Hirshfeld and DFT analysis of the N-heterocyclic carbene proligand methyl­enebis(N-butyl­imid­a­zolium) as the aceto­nitrile-solvated diiodide salt

N-Heterocyclic carbene (NHC) based systems are usually exploited in the exploration of catalytic mechanisms and processes in organocatalysis, and homo- and heterogeneous catalysis. However, their mol­ecular structures have not received adequate attention. The NHC proligand methyl­enebis(N-butyl­imidazolium) has been synthesized as the aceto­nitrile solvate of the diiodide salt, C₁₅H₂₆N₄²⁺·2I⁻·CH₃CN [1,1′-methylenebis(3-butylimidazolium) diiodide acetonitrile monosolvate], and fully characterized. An inter­esting cation–anion connection pattern has been identified in the crystal lattice, in which three iodide anions inter­act simultaneously with the cisoid-oriented cation. A Hirshfeld surface analysis reveals the predominance of hydrogen bonding over anion–π inter­actions. This particular arrangement is observed in different methyl­ene-bridged bis­(imidazolium) cations bearing chloride or bromide counter-anions. Density functional theory (DFT) calculations with aceto­nitrile as solvent reproduce the geometry of the title cation.

S1. Introduction

The design, synthesis and study of N-heterocyclic carbene (NHC) based systems have grown exponentially over the last few years. Nowadays, they are assiduously utilized by organic and organometallic chemists, particularly in the exploration of catalytic mechanisms and processes in organocatalysis, and homogeneous and heterogeneous catalysis. However, despite their wide use and the fact that imidazolium salts have been known for many years, their molecular structures have not received adequate attention.

We report here the characterization of the bis­(imidazolium) salt methyl­enebis(N-butyl­imidazolium) diiodide, [H₂BisBuIm]I₂, and its isolation as the crystalline material [H₂BisBuIm]I₂·CH₃CN, (I), in combination with a Hirshfeld surface analysis and density functional theory (DFT) calculations. Although the [H₂BisBuIm]²⁺ cation has been frequently utilized, its solid-state structure has not been described previously (see, for example, Poyatos et al., 2003; Quezada et al., 2003, 2004; Jin et al., 2005; Lee et al., 2008; Yang et al., 2008, 2010, 2016; Cheng et al., 2010; Mercs et al., 2011; Sun et al., 2011; Saha et al., 2012; Lai et al., 2013; Zou et al., 2014; Aliaga-Lavrijsen et al., 2015; Cebollada et al., 2015; Li et al., 2015; Krüger et al., 2015; Sun et al., 2015).

S2. Experimental

S2.1. Synthesis and crystallization

[H₂BisBuIm]I₂ was synthesized according to the method of Cebollada et al. (2015). Colourless crystals of [H₂BisBuIm]I₂·CH₃CN, (I), were obtained from a saturated solution of [H₂BisBuIm]I₂ in aceto­nitrile (277 K, 10 ml, one week). Further information is summarized in the Supporting information.

S2.2. NMR and elemental analysis

NMR spectra were recorded on a Bruker Avance 300 MHz or a Bruker ARX 300 MHz instruments. To reference chemical shifts (p.p.m.) residual solvent peaks were used. Elemental analyses (C/H/N) were acquired with a PerkinElmer 2400 CHNS/O analyzer. ¹H NMR (CD₃CN, 300 MHz): δ 9.83 (s, 2H. H2), 8.09 (m, 2H, H5), 7.49 (m, 2H, H4), 6.85 (s, 2H, N–CH₂–N bridge), 4.21 (t, 4H, J_H–H = 7.3 Hz, N—CH₂–C), 1.87 (m, 4H, N—CH₂–CH₂—C), 1.36 (m, 4H, C—CH₂—CH₃), 0.95 (t, 6H, J_H–H = 7.3 Hz, C—CH₃). ¹³C NMR (CD₃CN, 300 MHz): δ 138.1 (C2), 124.0 (C4), 123.4 (C5), 58.5 (N—CH₂—N bridge), 50.9 (N—CH₂—C), 32.09 (N—CH₂—CH₂—C), 19.9 (C–CH₂–CH₃), 13.7 (C—CH₃). Analysis calculated for C₁₅H₂₄N₄I₂: C 34.88, H 5.08, N 10.85%; found: C 34.90, H 4.95, N 10.92. NMR characterization (¹³C, HMBC and HSQC) is compiled in the Supporting information.

S2.3. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H = 0.98 Å and U_iso(H) = 1.5U_eq(C) for methyl groups, C–H = 0.99 Å and U_iso(H) = 1.2U_eq(C) for methyl­ene groups, and C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C) for aryl groups. A low-angle reflection (011), with an intensity strongly affected by the beam stop, was omitted from the refinement.

S3. Results and discussion

For the preparation of the methyl­enebis(N-butyl­imidazolium) cation, [H₂BisBuIm]²⁺, several pathways have been reported over the years. A general synthetic description could be as follows: a mixture of 1-butyl­imidazole and CH₂X₂ [X = Cl (Lee et al., 2008; Lai et al., 2013; Li et al., 2015), Br (Cheng et al., 2010; Zou et al., 2014; Sun et al., 2015) or I (Poyatos et al., 2003; Quezada et al., 2003, 2004; Yang et al., 2008, 2010; Mercs et al., 2011; Sun et al., 2011; Aliaga-Lavrijsen et al., 2015)] was stirred in refluxing nonpolar or polar aprotic solvents until a white solid precipitated. This product was then isolated by filtration and washed, obtaining high yields in all cases. Particularly, when X = Cl, di­chloro­methane was utilized both as solvent and rea­ctant. There, the reaction mixture was heated to 358 K (1 d) using sealed containers. The obtained product was precipitated using either Et₂O (Lee et al., 2008; Lai et al., 2013) or a mixture of MeOH and tetra­hydro­furan (Li et al., 2015). Good yields were also obtained by refluxing 1-butyl­imidazole and CH₂I₂ in aceto­nitrile, followed by filtration and purification with Et₂O (Sun et al., 2015). This last procedure has been applied for the isolation of [H₂BisBuIm]I₂ in our case (Vellé et al., 2014; Cebollada et al., 2015). Further recrystallization from a saturated solution of [H₂BisBuIm]I₂ in aceto­nitrile afforded the corresponding [H₂BisBuIm]I₂·CH₃CN solvate, (I), which was suitable for X-ray structural investigation. Two additional options, used less frequently, are: (i) starting from bis­(imidazol-1-yl)methane, which after reacting with the adequate qu­antity of BuX (X = Br or I; Jin et al., 2005) yields the corresponding bis­(imidazolium) salt; (ii) following a ring closure synthetic strategy (Saha et al., 2012), which also offers the possibility of obtaining chiral imidazolium salts (Herrmann et al., 1996).

The resulting structure consists of two imidazole rings bridged through N atoms by a methyl­ene group, which incorporate two additional butyl pendants at their available N-atom sites. A view of the [H₂BisBuIm]²⁺ cation is shown in Fig. 1. Selected bond lengths and angles are summarized in Table 2. Both protonated C12 and C22 atoms form inter­nal N—C—N angles of 108.64 (17) (N13—C12—N11) and 108.14 (18)° (N23—C22—N21), which are not significantly different. This angle is usually strongly affected upon metal coordination and subsequent loss of H⁺; reported examples exhibit values of 101.9–105.2°. The rest of the geometrical values are not affected to such an extent. Both imidazolium rings are cisoid disposed and display a dihedral angle of 74.71 (7)° between their mean planes.

Regarding the crystal packing, mutual positioning of the iodide anions around the [H₂BisBuIm]²⁺ cation allows for hydrogen-bonding inter­actions, fashioned in a novel cation–anion inter­acting pattern (Fig. 2): C12(—H12)···I1 = 3.746 (2) Å, C22(—H22)···I1 = 3.790 (2) Å, C15(—H15)···I2 = 3.957 (2) Å and C25(—H25)···I2 = 3.857 (2) Å. As expected, C···I distances involving the C12 and C22 sites are shorter in comparison with C15 and C25. In addition, the I1 anion exhibits relatively short anion–π inter­actions: inter­molecular distances between I1 and the acidic C12 and C22 sites are 3.5736 (19) and 3.4995 (19) Å, respectively. We have also identified this inter­action pattern in chloride and bromide salts, in which methyl­ene-bridged bis­(imidazolium) cations with different N-atom pendant groups are involved (Leclercq et al., 2009; Ahrens & Strassner, 2006; Liu et al., 2009).

A Hirshfeld surface analysis (Spackman & Jayatilaka, 2009; Wolff et al., 2012) revealed that hydrogen-bonding inter­actions in [H₂BisBuIm]²⁺ are associated with 13.8% of the surface area, whereas anion–π contacts cover its 2.7% (Fig. 3). These numbers support the predominance of hydrogen bonding in the crystal packing, but also an important contribution of the anion–π inter­actions. For comparison, the N-phenyl derivative, i.e. methyl­enebis(N-phenyl­imidazolium) (Leclercq et al., 2009), which displays two crystallographically different cations (bearing N-phenyl pendants), two water molecules and four bromide anions in the asymmetric unit, exhibits anion–π inter­actions associated with ca 2.4% of the surface area, and hydrogen bonding occupying nearly 16% (including water molecules). The N-mesityl cation (Ahrens & Strassner, 2006) inter­acts with three Cl^- anions and exhibits smaller values, of 11.7% (hydrogen bonding) and 1.2% (anion–π), due probably to the bulky pendants, and the smaller size of the chloride anions. In this particular series, it seems to be a correlation between the size of the counteranions and the contribution of the anion–π inter­actions.

The ¹H NMR spectrum (room temperature, CD₃CN) of [H₂BisBuIm]I₂ (see Fig. S1 in the Supporting Information) shows the H2 proton signals (protons at the C12 and C22 atoms in Fig. 1) as a singlet at 9.83 p.p.m., and the H5 (at the C15 and C25 atoms) and H4 (at the C14 and C24 atoms) resonances as two pseudotriplets centred at 8.09 and 7.49 p.p.m., respectively. The methyl­ene bridge signal is observed as a singlet at 6.85 p.p.m., denoting rotation about this position in solution. The CH₂ groups of the side arms appear as a triplet, a pseudoquintuplet and a pseudosextuplet centered at 4.21, 1.87 and 1.36 p.p.m., respectively, and the methyl group as a triplet centred at 0.95 p.p.m. (see Fig. S1 in the Supporting Information).

Quantum chemical calculations were performed with the GAUSSIAN09 (Frisch et al., 2009) software using the M11L functional (Peverati & Truhlar, 2012) and the polarizable continuum method (SMD) (Marenich et al., 2009). This combination has demonstrated to reproduce accurately the geometry of the cationic N-heterocyclic hemicytosinium pair (Vellé et al., 2015). Here, we utilized aceto­nitrile as solvent – as the title compound is an aceto­nitrile solvate – and the 6-311++G(d,p) and SDD (Andrae et al., 1990; Dolg et al., 1993) basis sets. Salient geometrical parameters of the optimized molecules agree well with the solid-state structure of [H₂BisBuIm]²⁺: intra­molecular angles match within the standard deviation (3σ) limits, and bond distances deviate a maximum of 0.01 Å. From the precision exhibited, this theoretical approach is a well suited tool for the study of this kind of heterocyclic cations. However, the anion–π inter­actions exhibited in the solid-state structure of (I) are not anti­cipated by these calculations, which result in significantly longer I1···C12 and I1···C22 distances. Coordinates and tables including geometrical records are reported in the Supporting information.

In summary, we have synthesized and fully characterized [H₂BisBuIm]I₂ and its corresponding [H₂BisBuIm]I₂·CH₃CN solvate. The crystal arrangement of the latter exhibits a cation–anion connection pattern, which can be identified in related methyl­ene-bridged bis­(imidazolium) salts incorporating chloride and bromide as counter-anions. A Hirshfeld surface analysis reveals a broader surface area associated to hydrogen bonding in comparison to the relatively close anion–π contacts. Quantum chemical calculations (M11L, SMD aceto­nitrile) reproduce the molecular geometries exhibited by the [H₂BisBuIm]²⁺ cation in solid state with high precision.

Structure description

The design, synthesis and study of N-heterocyclic carbene (NHC) based systems have grown exponentially over the last few years. Nowadays, they are assiduously utilized by organic and organometallic chemists, particularly in the exploration of catalytic mechanisms and processes in organocatalysis, and homogeneous and heterogeneous catalysis. However, despite their wide use and the fact that imidazolium salts have been known for many years, their molecular structures have not received adequate attention.

We report here the characterization of the bis­(imidazolium) salt methyl­enebis(N-butyl­imidazolium) diiodide, [H₂BisBuIm]I₂, and its isolation as the crystalline material [H₂BisBuIm]I₂·CH₃CN, (I), in combination with a Hirshfeld surface analysis and density functional theory (DFT) calculations. Although the [H₂BisBuIm]²⁺ cation has been frequently utilized, its solid-state structure has not been described previously (see, for example, Poyatos et al., 2003; Quezada et al., 2003, 2004; Jin et al., 2005; Lee et al., 2008; Yang et al., 2008, 2010, 2016; Cheng et al., 2010; Mercs et al., 2011; Sun et al., 2011; Saha et al., 2012; Lai et al., 2013; Zou et al., 2014; Aliaga-Lavrijsen et al., 2015; Cebollada et al., 2015; Li et al., 2015; Krüger et al., 2015; Sun et al., 2015).

NMR spectra were recorded on a Bruker Avance 300 MHz or a Bruker ARX 300 MHz instruments. To reference chemical shifts (p.p.m.) residual solvent peaks were used. Elemental analyses (C/H/N) were acquired with a PerkinElmer 2400 CHNS/O analyzer. ¹H NMR (CD₃CN, 300 MHz): δ 9.83 (s, 2H. H2), 8.09 (m, 2H, H5), 7.49 (m, 2H, H4), 6.85 (s, 2H, N–CH₂–N bridge), 4.21 (t, 4H, J_H–H = 7.3 Hz, N—CH₂–C), 1.87 (m, 4H, N—CH₂–CH₂—C), 1.36 (m, 4H, C—CH₂—CH₃), 0.95 (t, 6H, J_H–H = 7.3 Hz, C—CH₃). ¹³C NMR (CD₃CN, 300 MHz): δ 138.1 (C2), 124.0 (C4), 123.4 (C5), 58.5 (N—CH₂—N bridge), 50.9 (N—CH₂—C), 32.09 (N—CH₂—CH₂—C), 19.9 (C–CH₂–CH₃), 13.7 (C—CH₃). Analysis calculated for C₁₅H₂₄N₄I₂: C 34.88, H 5.08, N 10.85%; found: C 34.90, H 4.95, N 10.92. NMR characterization (¹³C, HMBC and HSQC) is compiled in the Supporting information.

For the preparation of the methyl­enebis(N-butyl­imidazolium) cation, [H₂BisBuIm]²⁺, several pathways have been reported over the years. A general synthetic description could be as follows: a mixture of 1-butyl­imidazole and CH₂X₂ [X = Cl (Lee et al., 2008; Lai et al., 2013; Li et al., 2015), Br (Cheng et al., 2010; Zou et al., 2014; Sun et al., 2015) or I (Poyatos et al., 2003; Quezada et al., 2003, 2004; Yang et al., 2008, 2010; Mercs et al., 2011; Sun et al., 2011; Aliaga-Lavrijsen et al., 2015)] was stirred in refluxing nonpolar or polar aprotic solvents until a white solid precipitated. This product was then isolated by filtration and washed, obtaining high yields in all cases. Particularly, when X = Cl, di­chloro­methane was utilized both as solvent and rea­ctant. There, the reaction mixture was heated to 358 K (1 d) using sealed containers. The obtained product was precipitated using either Et₂O (Lee et al., 2008; Lai et al., 2013) or a mixture of MeOH and tetra­hydro­furan (Li et al., 2015). Good yields were also obtained by refluxing 1-butyl­imidazole and CH₂I₂ in aceto­nitrile, followed by filtration and purification with Et₂O (Sun et al., 2015). This last procedure has been applied for the isolation of [H₂BisBuIm]I₂ in our case (Vellé et al., 2014; Cebollada et al., 2015). Further recrystallization from a saturated solution of [H₂BisBuIm]I₂ in aceto­nitrile afforded the corresponding [H₂BisBuIm]I₂·CH₃CN solvate, (I), which was suitable for X-ray structural investigation. Two additional options, used less frequently, are: (i) starting from bis­(imidazol-1-yl)methane, which after reacting with the adequate qu­antity of BuX (X = Br or I; Jin et al., 2005) yields the corresponding bis­(imidazolium) salt; (ii) following a ring closure synthetic strategy (Saha et al., 2012), which also offers the possibility of obtaining chiral imidazolium salts (Herrmann et al., 1996).

The resulting structure consists of two imidazole rings bridged through N atoms by a methyl­ene group, which incorporate two additional butyl pendants at their available N-atom sites. A view of the [H₂BisBuIm]²⁺ cation is shown in Fig. 1. Selected bond lengths and angles are summarized in Table 2. Both protonated C12 and C22 atoms form inter­nal N—C—N angles of 108.64 (17) (N13—C12—N11) and 108.14 (18)° (N23—C22—N21), which are not significantly different. This angle is usually strongly affected upon metal coordination and subsequent loss of H⁺; reported examples exhibit values of 101.9–105.2°. The rest of the geometrical values are not affected to such an extent. Both imidazolium rings are cisoid disposed and display a dihedral angle of 74.71 (7)° between their mean planes.

Regarding the crystal packing, mutual positioning of the iodide anions around the [H₂BisBuIm]²⁺ cation allows for hydrogen-bonding inter­actions, fashioned in a novel cation–anion inter­acting pattern (Fig. 2): C12(—H12)···I1 = 3.746 (2) Å, C22(—H22)···I1 = 3.790 (2) Å, C15(—H15)···I2 = 3.957 (2) Å and C25(—H25)···I2 = 3.857 (2) Å. As expected, C···I distances involving the C12 and C22 sites are shorter in comparison with C15 and C25. In addition, the I1 anion exhibits relatively short anion–π inter­actions: inter­molecular distances between I1 and the acidic C12 and C22 sites are 3.5736 (19) and 3.4995 (19) Å, respectively. We have also identified this inter­action pattern in chloride and bromide salts, in which methyl­ene-bridged bis­(imidazolium) cations with different N-atom pendant groups are involved (Leclercq et al., 2009; Ahrens & Strassner, 2006; Liu et al., 2009).

A Hirshfeld surface analysis (Spackman & Jayatilaka, 2009; Wolff et al., 2012) revealed that hydrogen-bonding inter­actions in [H₂BisBuIm]²⁺ are associated with 13.8% of the surface area, whereas anion–π contacts cover its 2.7% (Fig. 3). These numbers support the predominance of hydrogen bonding in the crystal packing, but also an important contribution of the anion–π inter­actions. For comparison, the N-phenyl derivative, i.e. methyl­enebis(N-phenyl­imidazolium) (Leclercq et al., 2009), which displays two crystallographically different cations (bearing N-phenyl pendants), two water molecules and four bromide anions in the asymmetric unit, exhibits anion–π inter­actions associated with ca 2.4% of the surface area, and hydrogen bonding occupying nearly 16% (including water molecules). The N-mesityl cation (Ahrens & Strassner, 2006) inter­acts with three Cl^- anions and exhibits smaller values, of 11.7% (hydrogen bonding) and 1.2% (anion–π), due probably to the bulky pendants, and the smaller size of the chloride anions. In this particular series, it seems to be a correlation between the size of the counteranions and the contribution of the anion–π inter­actions.

The ¹H NMR spectrum (room temperature, CD₃CN) of [H₂BisBuIm]I₂ (see Fig. S1 in the Supporting Information) shows the H2 proton signals (protons at the C12 and C22 atoms in Fig. 1) as a singlet at 9.83 p.p.m., and the H5 (at the C15 and C25 atoms) and H4 (at the C14 and C24 atoms) resonances as two pseudotriplets centred at 8.09 and 7.49 p.p.m., respectively. The methyl­ene bridge signal is observed as a singlet at 6.85 p.p.m., denoting rotation about this position in solution. The CH₂ groups of the side arms appear as a triplet, a pseudoquintuplet and a pseudosextuplet centered at 4.21, 1.87 and 1.36 p.p.m., respectively, and the methyl group as a triplet centred at 0.95 p.p.m. (see Fig. S1 in the Supporting Information).

Quantum chemical calculations were performed with the GAUSSIAN09 (Frisch et al., 2009) software using the M11L functional (Peverati & Truhlar, 2012) and the polarizable continuum method (SMD) (Marenich et al., 2009). This combination has demonstrated to reproduce accurately the geometry of the cationic N-heterocyclic hemicytosinium pair (Vellé et al., 2015). Here, we utilized aceto­nitrile as solvent – as the title compound is an aceto­nitrile solvate – and the 6-311++G(d,p) and SDD (Andrae et al., 1990; Dolg et al., 1993) basis sets. Salient geometrical parameters of the optimized molecules agree well with the solid-state structure of [H₂BisBuIm]²⁺: intra­molecular angles match within the standard deviation (3σ) limits, and bond distances deviate a maximum of 0.01 Å. From the precision exhibited, this theoretical approach is a well suited tool for the study of this kind of heterocyclic cations. However, the anion–π inter­actions exhibited in the solid-state structure of (I) are not anti­cipated by these calculations, which result in significantly longer I1···C12 and I1···C22 distances. Coordinates and tables including geometrical records are reported in the Supporting information.

In summary, we have synthesized and fully characterized [H₂BisBuIm]I₂ and its corresponding [H₂BisBuIm]I₂·CH₃CN solvate. The crystal arrangement of the latter exhibits a cation–anion connection pattern, which can be identified in related methyl­ene-bridged bis­(imidazolium) salts incorporating chloride and bromide as counter-anions. A Hirshfeld surface analysis reveals a broader surface area associated to hydrogen bonding in comparison to the relatively close anion–π contacts. Quantum chemical calculations (M11L, SMD aceto­nitrile) reproduce the molecular geometries exhibited by the [H₂BisBuIm]²⁺ cation in solid state with high precision.

Synthesis and crystallization

[H₂BisBuIm]I₂ was synthesized according to the method of Cebollada et al. (2015). Colourless crystals of [H₂BisBuIm]I₂·CH₃CN, (I), were obtained from a saturated solution of [H₂BisBuIm]I₂ in aceto­nitrile (277 K, 10 ml, one week). Further information is summarized in the Supporting information.

Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H = 0.98 Å and U_iso(H) = 1.5U_eq(C) for methyl groups, C–H = 0.99 Å and U_iso(H) = 1.2U_eq(C) for methyl­ene groups, and C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C) for aryl groups. A low-angle reflection (011), with an intensity strongly affected by the beam stop, was omitted from the refinement.

Computing details

Data collection: APEX2 (Bruker, 2011); cell refinement: SAINT (Bruker, 2011); data reduction: SAINT (Bruker, 2011); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: SHELXTL (Bruker, 2011); software used to prepare material for publication: SHELXTL (Bruker, 2011).

Figures

	Fig. 1. View of the solid-state structure of the [H2BisBuIm]^2+ cation of (I). Displacement ellipsoids are drawn at the 40% probability level.
	Fig. 2. View of the disposition of the diiodide anions around the [H2BisBuIm]^2+ cation in (I).
	Fig. 3. Contour of the Hirshfeld surface for the [H2BisBuIm]^2+ cation Of (I).

1,1'-Methylenebis(3-butylimidazolium) diiodide acetonitrile monosolvate

Crystal data

C15H26N4^2+·2I^−·C2H3N	Z = 2
Mr = 557.25	F(000) = 544
Triclinic, P1	Dx = 1.636 Mg m^−3
a = 5.2513 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 13.9534 (6) Å	Cell parameters from 9931 reflections
c = 16.0336 (7) Å	θ = 2.2–28.5°
α = 101.7655 (5)°	µ = 2.79 mm^−1
β = 93.2300 (5)°	T = 100 K
γ = 99.0746 (5)°	Prisms, colourless
V = 1130.99 (8) Å^3	0.45 × 0.25 × 0.15 mm

Data collection

Bruker APEXII CCD diffractometer	4794 reflections with I > 2σ(I)
Radiation source: sealed tube	Rint = 0.017
φ and ω scans	θmax = 28.6°, θmin = 1.5°
Absorption correction: multi-scan (SADABS; Bruker, 2011)	h = −6→6
Tmin = 0.441, Tmax = 0.658	k = −18→18
14589 measured reflections	l = −20→21
5242 independent reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.019	H-atom parameters constrained
wR(F^2) = 0.047	w = 1/[σ^2(Fo^2) + (0.0224P)^2 + 0.5576P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max = 0.001
5242 reflections	Δρmax = 0.92 e Å^−3
220 parameters	Δρmin = −0.42 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
I1	0.42021 (2)	0.58093 (2)	0.35311 (2)	0.01844 (4)
I2	0.72032 (2)	0.76194 (2)	0.00980 (2)	0.02117 (4)
N11	−0.1149 (3)	0.36742 (12)	0.23753 (10)	0.0182 (3)
C12	−0.1418 (4)	0.39156 (14)	0.32081 (12)	0.0182 (4)
H12	−0.2492	0.4357	0.3468	0.022*
N13	0.0060 (3)	0.34381 (12)	0.36144 (10)	0.0162 (3)
C14	0.1377 (4)	0.28869 (15)	0.30215 (13)	0.0195 (4)
H14	0.2585	0.2481	0.3140	0.023*
C15	0.0630 (4)	0.30320 (15)	0.22457 (13)	0.0204 (4)
H15	0.1206	0.2750	0.1714	0.024*
C16	0.0363 (4)	0.35405 (15)	0.45488 (12)	0.0192 (4)
H161	−0.0679	0.4031	0.4820	0.023*
H162	0.2201	0.3797	0.4760	0.023*
C17	−0.0480 (4)	0.25647 (15)	0.48106 (13)	0.0201 (4)
H171	−0.0251	0.2677	0.5442	0.024*
H172	0.0656	0.2092	0.4576	0.024*
C18	−0.3285 (4)	0.20997 (15)	0.45049 (13)	0.0216 (4)
H181	−0.4391	0.2614	0.4634	0.026*
H182	−0.3441	0.1853	0.3877	0.026*
C19	−0.4247 (5)	0.12446 (17)	0.49273 (16)	0.0313 (5)
H191	−0.5990	0.0923	0.4671	0.047*
H192	−0.4298	0.1501	0.5541	0.047*
H193	−0.3073	0.0760	0.4841	0.047*
N21	−0.0729 (3)	0.49440 (12)	0.15562 (10)	0.0196 (3)
C22	−0.0651 (4)	0.58842 (15)	0.19695 (13)	0.0190 (4)
H22	−0.1740	0.6105	0.2396	0.023*
N23	0.1212 (3)	0.64552 (13)	0.16814 (11)	0.0188 (3)
C24	0.2411 (4)	0.58611 (16)	0.10818 (13)	0.0237 (4)
H24	0.3823	0.6079	0.0782	0.028*
C25	0.1201 (4)	0.49146 (16)	0.10025 (13)	0.0232 (4)
H25	0.1596	0.4340	0.0638	0.028*
C26	0.2100 (4)	0.75326 (15)	0.19954 (14)	0.0225 (4)
H261	0.2452	0.7841	0.1500	0.027*
H262	0.3748	0.7640	0.2361	0.027*
C27	0.0177 (4)	0.80450 (15)	0.25005 (13)	0.0219 (4)
H271	−0.0055	0.7790	0.3029	0.026*
H272	−0.1520	0.7899	0.2157	0.026*
C28	0.1121 (4)	0.91589 (16)	0.27323 (16)	0.0290 (5)
H281	0.1403	0.9404	0.2201	0.035*
H282	0.2807	0.9298	0.3081	0.035*
C29	−0.0770 (5)	0.9724 (2)	0.3228 (2)	0.0431 (6)
H291	−0.0081	1.0438	0.3352	0.065*
H292	−0.1005	0.9504	0.3765	0.065*
H293	−0.2441	0.9593	0.2884	0.065*
C31	−0.2422 (4)	0.40854 (15)	0.17320 (13)	0.0232 (4)
H311	−0.4040	0.4288	0.1937	0.028*
H312	−0.2884	0.3570	0.1198	0.028*
N41	0.4743 (4)	0.13329 (17)	0.21320 (14)	0.0380 (5)
C42	0.5987 (4)	0.10146 (17)	0.16261 (15)	0.0286 (5)
C43	0.7612 (5)	0.06174 (19)	0.09817 (19)	0.0414 (6)
H431	0.7504	0.0945	0.0498	0.062*
H432	0.7016	−0.0099	0.0782	0.062*
H433	0.9412	0.0740	0.1231	0.062*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.01837 (7)	0.02001 (7)	0.01690 (7)	0.00343 (5)	0.00282 (5)	0.00347 (5)
I2	0.02533 (7)	0.02081 (7)	0.01639 (7)	0.00167 (5)	0.00536 (5)	0.00265 (5)
N11	0.0206 (8)	0.0169 (8)	0.0165 (8)	0.0000 (6)	0.0020 (6)	0.0046 (6)
C12	0.0171 (9)	0.0172 (9)	0.0194 (9)	0.0004 (7)	0.0034 (7)	0.0037 (7)
N13	0.0180 (8)	0.0153 (8)	0.0163 (8)	0.0022 (6)	0.0049 (6)	0.0050 (6)
C14	0.0200 (9)	0.0173 (9)	0.0220 (10)	0.0034 (7)	0.0086 (8)	0.0043 (8)
C15	0.0225 (10)	0.0178 (10)	0.0201 (10)	0.0014 (7)	0.0074 (8)	0.0026 (8)
C16	0.0225 (10)	0.0201 (10)	0.0145 (9)	0.0021 (7)	0.0024 (7)	0.0035 (7)
C17	0.0215 (10)	0.0226 (10)	0.0186 (9)	0.0046 (8)	0.0037 (8)	0.0084 (8)
C18	0.0231 (10)	0.0200 (10)	0.0222 (10)	0.0018 (8)	0.0045 (8)	0.0067 (8)
C19	0.0320 (12)	0.0255 (11)	0.0400 (13)	0.0025 (9)	0.0106 (10)	0.0154 (10)
N21	0.0243 (9)	0.0189 (8)	0.0156 (8)	0.0010 (7)	0.0013 (7)	0.0061 (6)
C22	0.0179 (9)	0.0227 (10)	0.0182 (9)	0.0035 (7)	0.0031 (7)	0.0078 (8)
N23	0.0202 (8)	0.0202 (8)	0.0179 (8)	0.0038 (6)	0.0045 (6)	0.0074 (6)
C24	0.0275 (11)	0.0273 (11)	0.0192 (10)	0.0073 (8)	0.0082 (8)	0.0080 (8)
C25	0.0306 (11)	0.0232 (11)	0.0173 (9)	0.0064 (8)	0.0049 (8)	0.0057 (8)
C26	0.0218 (10)	0.0181 (10)	0.0280 (11)	0.0011 (8)	0.0073 (8)	0.0064 (8)
C27	0.0215 (10)	0.0231 (10)	0.0218 (10)	0.0029 (8)	0.0039 (8)	0.0067 (8)
C28	0.0253 (11)	0.0234 (11)	0.0383 (13)	0.0037 (8)	0.0071 (9)	0.0055 (9)
C29	0.0397 (14)	0.0299 (13)	0.0573 (17)	0.0101 (11)	0.0118 (13)	−0.0013 (12)
C31	0.0239 (10)	0.0225 (11)	0.0220 (10)	−0.0025 (8)	−0.0032 (8)	0.0087 (8)
N41	0.0377 (12)	0.0404 (12)	0.0370 (12)	0.0106 (9)	0.0096 (10)	0.0059 (10)
C42	0.0304 (12)	0.0210 (11)	0.0337 (12)	0.0023 (9)	0.0019 (10)	0.0059 (9)
C43	0.0442 (15)	0.0279 (13)	0.0510 (16)	0.0065 (11)	0.0214 (13)	0.0016 (11)

Geometric parameters (Å, º)

N11—C12	1.330 (3)	C22—H22	0.9500
N11—C15	1.389 (3)	N23—C24	1.384 (3)
N11—C31	1.457 (3)	N23—C26	1.475 (3)
C12—N13	1.324 (3)	C24—C25	1.350 (3)
C12—H12	0.9500	C24—H24	0.9500
N13—C14	1.385 (2)	C25—H25	0.9500
N13—C16	1.473 (2)	C26—C27	1.507 (3)
C14—C15	1.347 (3)	C26—H261	0.9900
C14—H14	0.9500	C26—H262	0.9900
C15—H15	0.9500	C27—C28	1.517 (3)
C16—C17	1.513 (3)	C27—H271	0.9900
C16—H161	0.9900	C27—H272	0.9900
C16—H162	0.9900	C28—C29	1.523 (3)
C17—C18	1.523 (3)	C28—H281	0.9900
C17—H171	0.9900	C28—H282	0.9900
C17—H172	0.9900	C29—H291	0.9800
C18—C19	1.522 (3)	C29—H292	0.9800
C18—H181	0.9900	C29—H293	0.9800
C18—H182	0.9900	C31—H311	0.9900
C19—H191	0.9800	C31—H312	0.9900
C19—H192	0.9800	N41—C42	1.134 (3)
C19—H193	0.9800	C42—C43	1.456 (3)
N21—C22	1.337 (3)	C43—H431	0.9800
N21—C25	1.384 (3)	C43—H432	0.9800
N21—C31	1.461 (2)	C43—H433	0.9800
C22—N23	1.327 (3)
C12—N11—C15	108.78 (16)	C25—C24—N23	107.27 (18)
N13—C12—N11	108.64 (17)	C25—C24—H24	126.4
N13—C12—H12	125.7	N23—C24—H24	126.4
N11—C12—H12	125.7	C24—C25—N21	106.63 (19)
C12—N13—C14	108.63 (16)	C25—N21—C31	126.08 (18)
C15—C14—N13	107.39 (18)	C22—N23—C26	126.91 (17)
C15—C14—H14	126.3	C24—N23—C26	123.88 (17)
N13—C14—H14	126.3	C24—C25—H25	126.7
C14—C15—N11	106.54 (17)	N21—C25—H25	126.7
C12—N11—C31	124.01 (18)	N23—C26—C27	113.44 (16)
C15—N11—C31	127.10 (17)	N23—C26—H261	108.9
C12—N13—C16	124.92 (16)	C27—C26—H261	108.9
C14—N13—C16	126.33 (17)	N23—C26—H262	108.9
C14—C15—H15	126.7	C27—C26—H262	108.9
N11—C15—H15	126.7	H261—C26—H262	107.7
N13—C16—C17	112.29 (16)	C26—C27—C28	110.24 (17)
N13—C16—H161	109.1	C26—C27—H271	109.6
C17—C16—H161	109.1	C28—C27—H271	109.6
N13—C16—H162	109.1	C26—C27—H272	109.6
C17—C16—H162	109.1	C28—C27—H272	109.6
H161—C16—H162	107.9	H271—C27—H272	108.1
C16—C17—C18	113.26 (17)	C27—C28—C29	112.85 (19)
C16—C17—H171	108.9	C27—C28—H281	109.0
C18—C17—H171	108.9	C29—C28—H281	109.0
C16—C17—H172	108.9	C27—C28—H282	109.0
C18—C17—H172	108.9	C29—C28—H282	109.0
H171—C17—H172	107.7	H281—C28—H282	107.8
C19—C18—C17	112.06 (18)	C28—C29—H291	109.5
N11—C31—N21	110.80 (16)	C28—C29—H292	109.5
C19—C18—H181	109.2	H291—C29—H292	109.5
C17—C18—H181	109.2	C28—C29—H293	109.5
C19—C18—H182	109.2	H291—C29—H293	109.5
C17—C18—H182	109.2	H292—C29—H293	109.5
H181—C18—H182	107.9	N11—C31—H311	109.5
C18—C19—H191	109.5	N21—C31—H311	109.5
C18—C19—H192	109.5	N11—C31—H312	109.5
H191—C19—H192	109.5	N21—C31—H312	109.5
C18—C19—H193	109.5	H311—C31—H312	108.1
H191—C19—H193	109.5	N41—C42—C43	179.2 (3)
H192—C19—H193	109.5	C42—C43—H431	109.5
C22—N21—C25	109.01 (17)	C42—C43—H432	109.5
C22—N21—C31	124.65 (18)	H431—C43—H432	109.5
N23—C22—N21	108.14 (18)	C42—C43—H433	109.5
N23—C22—H22	125.9	H431—C43—H433	109.5
N21—C22—H22	125.9	H432—C43—H433	109.5
C22—N23—C24	108.93 (17)
C15—N11—C12—N13	−1.5 (2)	N21—C22—N23—C24	−1.6 (2)
C31—N11—C12—N13	−177.84 (16)	N21—C22—N23—C26	−175.68 (18)
N11—C12—N13—C14	1.5 (2)	C22—N23—C24—C25	1.0 (2)
N11—C12—N13—C16	177.62 (17)	C26—N23—C24—C25	175.23 (18)
C12—N13—C14—C15	−0.9 (2)	N23—C24—C25—N21	0.1 (2)
C16—N13—C14—C15	−176.96 (17)	C22—N21—C25—C24	−1.1 (2)
N13—C14—C15—N11	0.0 (2)	C31—N21—C25—C24	−175.36 (18)
C12—N11—C15—C14	0.9 (2)	C22—N23—C26—C27	−18.8 (3)
C31—N11—C15—C14	177.14 (18)	C24—N23—C26—C27	168.00 (18)
C12—N13—C16—C17	119.9 (2)	N23—C26—C27—C28	−174.97 (18)
C14—N13—C16—C17	−64.6 (2)	C26—C27—C28—C29	178.7 (2)
N13—C16—C17—C18	−58.1 (2)	C12—N11—C31—N21	94.2 (2)
C16—C17—C18—C19	−168.04 (18)	C15—N11—C31—N21	−81.5 (2)
C25—N21—C22—N23	1.7 (2)	C22—N21—C31—N11	−90.3 (2)
C31—N21—C22—N23	176.07 (17)	C25—N21—C31—N11	83.1 (2)