Mixed-Spin Diamond Chain Cu2FePO4F4(H2O)4 with a Noncollinear


Jul 25, 2017 - Synopsis. The first mixed-spin diamond system Cu2FePO4F4(H2O)4 (S1 = 1/2, S2 = 5/2) has been experimentally realized. Magnetic suscepti...
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Mixed-Spin Diamond Chain Cu2FePO4F4(H2O)4 with a Noncollinear Spin Order and Possible Successive Phase Transitions Hongcheng Lu,† Naoaki Hayashi,‡,§ Yuki Matsumoto,† Hiroshi Takatsu,† and Hiroshi Kageyama*,† †

Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan Research Institute for Production Development, 15 Morimoto, Shimogamo, Sakyo, Kyoto 606-0805, Japan § Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University, Yoshida-ushinomiya, Sakyo, Kyoto 606-8501, Japan ‡

S Supporting Information *

ABSTRACT: A diamond spin chain system, one of the one-dimensional frustrated lattices, is known to exhibit novel properties, but experimental studies have been exclusively confined to materials with a single spin component. Here, we report on the synthesis, structure, and magnetic properties of a new diamond chain compound Cu2FePO4F4(H2O)4 1 composed of mixed-spins of Cu2+ (S = 1/2 × 2) and Fe3+ (S = 5/2). Compound 1 crystallizes in the space group C2/c of the monoclinic crystal system with a = 7.7546(4) Å, b = 12.1290(6) Å, c = 9.9209(6) Å, β = 105.29(1)°, and Z = 4. DC magnetization, Mössbauer spectroscopy, and heat capacity measurements revealed an antiferromagnetic order at 11.3 K with a small ferromagnetic component. It is suggested that ferrimagnetic diamond chains are arranged in an antiferromagnetic fashion (i.e., [...Fe(↑)-2Cu(↓↓)-Fe(↑)...] and [...Fe(↓)2Cu(↑↑)-Fe(↓)...]) within the ab plane to cancel net magnetization, and the spin orientation of the diamond chains changes alternately along the c axis due to the magnetic anisotropy, leading to a noncollinear spin order. Furthermore, another anomaly is observed in the heat capacity at around 3 K, suggesting a successive magnetic transition or crossover due to competing magnetic interactions.



INTRODUCTION Frustrated spin systems, including two-dimensional (2D) triangular (e.g., YbMgGaO4), Kagomé (e.g., ZnCu3(OH)6Cl2),

exhibit exotic phenomena such as spin liquids, nontrivial spin order, and successive phase transitions.14−18 A diamond chain system, shown in Figure 1(a), is one of the one-dimensional (1D) versions of frustrated spin−lattices. Theoretical studies for the S = 1/2 diamond chain (S1 = S2 = 1/2) have identified three phases depending on magnetic interactions J2/J1 (where J1 and J2 represent, respectively, side coupling and inner coupling in diamond-shape lattice, as shown in Figure 1): a ferrimagnetic phase, a dimer phase, and a spin fluid phase.19−21 Moreover, a quantized plateau corresponding to one-third of the saturation magnetization is predicted to appear in the presence of a magnetic field for the ferrimagnetic and dimer phases.19−21 Experimentally, Cu3Cl6(H2O)2·2H8C4SO2 exhibits a dimer singlet ground state with a finite excitation gap.22 A fieldinduced 1/3 magnetization plateau has been observed in Cu3(CO3)2(OH)223−26 and [H2en]Cu(H2O)2[V2O2F8] (en = ethylenediammonium)27 and the ferrimagnetic phase of A3Cu3(PO4)4 (A = Ca, Sr, Pb).28,29 Bi4Cu3V2O14,30 α[Cu3(OH)2(CH3CO2)2(H2O)4](C6H5SO3)2,31 K3Cu3AlO2(SO4)4,32 and Cu3(TeO3)2Br233 are also investigated in terms of spin frustration. However, all the model materials experimentally reported to date are exclusively confined with the S = 1/2 system derived from Cu2+ or V4+ cations, limiting understanding of the physics of diamond spin

Figure 1. Sketch of the (a) idealized and (b) distorted diamond chain model with 2S1 and S2 with magnetic interactions of J1 (and J1′ for (b)) and J2.

and Shastry−Sutherland (e.g., SrCu2(BO3)2) lattices, and threedimensional (3D) pyrochlore (e.g., Pr2Zr2O7), double perovskite (e.g., Sr2YOsO6), and hyper-Kagomé (Na4Ir3O8) lattices, with competing magnetic interactions arising from frustrated geometry have attracted a great deal of attention.1−13 They © 2017 American Chemical Society

Received: June 15, 2017 Published: July 25, 2017 9353

DOI: 10.1021/acs.inorgchem.7b01533 Inorg. Chem. 2017, 56, 9353−9360

Article

Inorganic Chemistry

temperature to 900 °C. The material was held at this temperature for 2 h and then cooled to room temperature at a rate of 5 °C/min. Magnetometer. A Quantum Design MPMS-XL superconducting quantum interference device (SQUID) magnetometer was used to collect DC magnetic susceptibility data for 1 between 2 and 350 K at 0.1 and 6 T and magnetization data under a magnetic field between −7 and 7 T at 2 and 300 K. Several single crystals were ground, loaded into Al foil, and then inserted into a straw to connect an MPMS stick for magnetic measurements. Specific Heat. The specific heat of a pellet (mixed by sample 1 and fine Ag powder) solidified at 6 GPa in a cubic-anvil-type high-pressure apparatus was measured at temperatures between 2 and 30 K at magnetic fields of 0, 0.1, 1, 3, 5, and 7 T by a relaxation method with a Quantum Design PPMS. Addenda of fine Ag powder (ASP-100, Wakenyaku Co., Ltd.) for better conduction and alumina platform has been subtracted. Mö ssbauer Spectroscopy. 57Fe-Mössbauer spectra on the sample of 1 were taken at room temperature and low temperatures in transmission geometry using a 57Co/Rh γ-ray source. The source velocity was calibrated by α-Fe as a standard. The resulting spectra were least-squares-fitted using the Lorentzian function.

chains, although some theoretical study about mixed spin diamond chains with S′ = 1/2 and S″ = 1 have been reported.34−43 Thus, it is interesting to explore diamond chain systems with other spins (e.g., S = 1) or mixed-spins (S1 ≠ S2). In this study, we report a new compound, Cu2FePO4F4(H2O)4 1, composed of 1D arrays of dimeric Cu2+ (S1 = 1/2) units connected by Fe3+ ions (S2 = 5/2), thus forming mixed-spin diamond chains. Together with the synthesis and crystal structure, we show that material 1 exhibits a noncollinear magnetic structure and possibly successive phase transitions.



EXPERIMENTAL SECTION

Caution! Hydrof luoric acid is toxic and corrosive! It must be handled with extreme caution and the appropriate protective gear.44−46

Table 1. Crystal Data, Structure Solutions, and Refinements for Compound 1 compound formula formula weight (g mol−1) temperature (K) crystal system space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z maximum θ (deg) λ (Mo/Cu Kα) (Å) ρcalc (g cm−3) Rint R1 wR2 goodness-of-fit

Cu2FePO4F4(H2O)4 425.98 296(2) monoclinic C2/c 7.7546(4) 12.1290(6) 9.9209(6) 105.29(1) 900.09(8) 4 25.3 0.71073 3.144 0.029 0.017 0.049 1.03



RESULTS Structural Descriptions. Phase purity was examined by powder X-ray diffraction (PXRD) as shown in Figure S1.

Synthesis. Copper oxide (CuO, 99.9%, Kojundo Chemical Laboratory Co., Ltd.), iron(III) phosphate dihydrate (FePO4·2H2O, Fe wt % >29%, Aldrich), and aqueous hydrofluoric acid (46.0−48.0% HF by weight, Wako) were used as received. Blue single crystals of Cu2FePO4F4(H2O)4 1 were synthesized by adding 0.318 g (4 mmol) of CuO, 0.374 g (2 mmol) of FePO4·2H2O, and 0.8 mL (∼22.08 mmol) of 48% aqueous HF to a Teflon [fluoro(ethylenepropylene), FEP] pouch made as described previously.47−51 All reagents were sealed with a sealer in Teflon pouches and placed into a 125 mL Parr autoclave with a backfill of 45 mL of pure water. The autoclave was quickly heated to 200 °C, held at this temperature for 24 h, and cooled to ambient temperature for 30 h. The single crystals were recovered in air after vacuum filtration. The yield of 1 was 18.4% (based on Fe). Crystallographic Determination. The powder X-ray diffraction pattern was collected on a Bruker D8 ADVANCE using Cu Kα radiation (λ = 1.54056 Å) at a 0.1° step size and 1 s dwell time. The single-crystal X-ray diffraction experiment for 1 was conducted at room temperature (296 K) on a Rigaku R-AXIS RAPID image plate diffractometer with Mo Kα radiation (λ = 0.71073 Å). The crystal-todetector distance was 127 mm, and data integrations were made using Rigaku RAPID-AUTO.52 Multiscan absorption corrections were applied with Rigaku RAPID-AUTO. The structures were determined by direct methods, completed by Fourier difference syntheses with SIR97,53 and refined using SHELXL-2014.54 Additional symmetry elements were checked using the program PLATON.55 Crystallographic data are reported in Table 1. Thermogravimetric Analysis (TG-DTA). The thermogravimetric measurement for 1 was performed on a Rigaku Thermo plus TG8121 using a Pt pan with a heating rate of 1 °C/min in air from ambient

Figure 2. Crystal structure of 1: (a) view for layers in a 3D framework; the right one is rotated by 65.2° in the ab plane from the left one, (b) triangular “Cu2Fe” chain, (c) linking of “Cu2Fe” chains by the PO4 group, and (d) triangular unit of “Cu2Fe”.

Compound 1 crystallizes in the space group C/2c with unit cell parameters of a = 7.7546(4) Å, b = 12.1290(6) Å, c = 9.9209(6) Å, β = 105.29(1)°, and Z = 4. In its asymmetric unit, there is one Cu atom, one Fe atom, one P atom, two F atoms, two O atoms, and two water molecules. As shown in Figure 2, the infinite diamond chains lie parallel to form a layer in the ab plane. The parallel diamond-chains group (in layer A) form an angle of 65.2° with another parallel diamond-chains group in the neighboring layer (layer B) (Figure 2a and b). The layers alternately stack in sequence of ...ABAB... and are linked by the [PO4]3− anions to form a three-dimensional (3D) framework. The infinite diamond chain in 1 contains a triangular [Cu2FeF4(H2O)4]3+ having one dimeric CuO4F2 octahedral unit and one single FeO2F4 octahedron as shown in Figure 2d. Two crystallographically equivalent copper-centered octahedra in the copper dimer are edge-shared through the bridging oxygen ligands O2 with Cu−O2 bond lengths of 1.977(2) Å and 9354

DOI: 10.1021/acs.inorgchem.7b01533 Inorg. Chem. 2017, 56, 9353−9360

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Inorganic Chemistry

d(Cu−F2) = 2.394(2) Å. Then, the single iron-centered octahedron is corner-shared with two copper-centered octahedra by the bridging fluorine ligands, F1 and F2, to form the triangular unit of [Cu2FeF4(H2O)4]3+ with bond lengths of d(Fe−F1) = 1.935(2) Å and d(Fe−F2) = 1.933(2) Å, and the bridging angles, in the triangular units, are ∠Cu−O2−Cu = 97.5°, ∠Cu−F1−Fe = 117.6°, and ∠Cu−F2−Fe = 135.3°. The [PO4]3− anions link the chains of neighboring layers by sharing the bridging-O2 of the copper dimer and trans-O1 of ironcentered octahedron with bond lengths of d(P−O1) = 1.531(2) Å and d(P−O2) = 1.577(2) Å. Additionally, two water ligands are coordinated to each copper octahedron. Other bond lengths and angles are summarized in Table 2. The oxidation states of +2 in copper and +3 in iron are confirmed by bond valence sum (BVS) calculations using values reported by Brese and O’Keefe (see Table 2).56 The Mössbauer spectrum of 1 at 297 K (Figure 3) consists of a sharp doublet with the full width at half maximum (fwhm) of 0.31 mm/s being close to the instrumental resolution (Table S1). This provides microscopic support for the presence of a single iron site suggested from the structural analysis and also

Table 2. Selected Bond Lengths, Angles, and BVS Calculations for Compound 1 bond

bond length (Å)

Cu−F1

2.480(1)

0.093

Cu−F2

2.394(2)

0.117

Cu−O2

1.977(2)

0.447

Cu−O2i Cu−O3 Cu−O4

2.003(2) 1.916(2) 1.947(2)

Fe−F1 Fe−F2 Fe−O1

2 × 1.935(2) 2 × 1.933(2) 2 × 2.031(2)

sij

0.416 0.527 0.485 Σsij = 2.09 2 × 0.492 2 × 0.489 2 × 0.479 Σsij = 2.92

angle

degree (deg)

Cu−O2− Cu Cu−F1− Fe Cu−F2− Fe

117.6

P−O1 P−O2

2 × 1.531(2) 2 × 1.577(2)

97.5

135.3

2.003(2) Å. Owing to the Jahn−Teller (JT) effect, each heteroleptic octahedral coordination around Cu is distorted with elongated bond lengths of d(Cu−F1) = 2.480(1) Å and

Figure 3. (a) 57Fe Mössbauer spectra of 1 at various temperatures. The circles and solid lines represent experimental and fitting curves, respectively; (b) temperature dependence of isomer shift, quadrupole splitting, hyperfine field for 1. 9355

DOI: 10.1021/acs.inorgchem.7b01533 Inorg. Chem. 2017, 56, 9353−9360

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Figure 4. Temperature dependence of (a) χ, (b) χT (green), and χ−1 (blue) for 1 measured at 0.1 T.

assures the excellent quality of the specimen. The value of the isomer shift, 0.442 mm/s, is typical for a trivalent iron in a high spin state. Thermogravimetric Analysis. The thermal stability of 1 was examined by TG-DTA measurement. Sample 1 starts to decompose around 200 °C, accompanied by an endothermic peak following two small endothermic peaks in the DTA curve (see Figure S2). Magnetic Properties. The temperature dependence of the magnetic susceptibility of 1 (Figure 4a) exhibits a sharp upturn around 12 K, which suggests a long-range magnetic order. A Curie−Weiss fitting in a high temperature range between 50 and 350 K (Figure 4b) yielded the effective magnetic moment of Peff = 6.53(1) μB and Weiss temperature of θ = −13.9(1) K. The value of Peff is fairly consistent with the theoretical value of 6.40 μB for free Cu2+ (S1 = 1/2 × 2) and Fe3+ (S2 = 5/2) moments. The present system offers the first example of mixedspin diamond chains arranged as −2S1−S2−2S1−S2−. The negative Weiss constant indicates antiferromagnetic (AFM) interactions, as also seen in the χT vs T plot (Figure 4b). The χT decreases with decreasing temperature to 2.39 emuK/mol at 13 K then suddenly increases to a maximum value of 3.60 emuK/mol at 10 K, suggesting an AFM order with a weak ferromagnetic component. The weak ferromagnetism or the canted antiferromagnetism possibly arises from Dzyaloshinskii−Moriya interactions, which is suppressed at 6 T (P′eff = 6.39(1) μB and θ′ = −13.8(1) K, Figure S4). Though only one anomaly around 12 K is observed in heat capacity (discuss below), we cannot completely rule out the possibility that the anomalies at 13 and 10 K correspond to successive phase transitions. The magnetization curve at 2 K in Figure 5 manifests the canted AFM order with a remnant magnetization of 0.1 μB/

Figure 5. Magnetization M(H) for 1 (a) at 300 K (square) and 2 K (circle) and (b) magnified M(H) at 2 K between −0.3 and 0.3 T.

mol. A hysteresis is observed in a small field region below ∼0.3 T; beyond this field, the magnetization linearly increases up to the maximum field of 7 T applied in this study, again consistent with the picture of canted AFM ground state. Mössbauer Spectra. Mössbauer spectra of 1 collected down to 2.6 K are shown in Figure 3a and Figure S3. For 12 K ≤ T, all of the spectra have a single and well-defined doublet, showing that 1 is always in a paramagnetic state with the single iron site, as already demonstrated by the room temperature spectrum. A clear sextet appeared at 10 K, providing firm evidence of the long-range magnetic order at TN = 12 K. The hyperfine field is 18 T at 12 K (Figure 3b), and upon further cooling, it increases systematically and becomes 55 T at 2.6 K, which is consistent with the high spin state. Although the isomer shift changes only slightly below TN, the magnitude of the quadrupole splitting becomes nearly half of that above TN (0.44 and −0.24 mm/s at 13 and 6 K, respectively). Here, the quadrupole splitting in the ordered state is determined from | W1 − W2| in Figure 3b (W1 is the width between the 1st and 2nd peak; W2 is the width between the 5th and 6th peak of the sextet). The implication of the drastic change in the quadrupole splitting across TN will be discussed later. Heat Capacity. The low temperature specific heat of 1 at various magnetic fields is shown in Figure 6a. In the absence of a magnetic field, a λ-type anomaly is clearly seen at 11.3 K, indicating a phase transition of second order associated with the magnetic order. The transition temperature agrees well with the results of magnetic susceptibility and Mössbauer spectroscopy. This peak becomes slightly broader when the magnetic field is 9356

DOI: 10.1021/acs.inorgchem.7b01533 Inorg. Chem. 2017, 56, 9353−9360

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Figure 7. Proposed noncollinear magnetic structure for 1.

superexchange interactions of J1, J1′, and J2 (Figure 1b). The Cu(II) octahedron (Figure 1d) has the elongated JT axis along the F1−Cu−F2 direction, meaning that their magnetic orbitals (d x 2 − y2 ) are oriented in the equatorial CuO4 plane. Because the bond angle of Cu−O2−Cu is 97.5°, the corresponding magnetic interaction, J2, should be rather weak57−59 despite the short Cu−Cu distance of 2.993 Å. On the other hand, the bridging angles of Fe−F1−Cu and Fe−F2−Cu are much larger, 117.6° and 135.3°, respectively, such that J1 through Fe−F1− Cu and J1′ through Fe−F2−Cu should be both antiferromagnetic, and J1′ is stronger than J1 according to the Goodenough− Kanamori rule.60,61 Estimation of the interchain super-super exchange interaction through Fe−O1−P−O2−Cu is difficult, but it could be very small. These considerations suggest that, within the diamond chain, the Fe and 2Cu moments are arranged in a ferrimagnetic fashion with the sequence of ...Fe(↑)-2Cu(↓↓)-Fe(↑)... below TN (11.3 K). This arrangement gives rise to 3 μB (5−2 × 1 μB) per triangular [Cu2FeF4(H2O)4]3+ unit. Because the ground state is the AFM state with a very tiny spontaneous magnetization (0.3 μB at 2 K), there exists an equal number of [...Fe(↑)-2Cu(↓↓)-Fe(↑)...] and [...Fe(↓)-2Cu(↑↑)-Fe(↓)...] diamond chains. The comparison of the quadrupole splitting in the Mössbauer spectra above and below TN allows us to determine the direction of magnetic moments. As already addressed, the quadrupole splitting value below TN is nearly half the magnitude of that above TN, meaning that the orientation of the iron nuclear spins (i.e., the iron moments) is considerably tilted from the principle axis of the electric field gradient around iron. Here, the quadrupole splitting below TN (QS′) is related to that above TN (QS) by QS′ = QS(3cos2θ−1)/2, where θ denotes the angle between the orientation of iron spin moments and the principle axis of the electric field gradient around iron. Using the experimental data, we estimate θ to be close to 90°. Because the local principle axis for Fe in the FeF4O2 octahedron is along the O−Fe−O direction, the magnetic Fe3+ moments should be lying within the FeF4 plane. Furthermore, the Cu2+ spin in general has an easy plane anisotropy, such that the Cu2+ moments are within the CuO4 plane. With these constraints, one can uniquely determine the

Figure 6. Low temperature-dependent (a) specific heat C(T), and the inset shows C(T) at 0 T between 2 and 30 K; (b) C/T(T) at various magnetic fields between 2 and 16 K for 1.

increased (0 < H < 7 T). Interestingly, the C− T curve exhibits a broad peak centered at around 3 K, which is more clearly seen in the C/T−T plot in Figure 6b. This second anomaly may suggest a second phase transition or some kind of crossover. In contrast to the first transition at 11.3 K, the second one is strongly field-dependent. The second peak in the C/T−T curve shifts systematically to higher temperatures with increasing applied magnetic field from 3 K at 0 T to 4 K at 7 T. The fielddependent peak shift suggests a magnetic origin of this transition or crossover. Some local spin excitation may also be possible. Owing to the absence of an available isostructural nonmagnetic compound, a phonon contribution of CL ∼ βT3 in a low temperature regime was roughly subtracted by assuming β as 5 mJ K−4 mol−1), which is indicated by the red dotted line in Figure 6a. Then, the magnetic entropy of 12.6 mJ K−1 mol−1 was estimated by integrating the CM/T between 2 and 16 K, which is somewhat lower than the expected value, Rln(2S1 + 1) + 2Rln(2S2 + 1) = 26.4 mJ K−1 mol−1, where S1 = 1/2 and S2 = 5/2. This deviation may be related to the development of shortrange spin correlations due to low-dimensional spin fluctuations or frustration.



DISCUSSION In 1, the mixed-spin diamond chains contain the triangular [Cu2FeF4(H2O)4]3+ units with Cu2+ (S1 = 1/2 × 2) and Fe3+ (S2 = 5/2). Because the two Cu−Fe bonds in this unit are not equivalent, the magnetic properties in this compound should be better described as distorted mixed-spin diamond chains with 9357

DOI: 10.1021/acs.inorgchem.7b01533 Inorg. Chem. 2017, 56, 9353−9360

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Inorganic Chemistry spin orientation of the ferrimagnetic Fe3+/Cu2+ diamond chains as being (anti)parallel to [1, 0.36, 0.114] for A layers and to [1, −0.36, 0.114] for B layers (Figure S5), meaning that the spins of two types of diamond chains are aligned in a noncollinear manner, though the A and B layers are crystallographically equivalent. Given the (slightly canted) antiferromagnetic order, the ferrimagnetic diamond chains in each layer must be aligned in an antiferromagnetic fashion to force the net magnetization to be zero. This gives a noncollinear magnetic structure as shown in Figure 7. Successive transitions have often been observed in lowdimensional frustrated spin systems such as CsCoCl3, Ca3Co2O6, and (NiCl)Sr2Ta3O10.17,18,62 Thus, the observation of the successive transition at around 3 K in our compound is highly interesting and could be related to enhanced fluctuations within and between mixed-spin diamond chains, or the frustration effect by the contribution of additional competing interactions at low temperatures. However, the smooth evolution of the hyperfine field across this temperature and nearly constant quadrupole splitting below 12 K implies at least that the drastic change in the magnetic structure does not occur at 3 K. For further understanding of the nature of the ground state for the mixed-spin diamond chain system, it is necessary to perform other experiments such as neutron diffraction and nuclear magnetic resonance, which will be left for our future study.

ORCID

Hongcheng Lu: 0000-0003-0414-4768 Hiroshi Kageyama: 0000-0002-3911-9864 Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS This work was supported by the Creation of Innovative Functions of Intelligent Materials on the Basis of Element Strategy (CREST) and Grant-in-Aid for Scientific Research on Innovative Areas “Mixed anion” (JP16H06439) from MEXT.





CONCLUSIONS Cu2FePO4F4(H2O)4 with mixed-spin diamond chain of S = 1/2 × 2 (Cu2+) and S = 5/2 (Fe3+) has been hydrothermally synthesized and magnetically characterized. Magnetic susceptibility and magnetization curve revealed a (canted) antiferromagnetic order of the ferrimagnetic [...Fe(↑)-2Cu(↓↓)-Fe(↑)...] chains at 11.3 K, which is confirmed by Mössbauer spectra and heat capacity. Heat capacity results further suggest another phase transition or crossover at 3 K. The analysis of quadrupole splitting of the Mössbauer spectroscopy in consideration of the crystal structure revealed a noncollinear magnetic structure, where the layers of ferrimagnetic chains are arranged noncollinearly. We believe that this study will trigger research on exploring materials with mixed-spin diamond chains to determine exotic magnetic properties together with theoretical studies.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01533. Characterization data including PXRD, TGA, and additional Mössbauer data (PDF) Accession Codes

CCDC 1040862 contains 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 data_ [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]; fax: +81-75-383-2510. 9358

DOI: 10.1021/acs.inorgchem.7b01533 Inorg. Chem. 2017, 56, 9353−9360

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