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• The interest in switchable bistable spin crossover (SCO) materials has surged in recent years. These materials, typically incorporate 3d transition metal ions with a d⁴-d⁷ electron configuration have the potential to induce significant changes in a variety of physical properties, including magnetism, conductivity, dielectricity, and so on, opening up exciting possibilities for applications in areas such as sensors, displays, and information storage device^[1-3].

  Although most research efforts have primarily focused on Fe^Ⅱ and Fe^Ⅲ SCO complexes^[4-10], the investigation of Co^Ⅱ SCO complexes has also emerged as an area of great interest^[11-13]. In the case of Co^Ⅱ in an octahedral geometry, the spin state can be interconverted between the low-spin (LS) state (t_2g⁶e_g¹, S=1/2, ²E) and the high-spin (HS) state (t_2g⁵e_g², S=3/2, ⁴T₁) through the transfer of one electron. This process results in relatively small changes in the coordination bond distances, typically about 0.010 nm, which is smaller compared to the changes observed in Fe^Ⅱ and Fe^Ⅲ SCO complexes (0.020 and 0.015 nm, respectively). Consequently, Co^Ⅱ complexes typically exhibit gradual, incomplete, and non-hysteretic SCO behaviors^[14-18].

  To enhance the cooperativity of SCO complexes, several strategies have been employed to deliberately incorporate a range of intermolecular interactions. These interactions include the integration of coordination bonds within extended frameworks, as well as the utilization of supramolecular interactions such as hydrogen bonding, halogen bonding, π-π interactions, and so on^[19-20]. Amongst these various interactions, hydrogen bonds have been established to exert a significant influence on the SCO properties, primarily by tuning the ligand field strength and the cooperative effect^[21-22]. For instance, hydrogen bonds have demonstrated crucial roles in enhancing the cooperativity within numerous SCO complexes, particularly those exhibiting wide hysteresis loops, such as the [Fe(L)(HIm)₂] complexes where L presents a ligand with an N₂O₂ pocket^[23], the famous 1D Fe^Ⅱ-1, 2, 4-triazole coordination polymers^[24], as well as the 2D/3D Hofmann-type frameworks^[25-26].

  In recent studies, both our group and others have focused on the utilization and modification of organosulfonate anions to introduce and manipulate hydrogen bond interactions within SCO materials^[27-34]. These anions, characterized by the presence of —SO₃ groups, not only exhibit remarkable hydrogen bond-accepting capabilities but also offer a diverse range of derivatives with different sizes and shapes. Consequently, they hold promise for yielding various structures with diverse hydrogen-bond patterns. For instance, we were able to finely tune the SCO properties, such as the temperatures and the cooperativity of the SCO transition, of a series of Fe^Ⅱ SCO complexes by using different organosulfonates^[30-31]. Moreover, our group also employed organosulfonates in the preparation of Co^Ⅱ complexes, thereby yielding a number of interesting results. By utilizing either the 4-(phenylamino)benzenesulfonate (DPAS^-) anion or a benzene-1, 3-disulfonic anion (BDS^2-), two Co^Ⅱ complexes were synthesized and characterized as [Co(Brphtpy)₂](DPAS)₂·DMF·2H₂O and [Co(Brphtpy)₂][BDS]·2H₂O (Brphtpy=4′-(4-bromophenyl)-2, 2′∶6′, 2″-terpyridine). Notably, we have achieved reversible on-off switching of both SCO and SMM behaviors in the former compound, as well as reversible on-off switching of the hysteretic SCO property in the latter compound, both via a crystal-to-crystal dehydration-rehydration process^[32]. Moreover, Shao et al.^[33-34] recently found a significant dependence of the magnetic properties and the proton conductivity on the organosulfonates in similar [Co(Brphtpy)₂]²⁺ SCO complexes.

  Following our previous studies, we aim to synthesize new Co^Ⅱ SCO complexes featuring the [Co(pytpy)₂]²⁺ cation (pytpy=4′-(4-pyridyl)-2, 2′∶6′, 2″-terpyridine), along with two organosulfonates as the counter anions (2-NH₂-1-NS^- and 4-NH₂-1-NS^-, Scheme 1). The ligand pytpy was chosen as the focus of this study because it not only incorporates the terpyridine moiety but also features a terminal pyridine group, enabling intermolecular hydrogen bonding and π-π interactions. To modulate the supramolecular interactions, two naphthalenesulfonate anions with NH₂ and SO₃ groups in different positions of the naphthalene ring were selected. Herein, we present the syntheses, structures, and magnetic properties of two Co^Ⅱ complexes [Co(pytpy)₂](2-NH₂-1-NS)₂·MeOH·H₂O (1) and [Co(pytpy)₂](4-NH₂-1-NS)₂·H₂O (2).

  Scheme 1

  

  Scheme 1.  Structures of the ligand pytpy and two organosulfonate anions

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  1.   Experimental

  1.1   Synthesis of complexes 1 and 2

  All experimental procedures were performed under ambient aerobic conditions. All reagents utilized in this study were acquired from commercial sources and used as received without further purification.

  CoCl₂·6H₂O (1 mmol, 237 mg) and pytpy (2 mmol, 620 mg) were dissolved in 20 mL of MeOH, and the solution was heated at reflux for 2 h. Subsequently, the resulting dark red solution was allowed to cool, followed by the addition of sodium 2-amino-1-naphthalenesulfonate (490 mg, 2 mmol) dissolved in H₂O (10 mL) under vigorous stirring. The resulting mixture was then filtered and left undisturbed at room temperature for slow evaporation. After a week, dark-red single crystals suitable for single-crystal X-ray diffraction were obtained. The crystals were filtered, washed with a small amount of methanol, and dried in the air. Yield: 75% (based on Co^Ⅱ). The synthesis of complex 2 followed a similar procedure to that of complex 1, with the exception that 2 mmol of sodium 4-amino-1-naphthalenesulfonate was employed for complex 2. The yield is around 70%. Elemental analysis(%) calculated for 1 (C₆₁H₅₀CoN₁₀O₈S₂): C, 62.40; H, 4.29; N, 11.93. Found(%): C, 62.33; H, 4.21; N, 12.01. Elemental analysis(%) calculated for 2 (C₆₀H₄₆CoN₁₀O₇S₂): C, 63.10; H, 4.06; N, 12.26. Found(%): C, 63.05; H, 4.12; N, 12.18. Selected FTIR (ATR, cm^-1) for 1: 3 286(s), 3 040(s), 1 596(s), 1 430(s), 1 403(s), 1 177(s), 1 034(s), 820(s), 787(s), 621(s). Selected FTIR (ATR, cm^-1) for 2: 3 259(s), 3 058(s), 1 594(s), 1 468(s), 1 402(s), 1 151(s), 1 040(s), 831(s), 757(s), 622(s).

  1.2   Physical measurements

  Elemental analyses for C, H, and N were conducted using an Elementar Vario MICRO analyzer. Powder X-ray diffraction (PXRD) data were recorded on a Bruker D8 Advance diffractometer equipped with a Cu Kα X-ray source (λ=0.154 06 nm) operated at 40 kV and 40 mA with the scanning range changing from 5° to 50°. Thermogravimetric analysis (TGA) measurements were performed in Al₂O₃ crucibles using a PerkinElmer Thermal Gravimetric Analysis instrument in a temperature range of 30-600 ℃ under N₂ flow at a heating rate of 10 ℃·min^-1. The ATR FTIR absorption spectra were recorded at room temperature in a range of 4 000-400 cm^-1 using an FT-IR Bruker model Vertex 70 V spectrometer (Germany). A Platinum‑ATR (Bruker) accessory, equipped with a pure diamond crystal, was utilized for the ATR measurement. Magnetic measurements were performed under a DC field of 1 000 Oe with a Quantum Design VSM magnetometer. Pascal′s constants were employed to estimate the diamagnetic correction for the complex and adjust the calculated molar susceptibility values.

  1.3   X-ray crystallography

  Complexes 1 and 2 were analyzed using single-crystal X-ray crystallography on a Bruker APEX-Ⅱ diffractometer, which was equipped with a CCD area detector. The experiments were conducted using either Mo Kα radiation (λ=0.071 073 nm) for 1 or Ga Kα radiation (λ=0.134 139 nm) for 2. The unit cell parameters and data collection were performed using the APEX Ⅱ program. Subsequently, the data were integrated and corrected for Lorentz and polarization effects employing SAINT. Absorption corrections were applied using SADABS. The structures were solved using direct methods and refined using the full-matrix least-squares method based on F ² with the crystallographic software package SHELXTL and OLEX 2. The refinement included anisotropic refinement of all non-hydrogen atoms, while hydrogen atoms associated with the organic ligands were refined as riding on their respective non-hydrogen atoms. Table 1 provides the details regarding the crystal data and structure refinement parameters. In addition, more specific structural parameters, such as selected bond lengths, continuous shape measure values (CShMs, calculated using SHAPE2.0 program), octahedral distortion parameters (∑ and Θ, determined using the OctaDisc software), and other relevant data (vide infra) are listed in Table 2 and 3.

  Table 1

  

  Table 1.  Crystal data and refinement parameters for complexes 1 and 2

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  Parameter	1	2
  Empirical formula	C61H50CoN10O8S2	C60H46CoN10O7S2
  Formula weight	1 174.16	1 142.12
  Temperature/K	193	193
  Crystal system	Orthorhombic	Orthorhombic
  Space group	P212121	Fdd2
  a/nm	0.904 23(4)	2.355 74(6)
  b/nm	1.382 18(6)	4.878 38(14)
  c/nm	4.285 89(17)	0.901 97(2)
  Volume/nm3	5.356 5(4)	10.365 6(5)
  Z	4	8
  Dc/(g·cm-3)	1.456	1.464
  F(000)	2 436	4 728
  2θ range/(°)	3.51-55.14	6.30-107.88
  Index ranges	-11 ≤ h ≤ 11, -17 ≤ k ≤ 14, -55 ≤ l ≤ 55	-28 ≤ h ≤ 26, -58 ≤ k ≤ 56, -10 ≤ l ≤ 10
  Reflection collected	50 706	27 494
  Independent reflection	12 347	4 719
  Rint	0.050 3	0.053 6
  Data, restraint, number of parameters	12 347, 77, 747	4 719, 2, 367
  Goodness-of-fit on F 2	1.036	1.040
  Final R indexes [I≥2σ(I)]	R1=0.054 4, wR2=0.137 6	R1=0.028 8, wR2=0.073 9
  Final R indexes (all data)	R1=0.073 7, wR2=0.148 4	R1=0.029 9, wR2=0.074 5
  (Δρ)max, (Δρ)min/(e·nm-3)	590, -600	240, -570

  Table 2

  

  Table 2.  Selected bond lengths (nm) and structural parameters for complexes 1 and 2

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  Bond	1	2
  Co1—N1	0.211 9(4)	0.215 7(3)
  Co1—N3	0.212 3(4)	0.215 2(3)
  Co1—N4	0.204 3(5)
  Co1—N6	0.203 2(5)
  Co—Nequatorial	0.207 9	0.215 4
  Co1—N2	0.192 6(3)	0.204 5(2)
  Co1—N5	0.189 3(4)
  Co—Naxial	0.190 9	0.204 5
  Co—Nav	0.202 3	0.211 8

  Table 3

  

  Table 3.  Structural parameters for complexes 1 and 2

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  Parameter	1	2
  CShM	2.477	4.609
  ∑a	89.75	146.51
  Θb	309.43	445.27
  a∑ is the sum of the deviation from 90° of the 12 cis angles of the CoN6 octahedron; bΘ is the sum of the deviation from 60° of the 24 trigonal angles of the projection of the CoN6 octahedron onto the trigonal faces.

  2.   Results and discussion

  2.1   Description of the crystal structures

  Single crystal X-ray analyses for complexes 1 and 2 were conducted at 193 K. Complex 1 crystallizes in the orthorhombic space group P2₁2₁2₁ (Z=4), while complex 2 crystallizes in the orthorhombic space group Fdd2 (Z=8). As depicted in Fig. 1, the asymmetric unit of complex 1 consists of one dicationic unit [Co(pytpy)₂]²⁺, two 2-NH₂-1-NS^- anions, one water molecule, and one MeOH molecule. However, in the case of complex 2, the asymmetric unit comprises half of the cobalt center positioned at a special position, one pytpy ligand, one 4-NH₂-1-NS^- anion, and half of the water molecule. In each complex, the cobalt center adopts a distorted octahedral CoN₆ environment, where the six nitrogen atoms are from two pytpy ligands in a bis- meridional fashion. The two axial positions of the Co^Ⅱ ion are occupied by the central pyridine nitrogen donor atoms of pytpy, while the remaining equatorial positions are occupied by the other distal pyridine nitrogen donor atoms. Notably, the CoN₆ octahedra in both complexes exhibit axial compression, with the Co—N_axial bonds being significantly shorter than the Co—N_equatorial bonds (Fig. 1 and Table 2), as also observed in other Co^Ⅱ complexes with two terpyridine-type ligands^[35-36].

  Figure 1

  

  Figure 1.  Asymmetric units for complexes 1 (a) and 2 (b) at 193 k

  Hydrogen atoms and solvent molecules are omitted for clarity.

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  At 193 K, the average Co—N bond distances for the axial (Co—N_axial) and equatorial (Co—N_equatorial) positions, as well as for all the Co—N bonds (Co—N_av) are 0.190 9, 0.207 9, and 0.202 3 nm for complex 1, and 0.204 5, 0.215 4, and 0.211 8 nm for complex 2, respectively (Table 2). The Co—N bond distances observed in complex 1 are consistent with the expected range for LS Co^Ⅱ complexes, especially those containing terpyridine-based ligands in an octahedral coordination geometry^[37-38]. On the other hand, the Co—N bond distances in complex 2 are significantly larger, which aligns with the typical values of HS Co^Ⅱ centers^[39-40].

  In particular, the distortion of the coordination sphere in 6-coordinate SCO complexes is commonly evaluated using the structural parameters ∑ and Θ. The parameter ∑ represents the sum of the deviations from 90° for the 12 cis N—Co—N angles within the Co^Ⅱ octahedron, while Θ is the sum of the deviations from 60° for the 24 trigonal angles of the projection of the CoN₆ octahedron onto the trigonal faces. As shown in Table 3, the values of ∑ and Θ at 193 K were calculated to be 89.75° and 309.43° for 1, and 146.51° and 445.27° for 2, respectively. These values indicate that the Co^Ⅱ center in complex 2 exhibits a significantly more distorted N₆ coordination sphere compared to complex 1. In addition, these values are approximately consistent with those observed in the LS and HS states of Co^Ⅱ complexes, providing additional evidence supporting the LS state of complex 1 and the HS state of complex 2 at 193 K^[41-42].

  2.2   PXRD and TGA

  Before conducting physical measurements, PXRD was performed on complexes 1 and 2 (Fig. 2). The experimental PXRD patterns align well with the simulated patterns based on the single crystal data, indicating the phase purity of these complexes. Moreover, the thermal stability of complexes 1 and 2 was assessed using TGA (Fig. 3). Complex 1 exhibited a gradual stepwise weight loss (4.09%) in a temperature range of 50-130 ℃, corresponding to the release of one H₂O molecule and one MeOH molecule per formula (Calcd. 4.26%). Then, complex 1 remained stable up to 255 ℃, beyond which it began to decompose. For complex 2, the TGA curve revealed the loss of water molecules in a temperature range of 68-140 ℃. The observed weight loss of 1.58% closely agrees with the theoretical loss of 1.57%. Despite the high stability of the desolvated sample, the crystal structures could not be determined due to the loss of crystallinity during the desolvation process.

  Figure 2

  

  Figure 2.  Experiment and simulated PXRD patterns of complexes 1 (a) and 2 (b)

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  Figure 3

  

  Figure 3.  TGA curves for complexes 1 (a) and 2 (b)

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  2.3   Magnetic property

  The variable-temperature magnetic susceptibilities of complexes 1 and 2 were measured on the crystal samples using a DC field of 1 kOe. The temperature was varied following the sequence of 300 → 5 → 400 → 5 K for complex 1 and 300 → 5 → 300 K for complex 2, respectively (Fig. 4). At room temperature, the measured χ_MT value for complex 1 was 1.57 cm³·mol^-1·K, which was significantly higher than the expected spin-only value for an octahedral Co^Ⅱ ion in the LS state (S=1/2, g=2.0, χ_MT=0.375 cm³·mol^-1·K), but lower than the expected spin-only value for the octahedral Co^Ⅱ ion in the HS state (S=3/2, g=2.0, χ_MT=1.875 cm³·mol^-1·K). In fact, due to magnetic anisotropy and a significant orbital contribution, the χ_MT value for the HS state octahedral Co^Ⅱ ion varies from 1.9 to 3.5 cm³·mol^-1·K^{[11, 43-45]}. Therefore, we believed that at 300 K, complex 1 has a mixed spin state containing both LS and HS states. Upon cooling, the χ_MT value gradually decreased to 0.45 cm³·mol^-1·K at 5 K, corresponding to the LS Co^Ⅱ state. When the temperature was increased from 5 to 300 K, identical magnetic behaviors were observed, suggesting that complex 1 exhibits gradual SCO behavior below 300 K without any hysteresis effect. As indicated by the TGA data, the sample began to desolvate above 323 K. Therefore, to investigate the SCO behavior of the desolvated sample of complex 1, it was heated at 400 K in the dynamic vacuum of SQUID for 1 h. Subsequent cooling measurements revealed a gradual SCO behavior for the desolvated complex 1. The transition temperature T_1/2 of the desolvated complex 1 was found to be slightly higher than the solvated complex. Similar behavior has been observed in many SCO complexes, indicating the influence of the solvents on the SCO behavior of complex 1^[46-47].

  Figure 4

  

  Figure 4.  χ_M^T vs T plots for complexes 1 (a) and 2 (b)

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  Compared to complex 1, complex 2 was found to be in the HS state above 5 K, which is in line with its crystal structure result. The χ_MT value decreased from 1.99 cm³·mol^-1·K at 300 K to 1.25 cm³·mol^-1·K at 5 K. Upon warming from 5 to 300 K, the χ_MT curve overlaps with the one upon cooling (Fig. 4b). The behavior observed for complex 2 is consistent with that commonly observed in other HS Co^Ⅱ complexes with a spin- orbit coupling and/or orbital angular momentum contribution^[48].

  2.4   Magneto-structural relationships

  As demonstrated in multiple studies, supramolecular interactions involving the dicationic [Co(L)]²⁺ unit, associated counteranions, and solvent molecules play a significant role in determining the SCO properties of Co^Ⅱ complexes containing the tridentate terpyridine-type ligands^{[36, 49]}. To gain a deeper understanding of the magneto-structural relationship in complexes 1 and 2, the supramolecular interactions within these complexes were examined. As expected, a multitude of supramolecular interactions can be found in both complexes, as depicted in Fig. 5-6 and Table 4.

  Figure 5

  

  Figure 5.  (a) Hydrogen-bonds and π-π interaction (centroid-centroid: 0.363 7 nm) in complex 1; (b) Crystal packing of 1

  Symmetry code: A: 2-x, 0.5+y, 1.5-z; Red dashed lines represent hydrogen bonds, and blue dashed lines represent π-π interactions between the pyridyl groups and the naphthalene ring.

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  Figure 6

  

  Figure 6.  (a) Hydrogen-bonded 1D chain along the a-axis formed by [Co(pytpy)₂]²⁺ cations and water molecules; (b) Hydrogen-bonded 2D layer of 4-NH₂-1-NS^- anions; (c) Crystal packing of complex 2

  Red dashed lines represent hydrogen bonds.

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  Table 4

  

  Table 4.  Intermolecular interaction parameters for complexes 1 and 2

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  D—H…A	d(D—H) / nm	d(H…A) / nm	d(D…A) / nm	∠DHA / (°)
  		1
  N9—H9B…N7	0.098	0.206	0.303 0(6)	169.8
  C32—H32…O1A	0.095	0.224	0.311 4(7)	152.5
  O8—H8A…O5	0.085	0.204	0.280 5(8)	149.4
  O8—H8B…O4A	0.085	0.217	0.282 9(10)	133.6
  C27—H27…O2	0.095	0.223	0.317 4(7)	174.3
  N10—H10B…O7	0.104	0.208	0.296 5(9)	141.6
  O7—H7A…O1	0.084	0.224	0.302 2(9)	155.9
  		2
  N5—H5A…O1	0.089	0.214	0.291 5(4)	145.6
  N5—H5B…O3	0.089	0.227	0.306 6(4)	148.6
  O4—H4A…N4	0.087	0.220	0.287 8(4)	134.9
  Symmetry code: A: 2-x, 0.5+y, 1.5-z.

  In complex 1, as shown in Fig. 5a, the 2-NH₂-1-NS^- anions have rich hydrogen bonding interactions with solvent molecules (O8…O5 0.280 5 nm, O8…O4 0.282 9 nm, O7…O1 0.302 2 nm, and N10…O7 0.296 5 nm) and the pytpy ligand (N9…N7 0.303 0 nm, C32…O1 0.311 4 nm, and C27…O2 0.317 4 nm). In addition, a π-π interaction is observed between the pyridyl group and the naphthalene ring. These hydrogen bonds and π-π interaction contribute to the formation of the packing structure, connecting the [Co(pytpy)₂]²⁺ cations, 2-NH₂-1-NS^- anions, and neighboring solvent molecules, as depicted in Fig. 5b. Compared to the reported complex [Co^Ⅱ(pytpy)₂](PF₆)₂·2MeOH^[42] with the abrupt hysteretic SCO behavior, the absence of significant π-π interactions between the pyridine rings of the adjacent cationic ligands might be responsible for the gradual rather than abrupt SCO behavior in complex 1.

  Different from complex 1, hydrogen bonding interactions in complex 2 are observed mainly among the 4-NH₂-1-NS^- anions (N5…O1 0.291 5 nm, N5…O3 0.306 6 nm), efficiently forming the 2D anionic layers (Fig. 6b). We believe that the formation of the hydrogen-bonded 2D layer is due to the fact that the NH₂ and SO₃ groups in the 4-NH₂-1-NS^- anion are at the para position of the naphthalene. Conversely, the adjacent position of the NH₂ and SO₃ groups in 2-NH₂-1-NS^- does not favor the formation of an extended hydrogen-bonded network, as observed in complex 1. Simultaneously, the [Co(pytpy)₂]²⁺ cations and neighboring water molecules are connected through O…N hydrogen bonds (O4…N4 0.287 8 nm), resulting in the formation of 1D chains along the a-axis (Fig. 6a). Notably, there are no significant hydrogen bonds or π‑π interactions observed between the anionic layers and cationic chains, indicating their almost independent existence. This lack of intermolecular interactions could hinder the SCO process in complex 2. The large distortion of the Co^Ⅱ octahedron in complex 2 favors the HS state and prevents the occurrence of SCO.

  Numerous complex factors determine the SCO behaviors of [Co(Rterpy)₂]²⁺ complexes, including substituent groups, counter ions, solvent molecules, and other factors. These factors can function synergistically or antagonistically, influencing the crystal field strength of the metal centers and the cooperativity of the networks. In the case of our two complexes, the situation is further complicated by the abundant supramolecular interactions present. However, although it remains challenging to establish a clear correlation between these factors and the SCO properties, it is evident that the strong O—H…O/N, π-π interactions, along with the presence of solvent molecules, collectively play a key role in determining the SCO properties of these Co^Ⅱ complexes that are based on the [Co(pytpy)₂]²⁺ SCO active unit.

  3.   Conclusions

  This study investigated the influence of organosulfonate anions on the spin crossover properties of Co^Ⅱ complexes. Two Co^Ⅱ complexes, both featuring the [Co(pytpy)₂]²⁺ cation with a substituted terpy ligand, have been synthesized and characterized structurally and magnetically. Analysis of the supramolecular interactions in these two complexes reveals the ability of the organosulfonate anions to form varying hydrogen- bonded networks based on the specific anions present. Magnetic measurements indicated that complex 1 exhibits gradual and incomplete SCO behavior, while complex 2 remains in the HS state. In addition, the desolvation of complex 1 slightly modifies its SCO property. These results highlight the significant impact of different organosulfonates in tuning the structures and SCO properties of the Co^Ⅱ complexes. Further efforts will focus on exploring new Co^Ⅱ SCO materials utilizing organosulfonates with varying sizes, charges, and functionalities.

  
  
• 1. [1]

     Bousseksou A, Molnar G, Salmon L, Nicolazzi W. Molecular spin crossover phenomenon: Recent achievements and prospects[J]. Chem. Soc. Rev., 2011, 40:  3313-3335. doi: 10.1039/c1cs15042a

  2. [2]

     Meng Y S, Liu T. Manipulating spin transition to achieve switchable multifunctions[J]. Acc. Chem. Res., 2019, 52:  1369-1379. doi: 10.1021/acs.accounts.9b00049

  3. [3]

     Kumar K S, Ruben M. Sublimable spin-crossover complexes: from spin-state switching to molecular devices[J]. Angew. Chem. Int. Ed., 2021, 60:  7502-7521. doi: 10.1002/anie.201911256

  4. [4]

     Hogue R W, Singh S, Brooker S. Spin crossover in discrete polynuclear iron(Ⅱ) complexes[J]. Chem. Soc. Rev., 2018, 47:  7303-7338. doi: 10.1039/C7CS00835J

  5. [5]

     Ni Z P, Liu J L, Hoque M N, Liu W, Li J Y, Chen Y C, Tong M L. Recent advances in guest effects on spin-crossover behavior in Hofmann-type metal-organic frameworks[J]. Coord. Chem. Rev., 2017, 335:  28-43. doi: 10.1016/j.ccr.2016.12.002

  6. [6]

     Gebretsadik T, Yang Q, Wu J, Tang J. Hydrazone based spin crossover complexes: Behind the extra flexibility of the hydrazone moiety to switch the spin state[J]. Coord. Chem. Rev., 2021, 431:  213666. doi: 10.1016/j.ccr.2020.213666

  7. [7]

     Shen K Y, Zhang C J, Qu L Y, Jiang S Q, Zhang Y, Tong M L, Bao X. Thermodriven, acidity-driven, and photodriven spin-state switching in pyridylacylhydrazoneiron(Ⅱ) complexes at or above room temperature[J]. Inorg. Chem., 2021, 60:  18225-18233. doi: 10.1021/acs.inorgchem.1c02866

  8. [8]

     Ye Y S, Chen X Q, De Cai Y, Fei B, Dechambenoit P, Rouzieres M, Mathoniere C, Clerac R, Bao X. Slow dynamics of the spin-crossover process in an apparent high-spin mononuclear Fe(Ⅱ) complex[J]. Angew. Chem. Int. Ed., 2019, 58:  18888-18891. doi: 10.1002/anie.201911538

  9. [9]

     Díaz-Torres R, Boonprab T, Gómez-Coca S, Ruiz E, Chastanet G, Harding P, Harding D J. Structural and theoretical insights into solvent effects in an iron(Ⅲ)SCO complex[J]. Inorg. Chem. Front., 2022, 9:  5317-5326. doi: 10.1039/D2QI01159J

  10. [10]

      Díaz-Torres R, Echeverría J, Loveday O, Harding P, Harding D J. Interplay of halogen and hydrogen bonding in a series of heteroleptic iron(Ⅲ) complexes[J]. CrystEngComm, 2021, 23:  4069-4076. doi: 10.1039/D1CE00480H

  11. [11]

      Hayami S, Komatsu Y, Shimizu T, Kamihata H, Lee Y H. Spin-crossover in cobalt(Ⅱ) compounds containing terpyridine and its derivatives[J]. Coord. Chem. Rev., 2011, 255:  1981-1990. doi: 10.1016/j.ccr.2011.05.016

  12. [12]

      Drath O, Boskovic C. Switchable cobalt coordination polymers: Spin crossover and valence tautomerism[J]. Coord. Chem. Rev., 2018, 375:  256-266. doi: 10.1016/j.ccr.2017.11.025

  13. [13]

      Olguín J. Unusual metal centres/coordination spheres in spin crossover compounds[J]. Coord. Chem. Rev., 2020, 407:  213148. doi: 10.1016/j.ccr.2019.213148

  14. [14]

      Zhang S Y, Sun H Y, Wang R G, Meng Y S, Liu T, Zhu Y Y. Construction of spin-crossover dinuclear cobalt(Ⅱ) compounds based on complementary terpyridine ligand pairing[J]. Dalton Trans., 2022, 51:  9888-9893. doi: 10.1039/D2DT00436D

  15. [15]

      Pfrunder M C, Whittaker J J, Parsons S, Moubaraki B, Murray K S, Moggach S A, Sharma N, Micallef A S, Clegg J K, McMurtrie J C. Controlling spin switching with anionic supramolecular frameworks[J]. Chem. Mater., 2020, 32:  3229-3234. doi: 10.1021/acs.chemmater.0c00375

  16. [16]

      Ma X, Suturina E A, De S, Negrier P, Rouzieres M, Clerac R, Dechambenoit P. A redox-active bridging ligand to promote spin delocalization, high-spin complexes, and magnetic multi-switchability[J]. Angew. Chem. Int. Ed., 2018, 57:  7841-7845. doi: 10.1002/anie.201803842

  17. [17]

      Palion-Gazda J, Machura B, Kruszynski R, Grancha T, Moliner N, Lloret F, Julve M. Spin crossover in double salts containing six- and four-coordinate cobalt(Ⅱ) ions[J]. Inorg. Chem., 2017, 56:  6281-6296. doi: 10.1021/acs.inorgchem.7b00360

  18. [18]

      Konarev D V, Khasanov S S, Shestakov A F, Ishikawa M, Otsuka A, Yamochi H, Saito G, Lyubovskaya R N. Spin crossover in anionic cobalt-bridged fullerene (Bu₄N⁺){Co(Ph₃P)}₂(μ₂-Cl^-)(μ₂-η², η²-C₆₀)₂ dimers[J]. J. Am. Chem. Soc., 2016, 138:  16592-16595. doi: 10.1021/jacs.6b09890

  19. [19]

      Halcrow M A. Structure: function relationships in molecular spin-crossover complexes[J]. Chem. Soc. Rev., 2011, 40:  4119-4142. doi: 10.1039/c1cs15046d

  20. [20]

      Zhao S Z, Zhou H W, Qin C Y, Zhang H Z, Li Y H, Yamashita M, Wang S. Anion effects on spin crossover systems: From supramolecular chemistry to magnetism[J]. Chem.-Eur. J., 2023, 29:  e202300554. doi: 10.1002/chem.202300554

  21. [21]

      Ni Z, Shores M P. Supramolecular effects on anion-dependent spin-state switching properties in heteroleptic iron(Ⅱ) complexes[J]. Inorg. Chem., 2010, 49:  10727-10735. doi: 10.1021/ic102004c

  22. [22]

      Lochenie C, Bauer W, Railliet A P, Schlamp S, Garcia Y, Weber B. Large thermal hysteresis for iron(Ⅱ) spin crossover complexes with N-(pyrid-4-yl)isonicotinamide[J]. Inorg. Chem., 2014, 53:  11563-11572. doi: 10.1021/ic501624b

  23. [23]

      Weber B, Bauer W, Obel J. An iron(Ⅱ) spin-crossover complex with a 70 K wide thermal hysteresis loop[J]. Angew. Chem. Int. Ed., 2008, 47:  10098-10101. doi: 10.1002/anie.200802806

  24. [24]

      Krober J, Codjovi E, Kahn O, Grolifcre F, Jay C. A spin transition system with a thermal hysteresis at room temperature[J]. J. Am. Chem. Soc. Rev., 1993, 115:  9810-9811. doi: 10.1021/ja00074a062

  25. [25]

      Neville S M, Halder G J, Chapman K W, Duriska M B, Southon P D, Cashion J D, Letard J F, Moubaraki B, Murray K S, Kepert C J. Single-crystal to single-crystal structural transformation and photomagnetic properties of a porous iron(Ⅱ) spin-crossover framework[J]. J. Am. Chem. Soc., 2008, 130:  2869-2876. doi: 10.1021/ja077958f

  26. [26]

      Li J Y, Chen Y C, Zhang Z M, Liu W, Ni Z P, Tong M L. Tuning the spin-crossover behaviour of a hydrogen-accepting porous coordination polymer by hydrogen-donating guests[J]. Chem.-Eur. J., 2014, 21:  1645-1651.

  27. [27]

      Koningsbruggen P J v, Garcia Y, Codjovi E, Lapouyade R, Kahn O, Fournes L, Rabardel L. Non-classical Fe^Ⅱ spin-crossover behaviour in polymeric iron(Ⅱ) compounds of formula[Fe(NH₂trz)₃]X₂·xH₂O (NH₂trz=4-amino-1, 2, 4-triazole; X=derivatives of naphthalene sulfonate)[J]. J. Am. Chem. Soc., 1997, 7:  2069-2075.

  28. [28]

      Garcia Y, Campbell S J, Lord J S, Linares J, D rtu M M, Vendrell Pérez A, Boland Y, Ksenofontov V, Gütlich P. Spin conversion detected by Mössbauer spectroscopy and μSR on a 1D Fe^Ⅱ paramagnetic chain[J]. Hyperfine Interact., 2014, 226:  217-221. doi: 10.1007/s10751-013-0909-3

  29. [29]

      Hung T Q, Terki F, Kamara S, Dehbaoui M, Charar S, Sinha B, Kim C, Gandit P, Gural'skiy I A, Molnar G, Salmon L, Shepherd H J, Bousseksou A. Room temperature magnetic detection of spin switching in nanosized spin-crossover materials[J]. Angew. Chem. Int. Ed., 2013, 125:  1223-1226. doi: 10.1002/ange.201205952

  30. [30]

      Zhao X H, Zhang S L, Shao D, Wang X Y. Spin crossover in[Fe(2-Picolylamine)₃]²⁺ adjusted by organosulfonate anions[J]. Inorg. Chem., 2015, 54:  7857-7867. doi: 10.1021/acs.inorgchem.5b00870

  31. [31]

      Shen F X, Pi Q, Shi L, Shao D, Li H Q, Sun Y C, Wang X Y. Spin crossover in hydrogen-bonded frameworks of Fe(Ⅱ) complexes with organodisulfonate anions[J]. Dalton Trans., 2019, 48:  8815-8825. doi: 10.1039/C9DT01326A

  32. [32]

      Shao D, Shi L, Yin L, Wang B L, Wang Z X, Zhang Y Q, Wang X Y. Reversible on-off switching of both spin crossover and single-molecule magnet behaviours via a crystal-to-crystal transformation[J]. Chem. Sci., 2018, 9:  7986-7991. doi: 10.1039/C8SC02774A

  33. [33]

      Shao D, Yang J, Wei X Q, Shi L, You M, Yang X, Ruan Z, Tian Z. A proton conducting cobalt(Ⅱ) spin crossover complex[J]. Chem.-Asian J., 2022, 17:  e202200949. doi: 10.1002/asia.202200949

  34. [34]

      Zhou Y, Wei X Q, Gu Y, Zhao Q Q, Shao D. Organosulfonate-modulated spin-crossover behavior in three halogen-functionalized cobalt(Ⅱ) complexes[J]. Eur. J. Inorg. Chem., 2022, 26:  e202200666.

  35. [35]

      Sun Y C, Chen F L, Wang K J, Zhao Y, Wei H Y, Wang X Y. Hysteretic spin crossover with high transition temperatures in two cobalt(Ⅱ) complexes[J]. Inorg. Chem., 2023, 62:  14863-14872. doi: 10.1021/acs.inorgchem.3c01188

  36. [36]

      Kanetomo T, Ni Z, Enomoto M. Hydrogen-bonded cobalt(Ⅱ)-organic framework: Normal and reverse spin-crossover behaviours[J]. Dalton Trans., 2022, 51:  5034-5040. doi: 10.1039/D2DT00453D

  37. [37]

      Kobayashi F, Komatsumaru Y, Akiyoshi R, Nakamura M, Zhang Y, Lindoy L F, Hayami S. Water molecule-induced reversible magnetic switching in a bis-terpyridine cobalt(Ⅱ) complex exhibiting coexistence of spin crossover and orbital transition behaviors[J]. Inorg. Chem., 2020, 59:  16843-16852. doi: 10.1021/acs.inorgchem.0c00818

  38. [38]

      Kobayashi F, Hiramatsu T, Sueyasu K, Tadokoro M. Proton conductive mononuclear hydrogen-bonded cobalt(Ⅱ) spin crossover complex[J]. Cryst. Growth Des., 2023, 23:  1633-1640. doi: 10.1021/acs.cgd.2c01243

  39. [39]

      Nakaya M, Kosaka W, Miyasaka H, Komatsumaru Y, Kawaguchi S, Sugimoto K, Zhang Y, Nakamura M, Lindoy L F, Hayami S. CO₂- induced spin-state switching at room temperature in a monomeric cobalt(Ⅱ) complex with the porous nature[J]. Angew. Chem. Int. Ed., 2020, 59:  10658-10665. doi: 10.1002/anie.202003811

  40. [40]

      Ghosh S, Kamilya S, Pramanik T, Rouzieres M, Herchel R, Mehta S, Mondal A. ON/OFF photoswitching and thermoinduced spin crossover with cooperative luminescence in a 2D iron(Ⅲ) coordination polymer[J]. Inorg. Chem., 2020, 59:  13009-13013. doi: 10.1021/acs.inorgchem.0c02136

  41. [41]

      Hayami S, Shigeyoshi Y, Akita M, Inoue K, Kato K, Osaka K, Takata M, Kawajiri R, Mitani T, Maeda Y. Reverse spin transition triggered by a structural phase transition[J]. Angew. Chem. Int. Ed., 2005, 44:  4899-4903. doi: 10.1002/anie.200500316

  42. [42]

      Guo Y, Yang X L, Wei R J, Zheng L S, Tao J. Spin transition and structural transformation in a mononuclear cobalt(Ⅱ) complex[J]. Inorg. Chem., 2015, 54:  7670-7672. doi: 10.1021/acs.inorgchem.5b01344

  43. [43]

      Krivokapic I, Zerara M, Daku M L, Vargas A, Enachescu C, Ambrus C, Tregenna Piggott P, Amstutz N, Krausz E, Hauser A. Spin-crossover in cobalt(Ⅱ) imine complexes[J]. Coord. Chem. Rev., 2007, 251:  364-378. doi: 10.1016/j.ccr.2006.05.006

  44. [44]

      Khakhlary P, Anson C E, Mondal A, Powell A K, Baruah J B. Structural and magnetic properties of oxyquinolinate clusters of cobalt(Ⅱ) and manganese(Ⅱ) and serendipitous intake of carbonate during synthesis[J]. Dalton Trans., 2015, 44:  2964-2969. doi: 10.1039/C4DT02999B

  45. [45]

      Akiyoshi R, Komatsumaru Y, Donoshita M, Dekura S, Yoshida Y, Kitagawa H, Kitagawa Y, Lindoy L F, Hayami S. Ferroelectric and spin crossover behavior in a cobalt(Ⅱ) compound induced by polar-ligand-substituent motion[J]. Angew. Chem. Int. Ed., 2021, 60:  12717-12722. doi: 10.1002/anie.202015322

  46. [46]

      Phonsri W, Harding P, Liu L, Telfer S G, Murray K S, Moubaraki B, Ross T M, Jameson G N L, Harding D J. Solvent modified spin crossover in an iron(Ⅲ) complex: Phase changes and an exceptionally wide hysteresis[J]. Chem. Sci., 2017, 8:  3949-3959. doi: 10.1039/C6SC05317C

  47. [47]

      Galet A, Gaspar A B, Munoz M C, Real J A. Influence of the counterion and the solvent molecules in the spin crossover system Co(4-terpyridone)₂X_p·nH₂O[J]. Inorg. Chem., 2006, 45:  4413-4422. doi: 10.1021/ic060090u

  48. [48]

      Zenno H, Kobayashi F, Nakamura M, Sekine Y, Lindoy L F, Hayami S. Hydrogen bond-induced abrupt spin crossover behaviour in 1-D cobalt(Ⅱ) complexes—The key role of solvate water molecules[J]. Dalton Trans., 2021, 50:  7843-7853. doi: 10.1039/D1DT01069G

  49. [49]

      Ghosh S, Ghosh S, Kamilya S, Mandal S, Mehta S, Mondal A. Impact of counteranion on reversible spin-state switching in a series of cobalt(Ⅱ) complexes containing a redox-active ethylenedioxythiophene-based terpyridine ligand[J]. Inorg. Chem., 2022, 61:  17080-17088. doi: 10.1021/acs.inorgchem.2c02313

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  Scheme 1  Structures of the ligand pytpy and two organosulfonate anions

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  Figure 1  Asymmetric units for complexes 1 (a) and 2 (b) at 193 k

  Hydrogen atoms and solvent molecules are omitted for clarity.

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  Figure 2  Experiment and simulated PXRD patterns of complexes 1 (a) and 2 (b)

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  Figure 3  TGA curves for complexes 1 (a) and 2 (b)

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  Figure 4  χ_M^T vs T plots for complexes 1 (a) and 2 (b)

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  Figure 5  (a) Hydrogen-bonds and π-π interaction (centroid-centroid: 0.363 7 nm) in complex 1; (b) Crystal packing of 1

  Symmetry code: A: 2-x, 0.5+y, 1.5-z; Red dashed lines represent hydrogen bonds, and blue dashed lines represent π-π interactions between the pyridyl groups and the naphthalene ring.

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  Figure 6  (a) Hydrogen-bonded 1D chain along the a-axis formed by [Co(pytpy)₂]²⁺ cations and water molecules; (b) Hydrogen-bonded 2D layer of 4-NH₂-1-NS^- anions; (c) Crystal packing of complex 2

  Red dashed lines represent hydrogen bonds.

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  Table 1.  Crystal data and refinement parameters for complexes 1 and 2

  Parameter	1	2
  Empirical formula	C61H50CoN10O8S2	C60H46CoN10O7S2
  Formula weight	1 174.16	1 142.12
  Temperature/K	193	193
  Crystal system	Orthorhombic	Orthorhombic
  Space group	P212121	Fdd2
  a/nm	0.904 23(4)	2.355 74(6)
  b/nm	1.382 18(6)	4.878 38(14)
  c/nm	4.285 89(17)	0.901 97(2)
  Volume/nm3	5.356 5(4)	10.365 6(5)
  Z	4	8
  Dc/(g·cm-3)	1.456	1.464
  F(000)	2 436	4 728
  2θ range/(°)	3.51-55.14	6.30-107.88
  Index ranges	-11 ≤ h ≤ 11, -17 ≤ k ≤ 14, -55 ≤ l ≤ 55	-28 ≤ h ≤ 26, -58 ≤ k ≤ 56, -10 ≤ l ≤ 10
  Reflection collected	50 706	27 494
  Independent reflection	12 347	4 719
  Rint	0.050 3	0.053 6
  Data, restraint, number of parameters	12 347, 77, 747	4 719, 2, 367
  Goodness-of-fit on F 2	1.036	1.040
  Final R indexes [I≥2σ(I)]	R1=0.054 4, wR2=0.137 6	R1=0.028 8, wR2=0.073 9
  Final R indexes (all data)	R1=0.073 7, wR2=0.148 4	R1=0.029 9, wR2=0.074 5
  (Δρ)max, (Δρ)min/(e·nm-3)	590, -600	240, -570

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  Table 2.  Selected bond lengths (nm) and structural parameters for complexes 1 and 2

  Bond	1	2
  Co1—N1	0.211 9(4)	0.215 7(3)
  Co1—N3	0.212 3(4)	0.215 2(3)
  Co1—N4	0.204 3(5)
  Co1—N6	0.203 2(5)
  Co—Nequatorial	0.207 9	0.215 4
  Co1—N2	0.192 6(3)	0.204 5(2)
  Co1—N5	0.189 3(4)
  Co—Naxial	0.190 9	0.204 5
  Co—Nav	0.202 3	0.211 8

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  Table 3.  Structural parameters for complexes 1 and 2

  Parameter	1	2
  CShM	2.477	4.609
  ∑a	89.75	146.51
  Θb	309.43	445.27
  a∑ is the sum of the deviation from 90° of the 12 cis angles of the CoN6 octahedron; bΘ is the sum of the deviation from 60° of the 24 trigonal angles of the projection of the CoN6 octahedron onto the trigonal faces.

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  Table 4.  Intermolecular interaction parameters for complexes 1 and 2

  D—H…A	d(D—H) / nm	d(H…A) / nm	d(D…A) / nm	∠DHA / (°)
  		1
  N9—H9B…N7	0.098	0.206	0.303 0(6)	169.8
  C32—H32…O1A	0.095	0.224	0.311 4(7)	152.5
  O8—H8A…O5	0.085	0.204	0.280 5(8)	149.4
  O8—H8B…O4A	0.085	0.217	0.282 9(10)	133.6
  C27—H27…O2	0.095	0.223	0.317 4(7)	174.3
  N10—H10B…O7	0.104	0.208	0.296 5(9)	141.6
  O7—H7A…O1	0.084	0.224	0.302 2(9)	155.9
  		2
  N5—H5A…O1	0.089	0.214	0.291 5(4)	145.6
  N5—H5B…O3	0.089	0.227	0.306 6(4)	148.6
  O4—H4A…N4	0.087	0.220	0.287 8(4)	134.9
  Symmetry code: A: 2-x, 0.5+y, 1.5-z.

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