Low Spin State Dinuclear FeIII,NiII and CuII Complexes Supported by 1-Amino-2-indanol Schiff Base Derivatives①

CUI Yn-Feng XU Y-Meng SUN Ho YANG Hu ZHANG Jin LI Y-Hong LIU Wei DONG Y-Ping

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Low Spin State Dinuclear FeIII,NiIIand CuIIComplexes Supported by 1-Amino-2-indanol Schiff Base Derivatives①

CUI Yan-Fenga②XU Ya-Menga②SUN HaoaYANG HuabZHANG JinaLI Ya-Honga③LIU Weia③DONG Ya-Pingc

a(215123)b(716000)c(810008)

Four complexes of compositions [Fe2(L1)2] (1), [Ni2(L1)2] (2), [Ni2(L2)2] (3) and [Cu2(L2)2] (4) (H2L1= 1-(((2-hydroxy-2,3-dihydro-1-inden-1-yl)imino)methyl)naphthalen-2-ol, H2L2= 4-((2-hydroxy-2,3-dihydro-1-inden-1-yl)imino)pentan-2-one) were synthesized under solvothermal conditions. The structures of 1～4 were characterized by X-ray single-crystal diffraction analysis. The magnetic properties of these four complexes are investigated. The dc magnetic measurements indicate that the metal ions of 1, 2 and 3 are in the low spin state, revealing the strong ligand field character of 1-amino-2-indanol. This work provides an effective approach to coordination complexes possessing low spin state metal centers.

transition metal, low spin state, Schiff base, magnetic property;

1 INTRODUCTION

The past two decades have witnessed continuous interest in constructing coordination complexes of transition metals supported by Schiff-base ligands due to the wide range of applications and structural features of these compounds[1-11]. Intensive attention has been devoted to the complexes based on 1-amino-2-indanol Schiff base derivatives. The reason is that incorporation of the imine nitrogen with the hydroxyl group of 1-amino-2-indanol could facilitate the chelation and afford the coordination compounds with stable structures[12-22]. Recent advances in this area revealed that the complexes supported by 1-amino-2-indanol Schiff base deriva- tives are active catalysts for many organic reactions. It was found that the FeIII[12]and CrIII[13-15]com- pounds could catalyze the hetero-Diels Alder reactions, molybdenum(VI) dioxo-complexes are active catalysts for the epoxidation of olefins[16], and titanium(IV) compounds could promote both trimethylcyanation of carbonyl compound[17]and the ring-openingpolymerization reactions of lactide[18]. In this regard, complexes supported by 1-amino-2-indanol Schiff base derivatives are in high demand.

We are interested in preparing the dinuclear transition metal complexes supported by 1-amino- 2-indanol Schiff base derivatives and investigating magnetic properties of the synthesized compounds. The driving forces for this interest are listed as follows: (i) The catalytic properties of coordination complexes supported by 1-amino-2-indanol Schiff base derivatives have been extensively studied, whereas the magnetic properties of these com- pounds have not been reported. It is found that most of the reported complexes exhibit four-coordinated square planar geometry, and they may display interesting magnetic properties[12-15]. (ii) The dinu- clear structure motifs are the simplest model for investigating the magnetic interactions between two metal centers. (iii) It is believed that a binuclear compound can be created in a controllable manner by dexterously tuning the structures of the ligands.

With these considerations in mind, we chose 1-(((2-hydroxy-2,3-dihydro-1-inden-1-yl)imino) methyl)naph-thalen-2-ol (H2L1)[18]and 4-((2-hy- droxy-2,3-dihydro-1-inden-1-yl)imino)pentan-2-one (H2L2)[19](Scheme 1) as ligands and conducted their reactions with transition metals. Four com- plexes of compositions [Fe2(L1)2] (1), [Ni2(L1)2] (2), [Ni2(L2)2] (3) and [Cu2(L2)2] (4) have been prepared. The magnetic properties of 1～4 revealed that the metal ions of 1～3 are in low spin states. Herein, we report the syntheses, structures and magnetic properties of 1～4.

Scheme 1. Structures of ligands H2L1(a) and H2L2(b)

2 EXPERIMENTAL

2. 1 Materials and physical measurements

All manipulations were performed under aerobic and solvothermal conditions using reagents and solvents as received. The H2L1ligand (H2L1= 1- (((2-hydroxy-2,3-dihydro-1-inden-1-yl)imino)- methyl)naphthalen-2-ol) was prepared by condensa- tion reaction between 1-amino-2-indanol and 2-hy- droxy-1-naphthaldehyde[18].Similarly, the H2L2ligand (H2L2= 4-((2-hydroxy-2,3-dihydro-1- inden-1-yl)imino)pentan-2-one) was synthesized via condensation reactions.

The C, H and N microanalyses were carried out with a Carlo-Erba EA1110 CHNO-S elemental analyser. FT-IR spectra were recorded from KBr pellets in the range of 400～4000 cm-1on a Nicolet MagNa-IR 500 spectrometer. Powder X-ray dif- fraction (PXRD) was recorded on a Rigaku D/Max- 2500 diffractometer at 40 kV and 100 Ma with a Cu-target tube and a graphite monochromator. Variable-temperature dc magnetic susceptibility data were collected using a Quantum Design MPMS-7 SQUID magnetometer.

2. 2 Syntheses of complexes 1～4

2. 2. 1 Synthesis of [Fe2(L1)2] (1)

A mixture of H2L1(0.0242 g, 0.08 mmol), FeCl3·6H2O (0.0216 g, 0.08 mmol) in MeOH (0.4 mL) solution, CH3COONH4(0.0062 g, 0.08 mmol) in MeOH (0.4 mL) solution, and MeOH (2 mL) was sealed in a Pyrex-tube (8 mL). The tube was heated at 110 °C for 3 days under autogenous pressure. Cooling of the resultant solution to room tem- perature gave black rod-like crystals. The crystals were collected by filtration, washed with MeOH (2 mL) and dried in air. Yield: 0.0223 g (58% based on the ligand). Anal. Calcd. (%) for C80H60Cl4Fe4N4O8: C, 61.68; H, 3.85; N, 3.57. Found (%): C, 60.94; H, 3.62; N, 3.46. Selected IR data for 1 (KBr, cm?1): 2900 (w), 1616 (s), 1474 (s), 1246 (s), 1182 (w), 1091 (m), 777 (s), 741 (s).

2. 2. 2 Synthesis of [Ni2(L1)2] (2)

A mixture of H2L1(0.0227 g, 0.075 mmol), Ni(CH3COO)2·2H2O (0.0159 g, 0.075 mmol), and MeOH (2 mL) was sealed in a Pyrex-tube (8 mL). The tube was heated at 110 °C for 2 days under autogenous pressure. Cooling of the resultant solu- tion to room temperature gave brown crystals. The crystals were collected by filtration, washed with MeOH (2 mL) and dried in air. Yield: 0.0357 g (86% based on the ligand). Anal. Calcd. (%) forC40H30N2Ni2O4: C, 66.72; H, 4.20; N, 3.89. Found (%): C, 66.13; H, 3.92; N, 3.57. Selected IR data for 2 (KBr, cm?1): 3019 (w), 2909 (w), 1610 (s), 1535 (s), 1213 (s), 1121 (w), 998 (m), 825 (s), 740 (s).

2. 2. 3 Synthesis of [Ni2(L2)2] (3)

A mixture of H2L2(0.0231 g, 0.1 mmol), Ni(CH3COO)2·2H2O (0.0212 g, 0.1 mmol), EtOH (1 mL) and CH3CN (0.5 mL) was sealed in a Pyrex-tube (8 mL). The tube was heated at 100 °C for 3 days under autogenous pressure. Cooling of the resultant solution to room temperature gave brown rod-like crystals. The crystals were collected by filtration, washed with EtOH (2 mL) and dried in air. Yield: 0.0196 g (34% based on the ligand). Anal. Calcd. (%) for C28H30N2O4Ni2: C, 58.39; H, 5.25; N, 4.86. Found (%): C, 57.95; H, 5.10; N, 4.56. Selected IR data for 3 (KBr, cm?1): 2925 (s), 1584 (m), 1514 (s), 1408 (s), 1368 (s), 1310 (s), 1264 (w), 1170 (m), 997 (m), 896 (m), 748 (s).

2.2.4 Synthesis of [Cu2(L2)2] (4)

A mixture of H2L2(0.0231 g, 0.1 mmol), Cu(CH3COO)2·H2O (0.0199 g, 0.1 mmol), and EtOH (2 mL) was sealed in a Pyrex-tube (8 mL). The tube was heated at 100 °C for 3 days under autogenous pressure. Cooling of the resultant solution to room temperature gave dark blue stripe crystals. The crystals were collected by filtration, washed with EtOH (2 mL) and dried in air. Yield: 0.0263 g (45% based on the ligand). Anal. Calcd. (%) forC28H30N2O4Cu2: C, 57.42; H, 5.16; N, 4.78. Found (%): C, 57.10; H, 5.10; N, 4.46. Selected IR data for 4 (KBr, cm?1): 2907 (m), 1587 (s), 1504 (s), 1402 (s), 1121 (w), 1049 (m), 780 (s).

2. 3 Structure determination

The data collections for 1～4 were carried out on a Bruker Smart ApexII diffractometer equipped with a graphite-monochromator utilizing Moradiation (= 0.71073) with an-2scan mode. The structures were solved by direct methods using SHELXS-97 and refined on2using full-matrix least-squares with SHELXL-97[23]. All non-hydro- gen atoms were refined anisotropically. The collec- ted crystal data for the four structures are shown in Table 1. Selected bond lengths and bond angles of complexes 1～4 are listed in Table 2.

Table 1. Crystallographic Data and Structure Refinement Information for 1～4

Table 2. Selected Bond Lengths (?) and Bond Angles (°) for 1～4

3 RESULTS AND DISCUSSION

3. 1 Structural description

3. 1. 1 Structure of 1

Single-crystal X-ray diffraction analysis indicates that complex 1 crystallizes in the monoclinic space group21. Bond valence calculations (Table S1)show that two Fe ions of 1 are in 3+ valence states[24-27]. This structure contains two identical but independent molecular units (Fig. 1). As Shown in Fig. 2, each FeIIIatom is coordinated by two bridging deprotonated hydroxyl oxygen atoms originated from the indanol moiety of two H2L1ligands (Fig. 2), one imino nitrogen atom, one hydroxyl oxygen atom from the naphthalen moiety of H2L1ligand and one terminal Cl-ion. Thus, both two FeIIIions display NO2Cl surrounded square- pyramidal geometry. The bridging oxygen atoms do not bind symmetrically to the two FeIIIions (, Fe(1)–O(4) 1.950(12) ?, Fe(1)–O(2) 1.994(10) ?, Fe(2)–O(4) 1.964(11) ?, Fe(2)–O(2) 1.985(11) ?), demonstrating the nonflexibility nature of the H2L1ligand.

As calculated with the PLATON program, there are weak hydrogen bonds between the carbon atom of H2L1ligand and Cl-atoms (C(3)–H(3)×××Cl(2) 3.36(2) ?, C(46)–H(46)×××Cl(3) 3.67(2) ?, C(62)– H(62)×××Cl(2) 3.657(16) ?, C(72)–H(72)×××Cl(3)3.694(16) ?; Table 3). The adjacent units are further joined together through hydrogen bonding interaction of C–H×××Cl to generate a layer structure. The layers are further linked together by the other hydrogen bonds to create a 3-D framework (Fig. 3).

Fig. 1. ORTEP view with 30% probability level of 1.The H atoms were omitted and the gray C atoms were not labeled for clarity

Fig. 2. View of the binuclear structure and the coordination environment of FeIIIions in 1

Fig. 3. 3-D network structure of 1 created by hydrogen bonding interactions

Table 3. Hydrogen Bond Lengths (?) and Bond Angles (°) for 1

Symmetry codes: (a) –, 1/2+, –; (b) –1+,,; (c) 1+, 1+,; (d) 2–, 1/2+, 1–

3. 1. 2 Structure of 2

Single-crystal X-ray diffraction reveals that com- plex 2 crystallizes in the monoclinic space group21(Fig. 4). The dinuclear complex 2 is assembled by two doubly deprotonated ligands and two NiIIions. Each ligand chelates to two NiIIions in a2:1:2:1mode. Two NiIIions are bridged by two alkoxo oxygen atoms originated from two ligand sets. Similarly, the bridging oxygen atoms do not bind symmetrically to the two NiIIions (, Ni(1)–O(3) 1.882(3) ?, Ni(1)–O(2) 1.843(3) ?; Ni(2)–O(3) 1.852(3) ?, Ni(2)–O(2) 1.874(3) ?). The four-coordinated NiIIcenter adopts a distorted square plane geometry. The 2,3-dihydro-1-indene rings of the two doubly-deprotonated ligands display ageometry with respect to the Ni2O2ring.

Fig. 4. View of the binuclear structure and the coordination environment of NiIIions in 2. The H atoms are omitted for clarity

No typical hydrogen bonds were determined in complex 2, whilethe six-membered ring of H2L1becomes an electron-poorsystem, which is easy to form C–H···stacking interactions. Weak C–H···interactions (the distances are 2.8448(7) and 3.2751(5) ?, respectively, as shown in Fig. 5) in theaxis occurred. Running along the direction of,athree-dimensional structure of 2 is formed by the mode of AAA stacking (Fig. 6).

Fig. 5. C–H…interactions of complex 2

Fig. 6. 3-D network structure of 2 created by C–H…interactions (Partial bonds are omitted for clarity)

3. 1. 3 Structures of 3 and 4

Single-crystal X-ray diffraction reveals that com- plexes 3 and 4 are isomorphous and crystallize in the monoclinic space group21. Therefore, as a representative, only the structure of 3 is discussed in detail (Fig. 7). Compound 3 is dinuclear and two NiIIions are bridged by two alkoxo oxygen atoms. The alkoxo oxygen atom of the doubly deproto- nated ligand coordinatesto the ketone oxygen atom andto the imine nitrogen atom of its own ligand set. The coordination geometry of NiIIion is well described as a distorted square. The distance between two NiIIions is 2.890 ?. The bond lengths of Ni(1)–O(1), Ni(1)–O(2), Ni(1)–N(1) and Ni(1)–O(3) are 1.814(3), 1.871(3), 1.830(3) and 1.847(3) ?, respectively. The bond angles of O(3)–Ni(1)–O(2) and O(2)–Ni(2)–O(3) are 94.3(5) and 79.84(12)°, respectively. The variation of bond lengths and bond angles reveals that the rigidity of the ligand influences the structure of 3.

The weak C–H···interactions between the molecules (the distance is 3.580～3.807 ?) are found (Fig. 8). Running the direction of, a three-dimensional structure of 3 is formed by the mode of AAA stacking (Fig. 9).

Fig. 7. Molecular structure of 3 with H atomsomitted for clarity

Fig. 8. C–H…interactions of complex 3

Fig. 9. Packing diagram of compound 3 shown by C–H…π interactions

Complexes 1～4 join a very small family of coor- dination compounds supported by 1-amino-2- indanol Schiff base derivatives[12-22, 28]. It is worth to mention that complex 1 is the second reported FeIIIcompound supported by 1-amino-2-indanol Schiff base derivatives[12].

3. 2 Magnetic properties of 1～4

Variable-temperature dc magnetic susceptibility data were recorded for 1～4 at the magnetic field of 1000 Oe in the temperature range of 2～300 K. TheχT value of 1 at 300 K is 1.57 cm3·mol-1K (Fig. 10), which is much smaller than the spin-only value of 8.75 cm3·mol-1K expected for two= 5/2 uncoupled spins, and also larger than the value of 0.75 for two= 1/2 uncoupled spins.However, this value is close to the summed data of magnetically isolated one= 1/2 FeIIIcenter and another= 3/2 FeIIIion. This value demonstrated that the two FeIIIions are in the low spin state. As the temperature is lowered, theχT value decreases gradually to a minimum value of 0.015 cm3·mol-1·K at 2 K. This behavior is indicative of the presence of antiferro- magnetic exchange interactions between the metal ions.

Fig. 10. Temperature dependence of magnetic susceptibilities in the form of χT.for 1 at 1 kOe

We tried to fit the magnetic data by assuming that the two FeIIIions are= 1/2,= 3/2 and= 5/2, respectively. Unfortunately, no satisfactory fit result was obtained. As theχT value of 1 is much smaller than that of two= 5/2 uncoupled spins, we conclued that the H2L1ligand possesses strong ligand field character.

Materials presenting a stable and reversible switch of physical properties have attracted intense atten- tion due to their potential industrial applica- tions[29-31]. Therefore the design of metal complexes showing rare spin states, which may undergo crossover from one spin state to another and lead to a major change of magnetic and optical properties, is of fundamental interest. The low spin state nature of 1 demonstrates its potential applications in the wide range of area. This work also provides an efficient approach towards low spin state FeIIIcomplexes.

TheχT value of 2 at 300 K is 0.24 cm3·mol-1·K (Fig. S11), which is much smaller than the spin-only value of 2.00 cm3·mol-1·K expected for two= 1 uncoupled spins. With the increase of temperature,χT values increase linearly with the temperature, indicating that complex 2 is diamagnetic. Thus, the NiIIions in 2 are in low spin state.

It is reported that the spin state of8nickel(II) ion is coordination number dependent. When the coordination geometry is square planar, it is in low spin state; whereas the octahedron configuration often results in high spin. Our results are consistent with those of the literature report compounds[32-35].

The magnetic property of 3 is quite similar with that of 2 (Fig. S10), which demonstrates that complex 3 is a low spin state compound.

TheχT value of 4 at 300 K is 0.79 cm3·mol-1·K (Fig. 12), which is close to the spin-only value of 0.75 cm3·mol-1·K expected for two= 1/2 uncoupled spins. As the temperature is lowered, theχT value increases gradually to a maximum value of 1.10 cm3·mol-1·K at 6 K. This behavior is indicative of the presence of ferromagnetic exchange interactions between the metal ions.

The two CuIIions are equivalent and the magnetic data were fit to the 1model of H = –2J??. A good fit was obtained (20～220 K) and the parameters of= 2.05 and= 25.08 cm-1were generated. The positivevalue proves the ferro- magnetic exchange interactions.

Fig. 11. Temperature dependence of magnetic susceptibilities in the form of χTfor 4 at 1 kOe. The red solid line corresponds to the best fit of the magnetic data

4 CONCLUSION

Four complexes supported by 1-amino-2-indanol Schiff base derivatives (H2L1and H2L2) were synthesized. The dc magnetic property measure- ments indicate that the metal centers in 1～3 are in low spin state, revealing the strong ligand field character of 1-amino-2-indanol. This work also provides an efficient strategy to prepare coor- dination complexes with low spin state.

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13 November 2017;

13 June 2018 (CCDC 1572437 for 1, 1572438 for 2, 1572439 for 3 and 1572440 for 4)

the National Natural Science Foundation of China (21272167), Natural Science Foundation of Jiangsu Province (BK20171213), the Innovation of Graduate Student Training Project of Jiangsu Province (KYLX16_0109),and the Priority Academic Program Development of Jiangsu Higher Education Institution

② These two authors contribute equally to this work

Born in 1968, professor, majoring in organometallic chemistry. E-mail: liyahong@suda.edu.cn and weiliu@suda.edu.cn

10.14102/j.cnki.0254-5861.2011-1889