Preparation, structure, and metal coordination of 2-(2-methyl-2,3-dihydro- 1H-perimidin-2-yl)benzene-1,3-diol

Article abstract of DOI:10.1016/j.tetlet.2012.12.088

A perimidine with four donor sites, 2-(2-methyl-2,3-dihydro-1H-perimidin-2- yl)benzene-1,3-diol has been prepared through InCl₃ catalysis from commercial precursors. It exhibits in solid state a bent structure, with two ring systems substantial

Full text of DOI:10.1016/j.tetlet.2012.12.088

Tetrahedron Letters 54 (2013) 1503–1506
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Preparation, structure, and metal coordination of
2-(2-methyl-2,3-dihydro-1H-perimidin-2-yl)benzene-1,3-diol
Maria Elena Cucciolito a, Barbara Panunzi b, , Francesco Ruffo a, Angela Tuzi a
⇑
a Dipartimento di Scienze Chimiche, Università di Napoli ‘Federico II’, Complesso Universitario di Monte S. Angelo, via Cintia, Napoli I 80126, Italy
b Dipartimento di Scienza degli Alimenti, Facoltà di Agraria, Università di Napoli ‘Federico II’, I-80055 Portici, (NA), Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
A perimidine with four donor sites, 2-(2-methyl-2,3-dihydro-1H-perimidin-2-yl)benzene-1,3-diol has
been prepared through InCl3 catalysis from commercial precursors. It exhibits in solid state a bent struc-
ture, with two ring systems substantially orthogonal. A ruthenium(II) complex catalyzes the transfer
hydrogenation of phenylalkyl ketones by isopropanol with good efficiency.
Received 26 October 2012
Revised 19 December 2012
Accepted 21 December 2012
Available online 12 January 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Perimidine
Crystal structure
Ruthenium
Transfer hydrogenation
1. Introduction
The presence of the methyl is expected to affect the conforma-
tion of the molecule, which, in the absence of suited steric con-
Chemistry of perimidines, whose first synthesis dates back to
1874,1 currently deserves large interest for several reasons, includ-
ing general biological relevance,2 pharmacological applications,3
and optoelectronic properties.4
straints, adopts an elongated shape, generally observed in
dihydroperimidines bearing a unique substituent on C-2.4b,21 This
expectation has been here preliminarily verified by determining
the structure of the known simple 2-methyl-2-phenyl-2,3-dihy-
dro-1H-perimidine10 (1), the first example for a 2-alkyl-2-arylper-
imidine, which has disclosed a substantial orthogonality between
the two aromatic systems, affording a sort of pocket. This steric
motif may favor the interaction through the pocket of the two
coordination spheres in a bimetallic complex, thus promoting the
synergic activity of the two metals. It should also be noted that
the six-membered metallated cycle provided by the N,O donor pair
of 2 (presumably as phenolate) in the case of chelation to a metal
center is quite similar to that involved in previously reported cat-
alytically active species.11 Moreover, even in the absence of metal,
free ligands of this type can behave as organic catalysts, for exam-
ple, for the addition of dialkyl zinc to ketones.12
As for their coordinating features, particular attention was ad-
dressed5 toward carbene species involving link of the metal to
the C-2 atom. Only a few studies dealt with complexes in which
the metal is bound to one nitrogen and to another donor atom
introduced on a ring present on C-2. This additional donor can be
a phenolate oxygen,6 an enolate oxygen,7 a –PPh2,8 or the same
ring is directly engaged through cyclometallation.9 In the two for-
mer cases, positions 2 and 3 are dehydrogenated, and, hence, the
two nitrogen atoms, respectively belong to an imino (the better do-
nor, involved in coordination) and an amino function.
Substantially, no example is known of the latter group (i.e., NH)
involved in metal coordination, even in the presence of another
chelating partner. The present study also aimed to assess if this
type of coordination is attainable.
We have explored the synthesis and the coordinating properties
of a perimidine (2 in Fig. 1) substituted on C-2 with a methyl and a
o,o0-dihydroxy-phenyl ring. In principle, this arrangement could
even allow chelation of each couple of adjacent N and OH to a me-
tal center, with attainment of a binuclear complex.
HO
OH
1
HN
1
3
NH
3
2
2
HN
NH
2
1
⇑
Corresponding author.
E-mail address: barbara.panunzi@unina.it (B. Panunzi).
Figure 1. Compounds 1 and 2.
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.12.088

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M. Elena Cucciolito et al. / Tetrahedron Letters 54 (2013) 1503–1506
Table 1
Beside an updated improved synthesis of 1 and the preparation
Selected bond lengths (Å), bond angles (°) and torsion angles (°) with e.s.d.’s in
parentheses for compound 1 and 2
of the new perimidine 2, their structures, and a complex of 2 with
ruthenium(II) displaying good catalytic ability in transfer hydroge-
nation of alkylaryl ketones are also described here.
1
2
N1–C1
N1–C11
N2–C9
N2–C11
O1–C13
O1–C17
C1–N1–C11
C9–N2–C11
C10–C1–N1–C11
C10–C9–N2–C11
C1–N1–C11–C12
C9–N2–C11–C12
N1–C11–C12–C13
N2–C11–C12–C17
1.383(2)
1.467(2)
1.368(2)
1.448(2)
1.429(3)
1.470(3)
1.433(3)
1.477(3)
1.359(3)
1.363(3)
115.9(2)
115.0(2)
19.2(3)
2. Results
2.1 Synthesis of 2-methyl-2-phenyl-2,3-dihydro-1H-perimidine
(1)
116.3(1)
119.0(1)
35.0(2)
Although this molecule has been known for a long time,10 a con-
venient synthesis has been only lately achieved by metal catalysis,
which has consented its isolation in 82% yield according to the
most recent report.13 Within this study, the yield has been im-
proved up to 92% by heating neat 1,8-diaminonaphthalene and
acetophenone with activated molecular sieves.14 Most of the prod-
uct precipitates as large crystals, already suitable for X-ray analy-
sis, upon diluting the filtered reaction mixture with n-hexane.
ꢁ23.3(2)
ꢁ25.6(3)
66.9(3)
76.5(3)
ꢁ71.1(29)
51.9(2)
ꢁ10.6(2)
ꢁ74.3(39)
32.4(39)
ꢁ33.9(3)
The six-membered heterocycle C4N2 ring adopts a half-chair
conformation, with C11 atom puckered out of the plain defined
by N1/N2/C1/C9/C10 (0.545(3) Å for 1 and 0.623(2) Å for 2). In both
compounds the aryl ring occupies the axial position and faces the
naphthalene moiety. The two aromatic mean planes are mutually
orthogonal (83.38(4)° in 1 and 89.62(5)° in 2), affording in this
way a sort of cavity.
2.2 Synthesis of 2-(2-methyl-2,3-dihydro-1H-perimidin-2-
yl)benzene-1,3-diol) (2)
This new ligand has been initially obtained in poor yield (ca. 6%)
with a procedure15 similar to that reported for related perimidines
with two substituents at C-2.16 Two subsequent fractional crystal-
lizations of the crude product yielded scarce crops of microcrystals.
Aiming to improve the yield, other attempts have been per-
formed in analogy with related literature reports based on metal
catalysis. Better results have been attained by using indium tri-
chloride, a catalyst employed for the preparation of spiroperimi-
dines,17 with absolute ethanol as the solvent instead of water. In
this case, the crude product contains only 25% of the desired per-
imidine, and it is necessary to recover a large amount of the unre-
acted precursors through washings with water, and re-
precipitation from ethanol solution by addition of water, with
the final yield of isolated 2 at 19%.
The crystal packing of compounds 1 and 2 is stabilized by weak
intermolecular NHꢀ ꢀ ꢀ
p interactions together with face-to-edge and
T-shaped aromatic interactions (see Fig. 3).
Only a few structural studies on 2-arylperimidine derivatives
were found in the literature.4b,c,21–23 A comparative analysis of
these structural studies suggests that the steric encumbrance at
N–C–N– positions of perimidine ring may favor the attainment of
a bent molecular shape. In fact, at variance with compounds 1
and 2, only an elongated molecular shape is observed for the less
encumbered 2-arylperimidines.4b,21 The bent molecular shape,
due to the axial position of the aryl ring, is observed4c,22,23 only
in the 2-arylperimidine encumbered by substituents at N atoms.
2.3 X-ray crystal structures of 1 and 218
2.4 Transfer hydrogenation of ketones
The molecular structures of 1 and 2 are shown in Figure 2. All
bond lengths and angles are in the normal range and a selection
of them is reported in Table 1.
As can be seen from the Figure 2, the two molecules exhibit a
non crystallographic Cs symmetry and have a similar bent shape.
The aminic nature of N atoms is unequivocally demonstrated by
the localization of the H atoms in the difference Fourier maps. A
Use of 2 in the Ru-catalyzed transfer hydrogenation of ketones
was examined,24 in i-propanol and in the presence of potassium
hydroxide:
R ꢁ CO ꢁ Ph þ Me2CHOH ! R ꢁ CHðOHÞ ꢁ Ph þ Me2C@O
Yields: R = Me, 87%; R = CHMe2, 61%; R = CMe3, 96%.
The beneficial role in this catalysis of a perimidine ligand can be
found in the acknowledged positive effect given by the presence of
an acidic –OH donor combined with a NH function.11d
pyramidal geometry at
OHꢀ ꢀ ꢀN hydrogen bonds are found in
2.607(3) Å, 150(2)°; O2Hꢀ ꢀ ꢀN2 = 0.96(3), 2.583 Å, 151(3)°).
N
atoms is observed. Intramolecular
2
(O1Hꢀ ꢀ ꢀN1 = 0.97(3),
Figure 2. Ortep view of compound 1 (left) and 2 (right). Thermal ellipsoids are drawn at 30% probability level.

M. Elena Cucciolito et al. / Tetrahedron Letters 54 (2013) 1503–1506
1505
Figure 3. Partial packing of compound 1 (left) and 2 (right) showing the NHꢀ ꢀ ꢀ
p
interactions, the aromatic face-to-edge and the T-shape contacts. The intramolecular OHꢀ ꢀ ꢀN
hydrogen bonds in 2 are drawn as dotted lines.
2. (a) Herbert, J. M.; Woodgate, P. D.; Denny, W. A. J. Med. Chem. 1987, 30, 2081–
2086; (b) Luthin, D. R.; Rabinovich, A. K.; Bhumralkar, D. R.; Youngblood, K. L.;
Bychowski, R. A.; Dhanoa, D. S.; May, J. M. Bioorg. Med. Chem. Lett. 1999, 9, 765–
770; (c) Bu, X.; Deady, L. W.; Finlay, G. J.; Baguley, B. C.; Denny, W. A. J. Med.
Chem. 2001, 44, 2004–2014.
3. (a) Undheim, K.; Benneche, C. In Comprehensive Heterocyclic Chemistry;
Pergamon: Oxford, 1996; Vol. 6,. Chapter 3 (b) Claramunt, R. M.; Dotor, J.;
Elguero, J. Ann. Quim. 1995, 91, 151–183.
The extent of reduction was calculated by the integrals of suited
signals in the 1H NMR of the crude reduced product depleted of so-
lid residues and excess i-propanol. The efficiency of the catalytic
system resulted to be similar to that displayed by comparable
catalysts.11d
An attempt to understand the nature of the pre-catalyst was
performed by adapting the procedure reported11d for a mononu-
4. (a) Nyulászi, L.; Pasinszki, T.; Réffy, J.; Veszprémi, T.; Fabian, J.; Thiel, W. Struct.
Chem. 1990, 1, 367–370; (b) Varsha, G.; Arun, V.; Robinson, P. P.; Sebastian, M.;
clear related species, starting from [(g
6-p-cymene)RuCl2]2, 2, and
Varghese, D.; Leeju, P.; Iayachandran, V. P.; Yusuff, K. K. M. Tetrahedron Lett.
2010, 51, 2174–2177; (c) Chou, C.-C.; Liu, H.-S.; Chao, L. H.-C. Chem. Commun.
2009, 6382–6384.
sodium carbonate in dichloromethane. The crude product dis-
played a 1H NMR pattern25 with largely prevailing signals in keep-
ing with
a mononuclear species where [(g
6-p-cymene)RuCl]
5. Bazinet, P.; Ong, T.-G.; O’Brien, J. S.; Lavoie, N.; Bell, E.; Yap, G. P. A.; Korobkov,
I.; Richeson, D. S. Organometallics 2007, 26, 2885–2895.
6. Enomoto, K.; Nishimura, K. Jpn. Kokai Tokkyo Koho 2003, JP 2003086378.
7. Sennikova, E. V.; Antsyshkina, A. S.; Sadikov, G. G.; Bicherov, A. V.; Korshunov,
O. Yu.; Borodkin, G. S.; Korobov, M. S.; Sergienko, V. S.; Kharabaev, N. N.;
Garnovskii, A. D. Russ. J. Coord. Chem. 2008, 34, 315–321.
8. Son, S. U.; Jang, H.-Y.; Lee, I. S.; Chung, Y. K. Organometallics 1998, 17, 3236–
3239.
9. Jung, I. G.; Son, S. U.; Park, K. H.; Chung, K.-C.; Lee, J. W.; Chung, Y. K.
Organometallics 2003, 22, 4715–4720.
fragments are chelated by ligand 2. However, both the spectrum
and elemental analyses show the presence of other species. At-
tempts to obtain the predominant complex in pure form by frac-
tional crystallization of the crude material from solutions in
methanol or chlorinated solvents, by concentration or by addition
of hydrocarbons, were unsuccessful.
In conclusion, these results show that suitably substituted
dihydroperimidines offer a useful coordination environment. Fur-
ther work is in progress, aiming to introduce donors of different
nature along with chiral substituents in the coordinating
framework.
10. Sachs, F. Justus Lieb. Ann. der Chem. 1909, 365, 135–166.
11. In fact, active species with metals clamped by the sequence C6H4(o-OH)-C-NH-
C
are involved in catalytic reactions. For cyanosilylation of carbonyl
compounds catalysed by scandium(III) derivatives, see: (a) Karimi, B.;
Ma’Mani, L. Org. Lett. 2004, 6, 4813–4815; For tungsten promotion of
catalytic methathesis of alkenes, see: (b) Hänninen, M. M.; Sillanpää, R.;
Kivelä, H.; Lehtonen, A. Dalton Trans. 2011, 40, 2868–2874; For chromium
catalysis of ethylene polymerization, see: (c) Gibson, V. C.; Norton, C.;
Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton
Trans. 1999, 11, 827–829; For ruthenium promoted transfer hydrogenation of
ketones, see: (d) Rath, R. K.; Nethaji, M.; Chakravarty, A. R. Polyhedron 2001, 20,
2735–2739.
Acknowledgments
The authors thank the CIMCF (Università di Napoli ‘Federico II’)
for NMR and X-ray facilities. The authors also thank the Polo delle
Scienze e Tecnologie (Università di Napoli ‘Federico II’) for funding
(Progetto FARO).
12. Cimarelli, C.; Palmieri, G.; Volpini, E. Tetrahedron: Asymmetry 2002, 13, 2417–
2426.
13. Zhang, S.-L.; Zhang, J.-M. Chin. J. Chem. 2008, 26, 185–189.
14. A4 molecular sieves were activated at 443 K and 18 Torr for 72 h. After cooling in
nitrogen, 1,8-diaminonaphtalene (1.58 g, 10 mmol) and acetophenone (2.40 g,
20 mmol), were added and the mixture was magnetically stirred at 65 °C during
24 h and at 80 °C for further 30 h. The mixture was extracted with 300 mL of n-
hexane (in portions of 30 mL). Most of the product could be recovered as large well
formed crystalsthat precipitated onstandingofthehexane phase. Concentration of
the filtered liquid afforded two other fractions, raising the total yield of the isolated
productto92%. 1HNMR(CDCl3): d7.58 (d, 2H, J = 7.2 Hz), 7.10–7.35 (m, 7H), 6.54(d,
2H, J = 7.2 Hz), 4.72 (s, 2H, NH), 1.82 (s, 3H, CH3).
15. On molecular sieves: To a stirred solution of 1,8-diaminonaphtalene (0.590 g,
3.73 mmol), 20,60-dihydroxyacetophenone (0.568 g, 3.73 mmol) and p-
toluenesulfonic acid monohydrate (0.071 g, 0.37 mmol) in toluene (10 mL)
were added freshly activated A4 molecular sieves (1.16 g), and stirring of the
mixture was continued 24 h at 378 K (36 h a 373 K). The liquid phase was
Supplementary data
CCDC 900749 (compound 1) and CCDC 900750 (compound 2)
contain the supplementary crystallographic data for this Letter.
These data can be obtained free of charge at www.ccdc.cam.a-
c.uk/conts/retrieving.html or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (inter-
net) +44 1223/336 033.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.12.
088.
separated and the sieves were washed with
3 portions (5 mL each) of
methylene chloride. These were added to the mother liquor, the liquid was
washed with water and the solvents were removed in vacuo. The dark gummy
residue was dissolved in ethanol, and the dark red liquid was filtered through a
pad of Celite. To the filtrate was added n-propanol (5 mL). Slow concentration
afforded several solid fractions, including two small crops of colorless
elongated crystals of the product (0.065 g in total, 6% yield).
References and notes
1. de Aguiar, A. Ber. Dtsch. Chem. Ges. 1874, 7, 309–319.

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M. Elena Cucciolito et al. / Tetrahedron Letters 54 (2013) 1503–1506
parameters: 3036/182; goodness-of-fit on F2: 1.076; final R indices [I > 2
By InCl3 catalysis: To a stirred solution of 1,8-diaminonaphtalene (0.590 g,
r
(I)],
3.73 mmol) in dry ethanol (15 mL), 20,60-dihydroxy acetophenone (0.568 g,
3.73 mmol) and indium trichloride (0.060 g, 0.27 mmol) were added under
nitrogen, and stirring of the mixture was continued 3 days at 343 K. After
removal by filtration of a scarce gray precipitate, the solvent was removed in
vacuo and the residue was washed with 3 portions (50 mL each) of water. After
drying in vacuo the gummy material, that according to 1H NMR spectrum
contained ca. 25% of the wanted product, this was dissolved in a minimum
amount of ethanol (ca. 10 mL) and water was added to precipitate the
perimidine. This procedure was repeated, to obtain the nearly pure product as
a light brown solid. (0.207 g, 19% yield). Recrystallization could be achieved
from methanol to afford nearly colourless microcrystals. 1H NMR (CD3OD): d
7.22 (apparent d, 4H, J = 4.0 Hz), 6.73 (t, 2H, J = 4.0 Hz), 6.69 (t, 1H, J = 8.2 Hz),
6.08 (d, 2H, J = 8.0 Hz), 1.82 (s, 3H). 13C NMR (CDCl3): d 146.3, 140.4, 134.9,
128.7, 127.9, 127.2, 126.2, 117.6, 113.8, 106.23, 68.3, 29.6.
R1: 0.0489, wR2: 0.1052; R indices (all data), R1: 0.0906, wR2: 0.1251; largest
diff. peak and hole: 0.168, ꢁ0.227 eÅꢁ3
.
Crystal data and structure refinement details for compound 2. Empirical
formula:
wavelength: 0.71073 Å; crystal system: monoclinic; space group:
unit cell dimensions: a: 9.141(2) Å, b: 8.104(1)Å, c: 19.119(2) Å,
C
18H16N2O2; formula weight: 292.33; temperature: 296(2) K;
21/c;
: 90°, b:
P
a
92.78(1)°, c
: 90°; volume: 1414.6(4)Å3; Z: 4; calculated density: 1.373 Mg/m3;
absorption coefficient: 0.091 mmꢁ1; F(000): 616; h range for data collection:
3.01–27.51°; reflections collected/unique: 7445/3074 [R(int) = 0.0613]; data/
parameters: 3074/212; goodness-of-fit on F2: 1.017; final R indices [I > 2
r (I)],
R1: 0.0647, wR2: 0.0991; R indices (all data), R1: 0.1804, wR2: 0.1279; largest
diff. peak and hole: 0.173, ꢁ0.238 eA-3
.
19. Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.;
Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr.
1999, 32, 115–119.
20. Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
21. Belmonte, M. M.; Escudero-Adan, E. C.; Benet-Buchholz, J.; Haak, R. M.; Kleij, A.
W. Eur. J. Org. Chem. 2010, 4823–4831.
16. Adler, R. W.; Hyland, N. P.; Jeffery, J. C.; Riis-Johannessen, T.; Riley, D. J. Org.
Biomol. Chem. 2009, 7, 2704–2715.
17. Yasaei, Z.; Mirzaei, P.; Bazgir, A. C. R. Chimia 2010, 13, 1308–1312.
18. Single crystals of compounds 1 and 2 were obtained by slow evaporation of
ethyl acetate solutions at ambient temperature. Crystals were mounted at
296 K on a Bruker-Nonius Kappa CCD diffractometer equipped with a graphite
monochromated MoK radiation (k = 0.71073 Å, CCD rotation images, thick
22. Sauer, M.; Yeung, C.; Chong, J. H.; Patrick, B. O.; MacLachlan, M. J. J. Org. Chem.
2006, 71, 775–788.
23. Espenbetov, A. A.; Pozharskii, A. F.; StruchKov, Yu. T.; Suslov, A. N. Chem.
Heterocycl. Compd. 1985, 814–821.
slices,
/ and x scans to fill asymmetric unit). Semiempirical absorbtion
correction (SADABS) was applied. Both the structures were solved by direct
methods19 and anisotropically refined by the full matrix least-squares method
on F2 against all independent measured reflections.20 In both the two
structures, hydrogen atoms were introduced in calculated positions and
24. A mixture of [(g
6-p-cymene)RuCl2]2 (0.030 g, 0.049 mmol), ligand 2 (0.014 g,
0.049 mmol) and sodium carbonate (0.025 g, 0.24 mmol) in dichloromethane
(5 mL) was stirred at room temperature for 6 h. After filtering on a small Celite
bed the solvent was removed in vacuo to give a brown solid. Freshly distilled i-
propanol (5 mL), potassium hydroxide (0.011 g, 0.2 mmol) and the ketone
(5.0 mmol) were added. After 12 h stirring at 90 °C the cooled reaction mixture
was filtered on Celite and most of unreacted i-propanol was removed in vacuo.
To assess the extent of the reduction the integrals of suited signals in 1H NMR
spectra (CDCl3) were compared, respectively for the ketone PhCOR and the
corresponding alcohol PhCH(OH)R (TOF: 3.7 hꢁ1 for R = Me; 2.6 hꢁ1 for R = i-Pr;
4.1 hꢁ1 for R = t-Bu).
refined according to
a riding model except for amine and hydroxylic H
atoms that were located in difference Fourier maps and refined with U(iso)
equivalent to 1.2U (eq) of the carrier atom. The final refinement converged to
R1 = 0.0489, wR2 = 0.1052 for compound 1 and R1 = 0.0647, wR2 = 0.0991 for
compound 2.
Crystal data and structure refinement details for compound 1. Empirical
formula:
wavelength: 0.71073 Å; crystal system: monoclinic; space group: P21/c; unit
cell dimensions: a: 8.627(2) Å, b: 10.753(1)Å, c: 14.538(2)(5) Å, : 90°, b:
C18H16N2; formula weight: 260.33; temperature: 296(2) K;
25. 1H NMR (CD3OD): d 7.22 (t, 2H, J = 7.8Hz), 7.04 (d, 2H, J = 7.8Hz), 6.42 (d, 2H,
J = 7.4Hz), 5.81 (t, 1H, J = 6.4Hz), 5.65 (ABq, 4H, J = 2.6Hz), 4.94 (d, 2H,
J = 6.4Hz), 2.50 (s, 3H), 2.10 (m, 1H), 0.94 (d, 3H, J = 7.0Hz), 0.80 (d, 3H,
J = 7.0Hz).
a
90.52(1)°, c
: 90°; volume: 1348.5(3)Å3; Z: 4; calculated density: 1.282 Mg/m3;
absorption coefficient: 0.076 mmꢁ1; F(000): 552; h range for data collection:
3.03–27.52°; reflections collected/unique: 13326/3036 [R(int) = 0.0373]; data/