4-([1,1′:3′,1′′-terphenyl]-2′-yloxy)-5-chlorophthalonitrile

Abstract

The study focuses on the synthesis and detailed crystal structure analysis of 4-([1,1′:3′,1′′-terphenyl]-2′-yloxy)-5-chlorophthalonitrile. Using X-ray diffraction methods, the authors achieved the precise refinement of the atomic arrangement, revealing the specific spatial organization of molecules within the crystal lattice. The manuscript thoroughly discusses the key intermolecular interactions—such as hydrogen bonding and π-π stacking—that govern the crystal packing. These interactions play a crucial role in stabilizing the structure and have a direct impact on the material’s physical and chemical properties, including its thermal stability and optical characteristics.

1. Introduction

Substituted phthalonitriles have been extensively studied for over a century due to their potential applications as high-conductivity resins, components in electrical engineering, pigments, and thermally stable composites. The physicochemical properties of these compounds are critically influenced by their crystalline packing, making the analysis of substituent effects essential for designing high-performance functional materials [1,2,3,4].

In previous studies, we investigated the crystal structures of methoxyphenoxy-substituted phthalonitriles with varying positions of the methoxy group (meta-, ortho-, and para-) [1,5]. It was demonstrated that substituent positioning significantly alters molecular packing, directly impacting the functional characteristics of the compounds. This work presents an analysis of a modified structure—4-(2,5-bisphenylphenoxy)-5-chlorophthalonitrile—where the introduction of a chlorine substituent at the 5-position of the phthalonitrile core and a bulky bisphenylphenoxy fragment induces unique steric and electronic effects.

2. Results

The structure is illustrated in Figure 1 (left). It was established that the asymmetric unit contains two independent molecules (A and B) of 4-([1,1′:3′,1′′-terphenyl]-2′-yloxy)-5-chlorophthalonitrile (. The molecules have a similar structure. The root-mean-square deviations of atomic positions (RMSD) are 0.428 Å for all non-hydrogen atoms of A and B molecules. The maximum deviation for chlorine atoms is 1.235 Å. The molecule has four planar fragments: the ClC₆(CN)₂O fragment, as well as three phenyl rings in the 2,6-bisphenylphenoxyl substituent. Molecules A and B also differ in the relative position of these segments. Thus, in molecule A, the plane of the central ring of the 2,6-bisphenylphenoxyl substituent is almost perpendicular to the ClC₆(CN)₂O fragment. The corresponding dihedral angle is 89.0°. In turn, in molecule B, this value deviates significantly from the orthogonal arrangement and is 80.0°. In addition, the phenyl substituents in bisphenylphenoxyl are rotated relative to the central ring by 40.8 and 36.7° in molecule A and by 39.8 and 53.1° in molecule B. This difference is apparently due to the effect of crystal packing. It should be noted that all the main bond lengths in independent molecules are in excellent agreement with each other (

Table 1. The selected bond lengths [Å] and angles [°] in the independent (A and B) molecules of 4-([1,1′:3′,1′′-terphenyl]-2′-yloxy)-5-chlorophthalonitrile.

Bond	Molecule A	Molecule B	Angle	Molecule A	Molecule B
C(1)-Cl(1)	1.7293(16)	1.7225(16)	C(2)-O(1)-C(7)	117.22(11)	116.31(12)
O(1)-C(2)	1.3579(18)	1.3611(18)	C(2)-C(1)-Cl(1)	119.23(12)	119.36(12)
O(1)-C(7)	1.4128(17)	1.4163(17)	C(6)-C(1)-Cl(1)	119.66(12)	120.17(12)
N(1)-C(25)	1.150(2)	1.149(2)	O(1)-C(2)-C(1)	116.23(13)	116.57(13)
N(2)-C(26)	1.147(2)	1.151(2)	O(1)-C(2)-C(3)	124.07(13)	123.91(13)
C(1)-C(2)	1.408(2)	1.409(2)	N(1)-C(25)-C(4)	179.77(18)	179.9(3)
C(2)-C(3)	1.393(2)	1.391(2)	N(2)-C(26)-C(5)	179.05(19)	179.7(2)
C(3)-C(4)	1.398(2)	1.394(2)	C(3)-C(4)-C(25)	120.07(14)	119.77(14)
C(4)-C(5)	1.412(2)	1.408(2)	C(5)-C(4)-C(25)	119.50(14)	120.19(14)
C(5)-C(6)	1.395(2)	1.393(2)	C(4)-C(5)-C(26)	119.76(14)	119.61(15)
C(1)-C(6)	1.382(2)	1.387(2)	C(6)-C(5)-C(26)	120.51(14)	120.56(14)
C(4)-C(25)	1.447(2)	1.444(2)	N/A	N/A	N/A
C(5)-C(26)	1.442(2)	1.441(2)	N/A	N/A	N/A

).

Indeed, A and B molecules in a crystal have a non-equivalent environment. The main structural motif is the formation of tetramers (B-A-A-B) due to strong π…π interactions of cyano groups, additionally stabilized by H…N contacts (Figure 2). It should be noted that, according to the literature, similar chloro-substituted phthalonitriles with a directly introduced phenoxy fragment also exhibit the presence of two independent molecules, A and B, in the unit cell [6,7,8]. However, when the fragment is introduced via a spacer bridge, the unit cell contains only one molecule [9].

The distances between the centers of C≡N bonds in neighboring molecules are 3.31 (A…B contact) and 3.45 Å (A…A). These geometric characteristics indicate the presence of strong intermolecular π…π interactions in the crystal, since the geometric criterion for such contacts is from 3.3 to 3.8 Å [10,11]. In addition, the nitrogen atoms of the cyano groups are involved in the formation of intermolecular hydrogen bonds. The N…H distances vary in the range of 2.53–2.68 Å (

Table 2. Short interactions geometry parameters (Å,°) in crystal 4-([1,1′:3′,1′′-terphenyl]-2′-yloxy)-5-chlorophthalonitrile.

D–H…A/D…A	D–H	H…A	D…A	D–H…A
C3A–H3AA…N1A i,*	0.95	2.65	3.509(2)	149.8
C6A–H6AA…N2B ii	0.95	2.53	3.352(2)	144.3
C6B–H6BA…N2A iii	0.95	2.68	3.501(2)	144.8
N1A…C25A i	N/A	N/A	3.451(2)	N/A
N2A…C26B ii	N/A	N/A	3.343(2)	N/A
C26A…N2B ii	N/A	N/A	3.280(2)	N/A
(C19B-C24B)center…(C19B-C24B)center iv	N/A	N/A	3.70	N/A
(C20A-C21A)center…(C14B-C15B)center v	N/A	N/A	3.37	N/A
(C5A-C6A)center…(C9B-C10B)center	N/A	N/A	3.57	N/A
Cl1A…(C13B-C18B)center	N/A	N/A	3.89	N/A
Cl1B…(C19A-C24A)center vi	N/A	N/A	3.41	N/A

* Symmetry code: (ⁱ): −x + 1, −y + 1, −z + 1; (ⁱⁱ): −x + 2, y − 1/2, −z + 1/2; (ⁱⁱⁱ): −x + 2, y + 1/2, −z + 1/2; (^iv): −x + 2, −y + 1, −z + 1; (^v): −x + 1, y − 1/2, −z + 1/2; (^vi): x + 1, y, z.

), which is comparable with the mean length of a normal van der Waals contact [12]. The tetramers in the crystal are linked to each other by weak π…π interactions between the phenyl substituents in the B molecules (Figure 3).

The distance between the centers of aromatic systems (3.70 Å) is significantly greater than the distances between the centers of C≡N bonds in a tetramer. However, this value is still less than the geometric criterion for the existence of intermolecular π…π interactions. As a result, infinite one-dimensional molecular chains are formed.

Thus, compared to analogous bifunctional chloro-phenoxy-substituted nitriles [6,7], the introduction of additional aromatic rings into the phenoxy fragment further stabilizes the molecular crystal packing through stacking interactions. Studies demonstrate that directly attached phenoxy groups are often spatially oriented in a way that prevents any significant contact due to steric hindrance. However, the incorporation of phenoxy groups via a spacer bridge can induce a partial overlap of the substituent’s p-orbitals with the aromatic system of the phthalonitrile ring, leading to molecular stabilization, as described in [9].

Despite the presence of a large number of aromatic rings in the molecule, all other distances between the centers of six-membered rings in neighboring molecules exceed 4 Å. This value significantly exceeds the geometric criterion for the presence of intermolecular π…π interactions. However, in some cases, the distances between the centers of C-C bonds in six-membered cycles are significantly shorter than the limiting value of 3.8 Å (Figure 4 (top), Table 2). This may indicate a partial overlap of the π-systems of molecules in the crystal.

Another significant structural motif in the crystal of 4-([1,1′:3′,1′′-terphenyl]-2′-yloxy)-5-chlorophthalonitrile should be noted. The chlorine atom of molecule B is located almost above the center of the aromatic system (Figure 4 (bottom)). All Cl…C distances are largely equalized and are 3.59–3.77 Å. The most important thing is that the distance between the chlorine atom and the center of the phenyl substituent (3.41 Å) is less than the sum of the van der Waals radius of the chlorine atom (1.80 Å) [13] and the half-width of the aromatic molecule (1.77 Å—the radius of the sp²-carbon atom) [14,15]. Thus, an intermolecular Cl…π interaction is realized in the crystal. In turn, for the chlorine atom in molecule A, a slightly different situation is observed. Firstly, it is significantly shifted relative to the center of the phenyl substituent of the neighboring molecule. The Cl…C distances are 3.70–4.53 Å. Secondly, the distance to the center of the aromatic system (3.89 Å) exceeds the sum of the van der Waals radius of the chlorine atom and the half-width of the aromatic molecule (3.57 Å). However, some studies [16,17] show that such geometry may still indicate the presence of intermolecular Cl...pi interactions. Similar contacts appear in f 4-chloro-5-(2,6-di-iso-propylphenoxy)phthalonitrile [6].

The detailed structure data information can be found in the Supplementary Materials part.

3. Materials and Methods

3.1. Synthesis of 4-([1,1′:3′,1″-terphenyl]-2′-yloxy)-5-chlorophthalonitrile

A solution of 0.5 g (0.0024 mol) of 4-chloro-5-nitrophthalonitrile and 0.6 g (0.0024 mol) of 2,6-diphenylphenol was prepared in 10 mL of dimethylformamide (DMF) (Scheme 1). To the resulting solution, a solution containing 0.8 g (0.006 mol) of potassium carbonate (K₂CO₃) in 3.3 mL of water was added, and the mixture was stirred at 30 °C for a duration of 1.5 h (Scheme 1). The resultant precipitate was filtered, washed with water, recrystallized from DMF, and subsequently dried in air at 75 °C. Yield: 0.66 g (68%). Melting point: 148–149 °C. IR (ν_max, cm⁻¹): 2235 (C≡N), 1586 (Cₐᵣ-Cₐᵣ), 1275 (Cₐᵣ-O-Cₐᵣ), 1011 (Cₐᵣ-Cl). ¹H NMR (500 MHz, CDCl₃) δ (ppm): 7.56 (3H, m), 7.53 (4H, d, J = 8.25 Hz), 7.49 (1H, s), 7.36 (4H, t, J = 8.41 Hz), 7.29 (2H, t, J = 7.98 Hz), 6.60 (1H, s). ¹³C NMR (126 MHz, CDCl₃) δ (ppm): 156.39, 146.32, 136.14, 135.48, 134.78, 131.07, 128.98, 128.54, 128.09, 127.81, 118.59, 114.65, 114.53, 114.28, 108.60. Mass spectrum, m/z: 406 [M]⁺. Calculated [M]⁺: 406.87. HPLC retention time: 17.962 min. Elemental analysis, found (%): C, 76.79; H, 3.74; N, 6.87. Calculated for C₂₆H₁₅ClN₂O (%): C, 76.75; H, 3.72; N, 6.89.

3.2. X-Ray Crystallography

The diffraction data for 4-([1,1′:3′,1′′-terphenyl]-2′-yloxy)-5-chlorophthalonitrile were collected with Rigaku OD Xcalibur E diffractometer (Mo-Kα radiation, ω-scan technique, λ = 0.71073 Å, Agilent, Poland, Varshava). The intensity data were integrated by the CrysAlisPro (ver. 38.41) program (Agilent, Polish, Varshava) [18]. The structure was solved by the dual methods [19] and was refined on $F_{hkl}^2$ using the SHELXTL 6.1 package (Sheldrick) [20]. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in calculated positions and were refined using the riding model (U_iso(H) = 1.2 U_eq(C)). The CrysAlisPro program was used to perform absorption corrections.

A colorless prism-shaped single crystal (0.44 × 0.43 × 0.32 mm) was selected for SC-XRD analysis. The crystal data for 4-([1,1′:3′,1′′-terphenyl]-2′-yloxy)-5-chlorophthalonitrile were as follows: monoclinic crystal system, space group P2₁/c, unit cell dimensions: a = 14.7913(4) Å, b = 14.9267(4) Å, c = 19.3713(6) Å, V = 4109.6(2) ų, Z = 8, d_calc = 1.315 g/cm³, μ = 0.206 mm⁻¹, F(000) = 1680, reflection collected/unique = 43772/9429, R_int = 0.0450, S = 1.009, R₁ = 0.0390 and wR₂ = 0.0828 [I > 2σ(I)], R₁ = 0.0643 and wR₂ = 0.0935 (all data), largest diff. peak and hole 0.272 and −0.292 e·Å⁻³.