English

• 1. INTRODUCTION

  Supramolecular complexes have attracted much attention in recent years due to their interesting structures and potential applications in fluorescence, electrochemistry, magnetism, catalysis, gas storage and so on^[1-8]. So far, many interesting supramolecular complexes have been designed and prepared by molecular design and crystal engineering methods, but it is still very difficult to obtain the target complexes with expected structures and properties. In the preparation of complexes, many factors may affect the structures of complexes, such as the coordination geometry of metal center, the structure of organic ligand, metal ligand ratio, pH value, solvent and even temperature^[9-13]. In addition, non-covalent interactions such as hydrogen bonds, π-π stacking interactions and anion-π interactions play important roles in the formation of various supramolecular structures^[14-25].

  In our previous studies, we reported the diversity of reactions of a polydentate ligand 2-morpholine-4-yl-4, 6- di-pyrazol-1-yl-1, 3, 5-triazine (L) with different metal ions such as Co(II), Mn(II), Cr(III) and Fe(III)^[22]. Recently, when we used ligand L to react with NiCl₂·2H₂O, an interesting coordination polymerization isomerism phenomenon appeared. A pair of nickel(II) supramolecular complexes monomer and dimer, (1) and (2), were synthesized under different temperature conditions, and their syntheses, crystal structures, non-covalent interactions and properties were discussed.

  2. EXPERIMENTAL

  2.1 Materials and methods

  The solvents used in the reactions were dried according to standard procedures. All chemicals were obtained from commercial sources with reagent grade and used without further purification. The polydentate ligand L was prepared according to the literature^[26]. C, H and N analyses were carried out using Vario elemental analysis III instrument. The FT-IR spectra were recorded on a Bruker Vector 22 infrared spectrometer using the KBr pellet method. Thermogravimetric (TG) analysis was carried out on a locally produced HCT-2 thermal analysis system. The sample was loaded in a sealed aluminum crucible (5~10 mg) and heated from room temperature to 800 ℃ at a heating rate of 10 ℃/min under nitrogen atmosphere in order to avoid oxidization. UV/Vis/NIR diffuse-reflectance spectra were obtained with a Cary 500 UV/Vis/NIR spectrophoto- meter. BaSO₄ powder was used as reference (100% reflectance). The fluorescence analysis was applied to characterize 1, 2 and L in the aqueous solution (1 × 10^–5 mol·L^–1) at room temperature.

  2.2 Synthesis of [NiCl₂(L)] (1)

  A solution of L (100 mg, 0.34 mmol) in acetonitrile (4 mL) was added dropwise to a solution of NiCl₂·2H₂O (98 mg, 0.34 mmol) in acetonitrile (15 mL) and the resulting solution was left undisturbed. Red block crystals (Fig. 1(a)) suitable for X-ray crystallography were deposited from the solution after several days by slow evaporation of the solvent at 35 ℃. Yield: 29% (based on Ni). Anal. Calcd. (%) for C₁₃H₁₄Cl₂N₈NiO: C, 36.49; H, 3.30; N, 26.19. Found (%): C, 36.36; H, 3.28; N, 26.15. IR (KBr, cm^–1): 3125 (w), 1650 (s), 1591 (m), 1550 (w), 1513 (s), 1479 (s), 1445 (m), 1396 (s), 1295 (w), 1267 (m), 1178 (w), 1116 (w), 1069 (w), 1025 (m), 953 (w), 936 (w), 908 (w), 812 (m), 794 (m), 780 (m), 593 (w).

  Figure 1

  

  Figure 1.  Crystal photos of the complexes. (a) Red crystal of 1; (b) Green crystal of 2

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  2.3 Synthesis of [Ni₂Cl₂(L)₂(μ-Cl)₂] (2)

  The preparation method of the reaction mixture of com- plex 2 was similar to that of 1. Green prism crystals (Fig. 1(b)) suitable for X-ray crystallography deposited from the solution after several days by slow evaporation of the solvent at 65 ℃. Yield: 27% (based on Ni). Anal. Calcd. (%) for C₂₆H₂₈Cl₄N₁₆Ni₂O₂: C, 36.49; H, 3.30; N, 26.19. Found (%): C, 36.28; H, 3.01; N, 26.22. IR (KBr, cm^–1): 3085 (w), 1639 (s), 1593 (m), 1548 (w), 1512 (s), 1488 (s), 1471 (s), 1405 (s), 1304 (w), 1294 (w), 1266 (m), 1185 (w), 1109 (w), 1076 (w), 1022 (w), 957 (m), 938 (w), 906 (w), 812 (m), 795 (m), 780 (m), 595 (w).

  2.4 Crystal structure determination

  Suitable single crystals of complexes 1 and 2 were mounted onto the end of a thin glass fiber using Fomblin oil. X-ray diffraction intensity data were measured on a Xcalibur, Eos, Gemini diffractometer using MoKα radiation (λ = 0.71073 Å). Using OLEX2^[27], the structures were solved by direct methods with SHELXS program^[28] and refined by full-matrix least-squares techniques on F² with SHELXL^[29]. H atoms on C atoms were positioned geometrically and refined as riding atoms. Crystal data, data collection and structure refinement details are summarized in Table 1. In the crystal structure of 1, the positions of N(5), O(1), C(6) and C(7) atoms of the morpholine ring were disordered between two sites. The occupancies were refined with the sum of the occupancies of disordered sites constrained to 1, which led to an occupancy ratio of 0.618(5): 0.382(5). Graphical pictures were prepared by Diamond software.

  Table 1

  

  Table 1.  Crystal Data and Structure Refinement Parameters for Complexes 1 and 2

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  Complex	1	2
  Chemical formula	C13H14Cl2N8NiO	C26H28Cl4N16Ni2O2
  Formula weight	427.91	855.86
  Temperature (K)	123.0	97.2
  Crystal system	Orthorhombic	Monoclinic
  Space group	Cmca	P21/c
  a (Å)	12.6569(18)	14.600(3)
  b (Å)	10.4622(7)	13.11(2)
  c (Å)	25.66(2)	9.183(3)
  α (°)	90.00	90.00
  β (°)	90.00	105.29(3)
  γ (°)	90.00	90.00
  V (Å3)	3398(3)	1695(3)
  Z	8	2
  μ (mm–1)	1.477	1.480
  Crystal size (mm3)	0.25 × 0.20 × 0.20	0.10 × 0.10 × 0.03
  Index ranges	–15≤h≤15, –7≤k≤12, –31≤l≤30	–18≤h≤14, –7≤k≤16, –9≤l≤11
  2θ range for data collection (°)	6.36 to 52	6.22 to 52
  F(000)	1743	872
  ρcalc (g·cm-3)	1.673	1.677
  Reflections collected	4897	7129
  Independent reflections (Rint)	1745 (0.0252)	3326 (0.0676)
  Data/restraints/parameters	1745/122/155	3326/0/226
  Goodness-of-fit on F2	1.054	0.999
  R/wR (I > 2σ(I))	0.0282/0.0642	0.0613/0.0694
  R/wR (all data)	0.0379/0.0680	0.1097/0.0806
  Largest diff. peak/hole (e·Å−3)	0.289/–0.412	0.487/–0.553

  3. RESULTS AND DISCUSSION

  3.1 Crystal structure of complex 1

  Crystal structure analysis shows that complex 1 belongs to orthorhombic space group Cmca. The nickel(II) center is coordinated by three nitrogen atoms from triazine and pyrazolyl rings of L and two chloride anions with a NiN₃Cl₂ donor set. The coordination geometry around the metal center can be best described as a distorted square pyramid, where the three nitrogen atoms N(1), N(3) and N(1)ⁱ (atom at –x+1, y, z) of L and the Cl(2) atom occupy the basal posi- tions, and the Cl(1) atom located at the apical one (Fig. 2(a)). The three aromatic rings of the L ligand are nearly coplanar. The dihedral angles between the triazine and pyrazolyl planes are both 7.325°. The selected bond lengths and bond angles for complex 1 are listed in Table 2.

  Table 2

  

  Table 2.  Selected Bond Lengths (Å) and Bond Angles (°) for 1

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  Bond	Dist.		Bond	Dist.		Bond	Dist.
  Ni(1)–Cl(1)	2.2902(14)		Ni(1)–Cl(2)	2.2527(15)		Ni(1)–N(1)	2.1601(17)
  Ni(1)–N(3)	1.981(2)		Ni(1)–N(1)i	2.1601(17)
  Angle	(°)		Angle	(°)		Angle	(°)
  Cl(1)–Ni(1)–Cl(2)	109.12(5)		Cl(1)–Ni(1)–N(1)	97.46(5)		Cl(1)–Ni(1)–N(3)	96.44(8)
  Cl(1)–Ni(1)–N1(i)	97.46(5)		Cl(2)–Ni(1)–N(1)	100.59(5)		Cl(2)–Ni(1)–N(1)i	100.59(5)
  Cl(2)–Ni(1)–N(3)	154.44(7)		N(3)–Ni(1)–N(1)	75.37(5)		N(3)–Ni(1)–N(1)i	75.37(5)
  N(1)–Ni(1)–N(1)i	148.37(9)
  Symmetry transformation: i: −x+1, y, z

  As shown in Fig. 2(b), the anion-π interactions on both sides of the triazine ring are observed between Cl(2)ⁱ (atom at x, –y + 1, –z), O(1)ⁱⁱ (atom at –x + 1, y + 1/2, –z + 1/2) and the triazine ring. The distance between Cl(2)ⁱ and the centroid of the triazine is 3.369 Å, while that between O(1)ⁱⁱ and the centroid of the triazine is 2.815 Å. The angles of the Cl(2)ⁱ···centroid and O(1)ⁱⁱ···centroid axes to the triazine ring plane are 73.22 and 77.69°, respectively. Though no classical hydrogen bonding interactions are observed between the molecules in 1, the C(3)–H(3)···Cl(1)ⁱ (atom at x + 1/2, y − 1/2, z) hydrogen bond interaction is present (Fig. 2(c) and Table 3). The molecules of 1 are interlinked through non-covalent interactions involving hydrogen bonding inter- actions, chloride-π interactions and oxygen-π interactions, which forms a three-dimensional network in the crystalline solid (Fig. 2(d)).

  Figure 2

  

  Figure 2.  Structure of complex 1. (a) ORTEP drawing, hydrogen atoms and solvent molecules have been omitted for clarity (symmetry code: (i) –x + 1, y, z); (b) Chloride-π interactions (red dashed lines) and the oxygen-π interaction (blue dashed line, symmetry codes: (i) x, –y + 1, –z; (ii) –x + 1, y + 1/2, –z + 1/2); (c) C(3)–H(3)···Cl(1) weak hydrogen bonding interaction (pink dashed lines) (Symmetry code: (i) x + 1/2, y − 1/2, z); (d) Molecular packing with non-covalent interactions

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  Table 3

  

  Table 3.  Hydrogen Bond Lengths (Å) and Bond Angles (°) for Complexes 1 and 2

  DownLoad: CSV

  Complex	D–H···A	d(D–H)	d(H···A)	d(D···A)	∠DHA
  1	C(3)–H(3)···Cl(1)i	0.95	2.67	3.437(1)	138
  2	C(6)–H(6)···O(1)i	0.93	2.52	3.361(5)	151
  	C(12)–H(12A)···O(1)ii	0.97	2.80	3.730(6)	162
  	C(13)–H(13A)···N(6)iii	0.97	2.61	3.424(6)	142
  	C(2)–H(2)···Cl(2)iv	0.93	2.96	3.581(5)	125
  	C(3)–H(3)···Cl(1)iii	0.93	2.56	3.481(5)	170
  	C(5)–H(5)···Cl(1)v	0.93	2.66	3.578(7)	171
  	C(11)–H(11A)···Cl(1)vi	0.97	2.71	3.653(5)	163
  	C(13)–H(13B)···Cl(1)iii	0.97	2.82	3.654(6)	144
  Symmetry codes for 1: (i) x + 1/2, y − 1/2, z; for 2: (i) −x, y − 1/2, −z + 1/2; (ii) x, −y + 3/2, z + 1/2; (iii) x, −y + 3/2, z − 1/2; (iv) −x + 1, y + 1/2, −z + 5/2; (v) x, −y + 1/2, z − 1/2; (vi) −x, −y + 1, −z + 1

  3.2 Crystal structure of complex 2

  Complex 2 crystallizes in the monoclinic space group P2₁/c, with the asymmetric unit containing one nickel(II) cation, one L ligand, one monodentate chloride ion and one bridging chloride ion. All the atoms in the asymmetric unit are in general positions. As shown in Fig. 3(a), an inversion center is located at the core of the complex formed by two nickel(II) ions (Ni(1) and Ni(1)ⁱ (atom at –x + 1, –y + 1, –z + 2) and two bridging chloride anions (Cl(2) and Cl(2)ⁱ (atom at –x+1, –y+1, –z+2). Each nickel(II) ion also has one L ligand and one monodentate chloride anion completing the coordination environment with a NiN₃Cl₃ donor set. The nickel(II) center has a distorted octahedral geometry and is coordinated by three N atoms from one L ligand and by three Cl atoms. The selected bond lengths and bond angles for complex 2 are listed in Table 4. The dihedral angles between the triazine and two pyrazolyl planes of the L ligand are 6.493° and 11.011°, respectively, and the difference may be due to the π-π stacking interaction between a pyrazolyl ring from one L ligand and a triazine ring from another L ligand (Fig. 3(b)). The centroid distance between aromatic rings is 3.437 Å and the dihedral angle is 2.356°.

  Figure 3

  

  Figure 3.  Structure of complex 2. (a) ORTEP drawing, hydrogen atoms and solvent molecules have been omitted for clarity (Symmetry code: (i) –x + 1, –y + 1, –z + 2); (b) π-π stacking interactions (blue dashed lines); (c) Molecular packing with weak hydrogen bonding interactions (pink dashed lines)

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  Table 4

  

  Table 4.  Selected Bond Lengths (Å) and Bond Angles (°) for 2

  DownLoad: CSV

  Bond	Dist.		Bond	Dist.		Bond	Dist.
  Ni(1)–Cl(1)	2.4040(14)		Ni(1)–Cl(2)	2.3290(14)		Ni(1)–Cl(2)i	2.5027(14)
  Ni(1)–N(1)	2.149(5)		Ni(1)–N(3)	2.163(5)		Ni(1)–N(5)	1.985(4)
  Angle	(°)		Angle	(°)		Angle	(°)
  N(1)–Ni(1)–Cl(1)	92.08(10)		N(1)–Ni(1)–Cl(2)	102.58(10)		N(1)–Ni(1)–Cl(2)i	87.63(10)
  N(1)–Ni(1)–N(3)	150.95(14)		N(1)–Ni(1)–N(5)	76.06(15)		N(3)–Ni(1)–Cl(1)	89.37(11)
  N(3)–Ni(1)–Cl(2)	106.13(12)		N(3)–Ni(1)–Cl(2)i	90.17(10)		N(3)–Ni(1)–N(5)	74.94(16)
  N(5)–Ni(1)–Cl(1)	89.48(11)		N(5)–Ni(1)–Cl(2)	174.64(11)		N(5)–Ni(1)–Cl(2)i	89.02(11)
  Cl(1)–Ni(1)–Cl(2)	95.77(5)		Cl(1)–Ni(1)–Cl(2)i	178.50(5)		Cl(2)–Ni(1)–Cl(2)i	85.73(5)
  Symmetry code: i: –x + 1, –y + 1, –z + 2

  As in complex 1, no classical hydrogen bonding interac- tions are present in complex 2. Nevertheless, many C–H···Cl, C–H···O and C–H···N weak hydrogen bonds are observed in the three-dimensional network of 2 (Fig. 3(c)) and the relevant parameters are listed in Table 3. Compared with complex 1, more weak hydrogen bonds further stabilize the structure of 2.

  3.3 TG analysis

  TG analysis was carried out to investigate the thermal stabilities of complexes 1 and 2. As shown in Fig. 4, complex 1 did not show any weight loss below 305 ℃ in accord with that no solvent molecules exist in the lattice of 1. It started to decompose from 305 ℃ and the total weight loss below 800 ℃ was observed to be 67.81%, which may correspond to the removal of 2-morpholine-4-yl-4, 6-di- pyrazol-1-yl-1, 3, 5-triazine ligand (calcd. 69.71%). The final product may be NiCl₂ (calcd. 30.29%). The TG curve of complex 2 was very similar to that of 1, indicating that they have the same compositions and similar thermal stabilities.

  Figure 4

  

  Figure 4.  TG analysis diagram of complexes 1 and 2 evaluated in a nitrogen atmosphere

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  3.4 UV/Vis/NIR diffuse reflectance spectroscopy

  We used UV/Vis/NIR spectroscopy in diffuse reflectance mode to get the solid absorption spectra (Fig. 5) for complexes 1, 2 and the free ligand L. Complexes 1 and 2 showed absorption bands in 220~390 nm similar to that of ligand L, which were assigned as π → π* and n → π* transitions of the ligand. From 390 to 1500 nm, the absorbance of complexes 1 and 2 was different. Complex 1 exhibited a d-d band with the maximum at 468 nm and a broad d-d band ranging from 651 to 1481 nm, which was consistent with its color of red and a square-pyramidal coordination of nickel(II) complexes^[30]. Complex 2 showed three d-d bands with the maximum at 423, 726 and 1140 nm, assignable to the transitions to ³A_2g → ³T_2g(F), ³A_2g → ³T_1g(P) and ³A_2g → ³T_1g(F), respectively. The presence and positions of these three bands suggested the green color of 2 and an octahedral environment for the nickel(II) ion^{[30, 31]}.

  Figure 5

  

  Figure 5.  UV/Vis/NIR solid absorption spectra in diffuse reflectance mode of 1, 2 and L

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  3.5 Fluorescence properties

  The fluorescence emission spectra of 1, 2 and L at room temperature are shown in Fig. 6. Complexes 1 and 2 exhibited a strong emission band at 429 nm upon excitation at 257 nm. The emissions of complexes 1 and 2 were similar to that of the free ligand L and can be attributed to intra-ligand π→π* transitions of L, not to LMCT (ligand-to-metal charge transfer) or MLCT (metal-to-ligand charge transfer). The difference of fluorescence intensity between 1 and 2 can be attributed to the fact that complex 2 is the dimer of 1.

  Figure 6

  

  Figure 6.  Fluorescence emission spectra of 1, 2 and L at room temperature

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  3.6 Effect of temperature

  We have obtained a nickel(II) complex monomer at 35 ℃ and its dimer at 65 ℃. As shown in Scheme 1, we speculate that there is a conversion reaction between the two complexes, and the transition from complexes 1 to 2 is an endothermic process^[32]. The color difference of complexes 1 and 2 can be attributed to their structural differences^[33-36].

  Scheme 1

  

  Scheme 1.  Conversion reaction of complexes 1 and 2

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  4. CONCLUSION

  In summary, two new nickel(II) supramolecular com- plexes monomer and dimer were successfully prepared using polydentate ligand L to react with NiCl₂·2H₂O under dif- ferent temperature conditions and characterized by thermal gravimetric analyses and spectroscopic methods. Complexes 1 and 2 showed different structures. Complex 1 is mononuclear, but complex 2 is binuclear. Non-covalent interactions such as π-π stacking interactions, anion-π interactions and weak hydrogen bonds were observed in the three-dimensional supramolecular structures of 1 and 2. This work not only realizes the controllable synthesis of nickel complex monomer and dimer under different temperature, but also provides a new pathway for the construction of chlorine bridge complex.

  
  
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  Figure 1  Crystal photos of the complexes. (a) Red crystal of 1; (b) Green crystal of 2

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  Figure 2  Structure of complex 1. (a) ORTEP drawing, hydrogen atoms and solvent molecules have been omitted for clarity (symmetry code: (i) –x + 1, y, z); (b) Chloride-π interactions (red dashed lines) and the oxygen-π interaction (blue dashed line, symmetry codes: (i) x, –y + 1, –z; (ii) –x + 1, y + 1/2, –z + 1/2); (c) C(3)–H(3)···Cl(1) weak hydrogen bonding interaction (pink dashed lines) (Symmetry code: (i) x + 1/2, y − 1/2, z); (d) Molecular packing with non-covalent interactions

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  Figure 3  Structure of complex 2. (a) ORTEP drawing, hydrogen atoms and solvent molecules have been omitted for clarity (Symmetry code: (i) –x + 1, –y + 1, –z + 2); (b) π-π stacking interactions (blue dashed lines); (c) Molecular packing with weak hydrogen bonding interactions (pink dashed lines)

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  Figure 4  TG analysis diagram of complexes 1 and 2 evaluated in a nitrogen atmosphere

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  Figure 5  UV/Vis/NIR solid absorption spectra in diffuse reflectance mode of 1, 2 and L

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  Figure 6  Fluorescence emission spectra of 1, 2 and L at room temperature

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  Scheme 1  Conversion reaction of complexes 1 and 2

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  Table 1.  Crystal Data and Structure Refinement Parameters for Complexes 1 and 2

  Complex	1	2
  Chemical formula	C13H14Cl2N8NiO	C26H28Cl4N16Ni2O2
  Formula weight	427.91	855.86
  Temperature (K)	123.0	97.2
  Crystal system	Orthorhombic	Monoclinic
  Space group	Cmca	P21/c
  a (Å)	12.6569(18)	14.600(3)
  b (Å)	10.4622(7)	13.11(2)
  c (Å)	25.66(2)	9.183(3)
  α (°)	90.00	90.00
  β (°)	90.00	105.29(3)
  γ (°)	90.00	90.00
  V (Å3)	3398(3)	1695(3)
  Z	8	2
  μ (mm–1)	1.477	1.480
  Crystal size (mm3)	0.25 × 0.20 × 0.20	0.10 × 0.10 × 0.03
  Index ranges	–15≤h≤15, –7≤k≤12, –31≤l≤30	–18≤h≤14, –7≤k≤16, –9≤l≤11
  2θ range for data collection (°)	6.36 to 52	6.22 to 52
  F(000)	1743	872
  ρcalc (g·cm-3)	1.673	1.677
  Reflections collected	4897	7129
  Independent reflections (Rint)	1745 (0.0252)	3326 (0.0676)
  Data/restraints/parameters	1745/122/155	3326/0/226
  Goodness-of-fit on F2	1.054	0.999
  R/wR (I > 2σ(I))	0.0282/0.0642	0.0613/0.0694
  R/wR (all data)	0.0379/0.0680	0.1097/0.0806
  Largest diff. peak/hole (e·Å−3)	0.289/–0.412	0.487/–0.553

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  Table 2.  Selected Bond Lengths (Å) and Bond Angles (°) for 1

  Bond	Dist.		Bond	Dist.		Bond	Dist.
  Ni(1)–Cl(1)	2.2902(14)		Ni(1)–Cl(2)	2.2527(15)		Ni(1)–N(1)	2.1601(17)
  Ni(1)–N(3)	1.981(2)		Ni(1)–N(1)i	2.1601(17)
  Angle	(°)		Angle	(°)		Angle	(°)
  Cl(1)–Ni(1)–Cl(2)	109.12(5)		Cl(1)–Ni(1)–N(1)	97.46(5)		Cl(1)–Ni(1)–N(3)	96.44(8)
  Cl(1)–Ni(1)–N1(i)	97.46(5)		Cl(2)–Ni(1)–N(1)	100.59(5)		Cl(2)–Ni(1)–N(1)i	100.59(5)
  Cl(2)–Ni(1)–N(3)	154.44(7)		N(3)–Ni(1)–N(1)	75.37(5)		N(3)–Ni(1)–N(1)i	75.37(5)
  N(1)–Ni(1)–N(1)i	148.37(9)
  Symmetry transformation: i: −x+1, y, z

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  Table 3.  Hydrogen Bond Lengths (Å) and Bond Angles (°) for Complexes 1 and 2

  Complex	D–H···A	d(D–H)	d(H···A)	d(D···A)	∠DHA
  1	C(3)–H(3)···Cl(1)i	0.95	2.67	3.437(1)	138
  2	C(6)–H(6)···O(1)i	0.93	2.52	3.361(5)	151
  	C(12)–H(12A)···O(1)ii	0.97	2.80	3.730(6)	162
  	C(13)–H(13A)···N(6)iii	0.97	2.61	3.424(6)	142
  	C(2)–H(2)···Cl(2)iv	0.93	2.96	3.581(5)	125
  	C(3)–H(3)···Cl(1)iii	0.93	2.56	3.481(5)	170
  	C(5)–H(5)···Cl(1)v	0.93	2.66	3.578(7)	171
  	C(11)–H(11A)···Cl(1)vi	0.97	2.71	3.653(5)	163
  	C(13)–H(13B)···Cl(1)iii	0.97	2.82	3.654(6)	144
  Symmetry codes for 1: (i) x + 1/2, y − 1/2, z; for 2: (i) −x, y − 1/2, −z + 1/2; (ii) x, −y + 3/2, z + 1/2; (iii) x, −y + 3/2, z − 1/2; (iv) −x + 1, y + 1/2, −z + 5/2; (v) x, −y + 1/2, z − 1/2; (vi) −x, −y + 1, −z + 1

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  Table 4.  Selected Bond Lengths (Å) and Bond Angles (°) for 2

  Bond	Dist.		Bond	Dist.		Bond	Dist.
  Ni(1)–Cl(1)	2.4040(14)		Ni(1)–Cl(2)	2.3290(14)		Ni(1)–Cl(2)i	2.5027(14)
  Ni(1)–N(1)	2.149(5)		Ni(1)–N(3)	2.163(5)		Ni(1)–N(5)	1.985(4)
  Angle	(°)		Angle	(°)		Angle	(°)
  N(1)–Ni(1)–Cl(1)	92.08(10)		N(1)–Ni(1)–Cl(2)	102.58(10)		N(1)–Ni(1)–Cl(2)i	87.63(10)
  N(1)–Ni(1)–N(3)	150.95(14)		N(1)–Ni(1)–N(5)	76.06(15)		N(3)–Ni(1)–Cl(1)	89.37(11)
  N(3)–Ni(1)–Cl(2)	106.13(12)		N(3)–Ni(1)–Cl(2)i	90.17(10)		N(3)–Ni(1)–N(5)	74.94(16)
  N(5)–Ni(1)–Cl(1)	89.48(11)		N(5)–Ni(1)–Cl(2)	174.64(11)		N(5)–Ni(1)–Cl(2)i	89.02(11)
  Cl(1)–Ni(1)–Cl(2)	95.77(5)		Cl(1)–Ni(1)–Cl(2)i	178.50(5)		Cl(2)–Ni(1)–Cl(2)i	85.73(5)
  Symmetry code: i: –x + 1, –y + 1, –z + 2

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