X-Ray Structure Analysis Online 2021, VOL. 37 25

High-spin octahedral or pseudo-tetrahedral cobalt(II) complexes have been attracting much attentions because they are potential candidates for single-ion magnets (SIMs).1–4 Although many SIMs with a first-row transition-metal have been reported,5 most of them do not exhibits a slow magnetic relaxation behavior in the absence of an external field due to fast relaxation via quantum tunneling. To prepare a zero-field SIM, not only a strong magnetic anisotropy, but also the molecular alignment of SIMs in the crystal, is important. Recently, zero-field SIM behavior in pseudo-tetrahedral cobalt(II) complexes with 2-(2-imidazolinyl)-6-methoxyphenolate (Hmimn–) was reported.4 It was suggested that hydrogen-bonded chain networks of [Co(Hmimn)2] play a crucial role for slow magnetic relaxation in the absence of an external field. To elucidate the correlation between intermolecular magnetic coupling and quantum tunneling of magnetization, partial substitution of a paramagnetic ion by a diamagnetic ion in the crystal is an effective method. For such magnetic dilution experiments, it is important to prepare a diamagnetic analogue which is isomorphic to the SIM. In this study, an isomorphic Zn complex analogue of [Co(Hmimn)2]·CH3OH, [Zn(Hmimn)2]·CH3OH, was prepared and crystallographically characterized (Fig. 1).

The ligand precursor 2-(2-imidazolinyl)-6-methoxyphenol (H2mimn) was synthesized according to a previously reported procedure.4 The title compound was obtained as colorless crystals from a reaction of ZnCl2 (13.6 mg, 0.10 mmol), H2mimn (38.4 mg, 0.20 mmol) and triethylamine (30 μL) in 10 mL methanol. Yield: 38.9 mg (81%).

The crystal data are included in Table 1. X-ray crystallographic data were collected on a Rigaku HyPix AFC diffractometer at 100(2)K. The integrated and scaled data were empirically

2021 © The Japan Society for Analytical Chemistry

Synthesis and Crystal Structure of Bis[2-(2-imidazolinyl)-6-methoxyphenolato]-zinc(II)

Ryoji MITSUHASHI

Institute of Liberal Arts and Science, Kanazawa University, Kakuma, Kanazawa 920–1192, Japan

The crystal structure of a pseudo-tetrahedral zinc(II) complex with a 2-(2-imidazolinyl)-6-methoxy phenolate ligand was determined by X-ray crystallography. The title compound was synthesized by a reaction of ZnCl2 and 2-(2-imidazolinyl)-6-methoxyphenolate in methanol. The compound crystallizes in the monoclinic space group P21/c and Z= 4 with cell parameters a = 14.6485(5)Å, b = 19.2428(6)Å, c = 7.5851(3)Å, β = 104.253(4)°, V = 2072.26(13)Å3. The R1 [I > 2σ(I)] and wR2 (all data) values are 0.0304 and 0.0833, respectively, for all 4597 independent reflections. The title compound was found to take the bis-bidentate coordination mode. Intermolecular hydrogen-bonds were formed between the complexes to form a dimeric structure. Furthermore, hydrogen-bonds were formed between the dimer and a methanal molecule of crystallization to construct one-dimensional chain networks.

(Received December 14, 2020; Accepted January 20, 2021; Published on web May 10, 2021)

E-mail: mitsuhashi@staff.kanazawa-u.ac.jp

Fig. 1　Chemical structure of [Zn(Hmimn)2]·CH3OH.

Table 1　Crystal and experimental data

Chemical formula: C21H26N4O5ZnFormula weight = 479.83T = 100(2)KCrystal system: monoclinic Space group: P21/ca = 14.6485(5)Å b = 19.2428(6)Å β = 104.253(4)°c = 7.5851(3)ÅV = 2072.26(13)Å3 Z = 4Dx = 1.538 g/cm3

Radiation: Mo Kα (λ = 0.71073 Å)μ(Mo Kα) = 1.227 mm–1 F(0 0 0) = 1000Crystal size = 0.18 × 0.07 × 0.07 mm3

No. of reflections collected = 14475No. of independent reflections = 4597 [R(int) = 0.0261]θ range for data collection: 2.557 to 27.483°Data/Restraints/Parameters = 4597/2/293Goodness-of-fit on F2 = 1.063R indices [I > 2σ(I)]: R1 = 0.0304, wR2 = 0.0801R indices (all data): R1 = 0.0402, wR2 = 0.0833(Δ/σ)max = 0.002(Δρ)max = 0.489 eÅ–3 (Δρ)min = –0.461 eÅ–3

Measurement: Rigaku XtaLAB AFC11 diffractometerProgram system: SHELXTLStructure determination: intrinsic phasing methods (SHELXT-2018/2)Refinement: full matrix least-squares (SHELXL-2018/1)CCDC deposition number: 2049851

26 X-Ray Structure Analysis Online 2021, VOL. 37

corrected with the ABSPACK scaling algorithm using CrysAlisPro.6 The initial structure was solved by an intrinsic phasing method with SHELXT-2018,7 and refined using a full-matrix least-squares method on F2 utilizing SHELXL-2018.8 The non-hydrogen atoms were refined anisotropically, and hydrogen atoms were refined using the riding model, except for the N–H atoms, which are located by a difference Fourier map and refined isotroically. Crystallographic data have been deposited with Cambridge Crystallographic Data Centre: Deposition number CCDC-2049851.

Single-crystal X-ray structural analysis indicated that the obtained crystal of [Zn(Hmimn)2]·CH3OH is isomorphous to the cobalt(II) complex. The asymmetric unit consists of a [Zn(Hmimn)2] molecule and a methanol molecule of crystallization (Fig. 2). The structural parameter for a tetrahedral geometry (τ4) of a tetracoordinated complex for [Zn(Hmimn)2], τ4 = 0.81, was close to that of the cobalt(II) analogue (0.80).9 As the value is smaller than 1.00, the coordination geometry of ZnII center is slightly deviated from an ideal tetrahedron. The bond distances around the metal center are nearly identical to the CoII analogue. An intermolecular hydrogen-bond was doubly formed between N–H bonds and phenolate groups of adjacent [Zn(Hmimn)2] molecules to form a centrosymmetric dimer (Table 2 and Fig. 3). Furthermore, the dimers were hydrogen-bonded via a methanol molecule of crystallization that resulted in the formation of 1-dimensional chain networks of dimers. The intradimer and interdimer Zn···Zn distances were 6.1468(4) and 8.6576(5)Å, respectively. The shortest interchain Zn···Zn distance was 7.5630(5)Å, which is much longer than

that within the dimer. These values are consistent with those in the cobalt(II) analogue.

In conclusion, a pseudo-tetrahedral zinc(II) complex [Zn(Hmimn)2]·CH3OH was successfully prepared and characterized. This crystal is isomorphous to a previously reported cobalt(II) analogue, which showed the SIM behavior in the absence of an external field. Since all of the structural parameters are nearly identical, a magnetic dilution experiment will shed light on the interesting zero-field single-ion magnetism.

Acknowledgements

This work was supported by a Grant-in-Aid for Scientific Research No. 19K15525 from MEXT, Japan. The crystallographic measurement was conducted at the Institute of Molecular Science, supported by the Nanotechnology Platform Program (Molecule and Material Synthesis).

Supporting Information

A CIF format file. This material is available free of charge on the Web at http://www.jsac.or.jp/xraystruct/.

References

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4. R. Mitsuhashi, S. Hosoya, T. Suzuki, Y. Sunatsuki, H. Sakiyama, and M. Mikuriya, RSC Adv., 2020, 10, 43472.

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6. Rigaku Oxford Diffraction, CrysAlis Pro1.171.39.43a, 2018, Rigaku Corporation, Oxford, UK.

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2007, 955.

Table 2　Selected geometric parameters (Å, °)

Distance Angle

Zn1–O1 1.9388(13) O1–Zn1–N2 95.17(6)Zn1–O3 1.9312(13) O1–Zn1–N4 118.89(6)Zn1–N2 1.9464(15) O3–Zn1–N2 109.33(6)Zn1–N4 1.9563(15) O3–Zn1–N4 94.60(5)

O1–Zn1–O3 112.07(6)N2–Zn1–N4 127.11(7)

D–H···A D–H H···A D···A D–H···A

N1–H1N···O5i 0.81(2) 2.06(2) 2.846(2) 162(2)N3–H3N···O1ii 0.80(2) 2.18(2) 2.908(2) 152(2)O5–H5A···O3 0.83 1.97 2.753(2) 156.7O5–H5A···O4 0.83 2.44 2.953(2) 121.0

Symmetry codes (i) –x+2, –y+1, –z+1; (ii) –x+1, –y+1, –z+1.Fig. 2　Molecular structure of [Zn(Hmimn)2]·CH3OH (50% probability level).

Fig. 3　One-dimensional chain structure along the a axis constructed by intermolecular hydrogen-bonding interactions in [Zn(Hminm)2]· CH3OH. The intrachain Zn···Zn distance is shown (6.15 and 8.66 Å). The magenta and cyan lines indicate the intermolecular hydrogen-bonds.