Chalcogen Bond versus Weak Hydrogen Bond: Changing Contributions in Determining the Crystal Packing of [1,2,5]-Chalcogenadiazole-Fused Tetracyanonaphthoquinodimethanes

Abstract

The crystal structures of a series of tetracyanonaphthoquinodimethanes fused with a selenadiazole or thiadiazole ring revealed that their molecular packing is determined mainly by two intermolecular interactions: chalcogen bond (ChB) and weak hydrogen bond (WHB). ChB between Se and a cyano group dictates the packing of selenadiazole derivatives, whereas the S-based ChB is much weaker and competes with WHB in thiadiazole analogues. This difference can be explained by different electrostatic potentials as revealed by density functional theory calculations. A proper molecular design that weakens WHB can change the contribution of ChB in determining the crystal packing of thiadiazole derivatives.

Key words

crystal engineering - weak hydrogen bonds - chalcogen bonds - chalcogenadiazoles - tetracyanoquinodimethanes - X-ray analysis

Introduction

The weak hydrogen bond (WHB) involving less acidic C–H groups[1] than O–H/N–H groups has been used as a supramolecular synthon in crystal engineering.[2] This approach takes advantage of intermolecular interactions to determine crystal packing and contributes to the design of new solids with desired physical and chemical properties.[3] In this regard, the chalcogen bond (ChB)[4] [5] has attracted much recent attention due to the high directionality of the interaction in crystal. In ChB, an electrophilic chalcogen atom (E) is bound to a Lewis base (LB) through n(LB) → σ*(E–R) electron donation in an atomic array of LB•••E–R, where R is an electron-withdrawing group. The strength of the ChB is influenced by the nature of the E atom (Se > S), the nature of the electron-deficient R group, the LB•••E–R angle (close to linear), and the basicity of LB.[6] The directionality of the ChB was explained by the existence of a σ-hole on the E atom, which defines a positive electrostatic potential region in the direction opposite the R–E bond. [1,2,5]-Chalcogenadiazoles are versatile units (R = N, LB = N) for the generation of supramolecular synthons, such as the (N•••E)₂ square dimer motif.[7]

In our continuing studies on the ChB observed in tetracyanoquinodimethane (TCNQ) derivatives fused with chalcogenadiazole(s),[8] we noted that the C≡N•••E motif[9] is often found in these pure organic crystals as C≡N•••E–N contacts,[10] by which a dyad structure is generated, as shown in [Scheme 1a] (R = N, LB = N coming from CN). This ChB motif can be used as a reliable supramolecular synthon to make an inclusion cavity in its clathrate compounds.[11] For example, in the crystal of the title molecule with a selenadiazole ring (1A), the dyad is further connected into an infinite "dyad-ribbon" network by another ChB. The networks are connected to each other by WHB ([Scheme 1b]) to complete the overall crystal structure. In a clathrate-type molecular complex of 1A with an electron-donating guest, the same dyad ribbons are also present, between which the inclusion cavity is formed with breaking of the original WHB and reconnection at different positions with WHB. The resulting three-dimensional cavity endows 1A with a remarkable ability to recognize the regioisomers of the guest, thus proving the importance of ChB through the C≡N•••Se–N contact in supramolecular chemisty.[12] In contrast, despite the similar molecular geometry and electronic structure, the sulfur analogue (2A) does not show similar recognition properties because WHB through C≡N•••H–C contacts is a predominant factor in determining its crystal packing due to the less-effective ChB through C≡N•••S–N contacts.

Scheme 1 Supramolecular synthons by ChB and WHB.

Since ChB-driven molecular recognition is still considered to be in its infancy,[13] the strikingly different recognition properties between 1A and 2A prompted us to further study the molecular packing of other tetracyanonaphthoquinodimethane (TCNNQ) analogues fused with a chalcogenadiazole (e.g., 1B, 1C, 2B, and 2C) ([Figure 1]). This study sought to clarify whether a change in the chalcogen atom (Se in 1 and S in 2) and/or proper subunit addition could alter the contribution of ChB in determining the crystal packing of the title molecules, especially in competition with WHB.

Figure 1 Dimethylation and further benzo-annulation on the TCNNQ skeleton to further weaken WHB in 1A and 1B.

Results and Discussion

For both TCNNQs fused with a selenadiazole (1A) and a thiadiazole (2A), modification should only be done on the fused benzene ring, so that ChB would be maintained as in 1A and 2A. We designed here new TCNNQs by attachment of methyl groups at the 6,7-positions (1B and 2B) or further annulation of a benzene ring (1C and 2C) by considering that such modification affects the WHB motif shown in [Scheme 1b]. The carbon hybridization at C–H affects the strength of WHB: C_sp3–H is less effective than C_sp2–H.[14] Thus, WHB would have less of an influence on crystal packing in dimethyl derivative 2B than in 2A. The acidity of the C–H group also determines the strength of WHB,[15] and the finding that the polar C form has less of a contribution than the polar A ([Scheme 1c]) suggests that further annulated analogue 2C has as less effective WHB than 2A. These are the central points of the molecular design, and suggest that the two kinds of modification would increase the contribution of ChB in determining the crystal packing of 2 in comparison to WHB. It is highly likely that all of the crystal structures of selenadiazole derivatives (1) would be dictated by ChB through C≡N•••Se–N contacts, and thus the molecular packing of 1A–1C can be used as a reference. Thus, a changeable contribution of ChB and WHB would be clarified when the crystal structures are compared between 1 and 2 upon weakening of the WHB through dimethylation in 2B and further benzo-annulation in 2C.

Electrostatic potentials can provide detailed information on molecular polarization. The V _s,_max and V _s,_min values are useful for evaluating of the intermolecular interactions such as ChB and WHB. Density functional theory (DFT) calculations were conducted for 1B, 1C, 2B, and 2C [M06-2X/6-31G(d,p)] ([Figure S1]) and the results were compared to those of 1A and 2A calculated using the same function and basis set.[12] The 6-31G(d,p) basis set with a reasonable calculation cost would be satisfactory since the results were compared only among 1A–1C and 2A–2C, which have similar geometrical and electronic structures.

As shown in [Figure 2], the electrostatic potentials of the present TCNNQs are similar to each other: large positive values on the E atom corresponding to the presence of σ-holes and on the C–H groups, and large negative values on the N atoms of cyano groups and those of chalcogenadiazoles. The V _s,_max values on Se in 1B and 1C (+33.3 and 33.6 kcal mol⁻¹, respectively) are similar to that in 1A (+35.0 kcal mol⁻¹). On the other hand, V _s,_max values of the C–H groups at the opposite region on the long molecular axis in 1B and 1C (+25.2 and 27.1 kcal mol⁻¹, respectively) are smaller than those of 1A (+30.5 kcal mol⁻¹) and the parent TCNNQ without a fused heterocycle (+29.9 kcal mol⁻¹). Thus, ChB should be the predominant intermolecular interaction in 1B and 1C with an even weaker WHB than in 1A.

Figure 2 Electrostatic potentials in (a) 1B, (b) 1C, (c) 2B, and (d) 2C calculated by the DFT method [M06-2X/6-31G(d,p)] (isoval. = 0.0004).

Thiadiazole compounds 2A–2C have smaller V _s,_max values (+28.7, 27.0, and 27.2 kcal mol⁻¹, respectively) on S than on Se in 1A–1C, and thus the V _s,_max value of the C–H groups in 2A (+31.2 kcal mol⁻¹) is larger than them. However, when two methyl groups are attached in 2B (+25.9 kcal mol⁻¹) and further benzo-annulation is applied in 2C (+27.6 kcal mol⁻¹), V _s,_max of the C–H groups is decreased. Thus, V _s,_max values related to ChB and WHB are comparable in 2B and 2C, and unlike in 2A, both ChB and WHB should contribute to determining their crystal packing.

After the theoretical studies shown above, newly designed TCNNQs (1B, 1C, 2B, and 2C) were prepared from the corresponding quinone derivatives[16] fused with a chalcogenadiazole ring upon condensation reactions with malononitrile in the presence of TiCl₄.[17] Voltammetric analyses in MeCN indicated that newly prepared TCNNQs undergo reversible electrochemical reduction (E ₁ ^red and E ₂ ^red/V vs. saturated calomel electrode (SCE): 1B, –0.37 and –0.48; 1C, –0.45 and –0.55; 2B, –0.25 and –0.41; 2C –0.35 and –0.41) as in other related TCNQ derivatives. The small separation between the first and second reduction potentials as in 1A (E ₁ ^red and E ₂ ^red/V: –0.35 and –0.46) and 2A (−0.22 and −0.41) indicates that these TCNNQs adopt a butterfly-shaped deformed structure,[18] which was predicted by calculation ([Figure 2]) and later revealed by X-ray analyses ([Figures S2–S5], [Table S1]). Recrystallization (vapor diffusion method) from CH₂Cl₂–hexane (for 2C) or CHCl₃–hexane (others) gave single crystals that were suitable for X-ray analyses as yellow plates (1B and 2B) or orange plates (1C and 2C).

Selenadiazolo-TCNNQ with two methyl groups (1B) crystallizes in triclinic P-1 (Z = 2). The packing arrangement is mainly characterized by two kinds of ChB through C≡N•••Se–N contacts [(i) and (ii)]. The geometries of ChB can be described by the distance (d _ChB) of (C≡)N•••E as well as two angles (θ1: < C≡N•••E; θ2: < N•••E–N) ([Table 1]). By the ChB through contact (i), two molecules of 1B form a centrosymmetric dyad, as shown in [Scheme 1a]. The dyad is further connected by ChB through contact (ii) along the crystallographic b-axis, thus forming an infinite dyad-ribbon network ([Figure 3]). The d _ChB values of (i) and (ii) are both smaller than the sum of the van der Waals (vdW) radii of N•••Se (3.50 Å),[19] by 7% and 9%, respectively ([Table 1a]). Thus, as also supported by suitable contact angles (θ1 and θ2), the ChB is proven to be a strong and important director of the crystal packing of 1B. The positions of hydrogen atoms in 1B were calculated geometrically, and thus there is some uncertainty regarding the parameters for WHB involving C–H of methyl groups. Despite such uncertainty, it is still clear that the dyad-ribbon networks are further connected to each other along the c-axis by WHB through C≡N•••H–C contacts of (iii) and (iv) ([Table 1b]), and thus a two-dimensional sheet-like structure is formed on the bc-plane. Since the sheets are repeated along the a-axis without significant interaction, the most characteristic feature is the sheet-like structure composed of dyad-ribbon networks. This packing is quite similar to that of 1A ([Figure S6]) without methyl substitution,[12] showing that attachment of two methyl groups does not alter the packing motif because strong ChB through C≡N•••Se–N is the dominant factor in determining the crystal structure in 1A and 1B.

Table 1 Geometrical description[a] for (a) ChB of C≡N•••E–N and (b) WHB of C≡N•••H–C in 1B, 1C, 2B, and 2C

a) ChB	d ChB /Å	θ 1/°	θ 2/°
1B (i)	3.24	123	153
1B (ii)	3.18	164	174
1C (i)	3.06	149	149
1C (ii)	3.14	139	153
2B (i)	3.44	92	130
2B (ii)	3.11	110	172
2C (i)	3.14	147	144
b) WHB	d WHB /Å	ϕ 1/°	ϕ 2/°
1B (iii)	2.79	113	110
1B (iv)	2.79	97	122
1C (iii)	2.77	108	140
1C (iv)	2.58	164	146
2B (iii)	2.68	92	143
2B (iv)	2.89	168	179
2B (v)	2.77	152	143
2B (vi)	2.76	108	138
2C (ii)	2.82	107	139
2C (iii)	2.56	162	146

^a The esd's for the distances and angles are less than 0.01 Å and 1°, respectively.

Figure 3 Sheet-like structure composed of dyad-ribbon networks in 1B. Molecules A1 and A1' forms a dyad by ChB through contact (i). Molecules A1, A2, and A3 (as well as A1', A2', and A3') are connected by ChB through contact (ii) to form the dyad-ribbon network. Two dyad ribbons (A1-A3' and B1-B3') are connected by WHB of (iii) and (iv) between A1'and B1 and between A2' and B1, respectively.

Selenadiazolo-TCNNQ with further annulation of a benzene ring (1C) crystallizes in triclinic P-1 (Z = 2). The packing arrangement is mainly characterized by two kinds of ChB [(i) and (ii)]. By the contact of C≡N•••Se–N (i), two molecules of 1C form a centrosymmetric dyad, as shown in [Scheme 1a]. This dyad is further connected by ChB through contact (ii) of a (N•••Se)₂ square dimer motif to furnish the dyad-ribbon network along the crystallographic b-axis. The additional contacts of WHB [(iii) and (iv)] are present within the dyad ribbon ([Figure 4a]). In contrast to 1A and 1B, the dyad ribbons of 1C are not further connected by WHB since the two C–H groups at the edge of the long molecular axis are not involved in WHB. Instead, the dyad ribbons are stacked in a layered-brick manner ([Figure 5a]) with two kinds of π − π overlaps (type-1: convex–convex; type-2: concave–concave) with the shortest C–C contact of 3.32 and 3.35 Å, respectively ([Figure S3]). Thus, the crystal packing of 1C is governed by ChB and π − π interaction, so that the relative importance of WHB in 1C is even less than those in 1A and 1B.

Figure 4 Dyad-ribbon network in 1C (left) and 2C (right). Molecules A1 and A1' forms a dyad by ChB through contact (i). Dyads are further connected along the b-axis to form a dyad-ribbon network (A1–A3').

Figure 5 Layered-brick stacking of dyad-ribbon networks in 1C (upper) and 2C (lower) with two kinds of π–π overlaps.

The crystal packing of thiadiazolo-TCNNQ with two methyl groups (2B) [orthorhombic, Pca2₁, (Z = 4)] is quite different from that in the corresponding selenadiazole derivative 1B. Molecules are connected to form a sheet-like network on the ab-plane by WHB (iii) and (iv). There also is a contact of C≡N•••S–N (i) with d _ChB of 3.44 Å, which is larger than the sum of the vdW radii of N•••S (3.35 Å)[19] and would not be considered as an effective ChB ([Figure 6]). Such a coplanar arrangement of molecules resembles the packing of 2A in its molecular complex with an electron-donating guest.[12] Each molecule is further connected along the screw axis extending to the crystallographic c-axis. Three kinds of catemer structures are formed not only by the C≡N•••S–N contact (ii) but also by C≡N•••C–H contacts of (v) and (vi) ([Figure S4]). In this way, the packing arrangement of 2B is determined by both ChB and WHB.

Figure 6 Sheet-like structure of 2B. Molecule A1 is connected to A1' and A2' by WHB through contact (iii) to form a double-ribbon network (A1–A3') along the a-axis. This ribbon is connected to another ribbon (B1–B3) by WHB of (iv) and ChB (i) to form a sheet-like network on the ab-plane.

In contrast, thiadiazolo-TCNNQ with further annulation of a benzene ring (2C) [triclinic P-1 (Z = 2)] crystallizes isomorphous to 1C ([Figures 4b], [5b], and [S5]). Thus, its packing is basically determined by ChB and π − π interaction, indicating a reduced contribution from WHB due to weakening via benzo-annulation in 2C. A notable difference is the absence of a (N•••S)₂ square dimer motif in 2C, due to the generally weaker ChB in thiadiazoles than in selenadiazoles.[7a]

Conclusions

Based on the above-mentioned four X-ray structures as well as their comparisons including those of 1A and 1B, we can safely conclude that the contribution of ChB in thiadiazolo-TCNNQs (2A–2C) is increased by weakening WHB through two different modifications of the molecular structure. By considering that crystal packing of all the selenadiazolo-TCNNQs (1A–1C) is dictated by ChB and that 2C has an isomorphous structure to that of 1C, a proper molecular design (e.g., further benzo-annulation) should successfully suppress the contribution from WHB while making ChB the decisive factor for packing arrangement.

ChB through C≡N•••E–N contacts is a useful supramolecular synthon in crystal engineering, and thus chalcogenadiazole-fused electron acceptors can recognize the regioisomers of electron-donating guests in their crystalline molecular complexes.[11d] By following the general trend with stronger interaction for a Se-involving ChB than for a S-involving ChB, thiadiazole-fused acceptors can only provide the less reliable synthon of C≡N•••S–N.[12] However, by proper design to suppress competing interactions such as WHB, S-involving ChB can become the decisive factor of crystal packing. In this way, this work has demonstrated that the contribution of ChB in crystal engineering can be altered.

Experimental Section

¹H and ¹³C NMR spectra were recorded on a BRUKER Ascend™ 400 (¹H/400 MHz and ¹³C/100 MHz) spectrometer. IR spectra were measured on a Shimadzu IRAffinity-1S FT/IR spectrophotometer in ATR mode. UV/Vis spectra were recorded on a Hitachi U-2910 spectrophotometer. Mass spectra were recorded on a JMS-T100GCV spectrometer in FD mode by Dr. Eri Fukushi and Mr. Yusuke Takata (GC-MS & NMR Laboratory, Research Faculty of Agriculture, Hokkaido University). Melting points were measured on a Yamato MP-21 and are uncorrected.

Calculation

DFT calculations were performed with the Gaussian 16W program package. The geometries of the compounds were optimized by using the M06-2X method in combination with the 6-31G(d,p) basis set. The coordinates are given in the Supporting Information.

Synthetic Procedures

A typical procedure for conversion of the precursor quinones to TCNQs is as follows: to a suspension of 6,7-dimethylnaphtho[2,3-c][1,2,5]selenadiazole-4,9-dione (2.53 g, 8.69 mmol) in dry CH₂Cl₂ (200 mL) was added TiCl₄ (4.67 g, 24.6 mmol). To the mixture was then added dropwise a solution of malononitrile (8.11 g, 123 mmol) in a mixed solvent of dry pyridine (20 mL) and dry CH₂Cl₂ (100 mL) over 80 min. After the mixture was stirred for 45 h at 25 °C, it was poured into 4N HCl aq (400 mL). The organic layer was separated and washed with water (350 mL × 5) and brine (300 mL × 3), and then dried over Na₂SO₄. Solvent was removed and the residue was chromatographed on silica gel (CH₂Cl₂) to give 1B as a yellow solid (3.34 g) in 99% yield. Similarly, 1C (orange crystal), 2B (yellow crystal), and 2C (orange crystal) were obtained in respective yields of 87% (224 mg), 74% (53 mg), and 82% (50 mg).

The selected spectral data for 1B, 1C, 2B, and 2C are as follows. The spectral charts are given in the Supporting Information.

1B: Mp 272–280 °C (dec); ¹H NMR (400 MHz, CDCl₃) δ = 8.31 (2 H, s), 2.49 (6 H, s), ¹³C NMR (100 MHz, CDCl₃) δ = 155.22, 152.24, 144.89, 130.59, 126.79, 113.35, 112.68, 84.07, 20.45; IR (ATR): 3155, 2957, 2226, 1602, 1554, 1441, 1402, 1284, 895, 751, 573, 480, 427 cm⁻¹; HRMS-FD: m/z [M]⁺ calcd for C₁₈H₈N₆Se: 387.99764; found: 387.99670; UV/Vis (CH₂Cl₂): λ_max (log ε) = 364sh (4.47), 336 (4.58), 266sh (3.85), 252 (3.94), 230 (4.06) nm.

1C: Mp > 400 °C; ¹H NMR (400 MHz, CDCl₃) δ = 9.03 (2 H, s), 8.11 (2 H, dd, J = 6.2, 3.2 Hz), 7.85 (2 H, dd, J = 6.2, 3.2 Hz), (400 MHz, DMSO-d ₆) δ = 9.11 (2H, s), 8.22 (2H, dd, J = 6.0, 3.2 Hz), 7.89 (2H, dd, J = 6.0, 3.2 Hz); ¹³C NMR (100 MHz, DMSO-d ₆) δ = 155.47, 155.40, 133.57, 131.79, 131.43, 129.90, 125.96, 115.13, 114.21, 82.88 ; IR (ATR): 3074, 2924, 2851, 2222, 1544, 1489, 1175, 914, 901, 768, 573, 469 cm⁻¹; HRMS-FD: m/z [M]⁺ calcd for C₂₀H₆N₆Se: 409.98200; found: 409.98257; UV/Vis (CH₂Cl₂): λ_max (log ε) = 452sh (3.80), 372 (4.43), 341 (4.72), 286sh (4.05), 258sh (4.13), 236 (4.60) nm.

2B: Mp 231–265 °C (dec); ¹H NMR (400 MHz, CDCl₃) δ = 8.42 (2H, s), 2.51 (6H, s), ¹³C NMR (100 MHz, CDCl₃) δ = 152.10, 148.89, 144.96, 130.58, 126.59, 113.36, 112.38, 83.57, 20.43; IR (ATR): 3054, 2925, 2851, 2229, 1604, 1554, 1409, 1273, 975, 837, 734, 577, 525, 423 cm⁻¹; HRMS-FD: m/z [M]⁺ calcd for C₁₈H₈N₆S: 340.05311; found: 340.05441; UV/Vis (CH₂Cl₂): λ_max (log ε) = 356 (4.46), 318 (4.49), 252sh (3.97), 230 (4.20) nm.

2C: Mp 361–362 °C; ¹H NMR (400 MHz, CDCl₃) δ = 9.13(2H, s), 8.13 (2H, dd, J = 6.1, 3.3 Hz), 7.57 (2H, dd, J = 6.1, 3.3 Hz); ¹³C NMR could not be measured due to low solubility; Anal. calcd for C₂₀H₆N₆S: C, 66.28; H, 1.67; N, 23.20%. Found: C, 66.49; H. 1.89; N. 23.15%; IR (ATR): 3076, 2925, 2853, 2223, 1590, 1543, 1487, 1443, 1249, 974, 914, 902, 845, 771, 580, 523, 470 cm⁻¹; HRMS-FD: m/z [M]⁺ calcd for C₂₀H₆N₆S: 362.03746; found: 362.03814; UV/Vis (CH₂Cl₂): λ_max (log ε) = 453sh (3.78), 350 (4.39), 324 (4.53), 270 (4.15), 232 (4.52) nm.

Redox Potential Measurement

Cyclic voltammetric analyses were conducted on a BAS ALS-600A electrochemical analyzer in dry MeCN containing 0.1 M Et₄NClO₄ as a supporting electrolyte. All of the values shown in the text are in E/V vs. SCE measured at the scan rate of 100 mV s⁻¹. Pt disk electrodes were used as the working and counter electrodes. All of the waves are reversible and the E ^red value was obtained as (E ^{cathodic peak} + E ^{anodic peak})/2. Under the similar conditions, the potential for Fe/Fc⁺ is +0.38 V.

X-Ray Analyses

1B: MF C₁₈H₈N₆Se, FW 387.26, triclinic P-1, a = 8.7829(2) Å, b = 9.6682(2) Å, c = 10.5357(2) Å, α  = 74.1400(19)°, β  = 71.387(2)°, γ  = 68.505(2)°, V = 776.37(3) ų, ρ(Z = 2) = 1.657 g cm⁻³. A total of 7569 independent reflections (2θ_max: 151.5°) were measured at 150 K by using CuKα. The structure was solved by the direct method and the atomic coordinates were refined with anisotropic temperature factors. The positions of hydrogen atoms were calculated and included in the refinement with isotropic temperature factors. The final R, wR, and GOF values are 3.43%, 9.13%, and 1.066, respectively, for all data (CCDC 2048002).

1C: MF C₂₀H₆N₆Se, FW 409.27, triclinic P-1, a = 7.3955(3) Å, b = 9.4496(4) Å, c = 12.4473(3) Å, α  = 86.492(3)°, β  = 78.650(3)°, γ  = 71.114(3)°, V = 806.95(5) ų, ρ(Z = 2) = 1.684 g cm⁻³. A total of 7907 independent reflections (2θ_max: 152.7°) were measured at 150 K by using CuKα. The structure was solved by the direct method and the atomic coordinates were refined with anisotropic temperature factors. The positions of hydrogen atoms were calculated and included in the refinement with isotropic temperature factors. The final R, wR, and GOF values are 4.66%, 11.53%, and 1.047, respectively, for all data (CCDC 2048003).

2B: MF C₁₈H₈N₆S, FW 340.36, orthorhombic, Pca2₁ , a = 12.18316(19) Å, b = 17.2162(3) Å, c = 7.28933(12) Å, V = 1528.92(4) ų, ρ(Z = 4) = 1.479 g cm⁻³. A total of 4735 independent reflections (2θ_max: 151.6°) were measured at 150 K by using CuKα. The structure was solved by the direct method and the atomic coordinates were refined with anisotropic temperature factors. The positions of hydrogen atoms were calculated and included in the refinement with isotropic temperature factors. The final R, wR, and GOF values are 5.54%, 14.88%, and 1.203, respectively, for all data (CCDC 2048004).

2C: MF C₂₀H₆N₆S, FW 362.37, triclinic P-1, a = 7.3004(5) Å, b = 9.4855(6) Å, c = 12.3573(6) Å, α  = 86.461(4)°, β  = 78.239(5)°, γ  = 71.110(6)°, V = 792.62(9) ų, ρ(Z = 2) = 1.518 g cm⁻³. A total of 7603 independent reflections (2θ_max: 151.6°) were measured at 150 K by using CuKα. The structure was solved by the direct method and the atomic coordinates were refined with anisotropic temperature factors. The positions of hydrogen atoms were calculated and included in the refinement with isotropic temperature factors. The final R, wR, and GOF values are 5.20%, 15.12%, and 1.109, respectively, for all data (CCDC 2048005).

Die Autoren geben an, dass kein Interessenkonflikt besteht.

Acknowledgment

This work was also supported by the Research Program of “Five-star Alliance” in “NJRC Mater. & Dev.” MEXT.

Supporting Information

Following data are given in the Supporting Information: details of DFT calculations of 1B, 1C, 2B, and 2C; supplementary figures and table of X-ray analyses of 1B, 1C, 2B, and 2C; spectral charts for 1B, 1C, 2B, and 2C. Supporting Information for this article is available online at https://doi.org/10.1055/s-0041-1725046.

Dedicated to Peter Bäuerle on the occasion of his 65th birthday.

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Publikationsverlauf

Eingereicht: 12. Januar 2021

Angenommen: 27. Januar 2021

Artikel online veröffentlicht:
01. April 2021