Crystal structure of fac-tricarbon­yl(cyclo­hexyl isocyanide-κC)(quinoline-2-carboxyl­ato-κ²N,O)rhenium(I)

In the title compound, [Re(C₁₀H₆NO₂)(C₇H₁₁N)(CO)₃], the Re^I atom is coordinated by three carbonyl ligands in a facial arrangement and by the N, O and C atoms from a chelating quinaldate anion and a monodentate isocyanide ligand, respectively. The resultant C₄NO coordination sphere is distorted octa­hedral. A lengthening of the axial Re—CO bond trans to the isocyanide ligand is indicative of the trans effect. Individual complexes are stacked into rods parallel to [001] through displaced π–π inter­actions. Weak C—H⋯O hydrogen-bonding inter­actions between the rods lead to the formation of layers parallel to (010). These layers are stacked along [010] by C—H⋯H—C van der Waals contacts.

1. Chemical context

Tri­carbonyl­rhenium(I) compounds are being explored as luminescent probes for cell imaging, photosensitizers in photocatalysis (Lyczko et al., 2015; Bertrand et al., 2014), and as potential radiopharmaceuticals based on the already extensive use of radioactive ^186/188Re compounds in nuclear medicine for pain palliation and radiosynovectomy (Schneider et al., 2005; Bodei et al., 2008). Recent studies have also revealed the potential of cold tri­carbonyl­rhenium(I) complexes as anti­cancer agents (Leodinova & Gasser, 2014).

As part of our ongoing research in the field of Re/Tc coordination compounds, the crystal structure of a new `2 + 1' tricarbonyl rhenium complex, fac-[M(CO)<sub>3</sub>(L)(QA-NO)], where M is Re,Tc, L is the monodentate ligand cyclo­hexyl­isocyanide, and QA-NO is deprotonated quinaldic acid, is presented. As a result of of the versatility of the `2 + 1' system, fac-[M(CO)₃(L)(QA-NO)] complexes can be used as model compounds in the development of targeted radiopharmaceuticals or anti­cancer agents by suitable replacement of either the bidentate or monodentate ligand. For example, the monodentate ligand may be the isocyanide derivative of a pharmacophore with affinity for a certain receptor. Alternatively, the bidentate ligand may be a more extensive conjugated system to act as a DNA inter­calator. Both quinaldate- and isocyanide-based ligands have been used as possible DNA inter­calators (Li et al., 2009; Agorastos et al., 2007).

2. Structural commentary

The mol­ecular structure of the title compound, [Re(C₁₀H₆NO₂)(C₇H₁₁N)(CO)₃], is shown in Fig. 1. The Re^I atom is six-coordinated by four C, one N and one O atoms in a distorted octa­hedral coordination sphere. The carbonyl C atoms are in a facial arrangement, with distances in the range 1.903 (8)–1.960 (8) Å, resulting in a cis arrangement of the bi- and monodentate ligands. The longest distance involving the carbonyl ligands [1.960 (8) Å; Re—C11] corresponds to the ligand trans to the isocyanide cyclo­hexyl ligand, defining the axial direction of the octa­hedral complex. The Re^I atom almost lies in the equatorial plane (deviation, 0.006 Å) defined by the C12, C13, O1 and N1 atoms. The bite angle (N1—Re—O1) of the chelating ligand, corresponding to a five-membered ring, has a typical value of 75.2 (2)° (Lyczko et al., 2015). The Re—N1 and Re—O1 bond lengths are 2.273 (5) and 2.149 (5) Å, respectively. The isocyanide carbon atom, C14, is at a distance of 2.107 (8) Å from the metal site. All these values are close to those of a complex with the same core (Agorastos et al., 2007). The isocyanide group is oriented within the equatorial plane of the cyclo­hexyl ring which exhibits a chair conformation.

Figure 1 The mol­ecular structure and atom-labelling scheme of the title compound. Displacement ellipsoids are drawn at the 50% probability level.

3. Supra­molecular features

Figs. 2 and 3 show the supra­molecular inter­actions of each complex mol­ecule with its neighbours. Displaced π–π inter­actions between the phenyl and pyridine rings of quinaldate ligands of neighbouring complexes are present, with a Cg1⋯Cg2ⁱ distance of 3.650 Å [Cg1 and Cg2 are the centroids of the (C5–C10) and (N1,C2,C3,C4,C5,C10) rings, respectively; symmetry code: (i): 4 − x, 1 − y, 2 − z]. These inter­actions help to consolidate the stacking of the mol­ecules into rods parallel to [001] (Figs. 3 and 4). Weak inter­molecular C—H⋯O hydrogen-bonding inter­actions (Table 1), including supra­molecular R₂²(7) loops (C20—H20A⋯O1 and C15—H15⋯O2) join neighbouring rods into sheets parallel to (010) (Fig. 4). An additional type of inter­actions, viz. short van der Waals forces of the C—H⋯H—C type (Sankolli et al., 2015), is realized through C18—H18⋯H18—C18 contacts. The cyclo­hexyl end of the isocyanide ligands is hanging above and below the sheets of mol­ecules (Figs. 3 and 4), creating a perhydrogenated outer wall (Sankolli et al., 2015) at both sides of the layers. Such layers are stacked along [010] (through centres of symmetry located at b/2) and inter­act through the aforementioned C—H⋯H—C contacts (Fig. 5).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C20—H20A⋯O1^i	0.99	2.61	3.260 (10)	123
C15—H15⋯O2^i	0.99	2.52	3.365	142
C7—H7⋯O2^ii	0.99	2.37	3.133	137
Symmetry codes: (i) x+1, y, z; (ii) .

Figure 2 Inter­molecular inter­actions of the title complex with its neighbours. π–π inter­actions, weak C—H⋯O hydrogen bonds and short van der Waals contacts are shown with green, orange and turquoise dashed lines, respectively. [Symmetry codes: (′) x + 1, y, z; (′′) 1 + x,  − y, − + z; (′′′) 4 − x,1 − y, 2 − z.]

Figure 3 A rod of complexes extending parallel to [001] through π–π inter­actions. The colour code is as in Fig. 2.

Figure 4 Sheet of complexes arranged parallel to (010) showing π–π and weak C—H⋯O inter­actions. The colour code is as in Fig. 2.

Figure 5 Stack of layers along [010] with C—H⋯H—C van der Waals contacts (light-blue dashed lines) developed among them, shown along the opposite [20] direction (see Fig. 4).

4. Hirshfeld surface analysis

The packing of the complexes in the structure was further investigated with Hirshfeld surface analysis using the Crystal Explorer package (Wolff et al., 2012). The d_norm and curvedness (Spackman & Jayatilaka, 2009) surface mappings are presented in Fig. 6a, 6b and 6c, respectively. All C—H⋯O and C—H⋯H—C contacts are recognized on the d_norm mapped surface as deep-red depression areas in Fig. 6a and 6b, which represent two different upper views of the complex. Arrows at these figures indicate the specific type of contacts at each red point. A bottom view of the surface mapped with curvedness (Fig. 6c) shows broad, relatively flat regions (indicated by letter A) characteristic of planar stacking of complexes (Spackman & Jayatilaka, 2009), corresponding to the π–π inter­actions. In the fingerprint plot (Rohl et al., 2008), shown in Fig. 6d, the points indicated by 1, 2A & 2B, 3A & 3B and 4 correspond to H⋯H, H⋯O, C⋯H and C⋯C inter­actions with relative contributions of 25.1, 44.2, 18.1 and 4.3%, respectively. These types of inter­actions add to 91.7% of the inter­molecular contacts of the Hirshfeld surface area. The remaining contributions (8.3%) correspond to N⋯H (2.1%), O⋯C (2.8%) and other less-important inter­actions (<1%).

Figure 6 Views of Hirshfeld surfaces mapped with dnorm (a)/(b), curvedness (c) properties and (d) fingerprint plots for the title complex. de and di are the distances to the nearest atom centre exterior and inter­ior to the surface. 1, 2, 3 and 4 indicate H⋯H, H⋯O, C⋯H and C⋯C inter­actions, and A and B stand for acceptor and donor atoms, respectively.

5. NMR investigation

In the solution NMR spectra of the complex, both the quinaldate and iso­cyano­cyclo­hexane moieties are distinguishable. Coordination by the quinaldate is evident from the downfield shifts of all its protons ranging from 0.10 to 0.44 p.p.m. compared to free quinaldic acid under the same conditions (our data). Downfield shifts are also recorded for most of the C atoms of quinaldic acid, the most notable one (4.8 p.p.m.) being the one of the carboxyl­ate carbonyl carbon. For the iso­cyano­cyclo­hexane moiety, downfield shifts are recorded for the C atom (2.7 p.p.m.) bearing the isocyanide group and for its H atom (0.31 p.p.m.) compared to the free ligand. The most characteristic sign of coordination of the iso­cyano­cyclo­hexane moiety is the sizable upfield shift of the isocyanide C atom of 15.5 p.p.m., attributed to an increased carbene character upon coordination (Stephany et al., 1974; Sagnou et al., 2010, 2011). In the ¹³C NMR spectrum of the complex, one of the carbonyl ligands of the Re(CO)₃⁺ core appears shielded (by 2.8 p.p.m. on average) compared to the other two, an observation that may also be attributed to the trans effect of the isocyanide ligand.

6. Database survey

A search of the Cambridge Structural Database (Groom & Allen, 2014) has revealed eight tricarbonyl complexes in facial arrangement and different N,O-bidentate ligands with a pyridine carboxyl­ato-2 group at the binding side of the corresponding ligand. The N,O-binding sites together with the two carbonyl groups trans to N and O atoms define an equatorial plane, and the third together with the monodentate ligand define the axial position. The Re—C bond lengths of axial carbonyl ligands (1.883–1.922 Å) trans to the monodentate ligand have values equal or smaller than the equatorial ones (1.892–1.945 Å) when the ligand is an aqua ligand (Schutte & Visser, 2008; Mundwiler et al., 2004). The carbonyl Re—C bond lengths are inter­mediate (1.914–1.917 Å) between the values of the Re—C bonds trans to the equatorial O (1.886–1.916 Å) and N (1.921–1.926 Å) atoms, if the trans ligand is bonded to Re through an N atom (Benny et al., 2009; Mundwiler et al., 2004). Finally, the respective bond length, 1.947 Å, is longer than both Re—C bonds trans to equatorial O (1.912 Å) and N (1.914 Å) atoms if the Re atom is bonded to a P atom of a phosphine ligand (Hayes et al., 2014). In the case of the isocyanide group trans to the axial Re—C bond (Agorastos et al., 2007), the results are indistinct. In one case (XIDPUW), the axial bond length (1.756 Å) is shorter than the equatorial one (1.849 Å trans to O and 1.901 Å trans to N) whereas in the other case (XIDQAD), the corresponding length (1.914 Å) is longer than the equatorial one (1.495 Å trans to O and 1.885 Å trans to N). In the present structure, the Re—C11 bond (1.960 Å), is longer than the Re—C13 (1.903 Å, trans to O) and Re—C12 (1.912 Å, trans to N) bonds. This result is supported by the NMR analysis and is indicative of the structural trans effect (Coe & Glenwright, 2000).

7. Synthesis and crystallization

To a stirred solution of quinaldic acid (17.3 mg, 0.1 mmol) in 5 ml methanol, a solution of [NEt₄]₂[ReBr₃(CO)₃] (77 mg, 0.1 mmol) in 5 ml methanol was added. The mixture was heated at 333 K, and after 30 min a solution of cyclo­hexyl isocyanide (0.1 mmol) in 3 ml methanol was added. The mixture was stirred at room temperature for 2 h and the reaction progress was monitored by HPLC. The solvent was removed under reduced pressure and the solid residue was recrystallized from di­chloro­methane/hexane. The resulting solid was redissolved in a minimum volume of di­chloro­methane, layered with hexane and left to stand at room temperature. After a few days crystals suitable for X-ray analysis were isolated (yield: 44 mg, 80%). ¹H NMR (DMSO-d₆, p.p.m.): 8.93 (1H), 8.58 (1H), 8.32 (1H), 8.28 (1H), 8.18 (1H), 7.94 (1H), 4.08 (1H), 1.50 (2H), 1.40 (2H), 1.13(2H), 1.08 (2H), 0.88 (2H); ¹³C NMR (DMSO-d₆, p.p.m.): 193.65, 193.12, 190.54, 172.06, 152.63, 146.23, 142.09, 138.85, 133.04, 130.47, 129.67, 129.61, 127.78, 122.78, 53.72, 30.48, 23.91, 20.70.

8. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were placed in idealized positions and refined using a riding model with C—H = 0.95 Å (aromatic H atoms), C—H = 0.99 Å (methyl­ene H atoms), and with U_iso(H) = 1.2U_eq(C).

Table 2
Experimental details

Crystal data
Chemical formula	[Re(C10H6NO2)(C7H11N)(CO)3]
Mr	551.55
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	170
a, b, c (Å)	7.1529 (1), 29.5703 (5), 9.6309 (2)
β (°)	105.572 (1)
V (Å^3)	1962.29 (6)
Z	4
Radiation type	Cu Kα
μ (mm^−1)	12.41
Crystal size (mm)	0.49 × 0.12 × 0.04
Data collection
Diffractometer	Rigaku R-AXIS SPIDER IPDS
Absorption correction	Multi-scan (CrystalClear; Rigaku 2005)
Tmin, Tmax	0.374, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	21436, 3283, 2723
Rint	0.069
(sin θ/λ)max (Å^−1)	0.588
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.038, 0.102, 1.17
No. of reflections	3283
No. of parameters	253
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å^−3)	1.30, −1.43
Computer programs: CrystalClear (Rigaku, 2005), SHELXS97 and SHELXTL (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015), DIAMOND (Crystal Impact, 2012) and PLATON (Spek, 2009).

Supporting information

S1. Chemical context

Tri­carbonyl­rhenium(I) compounds are being explored as luminescent probes for cell imaging, photosensitizers in photocatalysis (Lyczko et al., 2015; Bertrand et al., 2014), and as potential radiopharmaceuticals based on the already extensive use of radioactive ^186/188Re compounds in nuclear medicine for pain palliation and radiosynovectomy (Schneider et al. 2005; Bodei et al. 2008). Recent studies have also revealed the potential of cold tri­carbonyl­rhenium(I) complexes as anti­cancer agents (Leodinova & Gasser, 2014).

As part of our ongoing research in the field of Re/Tc coordination compounds, the crystal structure of a new `2 + 1' tri­carbonyl rhenium complex, fac-[M(CO)<sub>3</sub>(L)(QA—NO)], where M is Re,Tc, L is the monodentate ligand cyclo­hexyl­isocyanide, and QA—NO is deprotonated quinaldic acid, is presented. Because of the versatility of the `2 + 1' system, fac-[M(CO)₃(L)(QA—NO)] complexes can be used as model compounds in the development of targeted radiopharmaceuticals or anti­cancer agents by suitable replacement of either the bidentate or monodentate ligand. For example, the monodentate ligand may be the isocyanide derivative of a pharmacophore with affinity for a certain receptor. Alternatively, the bidentate ligand may be a more extensive conjugated system to act as a DNA inter­calator. Both quinaldate- and isocyanide-based ligands have been used as possible DNA inter­calators (Li et al., 2009; Agorastos et al., 2007).

S2. Structural commentary

The molecular structure of the title compound, [Re(C₁₀H₆NO₂)(C₇H₁₁N)(CO)₃], is shown in Fig. 1. The Re^I atom is six-coordinated by four C, one N and one O atoms in a distorted o­cta­hedral coordination sphere. The carbonyl C atoms are in a facial arrangement, with distances in the range 1.903 (8)–1.960 (8) Å, resulting in a cis arrangement of the bi- and monodentate ligands. The longest distance involving the carbonyl ligands [1.960 (8) Å; Re—C11] corresponds to the ligand trans to the isocyanide cyclo­hexyl ligand, defining the axial direction of the o­cta­hedral complex. The Re^I atom almost lies in the equatorial plane (deviation, 0.006 Å) defined by the C12, C13, O1 and N1 atoms. The bite angle (N1—Re—O1) of the chelating ligand, corresponding to a five-membered ring, has a typical value of 75.2 (2)° (Lyczko et al., 2015). The Re—N1 and Re—O1 bond lengths are 2.273 (5) and 2.149 (5) Å, respectively. The isocyanide carbon atom, C14, is at a distance of 2.107 (8) Å from the metal site. All these values are close to those of a complex with the same core (Agorastos et al., 2007). The isocyanide group is oriented within the equatorial plane of the cyclo­hexyl ring which exhibits a chair conformation.

S3. Supra­molecular features

Figs. 2 and 3 show the supra­molecular inter­actions of each complex molecule with its neighbours. Displaced π–π inter­actions between the phenyl and pyridine rings of quinaldate ligands of neighbouring complexes are present, with a Cg1···Cg2ⁱ distance of 3.650 Å [Cg1 and Cg2 are the centroids of the (C5–C10) and (N1,C2,C3,C4,C5,C10) rings, respectively; symmetry code: (i): 4 − x, 1 − y, 2 − z)]. These inter­actions help to consolidate the stacking of the molecules into rods parallel to [001] (Figs. 3 and 4). Weak inter­molecular C—H···O hydrogen-bonding inter­actions (Table 1), including supra­molecular R²₂(7) loops (C20—H20A···O1 and C15—H15···O2) join neighbouring rods into sheets parallel to (010) (Fig. 4). An additional type of inter­actions, viz. short van der Waals forces of the C—H···H—C type (Sankolli et al., 2015), is realised through C18—H18···H18—C18 contacts. The cyclo­hexyl end of the isocyanide ligands is hanging above and below the sheets of molecules (Figs. 3 and 4), creating a perhydrogenated outer wall (Sankolli et al., 2015) at both sides of the layers. Such layers are stacked along [010] (through centres of symmetry located at b/2) and inter­act through the aforementioned C—H···H—C contacts (Fig. 5).

S4. Hirshfeld surface analysis

The packing of the complexes in the structure was further investigated with Hirshfeld surface analysis using the Crystal Explorer package (Wolff et al., 2012). The d_norm and curvedness (Spackman & Jayatilaka, 2009) surface mappings are presented in Figs. 6a, 6b and 6c, respectively. All C—H···O and C—H···H—C contacts are recognized on the d_norm mapped surface as deep-red depression areas in Figs. 6a and 6b, which represent two different upper views of the complex. Arrows at these figures indicate the specific type of contacts at each red point. A bottom view of the surface mapped with curvedness (Fig. 6c) shows broad, relatively flat regions (indicated by letter A) characteristic of planar stacking of complexes (Spackman & Jayatilaka, 2009), corresponding to the π–π inter­actions. In the fingerprint plot (Rohl et al., 2008), shown in Fig. 6d, the points indicated by 1, 2 A & 2B, 3 A & 3B and 4 correspond to H···H, H···O, C···H and C···C inter­actions with relative contributions of 25.1, 44.2, 18.1 and 4.3%, respectively. These types of inter­actions add to 91.7% of the inter­molecular contacts of the Hirshfeld surface area. The remaining contributions (8.3%) correspond to N···H (2.1%), O···C (2.8%) and other less-important inter­actions (<1%).

S5. NMR investigation

In the solution NMR spectra of the complex, both the quinaldate and iso­cyano­cyclo­hexane moieties are distinguishable. Coordination by the quinaldate is evident from the downfield shifts of all its protons ranging from 0.10 to 0.44 p.p.m. compared to free quinaldic acid under the same conditions (our data). Downfield shifts are also recorded for most of the C atoms of quinaldic acid, the most notable one (4.8 p.p.m.) being the one of the carboxyl­ate carbonyl carbon. For the iso­cyano­cyclo­hexane moiety, downfield shifts are recorded for the C atom (2.7 p.p.m.) bearing the isocyanide group and for its H atom (0.31 p.p.m.) compared to the free ligand. The most characteristic sign of coordination of the iso­cyano­cyclo­hexane moiety is the sizable upfield shift of the isocyanide C atom of 15.5 p.p.m., attributed to an increased carbene character upon coordination (Stephany et al., 1974; Sagnou et al., 2010, 2011). In the ¹³C NMR spectrum of the complex, one of the carbonyl ligands of the Re(CO)₃⁺ core appears shielded (by 2.8 p.p.m. on average) compared to the other two, an observation that may also be attributed to the trans effect of the isocyanide ligand.

S6. Database survey

A search of the Cambridge Structural Database (Groom & Allen, 2014) has revealed eight tri­carbonyl complexes in facial arrangement and different N,O-bidentate ligands with a pyridine carboxyl­ato-2 group at the binding side of the corresponding ligand. The N,O-binding sites together with the two carbonyl groups trans to N and O atoms define an equatorial plane, and the third together with the monodentate ligand define the axial position. The Re—C bond lengths of axial carbonyl ligands (1.883–1.922 Å) trans to the monodentate ligand have values equal or smaller than the equatorial ones (1.892–1.945 Å) when the ligand is an aqua ligand (Schutte & Visser, 2008; Mundwiler et al., 2004). The carbonyl Re—C bond lengths are inter­mediate (1.914–1.917 Å) between the values of the Re—C bonds trans to the equatorial O (1.886–1.916 Å) and N (1.921–1.926 Å) atoms, if the trans ligand is bonded to Re through an N atom (Benny et al., 2009; Mundwiler et al., 2004). Finally, the respective bond length, 1.947 Å, is longer than both Re—C bonds trans to equatorial O (1.912 Å) and N (1.914 Å) atoms if the Re atom is bonded to a P atom of a phosphine ligand (Hayes et al., 2014). In the case of the isocyanide group trans to the axial Re—C bond (Agorastos et al., 2007), the results are indistinct. In one case (XIDPUW), the axial bond length (1.756 Å) is shorter than the equatorial one (1.849 Å trans to O and 1.901 Å trans to N) whereas in the other case (XIDQAD), the corresponding length (1.914 Å) is longer than the equatorial one (1.495 Å trans to O and 1.885 Å trans to N). In the present structure, the Re—C11 bond (1.960 Å), is longer than the Re—C13 (1.903 Å, trans to O) and Re—C12 (1.912 Å, trans to N) bonds. This result is supported by the NMR analysis and is indicative of the structural trans effect (Coe & Glenwright, 2000).

S7. Synthesis and crystallization

To a stirred solution of quinaldic acid (17.3 mg, 0.1 mmol) in 5 ml me thanol, a solution of [NEt₄]₂[ReBr₃(CO)₃] (77 mg, 0.1 mmol) in 5 ml me thanol was added. The mixture was heated at 333 K, and after 30 min a solution of cyclo­hexyl isocyanide (0.1 mmol) in 3 ml me thanol was added. The mixture was stirred at room temperature for 2 h and the reaction progress was monitored by HPLC. The solvent was removed under reduced pressure and the solid residue was recrystallized from di­chloro­methane/hexane. The resulting solid was redissolved in a minimum volume of di­chloro­methane, layered with hexane and left to stand at room temperature. After a few days crystals suitable for X-ray analysis were isolated (yield: 44 mg, 80%). ¹H NMR (DMSO-d₆, p.p.m.): 8.93 (1H), 8.58 (1H), 8.32 (1H), 8.28 (1H), 8.18 (1H), 7.94 (1H), 4.08 (1H), 1.50 (2H), 1.40 (2H), 1.13(2H), 1.08 (2H), 0.88 (2H); ¹³C NMR (DMSO-d₆, p.p.m.): 193.65, 193.12, 190.54, 172.06, 152.63, 146.23, 142.09, 138.85, 133.04, 130.47, 129.67, 129.61, 127.78, 122.78, 53.72, 30.48, 23.91, 20.70.

S8. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were placed in idealized positions and refined using a riding model with C—H = 0.95 Å (aromatic H atoms), C—H = 0.99 Å (methyl­ene H atoms), and with U_iso(H) = 1.2U_eq(C).

Structure description

Tri­carbonyl­rhenium(I) compounds are being explored as luminescent probes for cell imaging, photosensitizers in photocatalysis (Lyczko et al., 2015; Bertrand et al., 2014), and as potential radiopharmaceuticals based on the already extensive use of radioactive ^186/188Re compounds in nuclear medicine for pain palliation and radiosynovectomy (Schneider et al. 2005; Bodei et al. 2008). Recent studies have also revealed the potential of cold tri­carbonyl­rhenium(I) complexes as anti­cancer agents (Leodinova & Gasser, 2014).

As part of our ongoing research in the field of Re/Tc coordination compounds, the crystal structure of a new `2 + 1' tri­carbonyl rhenium complex, fac-[M(CO)<sub>3</sub>(L)(QA—NO)], where M is Re,Tc, L is the monodentate ligand cyclo­hexyl­isocyanide, and QA—NO is deprotonated quinaldic acid, is presented. Because of the versatility of the `2 + 1' system, fac-[M(CO)₃(L)(QA—NO)] complexes can be used as model compounds in the development of targeted radiopharmaceuticals or anti­cancer agents by suitable replacement of either the bidentate or monodentate ligand. For example, the monodentate ligand may be the isocyanide derivative of a pharmacophore with affinity for a certain receptor. Alternatively, the bidentate ligand may be a more extensive conjugated system to act as a DNA inter­calator. Both quinaldate- and isocyanide-based ligands have been used as possible DNA inter­calators (Li et al., 2009; Agorastos et al., 2007).

The molecular structure of the title compound, [Re(C₁₀H₆NO₂)(C₇H₁₁N)(CO)₃], is shown in Fig. 1. The Re^I atom is six-coordinated by four C, one N and one O atoms in a distorted o­cta­hedral coordination sphere. The carbonyl C atoms are in a facial arrangement, with distances in the range 1.903 (8)–1.960 (8) Å, resulting in a cis arrangement of the bi- and monodentate ligands. The longest distance involving the carbonyl ligands [1.960 (8) Å; Re—C11] corresponds to the ligand trans to the isocyanide cyclo­hexyl ligand, defining the axial direction of the o­cta­hedral complex. The Re^I atom almost lies in the equatorial plane (deviation, 0.006 Å) defined by the C12, C13, O1 and N1 atoms. The bite angle (N1—Re—O1) of the chelating ligand, corresponding to a five-membered ring, has a typical value of 75.2 (2)° (Lyczko et al., 2015). The Re—N1 and Re—O1 bond lengths are 2.273 (5) and 2.149 (5) Å, respectively. The isocyanide carbon atom, C14, is at a distance of 2.107 (8) Å from the metal site. All these values are close to those of a complex with the same core (Agorastos et al., 2007). The isocyanide group is oriented within the equatorial plane of the cyclo­hexyl ring which exhibits a chair conformation.

Figs. 2 and 3 show the supra­molecular inter­actions of each complex molecule with its neighbours. Displaced π–π inter­actions between the phenyl and pyridine rings of quinaldate ligands of neighbouring complexes are present, with a Cg1···Cg2ⁱ distance of 3.650 Å [Cg1 and Cg2 are the centroids of the (C5–C10) and (N1,C2,C3,C4,C5,C10) rings, respectively; symmetry code: (i): 4 − x, 1 − y, 2 − z)]. These inter­actions help to consolidate the stacking of the molecules into rods parallel to [001] (Figs. 3 and 4). Weak inter­molecular C—H···O hydrogen-bonding inter­actions (Table 1), including supra­molecular R²₂(7) loops (C20—H20A···O1 and C15—H15···O2) join neighbouring rods into sheets parallel to (010) (Fig. 4). An additional type of inter­actions, viz. short van der Waals forces of the C—H···H—C type (Sankolli et al., 2015), is realised through C18—H18···H18—C18 contacts. The cyclo­hexyl end of the isocyanide ligands is hanging above and below the sheets of molecules (Figs. 3 and 4), creating a perhydrogenated outer wall (Sankolli et al., 2015) at both sides of the layers. Such layers are stacked along [010] (through centres of symmetry located at b/2) and inter­act through the aforementioned C—H···H—C contacts (Fig. 5).

The packing of the complexes in the structure was further investigated with Hirshfeld surface analysis using the Crystal Explorer package (Wolff et al., 2012). The d_norm and curvedness (Spackman & Jayatilaka, 2009) surface mappings are presented in Figs. 6a, 6b and 6c, respectively. All C—H···O and C—H···H—C contacts are recognized on the d_norm mapped surface as deep-red depression areas in Figs. 6a and 6b, which represent two different upper views of the complex. Arrows at these figures indicate the specific type of contacts at each red point. A bottom view of the surface mapped with curvedness (Fig. 6c) shows broad, relatively flat regions (indicated by letter A) characteristic of planar stacking of complexes (Spackman & Jayatilaka, 2009), corresponding to the π–π inter­actions. In the fingerprint plot (Rohl et al., 2008), shown in Fig. 6d, the points indicated by 1, 2 A & 2B, 3 A & 3B and 4 correspond to H···H, H···O, C···H and C···C inter­actions with relative contributions of 25.1, 44.2, 18.1 and 4.3%, respectively. These types of inter­actions add to 91.7% of the inter­molecular contacts of the Hirshfeld surface area. The remaining contributions (8.3%) correspond to N···H (2.1%), O···C (2.8%) and other less-important inter­actions (<1%).

In the solution NMR spectra of the complex, both the quinaldate and iso­cyano­cyclo­hexane moieties are distinguishable. Coordination by the quinaldate is evident from the downfield shifts of all its protons ranging from 0.10 to 0.44 p.p.m. compared to free quinaldic acid under the same conditions (our data). Downfield shifts are also recorded for most of the C atoms of quinaldic acid, the most notable one (4.8 p.p.m.) being the one of the carboxyl­ate carbonyl carbon. For the iso­cyano­cyclo­hexane moiety, downfield shifts are recorded for the C atom (2.7 p.p.m.) bearing the isocyanide group and for its H atom (0.31 p.p.m.) compared to the free ligand. The most characteristic sign of coordination of the iso­cyano­cyclo­hexane moiety is the sizable upfield shift of the isocyanide C atom of 15.5 p.p.m., attributed to an increased carbene character upon coordination (Stephany et al., 1974; Sagnou et al., 2010, 2011). In the ¹³C NMR spectrum of the complex, one of the carbonyl ligands of the Re(CO)₃⁺ core appears shielded (by 2.8 p.p.m. on average) compared to the other two, an observation that may also be attributed to the trans effect of the isocyanide ligand.

A search of the Cambridge Structural Database (Groom & Allen, 2014) has revealed eight tri­carbonyl complexes in facial arrangement and different N,O-bidentate ligands with a pyridine carboxyl­ato-2 group at the binding side of the corresponding ligand. The N,O-binding sites together with the two carbonyl groups trans to N and O atoms define an equatorial plane, and the third together with the monodentate ligand define the axial position. The Re—C bond lengths of axial carbonyl ligands (1.883–1.922 Å) trans to the monodentate ligand have values equal or smaller than the equatorial ones (1.892–1.945 Å) when the ligand is an aqua ligand (Schutte & Visser, 2008; Mundwiler et al., 2004). The carbonyl Re—C bond lengths are inter­mediate (1.914–1.917 Å) between the values of the Re—C bonds trans to the equatorial O (1.886–1.916 Å) and N (1.921–1.926 Å) atoms, if the trans ligand is bonded to Re through an N atom (Benny et al., 2009; Mundwiler et al., 2004). Finally, the respective bond length, 1.947 Å, is longer than both Re—C bonds trans to equatorial O (1.912 Å) and N (1.914 Å) atoms if the Re atom is bonded to a P atom of a phosphine ligand (Hayes et al., 2014). In the case of the isocyanide group trans to the axial Re—C bond (Agorastos et al., 2007), the results are indistinct. In one case (XIDPUW), the axial bond length (1.756 Å) is shorter than the equatorial one (1.849 Å trans to O and 1.901 Å trans to N) whereas in the other case (XIDQAD), the corresponding length (1.914 Å) is longer than the equatorial one (1.495 Å trans to O and 1.885 Å trans to N). In the present structure, the Re—C11 bond (1.960 Å), is longer than the Re—C13 (1.903 Å, trans to O) and Re—C12 (1.912 Å, trans to N) bonds. This result is supported by the NMR analysis and is indicative of the structural trans effect (Coe & Glenwright, 2000).

Synthesis and crystallization

To a stirred solution of quinaldic acid (17.3 mg, 0.1 mmol) in 5 ml me thanol, a solution of [NEt₄]₂[ReBr₃(CO)₃] (77 mg, 0.1 mmol) in 5 ml me thanol was added. The mixture was heated at 333 K, and after 30 min a solution of cyclo­hexyl isocyanide (0.1 mmol) in 3 ml me thanol was added. The mixture was stirred at room temperature for 2 h and the reaction progress was monitored by HPLC. The solvent was removed under reduced pressure and the solid residue was recrystallized from di­chloro­methane/hexane. The resulting solid was redissolved in a minimum volume of di­chloro­methane, layered with hexane and left to stand at room temperature. After a few days crystals suitable for X-ray analysis were isolated (yield: 44 mg, 80%). ¹H NMR (DMSO-d₆, p.p.m.): 8.93 (1H), 8.58 (1H), 8.32 (1H), 8.28 (1H), 8.18 (1H), 7.94 (1H), 4.08 (1H), 1.50 (2H), 1.40 (2H), 1.13(2H), 1.08 (2H), 0.88 (2H); ¹³C NMR (DMSO-d₆, p.p.m.): 193.65, 193.12, 190.54, 172.06, 152.63, 146.23, 142.09, 138.85, 133.04, 130.47, 129.67, 129.61, 127.78, 122.78, 53.72, 30.48, 23.91, 20.70.

Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were placed in idealized positions and refined using a riding model with C—H = 0.95 Å (aromatic H atoms), C—H = 0.99 Å (methyl­ene H atoms), and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Crystal Impact, 2012); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular structure and atom-labelling scheme of the title compound. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. Intermolecular interactions of the title complex with its neighbours. π–π interactions, weak C—H···O hydrogen bonds and short van der Waals contacts are shown with green, orange and turquoise dashed lines, respectively. [Symmetry codes: (') x + 1, y, z; ('') 1 + x, 1/2 − y, −1/2 + z; (''') 4 − x,1 − y, 2 − z.]
	Fig. 3. A rod of complexes extending parallel to [001] through π–π interactions. The colour code is as in Fig. 2.
	Fig. 4. Sheet of complexes arranged parallel to (010) showing π–π and weak C—H···O interactions. The colour code is as in Fig. 2.
	Fig. 5. Stack of layers along [010] with C—H···H—C van der Waals contacts (light-blue dashed lines) developed among them, shown along the opposite [201] direction (see Fig. 4).
	Fig. 6. Views of Hirshfeld surfaces mapped with dnorm (a)/(b), curvedness (c) properties and (d) fingerprint plots for the title complex. de and di are the distances to the nearest atom centre exterior and interior to the surface. 1, 2, 3 and 4 indicate H···H, H···O, C···H and C···C interactions, and A and B stand for acceptor and donor atoms, respectively.

fac-Tricarbonyl(cyclohexyl isocyanide-κC)(quinoline-2-carboxylato-κ²N,O)rhenium(I)

Crystal data

[Re(C10H6NO2)(C7H11N)(CO)3]	F(000) = 1064
Mr = 551.55	Dx = 1.867 Mg m^−3
Monoclinic, P21/c	Cu Kα radiation, λ = 1.54178 Å
a = 7.1529 (1) Å	Cell parameters from 17036 reflections
b = 29.5703 (5) Å	θ = 6.6–71.9°
c = 9.6309 (2) Å	µ = 12.41 mm^−1
β = 105.572 (1)°	T = 170 K
V = 1962.29 (6) Å^3	Parallelepiped, colorless
Z = 4	0.49 × 0.12 × 0.04 mm

Data collection

Rigaku R-AXIS SPIDER IPDS diffractometer	2723 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.069
θ scans	θmax = 65.0°, θmin = 6.6°
Absorption correction: multi-scan (CrystalClear; Rigaku 2005)	h = −8→8
Tmin = 0.374, Tmax = 1.000	k = −33→27
21436 measured reflections	l = −11→11
3283 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)] = 0.038	H-atom parameters constrained
wR(F^2) = 0.102	w = 1/[σ^2(Fo^2) + (0.0314P)^2 + 5.6979P] where P = (Fo^2 + 2Fc^2)/3
S = 1.17	(Δ/σ)max = 0.001
3283 reflections	Δρmax = 1.30 e Å^−3
253 parameters	Δρmin = −1.43 e Å^−3

Special details

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

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

	x	y	z	Uiso*/Ueq
Re	0.92831 (4)	0.37585 (2)	0.37372 (3)	0.03094 (14)
N1	0.9723 (7)	0.30250 (18)	0.4300 (5)	0.0284 (12)
O1	0.7817 (7)	0.36522 (17)	0.5387 (5)	0.0416 (12)
O2	0.6499 (7)	0.31296 (18)	0.6478 (5)	0.0484 (13)
C1	0.7486 (9)	0.3239 (2)	0.5673 (7)	0.0355 (16)
C2	0.8488 (9)	0.2879 (2)	0.5021 (6)	0.0301 (14)
C3	0.8153 (10)	0.2429 (2)	0.5234 (7)	0.0346 (15)
H3	0.7263	0.2344	0.5762	0.042*
C4	0.9110 (9)	0.2111 (2)	0.4680 (7)	0.0364 (16)
H4	0.8825	0.1799	0.4757	0.044*
C5	1.0531 (9)	0.2242 (2)	0.3988 (7)	0.0350 (16)
C6	1.1665 (10)	0.1931 (2)	0.3467 (7)	0.0413 (17)
H6	1.1444	0.1616	0.3549	0.050*
C7	1.3075 (10)	0.2069 (3)	0.2848 (7)	0.0421 (18)
H7	1.3827	0.1855	0.2496	0.051*
C8	1.3385 (10)	0.2532 (2)	0.2742 (7)	0.0395 (17)
H8	1.4385	0.2629	0.2332	0.047*
C9	1.2302 (9)	0.2851 (2)	0.3207 (6)	0.0344 (15)
H9	1.2542	0.3164	0.3112	0.041*
C10	1.0834 (8)	0.2709 (2)	0.3826 (6)	0.0279 (14)
C11	0.6948 (11)	0.3602 (2)	0.2213 (8)	0.0386 (16)
O3	0.5615 (7)	0.3509 (2)	0.1301 (6)	0.0588 (16)
C12	0.8592 (10)	0.4384 (3)	0.3514 (8)	0.0419 (17)
O4	0.8223 (8)	0.47647 (18)	0.3391 (6)	0.0549 (14)
C13	1.0602 (10)	0.3846 (2)	0.2285 (8)	0.0381 (17)
O5	1.1396 (8)	0.39159 (19)	0.1404 (6)	0.0529 (13)
C14	1.1806 (11)	0.3915 (2)	0.5378 (8)	0.0381 (16)
N2	1.3213 (8)	0.40084 (19)	0.6200 (6)	0.0353 (13)
C15	1.5026 (9)	0.4170 (2)	0.7131 (7)	0.0365 (16)
H15	1.5983	0.3916	0.7321	0.044*
C16	1.4738 (12)	0.4329 (3)	0.8551 (7)	0.057 (2)
H16A	1.4335	0.4071	0.9061	0.068*
H16B	1.3704	0.4561	0.8376	0.068*
C17	1.6631 (17)	0.4527 (4)	0.9473 (10)	0.098 (4)
H17A	1.6427	0.4645	1.0384	0.117*
H17B	1.7629	0.4287	0.9717	0.117*
C18	1.7339 (18)	0.4906 (4)	0.8689 (17)	0.133 (6)
H18A	1.6382	0.5155	0.8505	0.160*
H18B	1.8582	0.5024	0.9302	0.160*
C19	1.7628 (14)	0.4744 (4)	0.7288 (17)	0.111 (5)
H19A	1.8662	0.4512	0.7479	0.133*
H19B	1.8056	0.5001	0.6788	0.133*
C20	1.5778 (10)	0.4546 (3)	0.6321 (9)	0.055 (2)
H20A	1.6038	0.4421	0.5437	0.066*
H20B	1.4784	0.4786	0.6032	0.066*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Re	0.0284 (2)	0.0315 (2)	0.0323 (2)	0.00254 (11)	0.00704 (15)	0.00250 (11)
N1	0.025 (3)	0.034 (3)	0.024 (3)	0.003 (2)	0.003 (2)	0.002 (2)
O1	0.044 (3)	0.041 (3)	0.046 (3)	0.011 (2)	0.022 (2)	0.004 (2)
O2	0.050 (3)	0.055 (3)	0.051 (3)	0.007 (3)	0.032 (3)	0.007 (3)
C1	0.031 (4)	0.037 (4)	0.036 (4)	0.007 (3)	0.006 (3)	−0.002 (3)
C2	0.023 (3)	0.035 (4)	0.029 (3)	0.002 (3)	0.001 (3)	−0.001 (3)
C3	0.038 (4)	0.040 (4)	0.029 (3)	0.001 (3)	0.015 (3)	0.003 (3)
C4	0.037 (4)	0.028 (4)	0.041 (4)	−0.001 (3)	0.007 (3)	0.002 (3)
C5	0.027 (3)	0.040 (4)	0.034 (4)	0.002 (3)	−0.001 (3)	−0.005 (3)
C6	0.044 (4)	0.029 (4)	0.048 (4)	0.007 (3)	0.007 (3)	−0.005 (3)
C7	0.033 (4)	0.049 (5)	0.046 (4)	0.007 (3)	0.014 (3)	−0.005 (4)
C8	0.031 (4)	0.049 (5)	0.040 (4)	0.005 (3)	0.012 (3)	−0.004 (3)
C9	0.027 (3)	0.044 (4)	0.032 (3)	0.002 (3)	0.008 (3)	0.006 (3)
C10	0.023 (3)	0.034 (4)	0.023 (3)	0.005 (3)	−0.001 (3)	0.001 (3)
C11	0.047 (4)	0.031 (4)	0.042 (4)	0.002 (3)	0.019 (4)	0.006 (3)
O3	0.038 (3)	0.059 (4)	0.066 (4)	−0.003 (3)	−0.010 (3)	0.001 (3)
C12	0.032 (4)	0.049 (5)	0.044 (4)	−0.006 (4)	0.008 (3)	−0.001 (4)
O4	0.063 (4)	0.036 (3)	0.067 (4)	0.010 (3)	0.021 (3)	0.013 (3)
C13	0.036 (4)	0.033 (4)	0.042 (4)	0.001 (3)	0.004 (4)	0.004 (3)
O5	0.052 (3)	0.057 (4)	0.055 (3)	−0.004 (3)	0.024 (3)	0.008 (3)
C14	0.042 (4)	0.028 (4)	0.044 (4)	0.004 (3)	0.012 (4)	0.001 (3)
N2	0.039 (3)	0.036 (3)	0.032 (3)	−0.003 (3)	0.009 (3)	−0.002 (2)
C15	0.034 (4)	0.035 (4)	0.038 (4)	0.003 (3)	0.005 (3)	−0.004 (3)
C16	0.077 (6)	0.055 (6)	0.029 (4)	0.013 (5)	−0.002 (4)	−0.005 (4)
C17	0.123 (9)	0.068 (7)	0.064 (6)	0.021 (7)	−0.042 (6)	−0.025 (5)
C18	0.093 (9)	0.073 (9)	0.172 (14)	−0.017 (7)	−0.072 (9)	−0.035 (9)
C19	0.051 (6)	0.066 (8)	0.203 (15)	−0.020 (5)	0.009 (8)	0.001 (9)
C20	0.047 (5)	0.037 (5)	0.085 (7)	−0.005 (3)	0.023 (5)	0.012 (4)

Geometric parameters (Å, º)

Re—C13	1.903 (8)	C9—C10	1.404 (8)
Re—C12	1.912 (8)	C9—H9	0.9500
Re—C11	1.960 (8)	C11—O3	1.144 (8)
Re—C14	2.107 (8)	C12—O4	1.155 (8)
Re—O1	2.149 (5)	C13—O5	1.159 (8)
Re—N1	2.237 (5)	C14—N2	1.135 (8)
N1—C2	1.333 (8)	N2—C15	1.446 (8)
N1—C10	1.380 (7)	C15—C16	1.512 (9)
O1—C1	1.289 (8)	C15—C20	1.537 (9)
O2—C1	1.224 (8)	C15—H15	1.0000
C1—C2	1.510 (9)	C16—C17	1.523 (12)
C2—C3	1.376 (9)	C16—H16A	0.9900
C3—C4	1.356 (9)	C16—H16B	0.9900
C3—H3	0.9500	C17—C18	1.512 (17)
C4—C5	1.411 (9)	C17—H17A	0.9900
C4—H4	0.9500	C17—H17B	0.9900
C5—C6	1.405 (9)	C18—C19	1.496 (17)
C5—C10	1.413 (9)	C18—H18A	0.9900
C6—C7	1.365 (9)	C18—H18B	0.9900
C6—H6	0.9500	C19—C20	1.516 (13)
C7—C8	1.394 (10)	C19—H19A	0.9900
C7—H7	0.9500	C19—H19B	0.9900
C8—C9	1.371 (9)	C20—H20A	0.9900
C8—H8	0.9500	C20—H20B	0.9900
C13—Re—C12	87.2 (3)	C10—C9—H9	120.5
C13—Re—C11	88.4 (3)	N1—C10—C9	120.1 (6)
C12—Re—C11	90.1 (3)	N1—C10—C5	120.4 (6)
C13—Re—C14	91.6 (3)	C9—C10—C5	119.6 (6)
C12—Re—C14	90.9 (3)	O3—C11—Re	178.3 (6)
C11—Re—C14	179.1 (3)	O4—C12—Re	178.3 (7)
C13—Re—O1	179.2 (2)	O5—C13—Re	177.4 (6)
C12—Re—O1	93.5 (2)	N2—C14—Re	175.9 (6)
C11—Re—O1	91.8 (2)	C14—N2—C15	173.2 (7)
C14—Re—O1	88.1 (2)	N2—C15—C16	110.3 (6)
C13—Re—N1	104.1 (2)	N2—C15—C20	107.6 (5)
C12—Re—N1	168.7 (2)	C16—C15—C20	112.7 (6)
C11—Re—N1	89.4 (2)	N2—C15—H15	108.7
C14—Re—N1	89.7 (2)	C16—C15—H15	108.7
O1—Re—N1	75.16 (18)	C20—C15—H15	108.7
C2—N1—C10	118.3 (5)	C15—C16—C17	109.4 (8)
C2—N1—Re	111.7 (4)	C15—C16—H16A	109.8
C10—N1—Re	129.2 (4)	C17—C16—H16A	109.8
C1—O1—Re	116.8 (4)	C15—C16—H16B	109.8
O2—C1—O1	123.8 (6)	C17—C16—H16B	109.8
O2—C1—C2	119.8 (6)	H16A—C16—H16B	108.2
O1—C1—C2	116.4 (6)	C18—C17—C16	111.0 (8)
N1—C2—C3	123.8 (6)	C18—C17—H17A	109.4
N1—C2—C1	116.4 (6)	C16—C17—H17A	109.4
C3—C2—C1	119.8 (6)	C18—C17—H17B	109.4
C4—C3—C2	119.1 (6)	C16—C17—H17B	109.4
C4—C3—H3	120.4	H17A—C17—H17B	108.0
C2—C3—H3	120.4	C19—C18—C17	111.2 (10)
C3—C4—C5	119.8 (6)	C19—C18—H18A	109.4
C3—C4—H4	120.1	C17—C18—H18A	109.4
C5—C4—H4	120.1	C19—C18—H18B	109.4
C6—C5—C4	123.1 (7)	C17—C18—H18B	109.4
C6—C5—C10	118.7 (6)	H18A—C18—H18B	108.0
C4—C5—C10	118.2 (6)	C18—C19—C20	111.6 (9)
C7—C6—C5	121.7 (7)	C18—C19—H19A	109.3
C7—C6—H6	119.2	C20—C19—H19A	109.3
C5—C6—H6	119.2	C18—C19—H19B	109.3
C6—C7—C8	118.4 (7)	C20—C19—H19B	109.3
C6—C7—H7	120.8	H19A—C19—H19B	108.0
C8—C7—H7	120.8	C19—C20—C15	109.5 (8)
C9—C8—C7	122.6 (7)	C19—C20—H20A	109.8
C9—C8—H8	118.7	C15—C20—H20A	109.8
C7—C8—H8	118.7	C19—C20—H20B	109.8
C8—C9—C10	119.0 (7)	C15—C20—H20B	109.8
C8—C9—H9	120.5	H20A—C20—H20B	108.2

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C20—H20A···O1^i	0.99	2.61	3.260 (10)	123
C15—H15···O2^i	0.99	2.52	3.365	142
C7—H7···O2^ii	0.99	2.37	3.133	137

Symmetry codes: (i) x+1, y, z; (ii) x+1, −y+1/2, z−1/2.