English

• 0.   Introduction

  In situ metal ion/ligand reactions have been arousing more interest not only in the crystal engineering of coordination polymers but also in synthetic organic chemistry to prepare novel organic molecules/ligands that are less available or very difficult to obtain under conventional conditions^[1-6]. It also acts as a bridge between coordination chemistry and synthetic organic chemistry to synthesize hybrid inorganic-organic complexes and to discover new synthetic organic reactions and understand their mechanisms^[7]. Hydro(solvo)thermal in situ ligand synthesis has been well studied from C—C bond formation^[8], hydroxylation^[9], hydrolysis^[10] to C—N coupling^[11] under high temperatures. Copper- catalyzed C—N bond formation continues to be one of the major interests of organic synthesis due to its important role in the construction of heterocyclic motifs^[12-17]. To the best of our knowledge, there are rare reported in situ ligand transformations involved in C—N coupling at normal conditions^[18]. The imidazo[1, 5-a]pyrazine systems are an important type of fused N- heterocyclic compounds due to their well-related biological and pharmacological activities. The unit structure has been found in some natural products, drugs, and drug candidates. A series of functionalized imidazo[1, 5-a]pyrazine derivatives have been synthesized and their biological activities as inhibitors or receptors are investigated^[19-20].

  Polynuclear Cu(Ⅱ) complexes are well investigated for the study of copper-containing enzymes, catalysis, and magnetic properties^[21-25]. Copper ion contains one unpaired electron (S=1/2) and exhibits various coordination modes. Pyrazine has a highly directive nature of the nitrogen lone pairs and attracts much attention in the construction of magnetic materials. Most pyrazine-bridged Cu complexes show antiferromagnetic properties, few examples are reported with ferromagnetic properties^[26]. We are interested in exploring the pyrazine-based N, N′-bis(pyrazin-2-ylmethyl)pyrazine-2, 3-dicarboxamide (H₂L1) ligand and its copper chemistry^[27]. Here, a novel trinuclear copper complex [Cu₃(L2)₂(SO₄)₂(H₂O)₇)]·8H₂O (1) (HL2=1-hydroxy-3-(pyrazin-2-yl)-N-(pyrazin-2-ylmethyl)imidazo[1, 5-a]pyrazine-8-carboxamide), was obtained by the reaction of H₂L1 with CuSO₄·5H₂O in aqueous solution under room temperature. The most interesting part is that an unexpected multi-substituted imidazo[1, 5-a]pyrazine scaffold ligand HL2 was serendipitously synthesized involving a C—N bond formation of C(sp³)H₂ with pyrazine N (Scheme 1).

  Scheme 1

  

  Scheme 1.  In situ ligand transformation from H₂L1 to HL2

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  1.   Experimental

  1.1   Materials and measurements

  All chemical reagents were commercially available and used as received. Elemental analyses for C, H, and N were performed on a Perkin-Elmer 240 analyzer. The FTIR spectra were recorded in KBr tablets in a range of 4 000-400 cm^-1 on a PerkinElmer FTIR spectrometer. Magnetic susceptibility measurements for the sample were performed on a Quantum Design PPMS instrument operated under a field of 1 kOe.

  1.2   Synthesis and characterization of H₂L1

  The ligand H₂L1 was prepared by the condensation reaction of dimethyl ester pyrazine-2, 3-di-carboxylate with 2-aminomethylpyrazine and characterized by X-ray crystal analysis^[26]. IR (KBr, cm^-1): 3 199 (w), 3 043 (w), 1 671(s), 1 655 (s), 1 576(w), 1 555(w), 1 517(m), 1 482(w), 1 471(w), 1 420(w), 1 411(m), 1 400 (m), 1 327(m), 1 295(m), 1 250(w), 1 215(w), 1 181(w), 1 156(w), 1 130(w), 1 037(s), 1 026(m), 929(w), 864(w), 820(m), 788(m), 730(w), 650(m), 631(w), 546(w), 495(w), 463(m).

  1.3   Synthesis of complex 1

  The aqueous solution of CuSO₄·5H₂O (0.125 g, 0.5 mmol) was dropped to the solution of H₂L1 (0.175 g, 0.5 mmol) in water, and the color changed from yellow to dark green. The mixed solution was kept stirring for 6 h. After the filtration, dark green filtrate was obtained. Slow evaporation of the filtrate for three weeks gave needle-like green crystals suitable for single-crystal X-ray analysis. Yield: 41% (based on CuSO₄·5H₂O). Anal. Calcd. for C₃₂H₅₂Cu₃N₁₆O₂₇S₂(%): C 28.52, H 3.89, N 16.63; Found(%): C 28.45, H 3.81, N 16.54. IR (KBr, cm^-1): 3 433 (m), 3 092 (w), 2 821 (w), 1 710(s), 1 624(s), 1 578(m), 1 530(m), 1 468(w), 1 406(m), 1 371(m), 1 328(s), 1 282 (w), 1 237(w), 1 199(m), 1 175(m), 1 153(m), 1 079(w), 1 032(w), 805(w), 724(m), 602(w), 569(w), 558(w).

  1.4   Structure determination

  Single-crystal X-ray diffraction data were recorded on a Bruker D8 QUEST diffractometer with Mo Kα (λ=0.071 073 nm) radiation at 296(15) K. The crystal structure was solved by direct methods. Hydrogen atom positions were initially determined by geometry and refined by a riding model. All non-hydrogen atoms were refined anisotropically by least squares on F ² using the SHELXTL 2014/7 program and OLEX2^[28-29]. The details of single-crystal diffraction data and selected bond lengths and bond angles are listed in Table 1 and 2, respectively.

  Table 1

  

  Table 1.  Crystal data and structure refinement for complex 1

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  Parameter	1		Parameter	1
  Empirical formula	C32H52Cu3N16O27S2		Dc / (g·cm-3)	1.784
  Formula weight	1 347.67		μ / mm-1	1.451
  Crystal system	Monoclinic		F(000)	2 764
  Space group	P21/c		θ range / (°)	0.944-27.593
  a / nm	2.166 4(3)		Reflection collected, unique	1 1374, 6 468 (Rint=0.054 0)
  b / nm	1.316 51(19)		Data, restraint, parameter	6 225, 39, 469
  c / nm	1.766 0(2)		Final R indices [I > 2σ(I)]*	R1=0.054 0, wR2=0.123 0
  β / (°)	95.053(2)		R indices (all data)	R1=0.116 5, wR2=0.149 1
  V / nm3	5.017 2(12)		Goodness of fit on F 2	1.013
  Z	4
  * R1=∑||Fo|-|Fc||/∑|Fo|, wR2=[∑w(Fo2-Fc2)2/∑w(Fo2)2]1/2.

  Table 2

  

  Table 2.  Selected bond distances (nm) and angles (°) for complex 1

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  Cu1—O1	0.235 0(3)	Cu1—O5	0.226 8(3)	Cu1—O6	0.199 2(3)
  Cu1—O7	0.199 0(3)	Cu1—N1	0.204 4(3)	Cu1—N9	0.203 7(4)
  Cu2—O8	0.192 9(3)	Cu2—O12	0.232 7(4)	Cu2—N2	0.202 3(3)
  Cu2—N3	0.192 6(3)	Cu2—N4	0.202 3(3)	Cu3—O15	0.193 9(3)
  Cu3—O16	0.257 9(5)	Cu3—O17	0.246 4(5)	Cu3—N10	0.201 1(4)
  Cu3—N11	0.192 2(3)	Cu3—N12	0.201 3(3)
  O5—Cu1—O1	149.49(13)	O6—Cu1—O1	90.32(13)	O6—Cu1—O5	89.18(13)
  O6—Cu1—N1	90.61(14)	O4—Cu1—N9	86.17(15)	O7—Cu1—O1	87.71(13)
  O7—Cu1—O5	92.79(13)	O7—Cu1—O6	177.99(14)	O7—Cu1—N1	88.97(16)
  O7—Cu1—N9	94.15(14)	N1—Cu1—O1	89.89(13)	N1—Cu1—O5	90.11(13)
  N9—Cu1—O1	87.46(13)	N9—Cu1—O5	92.52(13)	N9—Cu1—N1	175.81(16)
  O8—Cu2—O12	90.02(14)	O8—Cu2—N2	97.58(14)	O8—Cu2—N4	100.03(13)
  N2—Cu2—O12	94.96(14)	N2—Cu2—N4	160.35(14)	N3—Cu2—O8	173.33(16)
  N5—Cu2—O12	96.60(15)	N3—Cu2—N2	81.07(14)	N3—Cu2—N3	80.43(14)
  N4—Cu2—O12	93.69(14)	O15—Cu3—O16	83.43(14)	O15—Cu3—O17	85.20(14)
  O15—Cu3—N10	100.17(14)	O15—Cu3—N12	97.05(14)	O17—Cu3—O16	164.45(13)
  N10—Cu3—O16	84.30(14)	N10—Cu3—O17	87.31(15)	N10—Cu3—N12	162.77(14)
  N11—Cu3—N15	176.21(16)	N11—Cu3—O16	93.52(15)	N11—Cu3—O17	98.21(15)
  N11—Cu3—N10	81.72(14)	N11—Cu3—N12	81.05(14)	N12—Cu3—O16	97.11(14)
  N12—Cu3—O17	94.78(15)

  2.   Results and discussion

  2.1   Crystal structure

  X-ray crystal analysis reveals that complex 1 crystallizes in the monoclinic system with space group P2₁/c, and the structure is shown in Fig.1. It consists of a trinuclear copper unit and eight free water molecules. The central Cu1 is bound to two N atoms from in situ transformed L2^-, three O atoms from water molecules, and one O atom from a sulfate anion with a distorted octahedral geometry. The equatorial positions are occupied by two N atoms from the L2^- ligand and two O atoms from water molecules, the axial positions are occupied by one O atom from a sulfate ion and one O atom from a water molecule, with much longer Cu—O bond distances (0.235 0 and 0.226 8 nm) than the equatorial ones (in a range of 0.199 0-0.204 4 nm). It also functions as a bridging unit to connect two monomeric copper units. The coordination mode of Cu2 and Cu3 is different. Each deprotonated L2^- acts as a tridentate ligand, and the Cu2 ion is coordinated with three N atoms from L2^-, one O atom from water, and one O atom from sulfate respectively, forming a distorted square pyramidal geometry. The equatorial positions are occupied by three N atoms from the L2^- ligand and one O atom from a sulfate ion, and the axial positions are occupied by one O atom from a water molecule, with much longer Cu—O bond distances (0.232 7 nm) than the equatorial ones (in a range of 0.192 6-0.202 3 nm). Cu3 is coordinated with three N atoms from L2^- and three O atoms from water molecules, forming a distorted octahedral geometry. The equatorial positions are occupied by three N atoms from the L2^- ligand and one O atom from a water molecule, and the axial positions are occupied by two O atoms from water molecules, with much longer Cu—O bond distances (0.246 4 and 0.257 9 nm) than the equatorial ones (in a range of 0.192 2-0.201 3 nm). The three Cu ions are connected by two pyrazine rings from L2^-, forming a linear geometry. The Cu1…Cu2 and Cu1…Cu3 distances are similar: 0.682 0 and 0.678 3 nm, respectively, with an average value of 0.680 2 nm. Further investigation of the crystal packing structure of complex 1 reveals that there are multiple hydrogen bonding interactions among water molecules and sulfate anions. In addition, there is strong intramolecular hydrogen bonding between carbonyl O and phenol O (O14—H…O13, O19—H…O18). As seen in Fig.2, the trinuclear copper monomers are connected by multiple hydrogen bonding interactions between the coordinated water molecule and free water molecule or the sulfate oxygen atoms and water molecule to form a 2D network. A perspective view of hydrogen-bonding connectivity patterns of water molecules, sulfate oxygen atoms, and the surrounding Cu can be seen in Fig.3. The selected details of hydrogen bonding are listed in Table 3.

  Figure 1

  

  Figure 1.  Coordination environment of Cu(Ⅱ) ion in complex 1

  Solvent molecules and all hydrogen atoms except the OH group have been omitted for clarity.

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  Figure 2

  

  Figure 2.  Packing structure with multiple hydrogen bonding interactions in complex 1, where the atoms are drawn at the 30% probability level

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  Figure 3

  

  Figure 3.  A perspective view of hydrogen-bonding connectivity patterns of water molecules, sulfate oxygen atoms, and the surrounding Cu in complex 1, where the atoms are drawn at the 30% probability level

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  Table 3

  

  Table 3.  Selected hydrogen bond parameters for complex 1

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  D—H…A	d(D—H) / nm	d(H…A) / nm	d(H…A) / nm	∠DHA / (°)
  O14—H…O13	0.082	0.180	0.257 2(4)	155.6
  O19—H…O18	0.082	0.180	0.258 2(4)	158.7
  O5—H5A…O21ⅰ	0.089	0.186	0.272 7(5)	164.8
  O5—H5B…O2ⅱ	0.087	0.181	0.268 1(5)	176.9
  O6—H6A…O10ⅰ	0.082	0.194	0.270 1(5)	153.4
  O6—H6B…O2	0.083	0.181	0.259 9(5)	159.4
  O7—H7A…O10ⅲ	0.082	0.197	0.275 8(5)	162.3
  O7—H7B…O26ⅲ	0.083	0.187	0.261 9(6)	150.4
  O12—H12A…O3ⅲ	0.080	0.199	0.270 3(6)	147.8
  O12—H12B…O20ⅲ	0.091	0.190	0.276 5(5)	157.1
  O23—H23A…O11ⅰ	0.084	0.201	0.283 8(7)	165.1
  O23—H23B…O22	0.085	0.196	0.272 4(6)	149.7
  O25—H25A…O24	0.086	0.196	0.276 0(8)	164.3
  O25—H25B…O4	0.085	0.198	0.281 2(9)	147.2
  O27—H27A…O23	0.089	0.217	0.302 0(9)	160.0
  O27—H27B…O3ⅱ	0.086	0.211	0.294 8(8)	165.8
  Symmetry codes: ⅰ x, -y+1, z-1/2; ⅱ -x+1, y-1/2, -z+1/2; ⅲ -x+1, -y+1, -z+1.

  2.2   FTIR analysis

  As for the H₂L1 ligand, the weak absorption peaks at 3 199 and 3 043 cm^-1 are assigned to the C—H stretching vibration. Two strong absorption peaks at 1 671 and 1 655 cm^-1 can be attributed to the C=O stretching vibration. Those 1 555 and 1 518 cm^-1 peaks can be assigned to the C=N stretching vibration. As for complex 1, the broad absorption peak at 3 433 cm^-1 is assigned to the O—H stretching vibration from H₂O molecules. A strong band at 1 710 cm^-1 can be attributed to the stretching vibration of one C=O stretching vibration. These features are in good agreement with single-crystal X-ray analysis.

  2.3   Proposed reaction mechanism

  A reaction mechanism is proposed for the in situ transformation from H₂L1 to HL2 and the formation of complex 1 based on the structural analysis as shown in Scheme 2. The initial step involves the copper coordination with H₂L1, upon the coordination of H₂L1 to a copper ion, the properties (acidity, susceptibility to oxidation or reduction, electrophilic or nucleophilic character, etc.) can be significantly modified. In this case, the electrophilic copper center activates the carbonyl carbon and renders the amide-α-CH₂ group acidic so that deprotonation and subsequent nucleophilic attack from the pyrazine N occurs. The electron-withdrawing pyrazine substituent also facilitates the release of this hydrogen atom. Followed by the cyclization of the five-membered imidazo[1, 5-a]pyrazine scaffold. The driving force of this C—N bond formation could be the replacement of a less basic amide on the α-CH₂ carbon with a more basic one considering the electron-withdrawing nature of the pyrazine group.

  Scheme 2

  

  Scheme 2.  Probable mechanism of ligand transformation from H₂L1 to HL2

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  2.4   Magnetic property

  The temperature dependence of the magnetic susceptibilities of complex 1 was measured on a crystal sample in a temperature range of 2-300 K at 1 kOe as shown in Fig.4, the observed χ_MT value of 1 at 300 K was 0.828 cm³·mol^-1·K, which is significantly lower than expected for three isolated Cu(Ⅱ) ions (S=1/2, 1.125 cm³·mol^-1·K for g=2.0). When further cooling, the χ_MT value increased to reach a maximum of 1.175 cm³·mol^-1·K at around 26 K, this behavior reveals the presence of strong ferromagnetic interactions between the Cu(Ⅱ) ions. Then the χ_MT value decreased to 0.965 cm³·mol^-1·K at 2 K most likely due to weak intermolecular antiferromagnetic interactions. A spin Hamiltonian appropriate to describe the exchange interactions in a linear copper(Ⅱ) trimer can be written as Eq.1, where J describes the interaction between the adjacent copper ions and J′ describes the interactions between the outer copper ions. Assuming J′=0, from the Hamiltonian, the following Eq.2 for the thermal dependence of the magnetic susceptibility are given.

  $ H=-J(S_{1}S_{2}+S_{1}S_{3})-J′(S_{2}S_{3})$

  (1)

  $ {\chi }_{\mathrm{M}}=\frac{N{g}^{2}{\beta }^{2}}{4k(T-\theta )\left[1+\mathrm{e}\mathrm{x}\mathrm{p}\left(\frac{J}{kT}\right)+10\mathrm{e}\mathrm{x}\mathrm{p}\left(\frac{3J}{2kT}\right)\right]/\left[1+\mathrm{e}\mathrm{x}\mathrm{p}\left(\frac{J}{kT}\right)+2\mathrm{e}\mathrm{x}\mathrm{p}\left(\frac{3J}{2kT}\right)\right]} $

  (2)

  Figure 4

  

  Figure 4.  Temperature dependence of χ_MT and χ_M^-1 for the complex

  The red solid line corresponds to the best theoretical fit.

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  In Eq.2, we assume that the exchange integrals between the adjacent copper ions are the same and the integral between Cu2 and Cu3 is zero. The Weiss constant θ is introduced to consider the decrease in the magnetic moments at low temperature and the other symbols have their usual meaning. The best fitting for the experimental data gave J=94.03 cm^-3, θ=-0.45 K, g=1.60. The fitting results confirm the predominant ferromagnetic coupling in the adjacent Cu ions and weak antiferromagnetic interactions among the intertrimers. In comparison with other reported Cu-μ-pyz-Cu complexes, the coordination geometry of the adjacent Cu can be assigned as an equatorial-equatorial (eq-eq) combination of the two nitrogen lone pairs^[30-31]. To our knowledge, it is the first reported ferromagnetic complex in the eq-eq category of pyz-bridged Cu complexes.

  3.   Conclusions

  A novel trinuclear Cu(Ⅱ) complex [Cu₃(L2)₂(SO₄)₂(H₂O)₇)]·8H₂O has been serendipitously synthesized with in situ transformed HL2 ligand from the H₂L1 proligand and characterized by IR, single-crystal X-ray analysis and magnetic measurements. A possible in situ ligand transformation mechanism is proposed based on the structural analysis. A ferromagnetic coupling between the adjacent Cu(Ⅱ) ions was observed. It is the first reported ferromagnetic complex in the eq-eq category of pyz-bridged Cu complexes.

  
  
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  Scheme 1  In situ ligand transformation from H₂L1 to HL2

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  Figure 1  Coordination environment of Cu(Ⅱ) ion in complex 1

  Solvent molecules and all hydrogen atoms except the OH group have been omitted for clarity.

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  Figure 2  Packing structure with multiple hydrogen bonding interactions in complex 1, where the atoms are drawn at the 30% probability level

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  Figure 3  A perspective view of hydrogen-bonding connectivity patterns of water molecules, sulfate oxygen atoms, and the surrounding Cu in complex 1, where the atoms are drawn at the 30% probability level

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  Scheme 2  Probable mechanism of ligand transformation from H₂L1 to HL2

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  Figure 4  Temperature dependence of χ_MT and χ_M^-1 for the complex

  The red solid line corresponds to the best theoretical fit.

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  Table 1.  Crystal data and structure refinement for complex 1

  Parameter	1		Parameter	1
  Empirical formula	C32H52Cu3N16O27S2		Dc / (g·cm-3)	1.784
  Formula weight	1 347.67		μ / mm-1	1.451
  Crystal system	Monoclinic		F(000)	2 764
  Space group	P21/c		θ range / (°)	0.944-27.593
  a / nm	2.166 4(3)		Reflection collected, unique	1 1374, 6 468 (Rint=0.054 0)
  b / nm	1.316 51(19)		Data, restraint, parameter	6 225, 39, 469
  c / nm	1.766 0(2)		Final R indices [I > 2σ(I)]*	R1=0.054 0, wR2=0.123 0
  β / (°)	95.053(2)		R indices (all data)	R1=0.116 5, wR2=0.149 1
  V / nm3	5.017 2(12)		Goodness of fit on F 2	1.013
  Z	4
  * R1=∑||Fo|-|Fc||/∑|Fo|, wR2=[∑w(Fo2-Fc2)2/∑w(Fo2)2]1/2.

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  Table 2.  Selected bond distances (nm) and angles (°) for complex 1

  Cu1—O1	0.235 0(3)	Cu1—O5	0.226 8(3)	Cu1—O6	0.199 2(3)
  Cu1—O7	0.199 0(3)	Cu1—N1	0.204 4(3)	Cu1—N9	0.203 7(4)
  Cu2—O8	0.192 9(3)	Cu2—O12	0.232 7(4)	Cu2—N2	0.202 3(3)
  Cu2—N3	0.192 6(3)	Cu2—N4	0.202 3(3)	Cu3—O15	0.193 9(3)
  Cu3—O16	0.257 9(5)	Cu3—O17	0.246 4(5)	Cu3—N10	0.201 1(4)
  Cu3—N11	0.192 2(3)	Cu3—N12	0.201 3(3)
  O5—Cu1—O1	149.49(13)	O6—Cu1—O1	90.32(13)	O6—Cu1—O5	89.18(13)
  O6—Cu1—N1	90.61(14)	O4—Cu1—N9	86.17(15)	O7—Cu1—O1	87.71(13)
  O7—Cu1—O5	92.79(13)	O7—Cu1—O6	177.99(14)	O7—Cu1—N1	88.97(16)
  O7—Cu1—N9	94.15(14)	N1—Cu1—O1	89.89(13)	N1—Cu1—O5	90.11(13)
  N9—Cu1—O1	87.46(13)	N9—Cu1—O5	92.52(13)	N9—Cu1—N1	175.81(16)
  O8—Cu2—O12	90.02(14)	O8—Cu2—N2	97.58(14)	O8—Cu2—N4	100.03(13)
  N2—Cu2—O12	94.96(14)	N2—Cu2—N4	160.35(14)	N3—Cu2—O8	173.33(16)
  N5—Cu2—O12	96.60(15)	N3—Cu2—N2	81.07(14)	N3—Cu2—N3	80.43(14)
  N4—Cu2—O12	93.69(14)	O15—Cu3—O16	83.43(14)	O15—Cu3—O17	85.20(14)
  O15—Cu3—N10	100.17(14)	O15—Cu3—N12	97.05(14)	O17—Cu3—O16	164.45(13)
  N10—Cu3—O16	84.30(14)	N10—Cu3—O17	87.31(15)	N10—Cu3—N12	162.77(14)
  N11—Cu3—N15	176.21(16)	N11—Cu3—O16	93.52(15)	N11—Cu3—O17	98.21(15)
  N11—Cu3—N10	81.72(14)	N11—Cu3—N12	81.05(14)	N12—Cu3—O16	97.11(14)
  N12—Cu3—O17	94.78(15)

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  Table 3.  Selected hydrogen bond parameters for complex 1

  D—H…A	d(D—H) / nm	d(H…A) / nm	d(H…A) / nm	∠DHA / (°)
  O14—H…O13	0.082	0.180	0.257 2(4)	155.6
  O19—H…O18	0.082	0.180	0.258 2(4)	158.7
  O5—H5A…O21ⅰ	0.089	0.186	0.272 7(5)	164.8
  O5—H5B…O2ⅱ	0.087	0.181	0.268 1(5)	176.9
  O6—H6A…O10ⅰ	0.082	0.194	0.270 1(5)	153.4
  O6—H6B…O2	0.083	0.181	0.259 9(5)	159.4
  O7—H7A…O10ⅲ	0.082	0.197	0.275 8(5)	162.3
  O7—H7B…O26ⅲ	0.083	0.187	0.261 9(6)	150.4
  O12—H12A…O3ⅲ	0.080	0.199	0.270 3(6)	147.8
  O12—H12B…O20ⅲ	0.091	0.190	0.276 5(5)	157.1
  O23—H23A…O11ⅰ	0.084	0.201	0.283 8(7)	165.1
  O23—H23B…O22	0.085	0.196	0.272 4(6)	149.7
  O25—H25A…O24	0.086	0.196	0.276 0(8)	164.3
  O25—H25B…O4	0.085	0.198	0.281 2(9)	147.2
  O27—H27A…O23	0.089	0.217	0.302 0(9)	160.0
  O27—H27B…O3ⅱ	0.086	0.211	0.294 8(8)	165.8
  Symmetry codes: ⅰ x, -y+1, z-1/2; ⅱ -x+1, y-1/2, -z+1/2; ⅲ -x+1, -y+1, -z+1.

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