Hierarchical cobalt-formate framework series with (412⋅63)(49⋅66) n (n = 1–3) topologies exhibiting slow dielectric relaxation and weak ferromagnetism Ran Shang, Sa Chen, Ke-Li Hu, Ze-Chun Jiang, Bing-Wu Wang, Mohamedally Kurmoo, Zhe-Ming Wang, and Song Gao Citation: APL Materials 2, 124104 (2014); doi: 10.1063/1.4898648 View online: http://dx.doi.org/10.1063/1.4898648 View Table of Contents: http://scitation.aip.org/content/aip/journal/aplmater/2/12?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Investigation of dielectric relaxation, Jahn-Teller distortion, and magnetic ordering in Y substituted Pr1− x Y x MnO3 (0.1 ≤ x ≤ 0.4) J. Appl. Phys. 117, 093903 (2015); 10.1063/1.4913881 Magnetic, dielectric, and magneto-dielectric properties of rare-earth-substituted Aurivillius phase Bi6Fe1.4Co0.6Ti3O18 J. Appl. Phys. 116, 154102 (2014); 10.1063/1.4898318 Observation of a new cryogenic temperature dielectric relaxation in multiferroic Bi7Fe3Ti3O21 Appl. Phys. Lett. 103, 122901 (2013); 10.1063/1.4821435 Muon Spin Relaxation Study of an Impurity Doped Antiferromagnetic Triangular Lattice with a 1D Ferromagnetic Chain: Ca3(Co1−xZnx)2O6 AIP Conf. Proc. 850, 1095 (2006); 10.1063/1.2355086 Weak ferromagnetism in the antiferromagnetic magnetoelectric crystal LiCoPO 4 Low Temp. Phys. 27, 895 (2001); 10.1063/1.1414584
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APL MATERIALS 2, 124104 (2014)
Hierarchical cobalt-formate framework series with (412 · 63)(49 · 66)n (n = 1–3) topologies exhibiting slow dielectric relaxation and weak ferromagnetism Ran Shang,1 Sa Chen,1 Ke-Li Hu,1 Ze-Chun Jiang,1 Bing-Wu Wang,1 Mohamedally Kurmoo,2 Zhe-Ming Wang,1,a and Song Gao1,a 1
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China 2 Institut de Chimie de Strasbourg, CNRS-UMR 7177, Université de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg Cedex, France
(Received 16 September 2014; accepted 7 October 2014; published online 24 October 2014) The employment of linear di-, tri-, and tetra-ammoniums has generated a hierarchy in the binodal (412 · 63)(49 · 66)n topologies with n = 1, 2, and 3, respectively, for the cobalt formate frameworks with increasing length of the cavities to match the ammoniums. This indicates the length-directing effect of the polyammoniums. The dynamic movements of polyammoniums between favored sites or orientations within the cavities lead to slow dielectric relaxations. All materials are spin-canted antiferromagnets in low temperatures and show reduced spontaneous magnetizations from diand tri-, to tetra-ammoniums, because of the increased number of unique Co ions or the antiferromagnetically coupled sublattices. C 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4898648]
The last two decades have witnessed major developments in metal-organic frameworks (MOFs) through very active and intense studies.1–7 Such materials, classified as the “middle” in Cheetham and Rao quote “There is plenty of room in the middle,”2 have showed a very wide spectra of structures, properties, functionalities, and possible applications. Despite the continued great interest in their chemical aspects,1–3 MOFs have been exploited for the abundance in their physical properties and critical phenomena or phase transitions.4 Magnetism has been a long and extensive research subject for MOFs,5 but dielectric (DE) and ferro-/antiferro-electricities (FE/AFE) of MOFs have attracted even greater attention recently.6 MOFs showing synergy through the coexistence of magnetic and electric orderings have emerged as a field of MOF-multiferroics.7 However, the examples are still few. The recent research on ammonium metal formate frameworks (AMFFs, mainly for 3d metals or Mg, TM) has revealed not only the diversity in framework structures but more importantly, promising magnetic and/or electric properties, phase transitions, and others.8 The framework structures could be easily controlled, or templated, by the shape, size, and charge of the ammoniums. For mono-ammoniums (AH+), the small ones9–14 (e.g., NH4+) led to the chiral frameworks of [AH][TM(HCOO)3] with (49 · 66) topology. The larger sized ones15–18 (e.g., (CH3)2NH2+) resulted in many metal-formate perovskites, with (412 · 63) topology. AMFF analogous to the niccolite (NiAs) could be obtained by using di-ammoniums, as [dmenH2][TM(HCOO)3]2 series19 (dmenTM, dmenH22+ = CH3NH2(CH2)2NH2CH3) and [bnH2][Mg(HCOO)3]2 (bnMg, bnH22+ = H3N(CH2)4NH3),10 or mono-ammonium in [(CH3)2NH2][FeIIIMII(HCOO)6] (dmaFeM),20 and the framework topology is binodal (412 · 63)(49 · 66). Lanthanide21,22 and uranyl23 AMFFs have also been reported to show more complicated structures and framework topologies. The physics of AMFFs are found abundant, thanks to the combination of ammonium, metal ion, and the formate bridge, which provide the
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magnetic coupling, the H-bonding (HB) systems, and the order-disorder alteration of the ammonium components for creating various properties.8 For example, coexistence or synergy of magnetic and electric orderings, large dielectric anomalies and relaxor behaviors, negative thermal expansion, and so on, have all been documented in several [AH][TM(HCOO)3] series,9–18 especially in the perovskites. Some of them even have high phase transition temperatures comparable to the ferroelectric oxides.10,11,14 Magnetic/dielectric relaxation and temperature/pressure-induced structural transitions have been observed in several lanthanide AMFFs.21,22 The niccolite dmaFeFe displayed para- to antiferro-electric transition of unusual structural alternations and Néel N-Type ferrimagnetism.20 It is noted that the order-disorder alternations of ammoniums and the triggered phase transitions are closely relevant to these properties, and could occur in many AMFFs, with different patterns of the dynamics, such as vibration, flipping, or rotational motion of ammoniums, depending on the symmetry requirements and weak interactions between the ammoniums and the host frameworks, and the subtle balance of energies within the detailed structures.8 The development has been expanded to polyammoniums,8,24 and we reported here three compounds, [bnH2][Co(HCOO)3]2 (bnCo), [dptaH3][Co(HCOO)3]3 (dptaCo), and [tptaH4][Co(HCOO)3]4 (tptaCo) (dptaH33+ = H3N(CH2)3NH2(CH2)3NH3, and tptaH44+ = H3N(CH2)3NH2(CH2)3NH2(CH2)3NH3) having increasing length of the ammonium but retaining the width and most importantly, the flexibility. They form a family of hierarchical frameworks possessing the binodal (412 · 63)(49 · 66)n topologies of order n = 1, 2, and 3. The length of the polyammonium defines the order of the topology and thus the cavities in which they are located. The loose fitting of the flexible polyammonium within the cavity space provides dynamical motion between different sites or orientations, thus, results in slow dielectric relaxations. They are also spin-canted antiferromagnets (AF) or weak ferromagnets (WF), with the Néel temperatures (TN’s) around 10 K, and the reduced spontaneous magnetizations from bnCo and dptaCo to tptaCo. The crystals of the three compounds were prepared by the convenient solution methods and using commercial chemicals, as described before for other AMFFs,8 in satisfactory yields. Anal., bnCo, calcd for C10H20N2O12Co2: C, 25.12; H, 4.22; N, 5.86%; found: C, 25.04; H, 4.23; N, 5.75%; dptaCo, anal. calcd for C15H29N3O18Co3: C, 25.16; H, 4.08; N, 5.87%; found: C, 25.42; H, 4.24; N, 5.78%; tptaCo, anal. calcd for C21H42N4O24Co4: C, 26.05; H, 4.26; N, 5.79%; found: C, 26.16; H, 4.13; N, 5.80%. The single crystal X-ray diffraction data for bnCo, dptaCo, and tptaCo at room temperature were collected on a Nonius KappaCCD diffractometer using graphite monochromated Mo Kα radiation (λ = 0.71073 Å). The structures were solved by direct method and refined by full-matrix least-squares on F 2 using program.25 Crystallographic data are briefly listed in Table I, the full details and the selected molecular geometries are in Tables S1 and S2 of the supplementary material.26 The temperature-dependent alternative current (ac) dielectric permittivity measurements were performed against the capacitors prepared from powdered samples10,14 on a TH2828 Precision
TABLE I. The brief crystallographic data for bnCo, dptaCo, and tptaCo at room temperature. Compound (CCDC number)
bnCo (1024916)
dptaCo (1024917)
tptaCo (1024918)
Formula Fw Crystal system Space group a = b (Å) c (Å) α = β, γ (deg) V (Å3) Z , DC (g cm−3) Total, uniq. and obs.[I ≥ 2σ(I)] refls. R1, wR2[I ≥ 2σ(I)]
C10H20Co2N2O12 478.14 Trigonal P 31c 8.5322(2) 13.3228(3) 90, 120 839.94(3) 2, 1.891 15334, 649, 554 0.0238, 0.0668
C15H29Co3N3O18 716.20 Trigonal R 3c 8.4069(2) 61.921(3) 90, 120 3790.0(2) 6, 1.883 13053, 969, 518 0.0300, 0.0710
C21H40Co4N4O24 968.29 Trigonal P 31c 8.3617(1) 28.3983(5) 90, 120 1719.52(4) 2, 1.870 25884, 1329, 873 0.0260, 0.0705
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inductance-capacitance-resistance meter under dried N2 flow. Magnetic measurements were performed on a Quantum Design MPMS XL5 SQUID system using polycrystalline samples tightly packed. Diamagnetic corrections were estimated using Pascal constants27 (−197 × 10−6, −309 × 10−6, and −401 × 10−6 cm3 mol−1 for bnCo, dptaCo, and tptaCo, respectively) and background correction for sample holders. The experimental details of element analyses, powder X-ray diffraction (PXRD), FTIR spectra, UV-Vis reflectance spectra, and thermal analyses are given in the supplementary material.26 The experimental PXRD patterns for the bulk samples and the pressed pellets of the three compounds match well the simulated ones based on the crystal structures (Fig. S1, see supplementary material26), confirming the phase purity and no pressure-induced structural phase transitions.21 The three IR spectra (Fig. S2(a) and Table S3, see supplementary material26) are quite similar, with characteristic bands for polyammonium and HCOO− groups, indicating the similarity of the structures with similar components.28 Three bands, 15 600 cm−1 (sh), 19 300 cm−1 (s), and 20 900 cm−1 (sh) in the UV-Vis spectra (Fig. S2(b), see supplementary material26), correspond to the three transitions of 4 T1g(F)→4A2g(F), 4T1g(F)→4T2g(F), and 4T1g (C)→4T1g (V), respectively, typical for the octahedral CoO6 moiety,29 and similar to other reported Co-AMFFs.9,18 The three materials were thermally stable up to ca. 200 ◦C, then the departure of polyammonium formates occurred and was closely followed by the subsequent pyrolysis (Fig. S3(a), see supplementary material26). The differential scanning calorimetry (DSC) trace of bnCo revealed a reversible phase transition around −30 ◦C, but for dptaCo and tptaCo, no anomalies were observed (Fig. S3(b), see supplementary material26). The three structures are closely related to one another. They are all trigonal, space group P 31c for bnCo and tptaCo, R 3c for dptaCo with similar a/b dimensions but different c axes (Table I; Table S1, see supplementary material26). They all possess binodal 3D metal-formate frameworks containing two kinds of Co nodes, octahedral (412 · 63) and trigonal prismatic (49 · 66), connected by anti-anti formate ligands (Fig. 1). The (412 · 63) node has appeared in perovskites of [AH][M(HCOO)3] for larger AH = NH2NH+3 , CH3NH+3 , (CH3)2NH+2 , and so on,15–18 and the (49 · 66) one in the chiral phases of [AH][M(HCOO)3] for small AH = NH+4 , HONH+3 , and NH2NH+3 .9–14 In bnCo, dptaCo, and tptaCo, the ratios of the two nodes, (412 · 63) to (49 · 66), are 1:1, 1:2, and 1:3, respectively, or the three metal-formate frameworks have topologies of (412 · 63)(49 · 66)n with n = 1, 2, and 3 (Fig. 1, top). Such topologies for MOFs are still very rare and the hierarchy is unique. In fact, the topology of bnCo for n = 1, (412 · 63)(49 · 66), was observed in dmenTM series,19 the first MOF analogous to the mineral niccolite, then followed in dmaFeM20 and bnMg.10 We are unaware of any MOF with topologies of (412 · 63)(49 · 66)n for n = 2 and 3. These frameworks can also be considered as (4, 4) waved sheets linked along the normal direction, and in the sheet the same kind of nodes occupied the diagonal positions of the square grids to form arrays of (49 · 66) or (412 · 63) nodes. For bnCo, dptaCo, and tptaCo, there are one, two, and three arrays of (49 · 66) nodes between two arrays of (412 · 63) nodes, respectively, within the sheet, and the (412 · 63) node links only (49 · 66) nodes. The octahedral CoO6 moieties in the three structures have Co–O distances: 2.086(2)–2.108(2) Å, cis- O–Co–O angles 85.46(5)◦–94.54(5)◦, and trans- ones 174.26(5)◦–180◦, and the Co · · · Co distances via the formato bridge are 5.927–6.015 Å (Table S2, see supplementary material26). The frameworks possess longer and longer shaped cavities for accommodating longer and longer polyammoniums (Fig. 1, middle and bottom; Fig. S4, see supplementary material26). For bnCo, the cavity is formed by two one-corner-missing cubanes twinned together by sharing the three opening corners. In dptaCo, the two one-corner-missing cubanes are connected via their six opening corners. Finally, in tptaCo, three additional (49 · 66) nodes link the openings of the two one-corner-missing cubanes. Therefore, from bnCo to tptaCo, they show that the longer the ammoniums, the longer the cavity directed, and the accompanied addition of (49 · 66) nodes into the framework. The cations, 3+ 4+ [bnH2+ 2 ], [dptaH3 ], and [tptaH4 ] in the cavities are all trigonally disordered at room temperature. Most of the CH2 groups neighboring NH2 or NH3 groups locate on 3-fold axes, and other CH2 and ammonium groups are in three symmetry-related positions, except that the middle NH2 of [dptaH3+ 3 ] is still on the 3-fold axis, with a disk-like thermal ellipsoid (Fig. S4, see supplementary material26). The framework cavity of dptaCo looks staggered for the two half parts on both sides of the vertically central plane, but those in bnCo and tptaCo are symmetric. Consequently, the middle NH2 of
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FIG. 1. The structures of bnCo (a), dptaCo (b), and tptaCo (c). For each column, the top is the topological view of the Co-formate framework, with spheres being metal atoms and bonds the anti-anti HCOO bridges, and one cavity highlighted in red; the middle and the bottom are the side and top views of the cavity with the disordered polyammmonium in space-filling model. Color scheme: green, (412 · 63) nodes; violet blue, (49 · 66) nodes; red, O; dark gray/white, C; cyan, N; white, H.
[dptaH3+ 3 ] has different dynamics from the terminal NH3, and possesses smaller motion amplitude 4+ and looser binding. However, for [bnH2+ 2 ] and [tptaH4 ] cations, all ammoniums have same or similar dynamics and motion amplitudes. These are relevant to the dielectric properties. The NH2 and NH3 groups of the cations form HBs to the oxygen atoms of anionic frameworks (N · · · O contacts = 2.88– 3.25 Å, but 3.42 Å for the middle NH2 of [dptaH3+ 3 ] in dptaCo, Table S2, see supplementary material26) similar to that in the [(CH3)2NH2][TM(HCOO)3] and dmenTM series.15–19 The Co AMFF series with different ammonium components now has more than 10 members. [NH4][Co(HCOO)3], [HONH3][Co(HCOO)3], and [NH2NH3][Co(HCOO)3] possessing the chiral (49 · 66) topology;9–14 [CH3NH3][Co(HCOO)3], [(CH3)2NH2][Co(HCOO)3], [CH3CH2NH3] [Co(HCOO)3], [C(NH2)3][Co(HCOO)3], and [(CH2)3NH2][Co(HCOO)3] belong to the perovskite of (412 · 63) topology;15–18 dmenCo19 and bnCo have niccolite topology of (412 · 63)(49 · 66), and dptaCo and tptaCo showing novel topologies of (412 · 63)(49 · 66)n for n = 2 and 3. Running through this series, it is very clear that the structural evolution of AMFFs depends on the ammoniums, and the present three compounds clearly demonstrate the length-directing effect of the polyammoniums. This series, showing (412 · 63)m (49 · 66)n (m = 0, 1; n = 0, 1, 2, and 3) topologies, is one of the rare occasions that a 3D perovskite-related network can accommodate a progression in cation lengths by progressive change of framework structure. The temperature-dependence of the complex electric permittivity (ε ′ and ε ′′) for the three materials is shown in Figs. 2(a)–2(c) (bnCo, dptaCo, and tptaCo, respectively) and the characteristic data in Table S4 of supplementary material.26 They all feature strong dielectric dispersion. At a representative frequency ( f ) of 50 kHz, the ε ′ values were 32.2, 17.6, and 27.1 for bnCo, dptaCo, and tptaCo, respectively. On cooling, ε ′ of bnCo decreased continuously, first slowly to 280 K and then quickly, with 270 K as the fastest descending point (Tm ). Below 250 K, the decrease became slow again until a constant ε ′ value below 200 K. For lower/higher f ’s, the traces shift to lower/higher temperatures but retain the same features, and the Tm ’s ranged from 220 K to 315 K for 500 Hz to 1 MHz. The ε ′ traces of dptaCo and tptaCo show similar behaviors, and the descending are slower or flatter. The Tm ranges, from 500 Hz to 1 MHz, are 180–240 K (dptaCo) and 180–250 K (tptaCo).
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FIG. 2. Temperature-dependent traces of the dielectric permittivities for bnCo (a), dptaCo (b), and tptaCo (c), and the Arrhenius plots for the dielectric relaxations (d).
Below 150 K, the ε ′ values under all f ’s seemingly converged to 5.0, 6.0, and 6.5 for bnCo, dptaCo, and tptaCo, respectively. The ε ′′ traces clearly display strong f -dependence. For bnCo and tptaCo, the plots show single peaks corresponding to the fall in the ε ′ traces, and the temperatures of the peak positions (TP) are close to the Tm ’s of the ε ′ traces, due to the Kramers-Krönig relations.30 The f vs TP data could be fitted by the Arrhenius law of τ = τ0 × exp(Ea/k BT) (τ = (2π f )−1), resulting in the pre-exponential factor τ0 = 3.0 × 10−16 s and the activation energy Ea/k B = 6.3 × 103 K ∼ 0.54 eV for bnCo, and τ0 = 1.7 × 10−16 s and Ea/k B = 5.1 × 103 K ∼ 0.44 eV for tptaCo, respectively (Fig. 2(d)). For dptaCo, the broad peaks in the ε ′′ traces are composed of two peaks merged together, one in lower temperature (LT) and one in higher temperature (HT), or there are two dielectrics relaxations. By fitting the peak regions using a double-peak model, the individual TP data could be derived. Then the two sets of f vs TP data could be fitted by the Arrhenius law, leading to the parameters τ0 = 1.6 × 10−14 s and Ea/kB = 3.7 × 103 K ∼ 0.32 eV for the LT relaxation, and τ0 = 1.4 × 10−15 s and Ea/kB = 4.9 × 103 K ∼ 0.43 eV for HT one. These parameters of the dielectric relaxations are rational for dielectrics30 and comparable to other AMFFs.10,14 At room temperature, the flexible polyammoniums are all trigonally disordered in the framework cavities. As observed in several reported AMFFs, such as dmenTM,19 bnMg,10 and tmenEr,21 these disorders are related to the motion of the polyammoniums, i.e., the rotating, twisting, or flipping of the constituent parts between several preferred sites or orientations. Such motions induce the dipoles or polarizations and their fluctuations within the lattices, thus, contribute the dielectric responses, high ε ′ but low ε ′′ in HT region.30 It is expected that on cooling, the contraction of the frameworks and the increased HB interactions will slow or damp the movements and finally freeze them.9,10,12,14,21,22 The damped movements resulted in the decrease/increase in ε ′/ε ′′ and the strong dielectric dispersion. The activation energies are 0.32–0.54 eV, or 31–52 kJ mol−1, seemingly rational for the alternation of several N–H · · · O HBs and C–H · · · O interactions required for the movements.10,14 However, the dielectric data and behavior of bnCo are quite different from those of bnMg10 though they are isostructural at HT, indicating the different characters in lattice dynamics, disorder-order transition pattern, and phase transition. The two dielectric relaxations of dptaCo corroborate with the two different dynamics of the middle NH2 and the terminal NH3, as revealed by structural analysis. The former contributes the LT relaxation with the smaller Ea/kB = 0.32 eV, and the latter corresponds to
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the HT relaxation, with the slightly higher Ea/kB = 0.43 eV, as those of bnCo and tptaCo. On further cooling, the final freezing of the motions of the polyammoniums led to the low dielectric responses in LT region. Such relaxation mechanism as observed here adds to the multitudes and complexities provided by the family of AMFFs which requires further specialized studies to reveal the true state of arts in these novel materials. The phase transition of bnCo has been confirmed by DSC anomalies, but whether the phase transitions occurred for dptaCo and tptaCo need further investigation. The materials will be of interest for MOF-multiferroics7 because they have shown magnetic orderings, as below. The three compounds are all 3D spin-canted AFs showing WF in LT region but with interesting differences (Table S4, see supplementary material26). The plots of the temperature-dependent static susceptibilities of the three materials, measured under a field of 100 Oe, are shown in Fig. 3(a). Above 15 K, the three χT vs T plots are nearly overlapped. The χT values per mole Co are 3.21 (bnCo), 3.16 (dptaCo), and 3.21 (tptaCo) cm3 K mol−1 at 300 K, typical for the Co2+ ions.31,32 Upon cooling, the χT values decreased gradually. The HT susceptibilities obey the Curie-Weiss law (Fig. S5(a), see supplementary material26) with Curie constants (C) and Weiss temperatures (Θ) in cm3 K mol−1/K: 3.85/−60.5, 3.75/−54.4, and 3.90/−63.9 for bnCo, dptaCo, and tptaCo, respectively. Assuming S = 3/2, for Co2+, these C constants led to the Landé g-factors of 2.83–2.88, and the large negative Θ values indicate AF exchange within the materials, though the values include the effect of spin-orbit coupling of octahedral Co2+ ion, showing an effective S = 1/2 at LT from a S = 3/2 at HT due to the depopulation of the higher energy Kramers doublets (±3/2 and ±5/2), being equivalent to a Θ of ca. −20 K.32 When further cooled, the decreased χT values reach at minima around 10 K, then rise to maxima and after that they go down to 2 K. The minima are similar for the
FIG. 3. Magnetism of the three compounds: (a) plots of χT vs T under 100 Oe field, and inset, the ZFC/FC plots under 10 Oe field; (b) isothermal magnetization plots at 2 K, and inset, the zoomed part of the hysteresis loops in low fields.
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three compounds but the maxima χT values are quite different, and for tptaCo, it is small. Under 10 kOe field, the maxima were all suppressed (Fig. S5(b), see supplementary material26). All these observations indicate the occurrence of 3D long-range ordering (LRO) of spin-canted AF within the materials in LT. The materials were further characterized in LT region by measurements of zero-field-cooled (ZFC) and field-cooled (FC) magnetizations under 10 Oe field (Fig. 3(a), inset), isothermal magnetizations at 2 K (Fig. 3(b)), and ac susceptibilities at 10, 100, and 1000 Hz (Figs. S5(c) and S5(d), see supplementary material,26 ac data at 10 Hz only). The small spontaneous magnetizations and irreversibility observed in ZFC/FC plots clearly indicated the 3D LRO of spin-canted AF, and the TN’s were 9.9 K (bnCo), 12.5 K (dptaCo), and 10.9 K (tptaCo), by the negative peak positions in the dFC/dT (Fig. S5(b), inset, see supplementary material26). These are typical for Co-AMFFs.8,13,18,19 The second peak at 11.0 K in the dFC/dT plot of dptaCo is probably due to a spin-reorientation.8,19 The FC magnetizations below TN (Table S4, see supplementary material26) show bnCo > dptaCo ≫ tptaCo. This should be due to the increased number of unique Co ions or the AF-coupled sublattices from bnCo to tptaCo, resulting in the occurrence of hidden spin-canting.33 The isothermal magnetizations at 2.0 K (Fig. 3(b)) all display hysteresis, with the coercive fields (HC’s), being 0.97, 1.5, and 0.39 kOe for bnCo, dptaCo, and tptaCo, respectively, and small remnant magnetizations (RM’s) of 0.033 (bnCo), 0.017 (dptaCo), and 0.0035 (tptaCo) Nβ. The magnetizations around 0.5 Nβ at the highest applied field of 50 kOe, are significantly lower than the expected 2.2 Nβ assuming S = 1/2 and g = 4.3.32 The spin-flop transition (AF-SP) occurred above ca. 20 kOe. In the ac susceptibilities at 10 Hz, bnCo shows peaks at 9.9 K in both χ ′ and χ ′′ components, and the responses are strong. dptaCo exhibits double peaks (12.5 K and 11.3 K), but the responses are significantly weak. For tptaCo, there is only a broad cusp around 12 K in the very weak χ ′ response, and χ ′′ component noisy. The peak positions and the strengths of the χ ′ and χ ′′ are in agreement with the ZFC/FC data. No f -dependences were observed. These results confirm the spin canting AF LRO in the three materials whose structures, with the non-centrosymmetric bridges of anti-anti HCOO linking anisotropic Co2+ ions, satisfy the requirement for the antisymmetric interaction.34 Finally, the couplings (J/k B) between Co2+ ions via the anti-anti formato bridge, estimated from J/kB = 3Θ/[2zS(S + 1)],33 are −4.0 (bnCo), −3.6 (dptaCo), and −4.3 K (tptaCo), similar to those of Co-AMFFs with anti-anti HCOO linkages reported before.8,11,13,14,18,19 In conclusion, the results of varying the length of linear polyammonium cations demonstrate the progressive structure-directing effect in the formation of binodal (412 · 63)(49 · 66)n (n = 1, 2, and 3) topologies in Co AMFFs. This progressive development is a rare observation in the field of transition-metal perovskites chemistry. Due to the misfit of the polyammoniums in the spaces available that allow for their distortions and motions between crystallographically and energetically degenerate locations, a series of dielectric anomalies are observed as a function of temperature. These vary with the number of degrees of freedom in the motion of the polyammoniums. However, they all freeze at low temperature for the weak ferromagnetic ordering to set in at ca. 10 K. Thus, possible structural order-disorder is observed at high temperature while at low temperature 3D magnetic order is present. The present results add to the range of other properties already shown for AMFFs, which have proved very beneficial in the development of multifunctional MOF materials. Further studies of these materials will certainly enhance our academic understanding of the multitude of properties as well as the subtle synergy of the coexisting properties. This work was supported by the NSFC (Grant Nos. 21171010, 21290170, and 21290171) and the National Basic Research Program of China (Grant No. 2013CB933401). M. K. is funded by the CNRS (France). 1
H.-C. Zhou, J. R. Long, and O. M. Yaghi, Chem. Rev. 112, 673 (2012); J. R. Long and O. M. Yaghi, Chem. Soc. Rev. 38, 1213 (2009). 2 A. K. Cheetham and C. N. R. Rao, Science 318, 58 (2007). 3 H. Furukawa, K. E. Cordova, M. O’Keeffe, and O. M. Yaghi, Science 341, 1230444 (2013); S. T. Meek, J. A. Greathouse, and M. D. Allendorf, Adv. Mater. 23, 249 (2011); S. Kitagawa, R. Kitaura, and S. Noro, Angew. Chem., Int. Ed. 43, 2334 (2004); R. E. Morris and X. Bu, Nat. Chem. 2, 353 (2010); G. Férey, Chem. Soc. Rev. 37, 191 (2008). 4 I. E. Collings, A. B. Cairns, A. L. Thompson, J. E. Parker, C. C. Tang, M. G. Tucker, J. Catafesta, C. Levelut, J. Haines, V. Dmitriev, P. Pattison, and A. L. Goodwin, J. Am. Chem. Soc. 135, 7610 (2013); E. C. Spencer, R. J. Angel, N. L. Ross,
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://aplmaterials.aip.org/about/rights_and_permissions Downloaded to IP: 54.152.109.166 On: Thu, 29 Oct 2015 05:01:43
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B. E. Hanson, and J. A. K. Howard, ibid. 131, 4022 (2009); S. A. Moggach, T. D. Bennett, and A. K. Cheetham, Angew. Chem., Int. Ed. 48, 7087 (2009); A. B. Cairns and A. L. Goodwin, Chem. Soc. Rev. 42, 4881 (2013). 5 J. S. Miller and D. Gatteschi, Chem. Soc. Rev. 40, 3065 (2011); E. Coronado and K. R. Dunbar, Inorg. Chem. 48, 3293 (2009). 6 W. Zhang and R.-G. Xiong, Chem. Rev. 112, 1163 (2012); T. Hang, W. Zhang, H.-Y. Ye, and R.-G. Xiong, Chem. Soc. Rev. 40, 3577 (2011). 7 E. Pardo, C. Train, H. Liu, L. M. Chamoreau, B. Dkhil, K. Boubekeur, F. Lloret, K. Nakatani, H. Tokoro, S.-i. Ohkoshi, and M. Verdaguer, Angew. Chem., Int. Ed. 51, 8356 (2012); S.-i. Ohkoshi, H. Tokoro, T. Matsuda, H. Takahashi, H. Irie, and K. Hashimoto, ibid. 46, 3238 (2007); H. B. Cui, Z. M. Wang, K. Takahashi, Y. Okano, H. Kobayashi, and A. Kobayashi, J. Am. Chem. Soc. 128, 15074 (2006). 8 Z. M. Wang, K. L. Hu, S. Gao, and H. Kobayashi, Adv. Mater. 22, 1526 (2010); R. Shang, S. Chen, Z. M. Wang, and S. Gao, in Metal-Organic Framework Materials, edited by L. R. Macgillivray and C. M. Lukehart (John Wiley & Sons, Ltd, Weinheim, Germany, 2014), in press. 9 G. C. Xu, X. M. Ma, L. Zhang, Z. M. Wang, and S. Gao, J. Am. Chem. Soc. 132, 9588 (2010); G. C. Xu, W. Zhang, X. M. Ma, Y. H. Chen, L. Zhang, H. L. Cai, Z. M. Wang, R. G. Xiong, and S. Gao, ibid. 133, 14948 (2011). 10 R. Shang, G. C. Xu, Z. M. Wang, and S. Gao, Chem. - Eur. J. 20, 1146 (2014). 11 Z. M. Wang, B. Zhang, K. Inoue, H. Fujiwara, T. Otsuka, H. Kobayashi, and M. Kurmoo, Inorg. Chem. 46, 437 (2007); W. Li, M. R. Probert, M. Kosa, T. D. Bennett, A. Thirumurugan, R. P. Burwood, M. Parinello, J. A. K. Howard, and A. K. Cheetham, J. Am. Chem. Soc. 134, 11940 (2012). 12 R. Shang, S. Chen, Z. M. Wang, and S. Gao, “A Copper–Formate Framework Showing a Simple to Helical Antiferroelectric Transition with Prominent Dielectric Anomalies and Anisotropic Thermal Expansion, and Antiferromagnetism,” Chem. - Eur. J. (published online). 13 B. Liu, R. Shang, K. L. Hu, Z. M. Wang, and S. Gao, Inorg. Chem. 51, 13363 (2012). 14 S. Chen, R. Shang, K. L. Hu, Z. M. Wang, and S. Gao, Inorg. Chem. Front. 1, 83 (2014). 15 Z. M. Wang, B. Zhang, T. Otsuka, K. Inoue, H. Kobayashi, and M. Kurmoo, Dalton Trans. 2004, 2209; X. Y. Wang, L. Gan, S. W. Zhang, and S. Gao, Inorg. Chem. 43, 4615 (2004). 16 D. W. Fu, W. Zhang, H. L. Cai, Y. Zhang, J. Z. Ge, R. G. Xiong, S. D. Huang, and T. Nakamura, Angew. Chem., Int. Ed. 50, 11947 (2011); P. Jain, V. Ramachandran, R. J. Clark, H. D. Zhou, B. H. Toby, N. S. Dalal, H. W. Kroto, and A. K. Cheetham, J. Am. Chem. Soc. 131, 13625 (2009). 17 Z. Wang, P. Jain, K. Y. Choi, J. van Tol, A. K. Cheetham, H. W. Kroto, H. J. Koo, H. Zhou, J. Hwang, E. S. Choi, M. H. Whangbo, and N. S. Dalal, Phys. Rev. B 87, 224406 (2013); P. J. Baker, T. Lancaster, I. Franke, W. Hayes, S. J. Blundell, F. L. Pratt, P. Jain, Z.-M. Wang, and M. Kurmoo, ibid. 82, 012407 (2010). 18 K. L. Hu, M. Kurmoo, Z. M. Wang, and S. Gao, Chem. - Eur. J. 15, 12050 (2009); B. Zhou, Y. Imai, A. Kobayashi, Z. M. Wang, and H. Kobayashi, Angew. Chem., Int. Ed. 50, 11441 (2011). 19 M. Y. Li, M. Kurmoo, Z. M. Wang, and S. Gao, Chem. Asian J. 6, 3084 (2011); Z. M. Wang, X. Y. Zhang, S. R. Batten, M. Kurmoo, and S. Gao, Inorg. Chem. 46, 8439 (2007). 20 L. Cañadillas-Delgado, O. Fabelo, J. A. Rodríguez-Velamazán, M. Lemée-Cailleau, S. A. Mason, E. Pardo, F. Lloret, J. Zhao, X. Bu, V. Simonet, C. V. Colin, and J. Rodríguez-Carvajal, J. Am. Chem. Soc. 134, 19772 (2012); J. P. Zhao, B. W. Hu, F. Lloret, J. Tao, Q. Yang, X. F. Zhang, and X. H. Bu, Inorg. Chem. 49, 10390 (2010). 21 M. Y. Li, B. Liu, B. W. Wang, Z. M. Wang, S. Gao, and M. Kurmoo, Dalton Trans. 40, 6038 (2011); E. C. Spencer, M. S. R. N. Kiran, W. Li, U. Ramamurty, N. L. Ross, and A. K. Cheetham, Angew. Chem., Int. Ed. 53, 5583 (2014); B. Liu, H. B. Zheng, Z. M. Wang, and S. Gao, CrystEngComm 13, 5285 (2011). 22 M. Y. Li, Ph.D. thesis (Peking University), 2011. 23 Q. Q. Zhu, R. Shang, S. Chen, C. L. Liu, Z. M. Wang, and S. Gao, Inorg. Chem. 53, 8708 (2014). 24 K. L. Hu, Ph.D. thesis (Peking University), 2010; Z. C. Jiang, B.Sc. thesis (Peking University), 2007. 25 G. M. Sheldrick, SHELX-97, program for crystal structure determination, University of Göttingen, Germany, 1997. 26 See supplementary material at http://dx.doi.org/10.1063/1.4898648 for a PDF file containing experimental details of some characterizations, Tables S1 to S4, Figs. S1 to S5, and a CIF file for the 3 structures in this paper. 27 L. N. Mulay and E. A. Boudreaux, Theory and Applications of Molecular Diamagnetism (John Wiley & Sons, Inc, New York, 1976). 28 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds (Wiley, New York, 1986). 29 B. N. Figgis and M. A. Hitchman, Ligand Field Theory and Its Application (Wiley-VCH, New York, 2000). 30 A. K. Jonscher, Dielectric Relaxation in Solids (Chelsea Dielectrics Press, London, 1983); G. G. Raju, Dielectrics in Electric Fields (Marcel Dekker, Inc, New York, 2003). 31 A. T. Casey and S. Mitra, in Theory and Application of Molecular Paramagnetism, edited by L. N. Mulay and E. A. Boudreaux (Wiley, New York, 1976), pp. 183–243. 32 M. Kurmoo, Chem. Soc. Rev. 38, 1353 (2009). 33 R. L. Carlin, Magnetochemistry (Springer-Verlag, Berlin Heidelberg, 1986). 34 I. Dzyaloshinsky, J. Phys. Chem. Solid 4, 241 (1958); T. Moriya, Phys. Rev. 120, 91 (1960).
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