organics Article Switchg Local Symmetry from D 5h to D 4h for Sgle-Molecule Magnets by Non-Coordatg Solvents Xia-Li Dg 1, Qian-Cheng Luo 1, Yuan-Qi Zhai 1, Qian Zhang 2, *, Lei Tian 3, Xliang Zhang 4, Chao Ke 5, Xu-Feng Zhang 6, Yi Lv 6 Yan-Zhen Zheng 1, * Citation: Dg, X.-L.; Luo, Q.-C.; Zhai, Y.-Q.; Zhang, Q.; Tian, L.; Zhang, X.; Ke, C.; Zhang, X.-F.; Lv, Y.; Zheng, Y.-Z. Switchg Local Symmetry from D 5h to D 4h for Sgle-Molecule Magnets by Non-Coordatg Solvents. Inorganics 2021, 9, 64. https://doi.org/10.3390/ organics9080064 Academic Editors: Akseli Mansikkamäki Daniel B. Leznf Received: 2 June 2021 Accepted: 29 July 2021 Published: 16 August 2021 Publisher s Note: MDPI stays neutral with regard to jurisdictional claims published maps stitutional affiliations. Copyright: 2021 by authors. Licensee MDPI, Basel, Switzerl. This article is an open access article distributed under terms conditions Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Frontier Institute Science Technology (FIST), Xi an Jiaotong University Shenzhen Research School, State Key Laboratory for Mechanical Behavior Materials, MOE Key Laboratory for Nonequilibrium Synsis Modulation Condensed Matter, Xi an Key Laboratory Sustaable Energy Materials Chemistry, School Chemistry School Physics, 99 Yanxiang Road, Xi an 710054, Cha; dxl1457337646@163.com (X.-L.D.); luoqiancheng@stu.xjtu.edu.cn (Q.-C.L.); zhaiyuanqi@stu.xjtu.edu.cn (Y.-Q.Z.) 2 State Key Laboratory Military Stomatology & National Clical Research Center for Oral Diseases & Shaanxi International Jot Research Center for Oral Diseases, Department General Dentistry Emergency, School Stomatology, Air Force Medical University, 169 West Changle Road, Xi an 710032, Cha 3 State Key Laboratory Military Stomatology, National Clical Research Center Oral Diseases, Shaanxi Key Laboratory Oral Diseases, Department Cranio-facial Trauma Orthognathic Surgery, School Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi an 710032, Cha; tianleison@163.com 4 Department Spe Surgery, Honghui Hospital, Xi an Jiaotong University, 76 Nanguo Road, Xi an 710054, Cha; xaxliang@stu.xjtu.edu.cn 5 Department Orthopaedic Trauma, Honghui Hospital, College Medice, Xi an Jiaotong University, 28 West Xianng Road, Xi an 710054, Cha; kechao373855288@163.com 6 Department Hepatobiliary Surgery, The First Affiliated Hospital Xi an Jiaotong University, 277 West Yanta Road, Xi an 710061, Cha; xfzhang125@126.com (X.-F.Z.); luyi169@126.com (Y.L.) * Correspondence: laolvshu@126.com (Q.Z.); zheng.yanzhen@xjtu.edu.cn (Y.-Z.Z.); Tel.: +86-029-833-951-72 (Y.-Z.Z.) Abstract: A solvent effect towards performance two sgle-molecule magnets (SMMs) was observed. The tetrahydruran toluene solvents can switch equatorial coordated 4- Phenylpyride (4-PhPy) molecules from five to four, respectively, [Dy(O t Bu) 2 (4-PhPy) 5 ]BPh 4 1 Na{[Dy(O t Bu) 2 (4-PhPy) 4 ][BPh 4 ] 2 } 2thf hex 2. This alternation significantly changes local coordation symmetry Dy(III) center from D 5h to D 4h for 1 2, seperately. Magnetic studies show that magnetic anisotropy energy barrier 2 is higher than that 1, while relation blockg temperature is just on contrary due to symmetry effect. The calculations electrostatic potential successfully explaed drivg force solvents for molecular structure change, confirmg feasibility adjustg performance SMMs via diverse solvents. Keywords: dysprosium; local symmetry; sgle-molecule magnets; magnetic relaxation; solvent effect 1. Introduction There are considerable high performance sgle-molecule magnets (SMMs) contag dysprosium(iii) reported recent years [1 6], rangg from cyclopentadienyl (Cp) based system [7 10] to pentagonal-bipyramidal (PB) family [11 14]. Among se dysprosium(iii)-based complexes, highly axial crystal field [14,15] is essential to achieve good performance SMMs [16,17]. In this regard, or ancillary components, while unnecessary to this target, play, however, a key role to stabilize Dy(III) complexes because radii lanthanides are very large [3,4,18]. This is well demonstrated by Tong et al. who reported a text-book example solvent duced symmetry transformation between quasi-d 5h quasi-o h by losg its one coordated methanol molecule when exposed to dry air n recovered structure by soakg methanol for one Inorganics 2021, 9, 64. https://doi.org/10.3390/organics9080064 https://www.mdpi.com/journal/organics
Dy(III) complexes because radii lanthanides are very large [3,4,18]. This is well demonstrated by Tong et al. who reported a text-book example solvent duced symmetry transformation between quasi-d5h quasi-oh by losg its one coordated Inorganics 2021, 9, 64 methanol molecule when exposed to dry air n recovered structure 2 by 10 soakg methanol for one day [19]. The compounds with identical ligs are provided with completely different magnetic properties, as well as effective energy barrier (Ueff) day [19]. blockg The temperature compounds with (TB), which identical are ligs two pivotal are provided dexes evaluatg with completely properties different magnetic SMMs [20 22]. properties, as well as effective energy barrier (U eff ) blockg temperature (T B ), which Furrmore, are twoit pivotal has also dexes been discovered evaluatg that properties similar transform SMMs [20 22]. configuration triggered Furrmore, by it solvent has alsoeffect been discovered leads to that change similar related transform properties, configuration such as triggered hydrophobicity by solvent lumescence effect leads toresponse change [23 25]. related Zang s properties, group such syntized as hydrophobicity dendrimers lumescence Ag12@POSS6 response by troducg [23 25]. Zang s polyhedral groupoligomeric syntized silsesquioxane one dendrimers (POSS) one Ag with 12 @POSS thiol group 6 by troducg modifyg polyhedral observed oligomeric that its silsesquioxane core cluster went (POSS) through with a thiol structural group modifyg change with flattened observedcubo-octahedral that its core cluster went normal through cubo-octahedral a structuralcaused changeby with different flattened solvents cubo-octahedral acetone tetrahydruran, normal cubo-octahedral makg caused film bymatrix different embellished solvents by acetone m possess tetrahydruran, distctive hydrophobicity makg film[23]. matrix Zhang embellished et al. prepared by mone possess case distctive dumbbellshaped crystalle [23]. Zhang molecular et al. rotor prepared one y case found dumbbell-shaped that it its solvated crystalle crystal molecular possess hydrophobicity rotor a structural y difference found that itthat a its dihedral solvated angle crystal change possess about a structural 30 exists, difference leadg to a that lumescent a dihedral change angle change about 10 about nm [24]. 30 exists, leadg to a lumescent change about 10 nm However, [24]. or than direct coordatg solvent, here, we show that uncoordated However, or solvent than can also direct have a coordatg significant impact solvent, on here, fal wecoordation show that number uncoordated equatorial solvent can ligs also have two a significant dysprosium(iii) impact SMMs. on fal Usg coordation similar number syntic procedure equatorial with ligs only varyg two dysprosium(iii) reaction solvents, SMMs. we Usg observed that similar syntic tetrahydruran procedure (THF) with only toluene varyg solvents reaction can switch solvents, equatorial we observed coordated that tetrahydruran 4-Phenylpyride (THF) (4- PhPy) toluene molecules solvents from canfive switch to four, equatorial which fally coordated leads to 4-Phenylpyride two complexes, (4-PhPy) namely, molecules [Dy(O t from five to four, which fally leads to two complexes, namely, [Dy(O t Bu)2(4-PhPy)5]BPh4 1 Na{[Dy(O t Bu)2(4-PhPy)4][BPh4]2} 2thf hex 2. Bu) The 2 (4- PhPy) correspondg 5 ]BPh 4 1 pot Na{[Dy(O group t Bu) 2 molecule (4-PhPy) 4 ][BPh is altered 4 ] 2 } 2thf hex from local 2. D5h Theto correspondg D4h, respectively. pot It group should be noted molecule that ispb altered complexes from are local usually D 5h tocrystallized D 4h, respectively. THF or It pyride should be solvents noted that this PB is complexes first time arethat usually we isolated crystallized PB THF complex or pyride toluene. solvents We have calculated this is first electrostatic time that wepotentials isolated (ESPs) PB complex equatorial toluene. lig We havetwo calculated classes solvents, electrostatic from potentials which we (ESPs) could see equatorial configuration lig transition two classes different solvents, from was validated which wedue could to see varied configuration electrostatic transition teraction different between solvent solvent was validated lig. due toconsiderg varied electrostatic different teraction properties between both SMMs, solvent this variety lig. Considerg supramolecular different chemistry properties process realizes both SMMs, switch this variety magnetic supramolecular control compounds. chemistry process realizes switch magnetic control compounds. 2. Results Discussion 2. Results Discussion 2.1. 2.1. Synsis Synsis 1 2 1 2 The The synsis synsis steps steps se se two complexes two complexes are shown are shown Scheme 1. Scheme The only 1. difference The only is difference treatments is treatments powder after powder begafter driedbeg fromdried previous from reaction previous usg reaction THF usg solvent. THF solvent. Scheme 1. The syntic route for Complex 1 2. 2. 2.2. 2.2. Sgle Crystal Structure The The X-ray X-ray sgle sgle crystal crystal structure structure analysis analysis reveals that reveals crystallographic that crystallographic asymmetric unit asymmetric 1 is composed unit 1 is composed a seven-coordate a seven-coordate mononuclear mononuclear cation [Dy(O cation t Bu) [Dy(O 2 (4-PhPy) t Bu)2(4-5 ] + PhPy)5] a charge-balancg + a charge-balancg counteranion counteranion BPh 4 (Table BPh4 S1). (Table The S1). central The central Dy(III) Dy(III) center center asymmetric asymmetric unit 2 unit is six-coordate 2 is six-coordate with formula with [Dy(O formula t Bu) 2 (4-PhPy) [Dy(O t Bu)2(4-PhPy)4] 4 ] + (Figure 1). + The structure 1 is very similar to previously reported dysprosium(iii) complexes belongg to family PB geometry. The average Dy-O distance 2.123(2) Å for 1 is a little (Figure 1). The structure 1 is very similar to previously reported dysprosium(iii) longer than that 2 (2.066(8) Å); five equatorial Dy-N bond lengths are rangg from 2.55 to 2.59 Å for 1, which are obviously longer than those 2 (averaged at 2.468(8) Å, see Table S2 for detail). Indeed, PB polyhedron is quite regular with an axial O-Dy-O angle 175.14(7) 180 for 1 2, respectively, N-Dy-N angles rangg from 69.44(12) to 73.41(11). These geometries lead to contuous shape measurement (CShM) calculations [26] for Dy III ions 0.889 for local D 5h symmetry 1 0.693 for
complexes belongg to family PB geometry. The average Dy-O distance 2.123(2) Å for 1 is a little longer than that 2 (2.066(8) Å); five equatorial Dy-N bond lengths are rangg from 2.55 to 2.59 Å for 1, which are obviously longer than those 2 (averaged Inorganics 2021, 9, 64 at 2.468(8) Å, see Table S2 for detail). Indeed, PB polyhedron is quite regular with 3 an 10 axial O-Dy-O angle 175.14(7) 180 for 1 2, respectively, N-Dy-N angles rangg from 69.44(12) to 73.41(11). These geometries lead to contuous shape measurement (CShM) calculations [26] for Dy III ions 0.889 for local D5h symmetry compressed 1 0.693 for octahedron compressed 2, namely octahedron with tetragonal bipyramidal 2, namely with tetragonal bipyramidal (D 4h ) local-symmetry (D4h) (Table local-symmetry S3). (Table S3). Figure 1. The molecular structures [Dy(O Bu)2(4-PhPy)5] + cation (a) [Dy(O Bu)2(4- Figure 1. The molecular structures [Dy(O t Bu) 2 (4-PhPy) 5 ] + cation 1 (a) [Dy(O t Bu) 2 (4- PhPy)4] + cation (b); or atoms disordered two THF molecules, one hexane molecule PhPy) one Na 4 ] + cation 2 (b); or atoms disordered two THF molecules, one hexane molecule + cation per formula unit channels are omitted for clarity 2. The polyhedron one Dy III Na ions + cation center per viewed formula respectively unit from channels front are (left) omitted for clarity top (right). 2. The polyhedron Dy III ions center viewed respectively from front (left) top (right). In molecular packg, shortest termolecular Dy Dy distance is 12.57(3) Å In molecular packg, shortest termolecular Dy Dy distance is 12.57(3) for 1 15.63(2) Å for 2 (Figures S2 S3), respectively. More terestgly, Å for 1 15.63(2) Å for 2 (Figures S2 S3), respectively. More terestgly, disordered organic THF/hexane molecules are easily lost 3D extended channels disordered organic THF/hexane molecules are easily lost 3D extended channels structure formed by termolecular π-π stackg teractions (Figure 2a c), with a 2/3 structure formed by termolecular π-π stackg teractions (Figure 2a c), with a voids existg 3D extended channels structure compound 2 accordg to 2/3 voids existg 3D extended channels structure compound 2 accordg to SQUEEZE route. Furr characterizations dicate that re are two disordered THF SQUEEZE route. Furr characterizations dicate that re are two disordered THF molecules, one disordered hexane molecule one Na cation per formula unit molecules, one disordered hexane molecule one Na + cation per formula unit channels as confirmed by ICP, TGA, elemental analysis, charge balance (details can channels as confirmed by ICP, TGA, elemental analysis, charge balance (details can be seen previous report [5]). There is no such special supermolecular structure for be seen previous report [5]). There is no such special supermolecular structure for 1 (Figure (Figure 2d). 2d). However, However, solvent solvent is is readily readily lost lost 2, 2, at at a temperature temperature THF THF with with no no structural structural changes, changes, only only losg losg guest guest molecules molecules while while host structure host was structure mataed. was We mataed. did not fd We did not structure fd structure compound 2 compound to revert to 2 to compound revert to compound 1 process 1 measurement. process measurement. It is possible It is that possible solubility that solubility Na[BPh Na[BPh4] THF vs. toluene is 4 ] THF vs. toluene is a large driver a large driver change change structure. structure. This also This manifests also manifests that solvation that has solvation an important has an fluence important on fluence coordation on coordation geometry geometry spatial packg spatial structure packg structure complexes, which complexes, probably which lead probably to havg lead different to havg effects different on effects magnetic on properties magnetic properties complexes. complexes.
Inorganics 2021, 9, 64 4 10 s 2021, 9, x FOR PEER REVIEW 4 10 Figure 2. (a) Figure The packg 2. (a) The diagram packg diagram ma skeleton ma structure skeleton for structure 2 one for asymmetric 2 one asymmetric unit cell. (b) unit The cell. 3D extended (b) The 3D extended channels structure for 2; BPh4 channels structure for 2; BPh disordered components channels are 4 disordered components channels are omitted for clarity. (c) The packg diagram omitted for clarity. (c) The packg diagram for 2 along a direction. (d) The packg diagram for for 2 along a direction. (d) The packg diagram for 1 along a direction. 1 along a direction. 2.3. Magnetic Properties 2.3. Magnetic Properties From temperature-dependent direct current (dc) magnetic susceptibilities, complexes 1 2 show similar paramagnetism. The temperature dependence magnetic From temperature-dependent direct current (dc) magnetic susceptibilities, complexes 1 2 show similar paramagnetism. The temperature dependence susceptibilities were carried out under 1 koe dc field temperature range 300 2 K magnetic susceptibilities were carried out under 1 koe dc field temperature range (Figure S4), which gave χt products ( unit cm 3 K mol 1 ) 14.08 for 1 at 300 K, 300 2 K (Figure S4), which gave χt products ( unit cm 3 K mol 1 ) 14.08 for which are very close to expected value 14.17 cm 3 K mol 1 for free Dy 3+ ion. Upon 1 at 300 K, which coolg, are very χt values close to two expected complexes value keep essentially 14.17 cm 3 constant. K mol 1 for At lower free Dy temperature 3+ about ion. Upon coolg, 20 K, χt values sudden drop two complexes χt product keep dicates essentially onset constant. magnetic At lower blockg (Figure S4). temperature about 20 The K, field sudden (H) dependence drop χt product magnetization dicates (M) for onset 1 (Figure magnetic 3a) were measured at blockg (Figure a 10 S4). Oe/s sweepg rate. For 1, magnetic hysteresis loops were not closed up to 13 K, The field (H) which dependence are substantial magnetization agreement with (M) for zero-field-cooled 1 (Figure 3a) were measured field-cooled (ZFC-FC) at a 10 Oe/s sweepg magnetizations rate. For 1, peak at magnetic about 11 hysteresis K for 1 (Figure loops were 3c). not Onclosed or up to h, 13 butterfly K, which are magnetic substantial hysteresis agreement loops with were observed zero-field-cooled only up to 5 K field-cooled did not have (ZFC- a peak ZFC-FC FC) magnetizations magnetizations peak at about for11 2 as K for shown 1 (Figure previously 3c). On [5]. Moreover, or h, we could butterfly see a smaller step magnetic hysteresis zero dc loops fieldwere regime observed even only a wider up to 5 hysteresis K did loop not athave 2 K for a peak 1 compared ZFC-to 2 (Figure 3b), FC magnetizations which for dicates 2 as shown a blockg previously temperature [5]. Moreover, SMM we with could Dsee 5h local a smaller symmetry step clearly higher zero dc field regime than oneeven witha Dwider 4h local hysteresis symmetry. loop We at 2 reasoned K for 1 compared that this is to because 2 (Figure pseudo-d 5h 3b), which dicates symmetric a blockg SMM can temperature better restra SMM quantum with D5h tunnelg local symmetry magnetization clearly (QTM) effect higher than at one zero with field D4h local hence, symmetry. T B is enhanced. We reasoned that this is because pseudo- D5h symmetric SMM can better restra quantum tunnelg magnetization (QTM) effect at zero field hence, TB is enhanced.
Inorganics 2021, 9, 64 5 10 Inorganics 2021, 9, x FOR PEER REVIEW 5 10 a) b) M /μ B 4 2 0 2.0 K 4.0 K 7.0 K 10 K 13 K M /μ B 4 2 0 1 2 T = 2 K 10 Oe/s -2-2 -4-4 -2-1 0 1 2 H / T c) d) χ /cm 3 mol -1 1.8 1.5 1.2 0.9 11 K ZFC FC τ -1 / s -1 10 4 10 3 10 2-2 -1 0 1 2 Exp Fit H / T 0.6 10 1 0.3 0 5 10 15 20 25 30 35 40 T / K 40 50 60 70 80 90 100 Figure 3. 3. (a) Magnetic hysteresis loops for for 1. 1. (b) (b) The The comparison magnetic magnetic hysteresis hysteresis at at 2 K2 K for 1 for 1 2. (c) 2. (c) Field-cooled Field-cooled (FC) (FC) zero-field-cooled zero-field-cooled (ZFC) (ZFC) magnetic magnetic susceptibilities susceptibilities 1 1 measured measured under dc field 1000 Oe. (d) Temperature dependence relaxation time τ a zero dc field under a dc field 1000 Oe. (d) Temperature dependence for 1, solid les are best fits accordg to equation relaxation = time τ a + zero dc field. for 1, solid les are best fits accordg to equation τ 1 = τ 1 0 e U e f f /T + CT n. Alternatg current (ac) susceptibilities under zero dc field were measured for 1 Alternatg current (ac) susceptibilities under zero dc field were measured for 1 (Figure S5 S6) at relatively high temperature range, for 2 details, y can be (Figure S5 S6) at a relatively high temperature range, for 2 details, y can be seen previous report [5]. The maxima both -phase (χ ) out--phase (χ ) seen previous report [5]. The maxima both -phase (χ ) out--phase components showed a clear temperature dependence (Figure S5). The frequencydependent ac susceptibilities were also measured peaks χ can be all observed (χ ) components showed a clear temperature dependence (Figure S5). The frequencydependent ac susceptibilities were also measured peaks χ can be all observed from 40 97 for (Figure S6a) at frequency rangg from 1 to 1218 Hz. Moreover, from 40 97 K for 1 (Figure S6a) at frequency rangg from 1 to 1218 Hz. Moreover, frequency-dependent data can be by modified Debye function to obta Cole Cole frequency-dependent data can be by a modified Debye function to obta Cole Cole plots for (Figure S7). The α value is less than 0.01 (Table S4) only has a peak, plots for 1 (Figure S7). The α value is less than 0.01 (Table S4) only has a peak, demonstratg narrow distributions relaxation times one relaxation mechanism for demonstratg narrow distributions relaxation times one relaxation mechanism this sample. Figure 3d for 1 shows plots τ 1 versus T for temperature-dependent for this sample. Figure 3d for 1 shows plots τ 1 versus T for temperaturedependent relaxation rate. The values are obtaed by fittg ac data with equation = relaxation + rate. The τ values are obtaed by fittg ac data with, givg followg parameters: for 1, Ueff = 1785(6) K, τ0 = 1.96(4) equation τ 10 12 s, C = 1 = τ 5.3(6) 1 0 e U e f f /T + CT 10 5 s 1 K n, n = 3.02(5). n, givg followg parameters: for 1, U These parameters are very similar to eff = 1785(6) or D5h K, τ SMMs 0 = 1.96(4) 10 due to fact 12 s, C = 5.3(6) 10 that y share 5 s same 1 K coordation n, n = 3.02(5). These parameters are geometry [27]. For 2, very similar to or D equation has been modified 5h SMMs due to fact that y share same coordation with an additional QTM term, which gives Ueff = 2075(11) K, geometry [27]. For 2, equation has been modified with an additional QTM term, which τ0 = 5.61(2) 10 13 s, C = 5.60(4) 10 3 s 1 K n, n = 2.85(4) τqtm = 0.46 s. From se results, gives U we could eff = 2075(11) K, τ see that higher 0 = 5.61(2) 10 temperature 13 s, C = 5.60(4) 10 relaxation mechanisms 3 s for 1 K both n, n = 2.85(4) complexes τ are similar, QTM = 0.46 s. From se results, we could see that higher temperature whereas low temperature region where QTM is effective, relaxation relaxation mechanisms for both complexes are similar, whereas low temperature behavior is disparate for two complexes. Due to its local D4h symmetry effect, 2 has region where QTM is effective, relaxation behavior is disparate for two complexes. Due stronger QTM effect compared to 1. For 1, due to nearly perfect D5h local symmetry, to its local D QTM is much 4h symmetry effect, 2 has stronger QTM effect compared to 1. For 1, due to suppressed. This can be also seen hysteresis loops (Figure 3). At 2 K nearly perfect D (Figure 3b) at zero 5h local symmetry, QTM is much suppressed. This can be also seen field region, hysteresis is much wider for 1 than that 2, hysteresis loops (Figure 3). At 2 K (Figure 3b) at zero field region, hysteresis is dicatg that QTM is well mitigated [28]. much wider for 1 than that 2, dicatg that QTM is well mitigated [28]. 10 0 T / K
Inorganics 2021, 9, 9, 64 x FOR PEER REVIEW 6 10 10 2.4. 2.4. Ab Ab itio itio Calculation Calculation To To ga ga sight sight to to magnetic magnetic properties properties electronic electronic structure, structure, ab itio ab calculation calculation towards towards 1 was performed 1 was performed at SA-CASSCF/RASSI at SA-CASSCF/RASSI level by usglevel OPENby MOLCAS usg OPEN (see itio Supportg MOLCAS (see Information Supportg for details). Information The for highly details). axial The g-tensor highly ground axial g-tensor Kramer Doublet ground (KD) Kramer could Doublet be observed (KD) could (g x = be g y observed (gx = 0, g z = 19.89) = gy as= well 0, gz as = local 19.89) prcipal as well as magnetizations local prcipal magnetizations that almost along that almost O-Dy-O along direction O-Dy-O (Figure direction 4, sert), (Figure 4, its sert), wave function its wave is rar function pure is rar with 99.9% pure with ±15/2> 99.9% (Table ±15/2> S5). (Table Meanwhile, S5). Meanwhile, calculated calculated LoProp charges LoProp also charges prove also prove existence existence a strong a axial strong crystal axial field crystal with field more with negative more negative charges charges on O atoms on O than atoms equatorial than equatorial N atoms N (Table atoms S7). (Table Moreover, S7). Moreover, excited KDs excited conta KDs relatively conta pure relatively wavepure function wave until function fourth until KD: fourth 99.8% ±13/2> KD: 99.8% (KD ±13/2> 2 ), 99.4% (KD2), ±11/2> 99.4% ±11/2> (KD 2 ), 87.1% (KD2), ±9/2> 87.1% ±9/2> (KD 3 )(KD3) 70.1% 70.1% ±1/2> ±1/2> (KD(KD4) 4 ) lyg lyg at 781 at 781 K, 1300 K, 1300 K, 1576 K, 1576 K K 1636 1636 K, K, respectively. The The third third excited excited KD KD with with highly highly mixed mixed characteristic its its g z gz angle 86.86 dicate that Orbach relaxation passes through this state, makg oretical oretical value value Ueff U eff around 1736 1736K, K, which is isclosely consistent with experimental value (Figure 4). Figure 4. 4. Ab itio calculated electronic states 1. 1. The numbers beside arrows express relative transition transition propensity. propensity. The The local local prcipal prcipal magnetizations magnetizations ground ground Kramer s Kramer s doublet doublet 1. For 1. For clarity, clarity, all hydrogen all hydrogen atoms atoms are are omitted omitted (sert). (sert). The terrelated complex 2 possessg local DD4h symmetry has already been discussed via crystal field field parameters parameters (CFPs) (CFPs) previous previous literature, literature, dicatg dicatg that such geometry that such adverts geometry adverts emergence emergence significant significant non-axial non-axial crystal field crystal terms field (Bterms q (, q 0) k, q = 0) can be can one be one cidates cidates to design to design high high performance SMMs. Notwithstg strong uniaxial crystal fields realized both complexes, UUeff value for 1 is is lower than that 2, which can be be understood by by means followg aspects. aspects. Firstly, Firstly, crement crement coordation coordation number number equator equator circle partly circle causes partly causes reduction reduction local symmetric local environment symmetric environment around Dy 3+ around ions, which Dy 3+ ions, proceeds which to proceeds changg to CFPs. changg WeCFPs. foundwe that found absolute that value absolute axial value parameter axial parameter B2 0 1 ( 6.53) 1 is( 6.53) less than is less thatthan 2 ( 9.50), that 2 htg ( 9.50), identical htg identical relationship relationship respect respective axiality respective ground axiality KD. ground Moreover, KD. Moreover, g z value ground gz value KD 1 ground (19.89) iskd also smaller 1 (19.89) compared is also with smaller 2 (19.98). compared Furrmore, with 2 from (19.98). perspective Furrmore, from magneto-structural perspective correlation, magneto-structural length correlation, Dy-O 1 is larger length than Dy-O 2 while 1 is larger relationship than 2 reverses while for relationship Dy-N bonds reverses (L Dy-O(avg) for Dy-N = 2.123 bonds Å, L(LDy-O(avg) Dy-N(avg) = 2.577 2.123 Å, for LDy-N(avg) 1, L Dy-O(avg) = 2.577 = Å 2.064 for 1, Å, LDy-O(avg) L Dy-N(avg) = 2.064 = 2.648 Å, LDy-N(avg) Å for 2). = Evidently, 2.648 Å for 2). shorter Evidently, Dy-O distance shorter plays Dy-O adistance leadg plays role a such leadg competitive role such effect competitive between both effect different between types both different bond length. types Meanwhile, bond length. angle Meanwhile, O-Dy-O angle latter O-Dy-O is 179.95, more latter lear is 179.95, than 1 (175.14 more lear ), makg than this 1 (175.14 ), variety makg coordation this variety mode more coordation suitable for mode ionsmore with suitable oblate electron for ions density. with oblate electron In addition, density. electrostatic potentials (ESPs) distctive solvents transversal ligs In were addition, calculated electrostatic to expla potentials configuration (ESPs) transformation distctive solvents distctive transversal solvents (Figure ligs 5). were It was calculated found that to expla THF configuration 4-PhPy possess transformation similar electrostatic distctive potential solvents distri-
Inorganics 2021, 9, x FOR PEER REVIEW 7 10 Inorganics 2021, 9, 64 7 10 (Figure 5). It was found that THF 4-PhPy possess similar electrostatic potential distribution, while while re was re nowas or only no or aonly little a negative little negative potential potential region region surface on surface toluene. Due toluene. pure Due electrostatic to pure electrostatic attractions between attractions Dy between N, Dy THF solvent N, environment, THF solvent molecules environment, THF molecules 4-PhPy are THF mutually 4-PhPy exclusive are mutually electrostatic exclusive teraction, electrostatic leadg to teraction, formation leadg ato complex formation with local a complex D 4h symmetry. with local Meanwhile, D4h symmetry. rotatability Meanwhile, carbon carbon rotatability sgle carbon carbon bond betweensgle twobond rgsbetween provides favorable two rgs conditions provides for favorable formation conditions this configuration for formation terms this configuration steric hdrance. terms Contrarily, steric ahdrance. compound with Contrarily, local Da 5h compound configuration with islocal formed D5h configuration toluene solvent is formed owg totoluene factsolvent that molecules owg tend to tact contact that molecules a complementary tend to contact way to maximize a complementary electrostatic way to teraction. maximize In short, electrostatic from teraction. nature bondg, In short, we from underst nature phenomenon bondg, we underst solvent-duced configuration phenomenon transformation, solvent-duced which affects configuration properties transformation, SMMs which it is affects flexibility properties supramolecular SMMs chemistry it that flexibility leads to se supramolecular terestg chemistry meangful that leads coordation to se reactions terestg emergg. meangful coordation reactions emergg. Figure Figure 5. 5. Electrostatic Electrostatic potentials potentials THF, THF, toluene, toluene, 4-PhPy 4-PhPy from from left left to to right, right, respectively. respectively. (isovalue 0.001). (isovalue = 0.001). 3. 3. Materials Methods 3.1. Synsis For 1, an argon glovebox, a mixture DyCl3 3 (0.5 mmol, 134 mg), NaO t Bu t Bu (1 (1 mmol, 96 mg) NaBPh4 4 (0.5 mmol, 171 171 mg) mg) was was added added with with about about 10 ml 10THF ml THF Schlenk Schlenk tube, tube, which which gave a gave cloudy a cloudy solution. solution. After stirrg After stirrg for 24 h, for 24solution h, solution was filtered was filtered solvent was solvent removed was removed by vacuum byto vacuum get a white to get powder a white powder products; 2 ml products; toluene 2 ml toluene 4-PhPy (3 mmol, 4-PhPy 465 (3mg) mmol, were 465n mg) added were n to added powder to with powder furr with stirrg. furr Colorless stirrg. Colorless crystals suitable crystalsfor suitable X-ray for diffraction X-ray diffraction were grown wereby grown slow by diffusion slow diffusion hexane hexane to to solution solution at room attemperature room temperature after three after days: three Yield days: 278 Yield mg, 36% 278(based mg, 36% on Dy); (based Elemental on Dy); Elemental analysis calcd analysis (%) for calcd C98H95BDyN5O2: (%) for C H 95 C BDyN 76.03, 5 OH 2 : 6.19, C 76.03, N 4.52; H 6.19, found: N 4.52; C 76.05, found: H 6.20, C 76.05, N H4.53. 6.20, IR Nwas 4.53. as IR showed was as showed Figure S1 (see Figure Supplementary S1 (see Supplementary Materials). Materials). The synsis process 2 is same as 1 with THF used stead [5]. 3.2. X-ray Crystallography Data All data were recorded on on a Bruker a Bruker SMART SMART CCD CCD diffractometer diffractometer with with MoKα MoKα radiation radiation (λ = (λ 0.71073 = 0.71073 Å). Å). The The structures were were solved by by direct methods refed on F 2 2 usg Olex2. CCDC 2086927 (1) contas supplementary crystallographic datafor forthis paper cludg Tables S1 S4. The CIF checkcif filesfor for 1 canbe be found Supplementary Materials. 3.3. 3.3. Magnetic Magnetic Properties Properties Magnetic Magnetic susceptibility measurements measurements were were carried carriedout outwith a Quantum QuantumDesign MPMS-XL7 MPMS-XL7 SQUID magnetometer (Quantum (QuantumDesign DesignCompany, San SanDiego, CA, CA, USA) USA) upon upon coolg coolg from from 300 300 to to 2 K variable variable applied applied fields. fields. Ac Ac susceptibility susceptibilitymeasurements were were performed performed at at frequencies frequencies between between 11 1500 1500 Hz Hz with with an an oscillatg oscillatg field field 3.5 3.5 Oe Oe with with variable variable dc applied dc applied field. field. Powder Powder samples samples were were embedded embedded eicosane eicosane to avoid to any avoid field any duced field duced crystal reorientation. crystal reorientation. Crystalle Crystalle powders powders were fixed were with fixed eicosane, with wrapped eicosane, wrapped with film, with film, placed placed center center a straw. a straw. A diamagnetic A diamagnetic correction correction has been has been calculated calculated from from Pascal Pascal constants constants embeddg embeddg eicosane eicosane has has been been applied applied to to observed magnetic susceptibility. The results are cluded Table S4 Figures S4 S7 (see Supplementary Materials).
Inorganics 2021, 9, 64 8 10 3.4. Electronic Structure Calculations Complete Active Space Self-Consistent Field (CASSCF) calculation was performed to underst magnetic properties 1 via its electronic structure usg OPEN MOL- CAS [29] its geometry structure was obtaed straightly from X-Ray sgle crystal structure without optimization. The basis sets from ANO-RCC library [30] were employed for all atoms: VTZP quality for Dy, VDZP quality for O N atoms, as well as VDZ quality for ors; 21 sextets, 224 quartets, 490 doublets were calculated RASSCF module to acquire state-averaged CASSCF orbitals. Then, a sp-orbit (SO) couplg Hamiltonian was constructed diagonalized RASSI module [31] through chosen 21 sextets, 128 quartets, 130 doublets. Ultimately, all magnetic properties Dy(III) ion, such as g-tensors, crystal field parameters, transition magnetic moment matrix, magnetic susceptibility, magnetization plot, were computed output was obtaed via SINGLE_ANISO program [32]. For assurg calculation accuracy, we also considered employg Cholesky decomposition for two-election tegrals. Includg Tables S5 S8 (see Supplementary Materials). 3.5. DFT Calculations To acquire wave function formation both complexes electrostatic potentials (ESP) distctive solvents transversal lig, calculations based on Density Function Theory (DFT) were performed usg Gaussian 09 E01 [33]. The PBE density functional [34] was employed all calculations with Grimme s D3 dispersion correction considered [35 37]. Primarily, positions hydrogen atoms 1 2 were optimized. We replaced Dy(III) ion to Y(III) light similar radius between m, set its atomic mass as 162.5 ( same as natural abundance-weighted mass dysprosium). The Stuttgart RSC 1997 effective core potential (ECP) [38,39] was applied for 28 core electrons Y(III) correspondg valence basis set was used for remag valence electrons, while rest atoms were treated with cc-pvdz basis set [40,41]. Then whole molecules toluene, THF 4-phenylpyride were optimized by same basis set. Harmonic vibrational calculations dicate that re is no imagary vibration mode all optimized mimumenergy structures have already been at stationary pots on potential energy surface. The results are cluded Tables S9 S13 (see Supplementary Materials). 4. Conclusions To summarize, we observed, for first time, that a non-coordatg solvent can also significantly impact coordate number equatorial ligs pentagonal bipyramidal geometry dysprosium(iii) SMMs. The performances SMMs are subsequently switched. The effective energy barrier 2 is higher than 1 while relation blockg temperature is just contrary. The structural transform is explaed by electrostatic teraction between solvent ligs, which confirmed feasibility adjustg performance SMMs by supramolecular chemistry solvents effect. Supplementary Materials: The followg are available onle at https://www.mdpi.com/article/ 10.3390/organics9080064/s1, Figure S1: The IR spectrum complex 1 2; Table S1: Crystallographic data for complex 1 2; Table S2: Selected Bond Lengths (Å) Bond Angles (deg) for complex 1 2; Table S3: The CShM s values first coordation sphere compound 1; Table S4: The CShM s values first coordation sphere compound 2; Figure S2: Packg diagram for complex 1; Figure S3: Packg diagram for complex 2; Table S4: Relaxation fittg parameters a generalized Debye model for 1; Figure S4: The variable-temperature dc magnetic susceptibility (1 koe) field dependence magnetization (set) at 2 K for 1; Figure S5: Temperature-dependence -phase χ out--phase χ ac susceptibility signals under zero dc field for 1; Figure S6: Frequency-dependence -phase χ out--phase χ a zero dc field for 1 with ac frequencies 1 1218 Hz; Figure S7: Cole-Cole plots for ac susceptibilities a zero dc field for 1; Table S5: Ab itio results for J = 15/2 multiple DyIII 1; Table S6: Ab itio calculated crystal field parameters for 1; Table S7: Ab itio calculated LoProp charges atoms near Dy center 1; Table S8: Average transition magnetic moment elements between states
Inorganics 2021, 9, 64 9 10 References 1; Table S9: Geometry coordates 1 population analysis calculations; Table S10: Geometry coordates 2 population analysis calculations; Table S11: Geometry coordates toluene molecule population analysis calculations; Table S12: Geometry coordates THF molecule population analysis calculations; Table S13: Geometry coordates 4-phenylpyride population analysis calculations. The CIF checkcif files for 1. Author Contributions: Conceptualization, X.-L.D. Y.-Z.Z.; methodology, X.-L.D., Q.-C.L., Y.-Q.Z. Y.-Z.Z.; stware, X.-L.D., Q.-C.L. Y.-Q.Z.; validation, X.-L.D., Q.-C.L., Y.-Q.Z., Q.Z., L.T., C.K., X.Z., X.-F.Z., Y.L. Y.-Z.Z.; formal analysis, X.-L.D.; Y.-Q.Z. Q.-C.L.; vestigation, Y.-Z.Z., Q.Z., L.T., C.K., X.Z., X.-F.Z. Y.L.; resources, Q.Z., L.T., C.K., X.Z., X.-F.Z. Y.L.; data curation, X.-L.D., Q.-C.L. Y.-Q.Z.; writg origal draft preparation, X.-L.D. Q.-C.L.; writg review editg, X.-L.D., Q.-C.L. Y.-Z.Z.; visualization, Y.-Z.Z.; supervision, Y.-Z.Z.; project admistration, Y.-Z.Z.; fundg acquisition, Y.-Z.Z., Q.Z., L.T., C.K., X.Z., X.-F.Z. Y.L. All authors have read agreed to published version manuscript. Fundg: This research was funded by National Natural Science Foundation Cha (21871219, 21773130 21620102002); Key Laboratory Construction Program Xi an Municipal Bureau Science Technology (201805056ZD7CG40); The Shenzhen Science Technology Program (JCYJ20180306170859634); The Fundamental Research Funds for Central Universities. Data Availability Statement: All data needed to evaluate paper are present ma text or Supplementary Materials. Additional data related to this paper may be requested from authors. Acknowledgments: This work was supported by followg fundg authors. We also thank Instrument Analysis Center Xi an Jiaotong University for assistance from Gang Chang. Conflicts Interest: The authors declare no conflict terest. 1. Goodw, C.A.P.; Ortu, F.; Reta, D.; Chilton, N.F.; Mills, D.P. Molecular Magnetic Hysteresis at 60 Kelv Dysprosocenium. Nature 2017, 548, 439 442. [CrossRef] [PubMed] 2. J, P.-B.; Zhai, Y.-Q.; Yu, K.-X.; Wpenny, R.E.P.; Zheng, Y.-Z. Dysprosiacarboranes as Organometallic Sgle-Molecule Magnets. Angew. Chem. Int. Ed. 2020, 59, 9350 9354. [CrossRef] 3. Canaj, A.B.; Dey, S.; Martí, E.R.; Wilson, C.; Rajaraman, G.; Murrie, M. Insight to D 6h Symmetry: Targetg Strong Axiality Stable Dysprosium(III) Hexagonal Bipyramidal Sgle-Ion Magnets. Angew. Chem. Int. Ed. 2019, 58, 14146 14151. [CrossRef] 4. Wang, J.; Li, Q.-W.; Wu, S.-G.; Chen, Y.-C.; Wan, R.-C.; Huang, G.-Z.; Liu, Y.; Liu, J.-L.; Reta, D.; Giansiracusa, M.J.; et al. Openg Magnetic Hysteresis by Axial Ferromagnetic Couplg: From Mono-Decker to Double-Decker Metallacrown. Angew. Chem. Int. Ed. 2021, 60, 5299 5306. [CrossRef] 5. Dg, X.-L.; Zhai, Y.-Q.; Han, T.; Chen, W.-P.; Dg, Y.-S.; Zheng, Y.-Z. A Local D 4h Symmetric Dysprosium(III) Sgle-Molecule Magnet with an Energy Barrier Exceedg 2000 K. Chem. Eur. J. 2021, 27, 2623 2627. [CrossRef] 6. Pedersen, K.S.; Ariciu, A.M.; McAdams, S.; Weihe, H.; Bendix, J.; Tuna, F.; Piligkos, S. Toward Molecular 4f Sgle-Ion Magnet Qubits. J. Am. Chem. Soc. 2016, 138, 5801 5804. [CrossRef] [PubMed] 7. Wang, H.; Wang, B.-W.; Bian, Y.; Gao, S.; Jiang, J. Sgle-Molecule Magnetism Tetrapyrrole Lanthanide Compounds with Swich Multiple-Decker Structures. Coord. Chem. Rev. 2016, 306, 195 216. [CrossRef] 8. Gould, C.A.; McCla, K.R.; Yu, J.M.; Groshens, T.J.; Furche, F.; Harvey, B.G.; Long, J.R. Synsis Magnetism Neutral, Lear Metallocene Complexes Terbium (II) Dysprosium (II). J. Am. Chem. Soc. 2019, 141, 12967 12973. [CrossRef] [PubMed] 9. Moutet, J.; Schleitz, J.; Droitte, L.L.; Tricoire, M.; Potillart, F.; Gendron, F.; Simler, T.; Clavaguéra, C.; Guennic, B.L.; Cador, O.; et al. Bis-Cyclooctatetraenyl Thulium (II): Highly Reducg Lanthanide Swich Sgle-Molecule Magnets. Angew. Chem. Int. Ed. 2021, 133, 6107 6111. [CrossRef] 10. Meihaus, K.R.; Long, J.R. Magnetic Blockg at 10 K a Dipolar-Mediated Avalanche Salts Bis(η 8 -Cyclooctatetraenide) Complex [Er(COT) 2 ]. J. Am. Chem. Soc. 2013, 135, 17952 17957. [CrossRef] [PubMed] 11. Liu, J.; Chen, Y.-C.; Jia, J.-H.; Liu, J.-L.; Vieru, V.; Ungur, L.; Chibotaru, L.F.; Lan, Y.; Wernsdorfer, W.; Gao, S.; et al. A Stable Pentagonal Bipyramidal Dy (III) Sgle-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K. J. Am. Chem. Soc. 2016, 138, 5441 5450. [CrossRef] 12. Chen, Y.-C.; Liu, J.-L.; Ungur, L.; Liu, J.; Li, Q.-W.; Wang, L.-F.; Ni, Z.-P.; Chibotaru, L.F.; Chen, X.-M.; Tong, M.-L. Symmetry- Supported Magnetic Blockg at 20 K Pentagonal Bipyramidal Dy (III) Sgle-Ion Magnets. J. Am. Chem. Soc. 2016, 138, 2829 2837. [CrossRef] [PubMed] 13. Yu, K.-X.; Kragskow, J.G.C.; Dg, Y.-S.; Zhai, Y.-Q.; Reta, D.; Chilton, N.F.; Zheng, Y.-Z. Enhancg Magnetic Hysteresis Sgle-Molecule Magnets by Lig Functionalization. Chem 2020, 6, 1777 1793. [CrossRef]
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