Tuning Magnetic Relaxation in a Tb-Nitronyl Nitroxide Complex by

Article pubs.acs.org/IC

Tuning Magnetic Relaxation in a Tb-Nitronyl Nitroxide Complex by Using Cocrystalline Paramagnetic Complex Juan-Juan Wang, Juan Sun, Meng Yang, and Li-Cun Li* Department of Chemistry, Key Laboratory of Advanced Energy Materials Chemistry and Tianjin Key Laboratory of Metal and Molecule-based Material Chemistry, Nankai University, Tianjin 300071, China S Supporting Information *

ABSTRACT: New 2p−4f and 2p−3d−4f compounds [Tb(hfac)3(NIT-PhNO2)2]·0.5C7H16 (1) and [Ln(hfac)3(NITPhNO2)2]2[Cu(hfac)2(NIT-PhNO2)2] (LnIII = Gd 2, Tb 3; hfac = hexafluoroacetylacetonate; NIT-PhNO2 = 2-(p-nitrophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been obtained. Complex 1 consists of mononuclear trispin [Tb(hfac)3(NIT-PhNO2)2] units in which two radical ligands are ligated to the Tb(III) ion as monodentate ligands through the NO groups, while complexes 2 and 3 contain two kinds of trispin moieties, namely, [Ln(hfac)3(NIT-PhNO2)2] and [Cu(hfac)2(NIT-PhNO2)2]. In the [Cu(hfac)2(NIT-PhNO2)2] moiety, the radicals are bonded to the copper(II) ion in the axial positions via the nitroxides. For three compounds, 1D supramolecular chains are formed via the π−π stacking interactions involving the radical ligands. Magnetic investigations show that both Tb complexes exhibit slow relaxation of magnetization at low temperature; strikingly, complex 3 displays a higher energy barrier than that of 1. It represents the first example to use the paramagnetic complex to tune magnetic relaxation of 4f-based compounds.

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INTRODUCTION In design and synthesis of single-molecule magnets (SMMs), a promising strategy is to use the lanthanide-based compounds owing to the strong magnetic anisotropy of lanthanides.1 Following this strategy, a large number of mono-2 and polynuclear3 lanthanide SMMs, mixed 3d−4f,4 and Ln−Rad systems5 have been obtained, and many significant results witness the tremendous progress of the SMM field. For instance, a mononuclear Tb(III) heteroleptic bisphthalocyanine complex [Tb(Pc)(Pc′)] displays a record magnetic reversal barrier of 652 cm−1.6 A record blocking temperature (TB) of 13.9 K has been observed in a N2•3− radical bridged binuclear Tb(III) complex.7 In spite of these achievements, it is still a challenge to improve the SMM performance so that the practical application can be achieved. As known, an inherent drawback in the employment of lanthanide ions is fast quantum tunneling of magnetization (QTM) that reduces the relaxation barrier and thus prevents the improvement of relaxation times.8 One of the reasons for producing the fast QTM arises from the dipole−dipole interactions between neighboring lanthanide ions in the crystalline solid. To overcome this problem, the lanthanide-based molecules must be far away from each other. In general, two kinds of strategies are available: one is to dissolve the complex into an organic solvent; the other is to dilute the complex molecules in isomorphous diamagnetic matrix which results in a solid solution. Using these approaches, some SMM behaviors have been remarkably improved.9 Very recently, another strategy has been reported, in which QTM is effectively suppressed by reducing the hyperfine coupling via using isotopic enrichment.10 © XXXX American Chemical Society

Initially, the aim of this work is to synthesize nitronyl nitroxide-bridged one-dimensional Ln/Cu−Ln chains; however, three zero-dimensional Ln-based complexes, namely, [Tb(hfac)3(NIT-PhNO2)2]·0.5C7H16 (1) and [Ln(hfac)3(NITPhNO2)2]2[Cu(hfac)2(NIT-PhNO2)2] (LnIII = Gd 2, Tb 3; hfac = hexafluoroacetylacetonate; NIT-PhNO2 = 2-(p-nitrophenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide), are obtained. Both 1 and 3 display slow magnetic relaxation behavior. Remarkably, the spin dynamics of complex 1 have been improved by introducing the paramagnetic complex molecule [Cu(hfac)2(NIT-PhNO2)2].

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EXPERIMENTAL SECTION

Synthesis. All chemicals and solvents used in the synthesis were analytical grade reagents purchased from commercial sources without further purification. The NIT-PhNO2 radical ligand was prepared according to the previous report.11 Preparation of [Tb(hfac)3(NIT-PhNO2)2]·0.5C7H16 1. This compound was synthesized by using the same procedure for our previously reported Gd−Rad complex12 with Tb(hfac)3·2H2O instead of Gd(hfac)3·2H2O. Yield 61%. Anal. Calcd for C44.5H43TbF18N6O14 (%): C 38.54; H 3.13; N 6.06. Found: C 38.44; H 3.43; N 6.04. IR (KBr, cm−1): 2925 (s) 1653(s), 1533(m), 1350 (s), 1256(s), 1204(m), 1147(s), 799(m), 661(m). Preparation of [Ln(hfac)3(NIT-PhNO2)2]2[Cu(hfac)2(NIT-PhNO2)2] (LnIII = Gd 2, Tb 3). A suspension of Gd(hfac)3·2H2O or Tb(hfac)3· 2H2O (0.1 mmol) in 25 mL of heptane was refluxed for 3 h, and then the obtained solution was cooled to 80 °C, and a dichloromethane solution (5 mL) of NIT-PhNO2 radical (0.2 mmol) was added. The Received: August 20, 2015

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DOI: 10.1021/acs.inorgchem.5b01915 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Crystal Data and Structure Refinement for Complexes 1−3 formula fw cryst syst space group a/Å b/Å c/Å α, deg β, deg γ, deg V/Å3 Z Dcalcd/g cm−3 F(000) θmin, θmax deg reflns collected unique reflns/Rint GOF (F2) R1/wR2 [I > 2σ(I)]

1

2

3

C89H86F36N12O28Tb2 2773.56 triclinic P1̅ 11.919(2) 12.667(3) 18.811(4) 83.44(3) 74.38(3) 84.24(3) 2710.1(11) 1 1.699 1382 1.78, 25.00 21 817 9535/0.0272 1.036 0.0278/0.0812

C118H104CuF48N18O40Gd2 3704.25 triclinic P1̅ 11.419(2) 17.926(4) 18.868(4) 110.10(3) 96.99(3) 90.66(3) 3594.1(15) 1 1.711 1847 1.35, 27.92 30 562 17 209/0.0666 1.007 0.0716/0.1731

C118H104CuF48N18O40Tb2 3707.61 triclinic P1̅ 11.444(2) 17.992(4) 18.959(4) 109.99(3) 97.14(3) 90.58(3) 3634.2(15) 1 1.694 1849 1.15, 27.90 37 469 17 373/0.0949 1.013 0.0850/0.1940

Table 2. Selected Bond Lengths [Å] and Angles [deg] for Complexes 1−3 Ln−O(rad) Ln−O(hfac) Ln−O−N O(rad)−Ln−O(rad) Cu−O(rad) Cu−O(hfac)

1 Tb

2 Gd

3 Tb

2.346(7) 2.356(6) 2.335(7)−2.392(7) 136.8(6) 138.2(6) 137.8(2)

2.359(4) 2.365(4) 2.351(4)−2.405(4) 135.0(3) 136.7(4) 137.08(14) 2.406(4) 1.928(4) 1.942(4) 136.7(4)

2.347(5) 2.373(5) 2.334(6)−2.392(5) 134.9(5) 138.0(5) 137.53(18) 2.413(6) 1.927(6) 1.943(6) 138.0(5)

Cu−O−N

Figure 1. (left) View of the molecular structure of 1 (heptane solvent molecules, H and F atoms are omitted for clarity) and (right) the coordination polyhedron of Tb(III) ion in 1. resulting solution was stirred for 15 min at 80 °C, followed by the addtion of Cu(hfac)2 solid (0.1 mmol). The mixture was mantained at this temperature for another 15 min with continuous stirring, and then cooled to room temperature. Deep green crystals were collected after 3 days of slow evaporation at room temperature. Complex 2 data follow. Yield: 65%. Anal. Calcd for C118H104Gd2CuF48N18O40(%): C 38.26; H 2.83; N 6.80. Found: C 38.42, H 2.69, N 7.03. IR (KBr, cm−1): 2925 (s), 1652 (s), 1530 (m), 1354 (s), 1254 (s), 1215 (s), 1148 (s), 802 (m), 661 (m). Complex 3 data follow. Yield: 55%. Anal. Calcd for C118H104Tb2CuF48N18O40 (%): C 38.23; H 2.83; N 6.80. Found: C 38.25, H 2.51, N 6.98. IR (KBr, cm−1): 2924 (s), 1652 (s), 1530 (m), 1344 (s), 1254 (s), 1217 (s), 1148 (s), 802 (m), 661 (m).

Measurements. Elemental analyses for C, H, and N were performed on a PerkinElmer elemental analyzer model 240 at the Institute of Elemental Organic Chemistry, Nankai University. IR spectra were performed on a Bruker Tensor 27 Spectrophotometer in the 400−4000 cm−1 region using KBr pellets. All magnetic measurements were measured on Quantum Design SQUID VSM/ MPMS XL-7 magnetometer. Diamagnetic corrections were carried out with Pascal’s constants for all of the constituent atoms. X-ray Crystallography. Single-crystal X-ray diffraction data for compounds 1−3 were collected at 113 K on a Rigaku Saturn diffractometer equipped with a CCD camera using graphitemonochromated Mo Kα radiation (λ = 0.710 73 Å). The multiscan technique was applied for the absorption corrections. Structure B


Article

Inorganic Chemistry solution for all three compounds was the employment of direct methods which produced the positions of non-H atoms. The structural data were refined by full-matrix least-squares methods on F2 using the SHELXS-97 and SHELXL-97 programs.13 All non-H atoms were refined with anisotropic thermal parameters. H atoms were set in calculated positions with a common fixed isotropic thermal parameter. Crystal data and refinement of three compounds can be found in Table 1. The important bond lengths and angles are included in Table 2.

Å. The axial sites are occupied by the oxygen atoms of the two NO groups of the radical ligands with larger bonding distances of 2.406(4) Å for 2 and 2.413(6) Å for 3, indicating the Jahn− Teller effect. As shown in the crystal packing diagrams (Figures 3 and 4 and Figure S2), the stacking of neighboring phenyl rings of NIT-PhNO2 radicals produces intermolecular π−π interactions, generating an infinite pseudo-one-dimensional chain for three compounds. Noticeably, for compounds 2 and 3, this pseudo1D chain is made up with a repeating [Cu−Ln−Ln] sequence. The centroid···centroid distances between two adjacent phenyl rings of the NIT-PhNO2 ligands are 3.909 Å for 1, 3.925 Å for 2, and 3.936 Å for 3. The shortest Ln···Ln distance between the neighboring mononuclear units are 10.354, 11.300, and 11.360 Å for 1, 2, and 3, respectively. The closest contacts between the uncoordinated nitroxide groups are 5.501 Å for 1, 2.693 Å for 2, and 2.719 Å for 3. Such short NO−ON distances observed in 2 and 3 may lead to important magnetic interactions. Thus, in the magnetic point of view, complexes 2 and 3 may possess twodimensional sheet structures (Figures S4 and S5). The strength of this magnetic coupling depends on not only the distance between two NO groups but also the relative orientation of the π* orbitals.16 The other two relevant geometrical parameters for this magnetic coupling resulting from these short contacts are the N−O···N angle (α) and the dihedral angle (β) between the plane of two adjacent NO groups and the plane of the π* system of the radical (O−N−C−NO) (Chart S1). The values of α and β are 129.73° and 60.71° for 2 and 127.21° and 57.10° for 3. Magnetic Properties. The variable-temperature magnetic susceptibility of three complexes was measured under applied field of 1000 Oe in the 2−300 K range (Figure 5). At 300 K, the χMT values are 12.33 cm3 K mol−1 for 1, 18.72 cm3 K mol−1 for 2, and 27.21 cm3 K mol−1 for 3, which are close to the expected spin-only values (12.57 cm3 K mol−1 for 1, 18.39 cm3 K mol−1 for 2, and 26.27 cm3 K mol−1 for 3, assuming gCu = 2.0). For 1, the χMT value increases continuously with decreasing temperature to reach a value of 14.35 cm3 K mol−1 at 2.0 K, indicating that the NIT-PhNO2 radical ferromagnetically interacts with the TbIII ion. For 2, the χMT versus T curve exhibits a continuous increase on lowering the temperature, and the χMT value reaches a peak with a value of 20.50 cm3 K mol−1 at 10 K, and then decreases to 16.41 cm3 K mol−1 at 2.0 K. For 3, upon decreasing the temperature, the χMT value gradually increases to 29.35 cm3 K mol−1 at 65 K, and then decreases drastically to 16.98 cm3 K mol−1 at 2 K. In 2 and 3, the magnetic coupling between the radical and Cu(II)

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RESULTS AND DISCUSSION Description of the Crystal Structures. Single-crystal Xray diffraction analyses indicate that compounds 1−3 crystallize in the triclinic space group P1.̅ The structure of 1 is similar to that of the previous report.12 In brief, complex 1 possesses a mononuclear structure in which two radical ligands behave as monodentate ligand toward the Tb(III) ion via the nitroxide groups (Figure 1). The Tb ion is eight-coordinated by six oxygen atoms from three bidentate β-diketonate coligands (Tb−O: 2.335(7)−2.392(7) Å) and two oxygen atoms from two NO groups of two NIT-p-PhNO2 ligands with Tb−ORad bond distances of 2.346(7) and 2.356(6) Å, respectively. Continuous Shape Measures by SHAPE software14 indicate that the Tb coordination sphere can be described as distorted dodecahedron (D2d) (Table 3). Table 3. Results of Shape Measures Analysis for the Ln Coordination Spheres compd

SAPR-8

TDD-8

JBTPR-8

BTPR-8

JSD-8

1 2 3

1.542 1.521 1.448

0.292 0.306 0.323

2.529 2.585 2.630

1.928 2.073 2.061

2.994 3.038 3.124

For complexes 2 and 3, the asymmetric unit consists of one [Ln(hfac) 3 (NIT-PhNO 2 ) 2 ] and a [Cu(hfac) 2 (NITPhNO2)2]1/2 (Figure 2 and Figure S1). The structure of the mononuclear Ln unit is similar to that of compound 1. The coordination polyhedron of Ln also exhibits the dodecahedral geometry. The Gd/Tb−Ohfac bond lengths are in the range 2.334(6)−2.405(4) Å, and two Ln−ORad bond lengths are 2.359(4) and 2.365(4) Å for 2, and 2.347(5) and 2.373(5) Å for 3, respectively. These bond parameters are typical of those found in similar systems.15 For the mononuclear copper(II) moiety, the Cu(II) ion adopts an elongated octahedral coordination geometry. Two hfac coligands are coordinated to the copper(II) by their four oxygen atoms, which are located in the basal plane with Cu−O distances of 1.927(6)−1.943(6)

Figure 2. (left) Partially labeled molecular structure of 3 (hydrogen and fluorine atoms are omitted for clarity) and (right) the core in 3. C


Article

Inorganic Chemistry

Figure 3. One-dimensional chain of 1 through π−π interactions. Heptane molecules, hydrogen, and fluorine atoms are omitted for clarity.

Figure 4. One-dimensional chain of 3 through π−π interactions. H and F atoms are omitted for clarity.

Scheme 1. Magnetic Coupling Pathways in Rad−Gd−Rad (Left) and Rad−Cu−Rad (Right) Units for 2

χM = 2χRad − Gd − Rad + χRad − Cu − Rad

χRad − Gd − Rad =

Ng12β 2 ⎧⎡ ⎛ −9JRad − Gd ⎞ ⎨⎢165 + 84 exp⎜ ⎟ ⎝ ⎠ 4kT ⎩⎣ kT ⎪

⎪

⎛ −7JRad − Gd − 2JRad − Rad ⎞ + 84 exp⎜ ⎟ ⎝ ⎠ kT ⎤ ⎛ −16JRad − Gd ⎞ + 35 exp⎜ ⎟⎥ kT ⎝ ⎠⎦

Figure 5. χMT versus T plots of complexes 1−3. The solid line represents the best simulation curve by using the magnetic model (see text).

⎡ ⎛ −9JRad − Gd ⎞ /⎢5 + 4 exp⎜ ⎟ ⎝ ⎠ kT ⎣ ⎛ −7JRad − Gd − 2JRad − Rad ⎞ + 4 exp⎜ ⎟ ⎝ ⎠ kT

ion is expected to be ferromagnetic due to the orthogonality of two magnetic orbitals (dx2‑y2 on copper and π* on the radical) resulting from the axial coordination of NO group to the Cu(II) ion.17 On the basis of structural analysis, there exists the short NO−ON contact (about 2.70 Å) in 2 and 3, which may produce important magnetic coupling. However, the resulted magnetic coupling is expected to be weak since the N−O···N angle (α) and the dihedral angle (β) are about 130° and 60°, respectively, which is unfavorable for the effective overlap of the magnetic orbitals.16,18 In the view of the magnetic point, complexes 2 and 3 can be regarded as two [Ln(hfac)3(NITPhNO2)2] units plus one [Cu(hfac)2(NIT-PhNO2)2] (Scheme 1). Thus, owing to no orbital contribution for Gd ion, the magnetic data of 2 could be analyzed through the given expression as

⎛ −16JRad − Gd ⎞⎤⎫ + 3 exp⎜ ⎟⎥⎬ kT ⎝ ⎠⎦⎭ ⎪

⎪

χRad − Cu − Rad =

Ng2 2β 2 4kT ⎡ ⎢ 1 + exp ×⎢ ⎢⎣ 1 + exp

−2JRad − Cu

( (

kT

) + 10 exp( ) ⎤⎥ ⎥ ) + 2 exp( ) ⎥⎦ JRad − Cu kT

−2JRad − Cu

JRad − Cu

kT

kT

χtotal = χM /[1 − (zJ ′χM /Ng 2β 2)] D


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Inorganic Chemistry

Figure 6. Temperature dependence of the in-phase and out-of-phase components of ac susceptibility for compounds 1 (left) and 3 (right) in zero dc field.

For the Rad−Gd−Rad unit, the Hamiltonian is defined as Ĥ = −2JRad−Gd(ŜRad1·ŜGd + ŜRad2·ŜGd) − 2JRad−RadŜRad1·ŜRad2, and for the Rad−Cu−Rad unit, Hamiltonian is defined as Ĥ = ̂ ·ŜCu + SRad2 ̂ ·ŜCu). The weak magnetic couplings −2JRad−Cu(SRad1 among the trispin units resulting from short NO−ON contacts and π−π interactions are introduced by using molecular field approximation (zJ′). Well-fitting the experimental data produces the following magnetic parameters: g1 = 2.0 (fixed), g2 = 2.12, g = 2.10, JRad−Gd = 2.00 cm−1, JRad−Rad = −6.24 cm−1, JRad−Cu = 15.06 cm−1, zJ′ = −0.05 cm−1, R = 1.27 × 10−4 (R value is defined as ∑[(χM)obs − (χM)calc]2/∑[(χM)obs]2). For the Rad−Gd−Rad unit, the determined JRad−Rad and JRad−Gd values are in good agreement with those in the previously reported complex [Gd(hfac)3(NIT-PhNO2)2]12 and other similar Gd(NIT-R)2 complexes.15,19 For the Rad−Cu−Rad moiety, the strength of magnetic coupling between the Cu(II) ion and coordinated NO group(JRad−Cu) is comparable with those reported in the literature for similar magnetic moieties.20 Field-dependent magnetization was measured at 2.0 K for three compounds (Figures S6−S8). For 2, M value increases with increasing magnetic field and reaches a value of 20.7 Nβ at 70 kOe, which is consistent with the expected saturation value of 21.0 Nβ. In addition, the magnetization value is higher at lower field than the magnetization calculated from the Brillouin function for noncorrelated seven S = 1/2 and two S = 7/2 spins using g = 2.0 and T = 2 K, confirming that the ferromagnetic interactions dominate in the system. For 1 and 3, both M versus H curves show that magnetization rapidly increases with magnetic field at low field and reaches 7.50 and 16.24 Nβ at 7.0 T for complexes 1 and 3, respectively, without clear saturation, indicating the existence of strong magnetic anisotropy in both complexes. The ac susceptibility measurements were carried out under zero dc field to explore spin dynamics for complexes 1 and 3. For 1, clear frequency-dependent out-of-phase (χM″) signals are observed (Figure 6), indicating slow magnetic relaxation behavior. However, no peaks for χM″ are found; thus, the Arrhenius law fitting cannot be performed to extract the energy barrier for the reversal of the magnetization. Alternatively,

presuming that there exists only one characteristic relaxation process, the equation ln(χ″/χ′) = ln(ωτ0) + Ea/kBT proposed by Bartolomé et al. can be employed to roughly estimate the value of the energy barrier.21 The best fit of the experimental data led to the energy barrier Ea/kB ≈ 2.4 K and the relaxation time τ0 ≈ 1.3 × 10−6 s (Figure S9). For 3, the out-of-phase (χM″) susceptibilities clearly exhibit frequency-dependent signals (Figure 6), and unexpectedly the maxima in χM″ signals are observed. The temperaturedependent relaxation time follows the Arrhenius law τ = τ0 exp(Ueff/kBT), and best fitting gives Ueff/kB = 19.5 K and τ0 = 1.12 × 10−7 s (Figure 7). These values are consistent with

Figure 7. ln τ versus 1/T plot for complex 3. The red line is the best fitting result using the Arrhenius law.

values previously observed for Ln-based SMMs.3d,22 Furthermore, Cole−Cole plots for 2.2 and 2.5 K at zero-dc field are constructed from the ac frequency-dependent susceptibility data and fitted to the generalized Debye model to yield α = 0.23 for 2.2 K and 0.22 for 2.5 K (Figure S10), indicating the mild distribution of relaxation times. As seen, when the paramagnetic mononuclear complex unit [Cu(hfac)2(NIT-PhNO2)2] is introduced, complex 3 exhibits a larger energy barrier value than complex 1. This observation E


Article

Inorganic Chemistry should be associated with different structural features. According to the above structural analyses, [Tb(hfac)3(NITPhNO2)2] moieties in 1 and 3 are isomorphous, and both coordination spheres of Tb are D2d; however, there are slight differences in structural parameters, especially the Tb−O−N bond angle (136.8(6)° for 1 and 134.9(5)° for 3). As wellknown, the magnetic anisotropy of lanthanide ion is very sensitive to the coordination environment. A subtle structural change around the Ln will produce a significant impact on the magnetic anisotropy. It has shown that the position of the hydrogen atom in the coordinated water has an important influence on the orientation of the magnetic easy axis in a Dy− DOTA complex.23 The slightly different coordination sphere around Tb in the two compounds will result in different single ion anisotropy, and, accordingly, different magnetic relaxation behaviors. On the other hand, the intermolecular magnetic interactions mainly arise from the short NO−ON contacts, π−π interactions through the phenyl rings of the radicals, and dipolar−dipolar interactions between the Tb ions. The π−π interactions should be close in 1 and 3 due to the similar distances. The weak magnetic coupling resulting from the short NO−ON contact just occurs between two adjacent NO groups, in which the Tb ion is not involved. But the important difference in the shortest Tb···Tb distance is observed for two compounds: 10.354 Å for 1 and 11.360 Å for 3. Thus, the faster QTM will occur in 1, which should reduce the energy barrier. Noticeably, although the [Cu(hfac)2(NIT-PhNO2)2] moieties are paramagnetic, they could not produce an effective random transversal field to affect Tb ions due to the large separations.24 All of these factors result in the much higher energy barrier observed for 3. At this stage, for the present complicated system, it is rather difficult to find which factor is more important or dominant; however, what is clear is that the magnetic relaxation behavior has been improved when the paramagnetic complex molecule is included in the present system.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 21471083) and MOE Innovation Team (IRT13022) of China.

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REFERENCES

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CONCLUSION Three 2p−4f and 2p−3d−4f complexes have been successfully achieved. All three complexes exhibit pseudo-one-dimensional chain structures owing to the π−π stacking between neighboring complex units. The slow magnetic relaxation is observed in two Tb compounds, but complex 3 shows the higher energy barrier. This remarkable discrepancy mainly arises from the slightly different coordination environment on Tb ions and different dipole−dipole interactions between Tb ions.25 In contrast to the commonly used isomorphous diamagnetic matrix to suppress the QTM of lanthanides, this work represents the first example to enhance the anisotropic energy barrier by including the cocrystalline paramagnetic complex species into the single ion Ln system.

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Crystallographic data for 2 (CIF) Crystallographic data for 3 (CIF)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b01915. Additional bond lengths and angles, chart of the relative disposition of adjacent nitronyl nitroxide, packing diagram, and additional magnetization and ac data (PDF) Crystallographic data for 1 (CIF) F


Article

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Tuning Magnetic Relaxation in a Tb-Nitronyl Nitroxide Complex by

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