowest temperatures in 4−6, as observed in Figure 3b, is not due to

Figure 4. Low-spin state of strongly spin−orbit-coupled (a) d5 ions with a doublet ground state (J = 1/2) and (b) d4 ions with a singlet ground state (J = 0) after further splitting by SOC. The numbers in parentheses are the numbers of degenerate multielectron states. The states for the Oh crystal field (3T1, 5E, etc.) are labeled in chemical notation, and those for SOC (Γ1, Γ4, etc.) are labeled in physics notation.

the emergence of long-range magnetic order, which is ruled out based on the results of magnetic susceptibility. More significantly, it is clearly evident that the experimental curves are in excellent agreement with the theoretically calculated Kotani curves for both 1−3 with d5 and 4−6 with d4, respectively. If we compare these values, representative compounds from the literature (with suitable χ0 values, as shown in Table S3) that contain strongly spin−orbit-coupled d4 (e.g., Ru4+ and Ir5+) and d5 (e.g., Ru3+ and Ir4+) octahedra (that are not necessarily isolated from each other), we find that they also follow the theoretically predicted Kotani curves excellently. Therefore, we find that the magnetic behaviors of these systems can be universally described using Kotani behavior perhaps with the exception of α-RuCl3. This is observed in d5 materials such as α-RuCl3 (with deviation at low temperature due to long-range order at TN = 14 K),46 [Ru(NH3)5Cl]Cl2·H2O,47 [Hbpy][Ru(bpy)Cl4]·H2O,47 [Ru(NH3)6]Cl3,47 and SrLa10Ir4O24 (deviation due to long-range order at TN = 11 K)19 and strongly spin−orbit-coupled d4 ions in Ag3LiRu2O6,48 NaIrO3,49 A2BIrO6 (A = Sr, Ba; B = Y, Sc),50−53 A3BIr2O9 (A = Sr, Ba; B = Ca, Zn),49,54 and Sr5La6Ir4O24,19 respectively. Therefore, the effects of SOC cannot be neglected or even approximated by adjusting the expected peff. Instead, single-ion physics plays a decisive role in the magnetic properties of 4d E

DOI: 10.1021/acs.inorgchem.8b02718 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

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and 5d materials. The geometric magnetic frustration in many of these compounds is reflective of single-ion physics.

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CONCLUSION Six newly synthesized ruthenium chlorides 1−6 with isolated RuCl6 octahedra with negligible magnetic exchange and small, negligible octahedral distortions have been targeted to investigate the exclusive effect of SOC on the magnetic properties of Ru3+ 4d5 and Ru4+ 4d 4. The magnetic susceptibilities of compounds 1−3 with Ru3+ 4d5 indicate paramagnetic behavior and nearly completely saturated magnetization at 7 T at 2 K in agreement with the value for J = 1/2. In contrast, the temperature-independent magnetic susceptibility and small magnetic moment observed from magnetization in compounds 4−6 are in agreement with a J = 0 ground state. For all compounds 1−6, the experimental data are in excellent agreement with the theoretically calculated behavior for single-ion d5 and d4 configurations. This extends to other representative materials in the literature that have previously been reported to exhibit signatures of exotic magnetic states.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b02718. Additional crystallographic and magnetic property data (PDF) Accession Codes

CCDC 1546914−1546919 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (T.M.M.). ORCID

Hongcheng Lu: 0000-0003-0414-4768 Tyrel M. McQueen: 0000-0002-8493-4630 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported as part of the Institute for Quantum Matter, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award DE-SC0019331. We thank Dr. Maxime A. Siegler for help with crystallographic data collection.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.8b02718 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.8b02718 Inorg. Chem. XXXX, XXX, XXX−XXX