Introduction

Thiazinanones, despite being rarely reported, are very interesting compounds due to their important role in medicinal chemistry [1,2,3]. Substituted thiazinanones exhibited antitumor [4], antifungal activity [5] and antimalarial activity which evaluated by Kumawat et al. [6], as well as anti-oxidant activity [7]. Reactions containing an amine, carbonyl compounds and a mercapto acid in one-pot three-component condensation or a two-step process afforded thiazinanone derivatives [5]. 3-Alkyl-2-aryl-1,3-thiazinan-4-ones containing a methylsulfonyl pharmacophore were synthesized, and their cyclooxygenase-2-[COX-2] inhibitory activity has been evaluated [8]. 3-Pyridin-2-ylmethyl-1,3-thiazinan-4-ones were synthesized, and their anti-oxidant activities were evaluated [7].

On the other hand, the behavior of 2,3-diphenylcyclopropenone 1 toward compounds containing C=N moieties with the formation of aza-cyclopentanones (pyrrolidinones) have been reported [9,10,11,12].

Amidrazones were reacted with 1 in EtOH/Et3N with eliminating a molecule of ammonia to give triphenylpyrimidinenones [13].

The aza-enamine reactivity is shown by the reaction of alkenylidenehydrazinecarbothioamides 2 with cyclopropenone 1 and the availability of azomethine carbon as well as sulfur atom as nucleophilic sites; thus 3,5-disubstituted 1,3,4-thiadiazolyl-2,3-diphenylpropenones 3 were formed [14] (Scheme 1).

Scheme 1
scheme 1

Previously reported interaction of 2,3-diphenylcyclopropenone 1 with alkenylidene hydrazinecarbothioamides 2 and 2,4-disubstituted thiosemicarbazides 4

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The reaction of 1 with various aldehyde 4-phenylthiosemicarbazones in acetic acid provided pyrrolo[2,1-b]oxadiazoles via [2 + 3]cycloaddition and elimination a molecule of H2S [15]. Also, thione derivatives such as 2,4-disubstituted thiosemicarbazides (4, R=C6H5; C6H5CH2) reacted with 1 via a nucleophilic attack of terminal-NH2 of 4 on the carbonyl group of 1 afforded pyridazines 5 (Scheme 1) [16].

The reaction of 2,3-diphenylcyclopropenone 1 with N-imidoylythiourease occurs with elimination phenylisothiocycanate and 3-substituted 2,5,6-triphenylpyrimidin-4-ones were formed [17].

El-Sheref subsequently reported that the reaction between pyrazolylthiourea and 1 followed by oxidation with DDQ afforded 5,6-diphenyl-1,3-thiazinones via the formation of pyrazolylimino-3,5,6-triphenyl-1,3-thiazinan-4-ones [18].

To date, no analogous reactions with 1 using hydrazinecarbothioamides 6a–e have been described. This remarkable versatility in reaction with thiosemicarbazides and bithioureas with 1 warrants further investigation of the reactivity of 6 toward 1 and a comparison of the behavior of 6 with another different thiosemicarbazides 2 and 4 or bithioureas with 1.

Optically active sulfur compounds play an important role in the biochemistry of many living organisms and are found in many synthetic drugs and bioactive natural products [19, 20]. Recently, the [3 + 3] cyclization of amides with cyclopropenethiones afforded the formation of 6H-1,3-oxazin-6-ones and 6H-1,3-thiazin-6-ones [21].

Results and discussion

Herein, we report the reaction of 1-(2,4-dinitrophenyl)-4-substituted hydrazinecarbothioamides 6a–e with 2,3-diphenylcyclopropenone 1 in absolute ethanol under reflux; (5S*,6S*,Z)-2-(2-(2,4-dinitrophenyl)-hydrazono)-3-substituted-5,6-diphenyl-1,3-thiazinan-4-ones 7a–e was precipitated as a major product (79–83%). The filtrate was subjected under chromatographic plates to give only one product namely (Z)-N′-(2,4-dinitrophenyl)-2,3-diphenylacrylohydrazide 8 as a minor product (8–12%) (Scheme 2).

Scheme 2
scheme 2

Preparation of 2-hydrazothiazinan-4-one derivatives 7a–e and (Z)-N′-(2,4-dinitrophenyl)-2,3-diphenylacrylohydrazide 8

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From the structural investigation, IR spectra of 7a–e showed the stretching frequency range between 3265 and 3229 cm−1 due to NH-stretching, 2935–2922 cm−1 for ali–CH, 1685–1675 cm−1 for C=O, 1616–1612 cm−1 for C=N and 1530–1524, 1344–1335 cm−1 due to nitro groups.

The 1H NMR spectrum of 7a (in CDCl3) as an example showed a broad singlet at δ = 11.1 ppm due to NH-group, which was confirmed further by D2O exchange experiment. A doublet of doublet as AX-system signals at 4.57–4.56 and 5.04–5.03 with coupling constant J = 4.0 Hz because of CH-6 and CH-5 of thiazinanones 7a. The 1H NMR spectra of 7a–e showed the absence of any signals due to H-N2 or H-N4 groups of 6a–e but compound 7a showed a doublet of doublet signals at 5.40–5.43 and 5.64–5.61 with coupling constant 15.0 Hz for diastereotopic benzyl-CH2 group.

The 13C NMR spectrum of 7a showed signals at δ = 47.15 and 47.90 ppm which were assigned to thiazinanone-CH6,5. Another signals at 56.36 ppm are assigned to CH2Ph, 168.85 ppm (C=O), 146.67 ppm (C=N) and 144.61 ppm ((NO2)2-Ar–C–NH). The similarities of 1H NMR spectra (see experimental part) reveal that the five compounds 7a–e belong to the same gross structure type namely 3-substituted 2-(2-(2,4-dinitrophenyl)hydrazono)-5,6-diphenyl-1,3-thiazinan-4-ones. The elemental analyses and mass spectrometry of 7a–e clearly showed that the products were formed during the addition of one molecule of 1 to one molecule of 6a–e without any elimination.

The X-ray crystallographic structure of compound 7a further supported its relative configurations as (rac-5S*,6S*,Z)-3-benzyl-2-(2-(2,4-dinitrophenyl)hydrazono)-5,6-diphenyl-1,3-thiazinan-4-one. The molecular of 7a (Fig. 1 and Tables 1–7, in the crystallographic data) revealed furthermore the formation of 3-benzyl-2-(2-(2,4-dinitrophenyl)hydrazono)-5,6-diphenyl-1,3-thiazinan-4-one in the cissiod (Z) structure.

Fig. 1
figure 1

Molecular structure of compound 7a (displacement parameters are drawn at 50% probability level). The crystallographic numbering does not reflect the IUPAC numbering

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The mechanism for the formation of products 7a–e is presented in scheme 3. The sulfur atom attacks the conjugate double bond of 1 forming the intermediate 9. Intramolecular nucleophilic attack of N4-H on C=O afforded the intermediate 11 which rearranged to give 7a–e (Scheme 3). On the other hand, N4-H attacks the carbonyl group of 1 with the formation of 7a–e via intermediate 12 (Scheme 3).

Scheme 3
scheme 3

Mechanism for the formation of 2-hydrazothiazinan-4-one derivatives 7a-e

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The ring opening of cyclopropenones has been reported earlier by Gomaa [22] during the reaction of N1,N2-diarylformamidines with diphenylcyclopropenone to give 3-aryl-(N-4-arylformamidoyl)amino-2,3-diphenylpropionic acids.

Recently, Wu et al. reported the ring-opening acylation of cyclopropenones with organoboronic acids afforded α,β-diaryl unsaturated ketones [23].

In our study, (Z)-N′-(2,4-dinitrophenyl)-2,3-diphenylacrylohydrazide 8 was formed as a minor product (8–12%) from the reaction of 1 with 6a–e.

The compound 8 shows IR absorption at 3320–3247 cm−1 due to the NH groups, strong band at 1673 cm−1 corresponding to carbonyl group and bands at 1528, 1344 cm−1 attributed to nitro groups. The 1H NMR spectrum of 8 showed multiplet signals at 6.42 due to trisubstituted acrylohydrazide-CH, 9.43 (NH), in addition to the aromatic protons. In the 13C NMR spectrum of 8, the signal at δ = 165.18 was assigned to amide-CO, 145.10 due to ((NO2)2-Ar–C–NH, 133.68 and 139.75 was attributed to acrylohydrazide C2 and C3.

The structure of (Z)-N′-(2,4-dinitrophenyl)-2,3-diphenylacrylohydrazide 8 was determined by X-ray analysis (Fig. 2, Tables 8–15 in supplementary data). The X-ray structure confirms the trans (E) geometry of the two phenyl groups with respect to the C2-C3 double bond (note that the crystallographic numbering does not correspond to the systematic IUPAC numbering rules).

Fig. 2
figure 2

Molecular structure of 8 (minor disordered part and solvent omitted for clarity, displacement parameters are drawn at 50% probability level)

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The hydrazide 8 was formed via the nucleophilic addition of N2-H on the C=O of 1 with the formation of intermediate 13. Elimination of RNCS from 13 afforded the formation of 8 (Scheme 4).

Scheme 4
scheme 4

The plausible mechanism for the formation of diazenyl-1,2,4-triazolthione 3a–e

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In order to optimize the reaction conditions, we change the solvent of the reaction to CH3CN or CH2Cl2, CH3OH, ethyl acetate and tetrahydrofuran. However, the yields of 7a–e decreased and in some cases such as ethyl acetate and tetrahydrofuran only traces of 7a–e were observed detectable by TLC. The excess of one of the reaction partners, namely diphenylcyclopropenone 1 or thiosemicarbazides 6a–e, led to a significant decrease in the yields.

Conclusion

Nucleophilic attack of dinitrophenyl-4-substituted thiosemicarbazides on 2,3-diphenylcyclopropenone afforded the formation of racemic 2-(2,4-dinitrophenyl)hydrazono)-5,6-diphenyl-1,3-thiazinan-4-ones as major products and (Z)-N′-(2,4-dinitrophenyl)-2,3-diphenylacrylohydrazide as minor product.

Experimental

Melting points were measured with Gallenkamp melting point apparatus. Infrared spectrum (IR) was recorded with Alpha, Bruker FT-IR instruments taken as KBr disks: 1H NMR at 400 MHz and 13C NMR at 100 MHz on a Bruker AM 400 spectrometry with TMS as internal standard (δ = 0), and data are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad). For 13C NMR, TMS (δ = 0) was used as internal standard and spectra were obtained with complete proton decoupling. Mass spectra were obtained using Finnigan MAT instrument (70 eV, EI-mode). Elemental analyses for C, H, N, and S were carried out using an Elmyer 306. Preparative layer chromatography (plc) was carried out on glass plates covered with a 1.0 mm thick layer of slurry-applied silica gel (Merck Pf254).

Starting materials

The start materials 6a–e 2-(2,4-dinitrophenyl)-N-substituted hydrazinecarbothioamides were prepared from the reaction between 1-(3,5-dinitrophenyl) hydrazine and the corresponding isothiocyanates in absolute ethanol under refluxing temperature according to reported literature [24, 25]. 2,3-Diphenylcycloprop-2-enone 1 was purchased from Fluka.

General procedure

An equimolar amounts of 2,3-diphenylcycloprop-2-enone 1 and the appropriate 1,4-disubstituted thiosemicarbazides 6a–e were mixed in absolute ethanol and refluxed for about 4–6 h, furnished reddish orange precipitates of (5S*,6S*,Z)-2-(2-(2,4-dinitrophenyl)hydrazono)-3-substituted-5,6-diphenyl-1,3-thiazinan-4-one derivatives 7a–e, and the residue were subjected to chromatographic separation using plc and toluene/ethyl acetate (10:3) as eluent to give (Z)-N′-(2,4-dinitrophenyl)-2,3-diphenylacrylohydrazide 8 as a separated zone.

(5S*,6S*,Z)-3-benzyl-2-(2-(2,4-dinitrophenyl)hydrazono)-5,6-diphenyl-1,3-thiazinan-4-one (7a)

Reddish orange crystals (acetonitrile), yield 470 mg (81%), mp. 240–242°C; IR (KBr) ν: 3265 (NH), 3072 (Ar–CH), 2928 (ali–CH), 1681 (C=O), 1612 (C=N), 1579 (Ar–C = C), 1530 and 1333 cm−1 (NO2); 1H NMR (400 MHz, CDCl3) δ: 4.56–4.57 (dd, 1H, J = 4.0 Hz, thiazinanone-H6), 5.03–5.04 (dd, 1H, J = 4.0 Hz, thiazinanone-H5), 5.40–5.43 (d, 1H, J = 15.0 Hz, CH2-benzyl), 5.61–5.64 (d, 1H, J = 15.0 Hz, CH2-benzyl), 6.81–6.88 (m, 3H, Ar–H), 7.13–7.56 (m, 13H, Ar–H), 8.27–8.30 (m, 1H, Ar–H), 9.10 (m, 1H, Ar–H), 11.02 (br, 1H, hydrazo-NH); 13C NMR (100 MHz, CDCl3) δ: 47.15 (thiazinanone-CH-6), 47.90 (thiazinanone-CH-5), 56.36 (CH2Ph), 116.05, 123.51, 127.47, 128.01, 128.16, 128.32, 128.44, 128.67, 128.76, 129.43, 130.08, 130.25 (Ar–CH), 129.21, 132.51, 133.77, 137.05, 137.87 (Ar–C), 144.61 (Ar–C–NH), 146.67 (C=N), 168.85 (C=O); MS (m/z): 553 (M+, 47), 462 (13), 347 (10), 207 (51), 182 (58), 149 (56), 91 (100), 77 (15); Anal. Calcd. for C29H23N5O5S (553.59): C, 62.92, H, 4.19, N, 12.65, S, 5.79. Found: C, 62.79, H, 4.06, N, 12.47, S, 5.65.

(5S*,6S*,Z)-2-(2-(2,4-dinitrophenyl)hydrazono)-3,5,6-triphenyl-1,3-thiazinan-4-one (7b)

Reddish orange crystals (acetonitrile), yield 447 mg (83%), mp. 230–232 °C; IR (KBr) ν: 3262 (NH), 3076 (Ar–CH), 2932–2922 (ali–CH), 1685 (C=O), 1615 (C=N), 1577 (Ar–C = C), 1532 and 1330 cm−1 (NO2); 1H NMR (400 MHz, CDCl3) δ: 4.54–4.55 (d, 1H, J = 4.12 Hz, thiazinanone-H6), 5.18–5.19 (d, 1H, J = 4.12 Hz, thiazinanone-H5), 6.80–7.00 (m, 4H, Ar–H), 7.10–7.32 (m, 9H, Ar–H), 7.35–7.52 (m, 3H, Ar–H), 8.04 (m, 1H, Ar–H), 8.98 (m, 1H, Ar–H), 10.98 (br, hydrazo-NH); 13C NMR (100 MHz, CDCl3) δ: 47.60 (thiazinanone-CH5), 47.95 (thiazinanone-CH6), 115.97, 123.62, 127.71, 127.99, 128.39, 128.87, 129.35, 129.62, 130.08, 130.66, 131.03, 131.21 (Ar–CH), 129.35, 132.32, 133.77, 136.88, 137.86 (Ar–C), 144.57 (Ar–C–NH), 147.31 (C=N), 168.70 (C=O); MS (m/z): 539 (M+, 62), 462 (23), 357 (48), 207 (61), 135 (37), 77 (100); Anal. Calcd. for C28H21N5O5S (539.56): C, 62.33; H, 3.92; N, 12.98; S, 5.94. Found: C, 62.18; H, 3.77; N, 12.87; S, 5.86.

(5S*,6S*,Z)-3-allyl-2-(2-(2,4-dinitrophenyl)hydrazono)-5,6-diphenyl-1,3-thiazinan-4-one (7c)

Reddish orange crystals (acetonitrile), yield 402 mg (80%), mp. 208–210°C; IR (KBr) ν: 3242 (NH), 3088 (Ar–CH), 2959–2925 (ali–CH), 1682 (C=O), 1614 (C=N), 1587 (Ar–C = C), 1529 and 1342 cm−1 (NO2); 1H NMR (400 MHz, CDCl3) δ: 4.42–4.43 (d, 1H, J = 4.08 Hz, thiazinanone-H6), 4.70–4.92 (m, 2H, allyl-CH2N), 4.96–4.97 (d, 1H, J = 4.08 Hz, thiazinanone-H5), 5.20–5.45 (m, 2H, allyl–CH2=), 5.90–6.10 (m, 1H, allyl-CH=), 6.60–6.70 (m, 2H, Ar–H), 6.75–6.82 (m, 2H, Ar–H), 7.00–7.30 (m, 6H, Ar–H), 7.65 (m, 1H, Ar–H), 8.24 (m, 1H, Ar–H), 9.05 (m, 1H, Ar–H), 11.02 (br, 1H, hydrazo-NH); 13C NMR (100 MHz, CDCl3) δ: 47.05 (allyl-CH2N), 47.15 (thiazinanone-CH6), 47.92 (thiazinanone-CH5), 118.87 (allyl–CH2=), 115.99, 123.60, 128.15, 128.31, 128.41, 129.24, 130.15, 130.22, 130.68 (Ar–CH), 133.75 (allyl–CH=), 128.79, 131.89, 133.69, 137.84 (Ar–C), 144.66 (Ar–C–NH), 146.32 (C=N), 168.43 (C=O); MS (m/z): 503 (M+, 72), 457 (18), 404 (26), 207 (55), 182 (100), 99 (66), 77 (87); Anal. Calcd. for C25H21N5O5S (503.53): C, 59.63; H, 4.20; N, 13.91; S, 6.37. Found: C, 59.45; H, 4.07; N, 13.74; S, 6.24.

(5S*,6S*,Z)-2-(2-(2,4-dinitrophenyl)hydrazono)-3-ethyl-5,6-diphenyl-1,3-thiazinan-4-one (7d)

Reddish orange crystals (acetonitrile), yield 387 mg (79%), mp. 200–202°C; IR (KBr) ν: 3238 (NH), 3093 (Ar–CH), 2935–2923 (ali–CH), 1678 (C=O), 1616 (C=N), 1585 (Ar–C = C), 1526 and 1330 cm−1 (NO2); 1H NMR (400 MHz, CDCl3) δ: 1.35 (t, 3H, J = 7.77 Hz, CH3), 4.15–4.18 (q, 2H, J = 7.77 Hz, CH2), 4.45–4.46 (d, 1H, J = 4.10 Hz, thiazinanone-H6), 4.96–4.97 (d, 1H, J = 4.10 Hz, thiazinanone-H5), 6.64–6.70 (m, 2H, Ar–H), 6.76–6.81 (m, 2H, Ar–H), 7.06–7.09 (m, 6H, Ar–H), 7.68 (m, 1H, Ar–H), 8.30 (m, 1H, Ar–H), 9.03 (m, 1H, Ar–H), 11.04 (br, 1H, hydrazo-NH); 13C NMR (100 MHz, CDCl3) δ: 12.86 (CH3), 29.06 (CH2), 47.20, 47.70 (thiazinanone-CH6,5), 116.11, 123.63, 128.00, 128.30, 128.79, 129.22, 129.78, 130.10, 130.47 (Ar–CH), 129.12, 133.43, 133.80, 134.00, 137.87 (Ar–C), 144.62 (Ar–C–NH), 146.63 (C=N), 168.60 (C=O); MS (m/z): 491 (M+, 48), 462 (27), 445 (35), 402 (19), 182 (100), 87 (70), 77 (91); Anal. Calcd. for C24H21N5O5S (491.52): C, 58.65; H, 4.31; N, 14.25; S, 6.52. Found: C, 58.51; H, 4.20; N, 14.07; S, 6.38.

(5S*,6S*,Z)-3-cyclohexyl-2-(2-(2,4-dinitrophenyl)hydrazono)-5,6-diphenyl-1,3-thiazinan-4-one (7e)

Reddish orange crystals (acetonitrile), yield 436 mg (80%), mp. 236–238°C; IR (KBr) ν: 3229 (NH), 3090 (Ar–CH), 2938–2923 (ali–CH), 1675 (C=O), 1613 (C=N), 1586 (Ar–C = C), 1527 and 1331 cm−1 (NO2); 1H NMR (400 MHz, CDCl3) δ: 1.08–1.98 (m, 10H, cyclohexyl-CH2), 2.02–2.46 (m, 1H, cyclohexyl-CH), 4.35–4.36 (d, 1H, J = 4.11 Hz, thiazinanone-H6), 4.80–4.81 (d, 1H, J = 4.11 Hz, thiazinanone-H5), 6.62–6.70 (m, 2H, Ar–H), 6.84–6.92 (m, 2H, Ar–H), 7.04–7.46 (m, 6H, Ar–H), 7.71 (m, 1H, Ar–H), 8.32 (m, 1H, Ar–H), 9.10 (m, 1H, Ar–H), 11.00 (br, hydrazo-NH); 13C NMR (100 MHz, CDCl3) δ: 25.74, 26.53, 29.78 (cyclohexyl-CH2), 47.63, 47.91 (thiazinanone-CH6,5), 57.08 (cyclohexyl-CH), 115.93, 123.64, 128.04, 128.22, 128.71, 129.57, 130.25, 130.37, 130.77 (Ar–CH), 129.11, 133.38, 133.69, 137.96 (Ar–C), 144.59 (Ar–C–NH), 146.51 (C=N), 168.87 (C=O); MS (m/z): 545 (M+, 51), 462 (43), 499 (28), 455 (39), 182 (100), 141 (68), 77 (91); Anal. Calcd. For C28H27N5O5S (545.61): C, 61.64; H, 4.99; N, 12.84; S, 5.88. Found: C, 61.48; H, 4.83; N, 12.74; S, 5.75.

(Z)-N′-(2,4-dinitrophenyl)-2,3-diphenylacrylohydrazide (8)

Yellow crystals (acetonitrile), yield 8–12%, mp. 168–169°C; IR (KBr) ν: 3247 (NH), 3130 (Ar–H), 2930 (ali–H), 1693 (C=O), 1591 (Ar–C = C), 1542 and 1334 cm−1 (NO2); 1H NMR (400 MHz, CDCl3) δ: 6.42 (s, 1H, acryl-CH), 7.10–7.55 (m, 10H, Ar–H), 7.94 (m, 1H, Ar–H), 8.48 (br, 1H, NH), 9.04 (m, 1H, Ar–H), 9.43 (br, 1H, amide-NH); 13C NMR (100 MHz, CDCl3) δ: 117.65, 123.18, 126.17, 127.52, 128.15, 128.26, 129.19, 129.38, 129.85 (Ar–CH), 133.68, 139.75 (C1 and C2-acrylohydrazide); 130.00, 134.34, 135.60, 137.80 (Ar–C); 145.10 (Ar–C–NH), 165.18 (C=O); MS (m/z): 404 (M+, 100), 356 (23), 221 (26), 205 (13), 195 (18), 181 (32), 138 (20), 77 (41); Anal. Calcd. for C21H16N4O5 (404.38): C, 62.37; H, 3.99; N, 13.86. Found: C, 62.25; H, 3.86; N, 13.77.

Single-crystal X-ray structure determination of 7a and 8

Suitable crystals were obtained by recrystallization from acetonitrile. The single-crystal X-ray diffraction study was carried out on a Bruker D8 Venture diffractometer with Photon100 detector at 123(2) K using Cu-Kα radiation (λ = 1.54178 Å). Direct Methods for 7a (SHELXS-97) [26] and dual space methods for 8 (SHELXT) [27] were used for structure solution and refinement was carried out using SHELXL-2014 (full-matrix least-squares on F2) [28]. Hydrogen atoms were localized by difference electron density determination and refined using a riding model (H(N) free). Semi-empirical absorption corrections were applied. For 8 an extinction correction was applied. In 8 the 2,3-diphenylacrylo substituent is disordered (see cif-files for details).

Compound 7a

Red crystals, C29H23N5O5S, Mr = 553.58, crystal size 0.24 × 0.06 × 0.02 mm, monoclinic, space group P21/c (No. 14), a = 19.9611(6) Å, b = 11.4148(4) Å, c = 10.9667(4) Å, β = 93.844(1)°, V = 2493.16(15) Å3, Z = 4, ρ = 1.475 Mg/m−3, µ(Cu-Kα) = 1.601 mm−1, F(000) = 1152, 2max = 144.2°, 21195 reflections, of which 4907 were independent (Rint = 0.030), 364 parameters, 1 restraint, R1 = 0.046 (for 4478 I > 2σ(I)), wR2 = 0.118 (all data), S = 1.08, largest diff. peak/hole = 0.723/− 0.490 e Å−3.

Compound 8

Yellow crystals, C21H16N4O5·C2H6OS, Mr = 482.50, crystal size 0.32 × 0.16 × 0.12 mm, triclinic, space group P-1 (No. 2), a = 9.0191(3) Å, b = 11.3050(3) Å, c = 11.8112(3) Å, α = 87.986(1)°, β = 69.079(1)°, γ = 79.272(1)°, V = 1104.58(6) Å3, Z = 2, ρ = 1.451 Mg/m−3, µ(Cu-Kα) = 1.732 mm−1, F(000) = 504, 2θmax = 144.0°, 15,897 reflections, of which 4309 were independent (Rint = 0.022), 313 parameters, 10 restraints, R1 = 0.038 (for 4234 I > 2σ(I)), wR2 = 0.093 (all data), S = 1.06, largest diff. peak/hole = 0.584/− 0.369 e Å−3.