Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
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Tunable Ferromagnetic Strength in Niccolite Structural Heterometallic Formate Framework Based on Orthogonal Magnetic Orbital Interactions Jiong-Peng Zhao,† Song-De Han,*,‡ and Fu-Chen Liu*,† †
Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF SASKATCHEWAN on 01/01/19. For personal use only.
School of Chemistry and Chemical Engineering, TKL of Organic Solar Cells and Photochemical Conversion, Tianjin University of Technology, Tianjin 300384, P. R. China ‡ College of Chemistry and Chemical Engineering, Qingdao University, Qingdao, Shandong 266071, P. R. China S Supporting Information *
ABSTRACT: A series of heterometallic formate framework templated by amines were solvothermally prepared. They feature the formula of [AI][CrMII(HCO2)6] (AI = NH4H2OI and M = Mn for 1, AI = CH3NH3I and M = Fe for 2, AI = CH3NH2CH3I and M = Co for 3, AI = CH3NH3I and M = Ni for 4). The title compounds exhibit isostructural niccolite architectures with differences only in the host metal ions and guest amines. Tunable ferromagnetic (FO) strength was realized in the resulting framework under the guidance of orthogonal magnetic orbital analysis of CrIII (t2g3eg) and MII (t2g3eg2 for MnII, t2g4eg2 for FeII, t2g5eg2 for CoII, t2g6eg2 for NiII) ions. The magnetic ordering temperatures derived from the experimental magnetic measurements for 1−4 are lower than 2, 10.3, 7.6, and 22.0 K, respectively. Notably, thanks to the weak FO coupling between CrIII and MnII ions, compound 1 displays a large magnetocaloric effect bearing the maximum of magnetic entropy change (−ΔSmmax) up to 43.9 J kg−1 K−1 with ΔH = 7 T and T = 3.5 K, larger than most reported transition metal-based complexes and commercial gadolinium gallium garnet (Gd3Ga5O12) (−ΔSmmax = 38.4 J kg−1 K−1 with ΔH = 7 T). From 1, 2/3, to 4, an enhancement of the magnetic ordering temperature is observable due to the increasing strength of FO interactions between CrIII and MII ions. Our work provides a successful instance to modulate the strength of FO exchange via analyzing the orthogonal magnetic orbitals of heterometallic ions.
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INTRODUCTION Recent years have seen the flourishing development of molecular magnetic materials because of their intrinsic characteristics compared with traditional materials.1 The assembly of suitable spin carriers and bridges provides extra freedom to the fabrication of desirable products driven by the crystal and magnetic engineering strategies. Among the various explored molecular magnetic materials, the organic aminedirected metal formate frameworks have gained tremendous attention of magnetochemist for their diverse magnetic behaviors, together with the potential multifunction.2−6 For example, Wang and co-workers have well-summarized the structural features of organoamines-directed metal formate architecture and the structure-related magnetism.2a The coexistence of magnetic ordering and electric ordering has also been achieved in the organoamines-directed metal-formate framework with perovskite structure.7 The efficiency of formate in the construction of weak ferromagnet has also been reviewed by Gao and co-worker.3a A view of literature indicated that pure formato−transitional metal (TM) systems usually feature anti-ferromagnetism and weak ferromagnetism (or canted anti-ferromagnetism).2a,3a We and others have demonstrated that the introduction of a suitable (paramagnetic) trivalent ion to pure format-TM © XXXX American Chemical Society
systems would generate heterometallic formate frame with niccolite structure.8−13 They feature the general formula of [AI][MIIIMII(HCO2)6] with abundant magnetism, together with the captivating order−disorder phase transition of various guest amines and potential magneto-dielectric response.8−13 For example, Néel N-Type ferrimagnet and exchange bias (EB) is observable in [NH2(CH3)2][FeIIIFeII(HCO2)6].8 Further characterisations indicates that the disorder−order transition of [NH2(CH3)2]I guest provides opportunities for the search of molecular multiferroics.9 Substituting the FeII with CoII and MnII generates isostructural architecture with Néel Q-type ferrimagnet (FeIII−CoII) and canted anti-ferromagnet (FeIII− MnII),8 and their magnetic structures have also been confirmed by neutron diffraction.10 [(CH3CH2)2NH2][FeIIIFeII(HCOO)6] features tunable EB fields and four distinct kinds of bistability with response to dielectric and magnetic stimulation.11 Large magnetocaloric effect (MCE) is achieved in [AI][CrIIIMnII(HCOO)6] (A = NH2(CH3)2 and CH3NH3) thanks to the weak magnetic interactions between CrIII and MnII ions,12 which gives us a hint that we could mediate the strength of magnetic coupling in niccolite-like Received: September 11, 2018
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DOI: 10.1021/acs.inorgchem.8b02587 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry Table 1. Crystal Data for 1−4 formula Mr (g mol−1) space group crystal system a (Å) c (Å) V (Å3) Dc (g cm−3) μ (mm−1) Ra/wRb GOF on F2
1
2
3
4
C6H12CrMnNO13 413.09 P3̅1/c trigonal 7.8225(11) 14.815(3) 797.2(3) 1.721 1.535 0.0521/0.1574 1.140
C7H12CrFeNO12 410.01 P3̅1/c trigonal 8.2 152(12) 13.977(3) 816.9(2) 1.667 1.608 0.0676/0.1372 1.305
C8H14CrCoNO12 427.13 P3̅1/c trigonal 8.1491(12) 13.477(3) 775.1(3) 1.830 1.832 0.0540/0.1122 1.220
C7H12CrNiNO12 412.86 P3̅1/c trigonal 8.0645(11) 13.746(3) 774.2(3) 1.771 1.976 0.0437/0.1284 1.243
R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = {∑[w(Fo2 − Fc2)2]/∑w(Fo2)2}1/2.
a
formamide−water solvent. Rose block crystals of 2 were obtained in an ∼35% yield based on Cr salt. Theoretical EA (%) for C7H12CrFeNO12 (410.01): C, 20.51; N, 3.42; H, 2.95. Experimental: C, 20.23; N, 3.66; H, 3.23. [CH3NH2CH3][CrCo(HCOO)6] (3). The synthesis of 3 was similar to that of 2, but CoCl 2 ·6H 2 O (0.48 g, 2 mmol) and dimethylformamide (DMF; 7.5 mL) were used to replace FeCl2 and N-methyl formamide, respectively. Red block crystals of 3 were obtained in an ∼30% yield based on Cr salt. Theoretical EA (%) for C8H14CrCoNO12 (427.13): C, 22.50; N, 3.28; H, 3.30. Experimental: C, 22.72; N, 3.54; H, 3.05. [CH3NH3][CrNi(HCOO)6] (4). The synthesis of 3 was similar to that of 2, but NiCl2·6H2O (0.48 g, 2 mmol) was used to replace FeCl2. Rose block crystals of 4 were obtained in an ∼30% yield based on Cr salt. Theoretical EA (%) for C7H12CrNiNO12 (412.86): C, 20.36; N, 3.39; H, 2.93. Experimental: C, 20.54; N, 3.15; H, 3.26. SCXRD Data Collection and Structure Determinations. SCXRD data were measured on an SCX-MINI diffractometer at 293(2) K with Mo Kα radiation (λ = 0.710 73 Å) by ω scan mode. Their structures were refined by SHELX-2014.14 Detailed crystallographic factors are present in Table 1, and the selected bond lengths are offered in Table S1. Full crystallographic data were stored (CCDC Nos. 1858491 (1), 1858490 (2), 1858492 (3), and 1858493 (4)).
heterometallic formate architecture under the guidence of orthogonal magnetic orbital analysis of prototype compounds. As our continuous search for investigating the magnetism of heterometallic formate frame, herein, we report four aminestemplated heterometallic formate frame with the general formula of [AI][CrMII(HCO2)6] (AI = NH4H2OI and M = Mn for 1, AI = CH3NH3I and M = Fe for 2, AI = CH3NH2CH3I and M = Co for 3, AI = CH3NH3I and M = Ni for 4). It is notable that the resulting isostructural niccolite-like structure features tunable ferromagnetic (FO) strength driven by orthogonal magnetic orbital analysis of CrIII (t2g3eg) and MII (t2g3eg2 for MnII, t2g4eg2 for FeII, t2g5eg2 for CoII, t2g6eg2 for NiII) ions. The magnetic ordering temperatures for 1−4 are lower than 2, 10.3, 7.6, and 22.0 K, respectively. Thanks to the weak FO coupling between CrIII and MnII ions, 1 exhibits a high MCE bearing the maximum of magnetic entropy change (−ΔSmmax) up to 43.9 J kg−1 K−1 (ΔH = 7 T and T = 3.5 K), larger than most of the reported TM-based complexes and commercial gadolinium gallium garnet (Gd 3 Ga 5 O 12 ) (−ΔSmmax = 38.4 J kg−1 K−1 with ΔH = 7 T). By contrast, the enhancement of the magnetic ordering temperature in form 1, 2/3, to 4 is observable due to the increasing strength of FO interactions between CrIII and MII ions.
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RESULTS AND DISCUSSION Description of Crystal Structure. Because the niccolite structural heterometallic formate frameworks have been reported,8−13 the structural descriptions of 1−4 are simplified. SCXRD and topological analysis indicate that the metal ions (MIII or MII) located in (4966) and (41263) nodes. The formate anions bridged two metal ions in (4966) and (41263) nodes in anti−anti mode. All metal ions exhibit octahedral geometry coordinated by six O atoms from formate ligands. The metal ions in (4966) node connected six metal ions in (41263) nodes through formate ligands to form a super-trigonal prism, while the (41263) node linked six (4966) nodes to result in a superoctahedron (Figure 1a). The MII ions occupy (4966) nodes, while the MIII ions occupy (41263) nodes. The AI cations serve as charge balancer to fill in the cavities of the cage constructed by 11 metal ions and 19 formate ligands (Figure 1b−d). In 1, the ammonium cations located in center of the cavities with one disorder water molecule swinging in two sides of the cations (Figure 1d). The occupancy of the water molecule was approved by the equivalent isotropic atomic displacement parameters (Ueq) and elemental analyses. The water and ammonium were stabilized by H bonds. In 2 and 4, the N atom of CH3NH3I displays threefold disorder, while the methyl C atom of CH3NH3I has a twofold disorder along the two sides of the plane generated by the disordered N atoms
EXPERIMENTAL SECTION
Materials and Physical Characterizations. All reagents are commercially available analytical grade, but the formate acid is 86%. The elemental analyses (EA) were characterized on a PerkinElmer 2400LS II elemental analyzer. The powder X-ray diffraction (PXRD) data was characterized on a Rigaku D/Max-2500 diffractometerfor a Cu-target tube and a graphite monochromator (40 kV, 100 mA). Simulated PXRD spectra were derived from modulating the singlecrystal X-ray diffraction (SCXRD) data via the Mercury software. Magnetic data were characterized on a Quantum Design MPMS-XL SQUID magnetometer with crushed crystalline sample. The data were corrected via Pascal’s constants to count the diamagnetic susceptibility. Synthesis of [NH4H2O][CrMn(HCOO)6] (1). The mixture of Cr(NO3)3·9H2O (1.2 g, 3 mmol), MnCl2·4H2O (0.39 g, 2 mmol), formic acid (6 mL), formamide (6 mL), and water (3 mL) in a sealed Teflon-lined stainless steel vessel was heated at 70 °C for 2 d and then cooled to ambitent temperature. Rose block crystals of 1 was obtained in an ∼30% yield based on Cr salt. Theoretical EA (%) for C6H12CrMnNO13 (413.09): C, 17.45; N, 3.39; H, 2.93. Experimental: C, 17.63; N, 3.16; H, 3.21. [CH3NH3][CrFe(HCOO)6] (2). The synthesis of 2 was similar to that of 1 with temperature 140 °C. FeCl2 (0.25 g, 2 mmol) was used to replace MnCl2·4H2O. Formic acid (7.5 mL) and N-methyl formamide (7.5 mL) were used to replace the mixed formic acidB
DOI: 10.1021/acs.inorgchem.8b02587 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 1. (a) Coordinated environment of the (41263) and (4966) nodes in 1−4. The trigonal prism and octahedron illustrate the surrounding metal ions of each node. (b) The CH3NH3I in the cavities of 2 and 4. (c) The CH3NH2CH3I in the cavities of 3. (d) The NH4H2OI interacted with the cavities of 1.
(Figure 1b). The CH3NH2CH3I cation in 3 behaved like the CH3NH3I in 2 but without the twofold disorder of the methyl group (Figure 1c). The charger blancers (AI) are close to MII ions with same coordinates position along c direction (Figure 2).
Figure 3. (a) Temperature-dependent χmT plot of 1 under 0.1 T field. (inset) Variable field-dependent magnetization plots at distinct temperatures. (b) −ΔSm derived from magnetization data of 1.
the CrIII−MnII ions in 1 hold great promise for lowtemperature magnetic cooler. As a vital parameter in evaluating MCE, the value of magnetic entropy change (−ΔSm) could be derived from the experimental data via the following equation ΔSm(T)ΔH = ∫ [∂M(T,H)/∂T]H dH.15 The field and temperature-dependent −ΔSm values of 1 are offered in Figure 3b, with a maximum value of −ΔSmmax = 43.9 J kg−1 K−1 (18.1 J mol−1 K−1) at 3.5 K with ΔH = 7 T. The −ΔSmmax is lower than the value of 26.4 J mol−1 K−1 for magnetically non-interacting CrIII and MnII ions (calculated by R[ln(2 × 5/2 + 1) + ln(2 × 2/3 + 1)], and R represents the gas constant). The −ΔSmmax of 1 is comparable with the anti-ferromagnetic (AF) [CH3NH2CH3][CrMn(HCOO)6] (Mr = 423.1 g mol−1, −ΔSmmax = 43.9 J kg−1 K−1) but smaller than the weak FO [CH3NH3][CrMn(HCOO)6] (Mr = 409.1 g mol−1, −ΔSmmax = 48.2 J kg−1 K−1) with similar formula weight.12 Thus, the deviation between experimental and theoretical value may be ascribed to the anisotropy of single ions or crystalline nature or shortrange order triggered by the weak magnetic couplings between the CrIII and MnII ions. Notably, the −ΔSmmax value of 1 is excellent and higher than most of known metal clusters,15 Gdbased complexes,15 and commercial gadolinium gallium garnet (Gd3Ga5O12) (−ΔSmmax = 38.4 J kg−1 K−1 with ΔH = 7 T).16 Notably, formate takes a key role in achieving large MCE, which not only realizes weak FO interactions between adjacent metal ions to hinder LRO but also maintains high magnetic density. Compared with the broadly investigated GdIII-based molecular magnetic coolers,15 less progress has been achieved in 3d complexes due to the huge difficulties in achieving weak magnetic interactions between targeted 3d ions and simultaneously holding high magnetic density (Table 2).17 The niccolite structure provides a new platform for the design of rare polymeric 3d complexes with excellent MCE via the heterometallic strategy.
Figure 2. Polyhedron view of two sublattices with (a) CH3NH2CH3I, CH3NH3I, and (b) NH4H2OI filling in the cavities.
Magnetism Studies. Although the structure of 1 has been reported,13i the magnetic and magnetocaloric investigation of 1 has not been conducted. Magnetic properties of 1−4 were studied on powder samples, and the phase purity is confirmed by the agreement between experimental PXRD curves and the fitted ones (Figures S1−S3). The magnetic susceptibility (χ) data are characterized in 2−300 K under 1 kOe field. The temperature-dependent χmT plot of 1 is present in Figure 3a. The experimental χmT product of 6.57 cm3 mol−1 K at 300 K for 1 matches with the spin-only values (g = 2.00) of one isolated CrIII and one MnII. When cooled, the χmT product increases gradually before 40 K, and then it quickly rises to 32.95 cm3 mol−1 K at 2 K. The χm data among 2−300 K can be fitted by the Curie−Weiss law, giving C = 6.53 cm3 mol−1 K and θ = 1.53 K (Figure. S4). The small positive θ suggests weak FO interactions in 1. However, no saturation of magnetizations was observed at low temperature under 0.1 T excluding long-range order (LRO) above 2 K. Magnetizations among 2−10 K were also gauged (Figure 3a). At low fields (
