A Three-Dimensional Channel Supramolecular Architecture Based on

DOI: 10.1021/cg900295n

A Three-Dimensional Channel Supramolecular Architecture Based on 3-Amino-2-(4-dimethylaminophenyldiazenyl)-1-phenylbut-2-en-1-one and Aromatic Guests†

2010, Vol. 10 85–91


^  unek, Vladimı´ r Mach
acek,*,^ Valerio Bertolasi,*,‡ Petr Sim Mark
eta Svobodov
a,^ # §  Jan Svoboda, and Eva Cernoskov
a

^

Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of a di Ferrara, Dipartimento Pardubice, Studentsk
a 573, CZ-532 10 Pardubice, Czech Republic, ‡Universit di Chimica and Centro di Strutturistica Diffrattometrica, Via L. Borsari 46, I-44100, Ferrara, Italy, # Joint Laboratory of Solid State Chemistry of IMC ASCR, v.v.i. and University of Pardubice, Heyrovsk
eho n
am estı´ 2, CZ-162 06 Prague 6, Czech Republic, and §Joint Laboratory of Solid State Chemistry of IMC ASCR, v.v.i. and University of Pardubice, Faculty of Chemical Technology, University of Pardubice, Studentsk
a 84, CZ-532 10 Pardubice, Czech Republic Received March 13, 2009; Revised Manuscript Received November 20, 2009

ABSTRACT: If crystallized from aromatic solvents (benzene, toluene, p-xylene, chlorobenzene), 3-amino-2-(4-dimethylaminophenyldiazenyl)-1-phenylbut-2-en-1-one (1) forms a three-dimensional supramolecular H-bonding network with molecular channels of approximately cylindrical shape in which the solvent molecules are placed in a defined manner. The aromatic molecules are bound with the molecules of the network by means of weak intermolecular interactions of varying nature. The X-ray structures provide detailed information on the binding motifs that consist of C-H 3 3 3 O and C-H 3 3 3 π bonds between the aromatic solvent molecules and the benzoyl moiety of 1. The motifs are identical in all the four inclusion compounds analyzed showing the robustness of this supramolecular synthon. Accordingly, the crystals adopt isostructural arrangements favored by the mutual orientation of the host molecules of 1 that make identical helical catemers by means of strong N-H 3 3 3 O intermolecular hydrogen bonds. Thermal stability of the inclusion compounds of compound 1 with benzene, toluene, p-xylene, and m-xylene has been studied by means of differential scanning calorimetry and thermogravimetric analysis methods. Introduction X-ray structural studies of small molecules have become a routine matter thanks to the availability of both instrumentation and software. Therefore, interest has shifted one story higher - to a supramolecular level. Investigation of supramolecular structures - nanostructures - has a distinct impact on a number of disciplines, such as supramolecular chemistry, crystal engineering, biochemistry, materials sciences, pharmaceutical chemistry, catalysis, separation techniques, sensors, and others.1 An arrangement of molecules in a crystal is a result of the optimum geometry of hydrogen bonds, if they are possible, and weak intermolecular noncovalent interactions. In the past few years, hundreds of papers have been focused on investigation of these interactions and their relationship to crystal packing.2 The weak interactions are essential in biochemistry (proteins, DNA, etc.) as well as in determining the conformation of organic and organometallic compounds. They also play an important role in chiral recognition, where host chiral molecules display crystal structures able to selectively enclathrate either of the enantiomers of a guest racemate into the host framework.3 Recently, the synthesis and structure of a number of nanometer-sized tubular inclusion compounds, where simple guest molecules are trapped in small channels only by means of weak C-H 3 3 3 X (X = O, N), C-H 3 3 3 π, π 3 3 3 π, and van der Waals interactions, have been reported. Host-guest inclusion compounds containing micropores have potential applications in catalysis, nonlinear optical materials, chemical separations, gas storage devices, and pharmaceutical sciences.4 The host molecules, packed by means of hydrogen bonds and/or halo-

gen-halogen interactions, belong to several chemical classes such as diols,5 steroids and bile acid derivatives,6 tetrakis(4nitrophenyl)methane,7 acridinylresorcinol,8 proteins and peptides,9 2,4,6-tris(4-halophenoxy)-1,3,5-triazine,10 etc. In other cases, the host network is built up by couples of hydrogen bonded complementary molecules or ions as observed in guanidinium/organodisulfonates,11 carboxylic acids/bipyridines,12 and caffeine/succinic acid13 inclusion complexes. We now describe the supramolecular properties of the molecule of 3-amino-2-(4-dimethylaminophenyldiazenyl)-1phenylbut-2-en-1-one (1), which can act as both a donor and an acceptor of several hydrogen bonds thanks to the presence of several nitrogen atoms, N-H groups and a carbonyl group. In addition, the presence of two benzene rings allows the exploitation of potential C(sp2)-H 3 3 3 π, π 3 3 3 π and C(sp2)-H 3 3 3 X (X = O, N, Cl) interactions and thus meets the requirements for formation of supramolecular structures. This study shows that, using a variety of strong and weak interactions, the molecules of 1 are able to produce crystal architectures characterized by channels that include small solvent molecules such as benzene and mono- or p-disubstituted benzenes.

Results and Discussion

† Dedicated to Prof. Milos Sedl
ak on the occasion of his 50th birthday. *To whom correspondence should be addressed. (V.M.) Phone: þ420 466 037 039; fax: þ420 466 037 068; e-mail: [email protected]. (V.B.) E-mail: [email protected].

This paper presents results of structural studies on solvates of 1 with molecules of some aromatic compounds. The

r 2009 American Chemical Society

Published on Web 12/15/2009

pubs.acs.org/crystal

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Crystal Growth & Design, Vol. 10, No. 1, 2010 Table 1. Crystal Data crystal

1a

1b

1ca

1d

1e

empirical formula system space group a (A˚) b (A˚) c (A˚) β () volume (A˚3) Z Dcalc (g 3 cm-3) T (K) μ (cm-1) θmin - θmax () unique reflns Rint obsd reflns [I > 2σ(Ι)] R (obsd reflns) wR (all reflns) S ΔFmax; ΔFmin (e 3 A˚-3) CCDC Nr. or REFCODE

C18H20N4O monoclinic P21/c 9.9279(2) 10.8905(2) 16.0206(4) 90.9820(8) 1731.89(6) 4 1.183 295 0.76 3.2-27.0 3760 0.027 2863 0.0569 0.1804 1.032 0.218; -0.318 721560

C18H20N4O 3 1/2(C6H6) monoclinic C2/c 25.6403(5) 10.6929(3) 15.7578(4) 117.470(2) 3833.2(2) 8 1.204 150 0.77 3.0-28.0 4482 0.035 3532 0.0524 0.1443 1.062 0.289; -0.195 721561

C18H20N4O 3 1/2(C7H8) monoclinic C2/c 25.8225(3) 10.7493(2) 15.6270(3) 117.694(1) 3840.7(1) 8 1.226 150 0.78 3.6-28.0 4585 0.039 4083 0.0519 0.1259 1.147 0.211; -0.178 RALKUL

C18H20N4O 3 1/2(C8H10) monoclinic C2/c 25.8220(6) 11.0522(3) 15.6353(4) 118.474(2) 3922.4(2) 8 1.224 150 0.77 2.8-30.0 5698 0.034 4061 0.0497 0.1419 1.029 0.245: -0.227 721562

C18H20N4O 3 1/2(C6H5Cl) monoclinic C2/c 25.6689(4) 10.7565(2) 15.6384(3) 117.632(1) 3825.4(1) 8 1.266 150 1.48 2.8-30.0 5573 0.038 4319 0.0452 0.1204 1.028 0.306; -0.349 721563

a

Ref 14. Table 2. Intra- and Intermolecular Hydrogen Bond Parameters (A˚ and degrees)a

N3-H31 3 N1-H1 3 3 N3-H32 3

3 3 N1 3 N3 3 3 O1

N3-H31 3 3 3 N1 N1-H1 3 3 3 N3 N3-H32 3 3 3 O1 N3-H31 3 N1-H1 3 3 N3-H32 3

3 3 N1 3 N3 3 3 O1

N3-H31 3 N1-H1 3 3 N3-H32 3

3 3 N1 3 N3 3 3 O1

N3-H31 3 3 3 N1 N1-H1 3 3 3 N3 N3-H32 3 3 3 O1 a

symm. op.

D-H

H3 3 3A

D3 3 3A

D-H 3 3 3 A

tautomers azo/hydrazone

1a 1.90(3) 2.11(15) 1.96(2)

2.636(2) 2.636(2) 2.896(2)

133(3) 113(12) 174(2)

86/14

1 - x, y - 1/2, -z - 1/2

0.95(3) 0.95(16) 0.94(2)

1b 1.92(3) 2.05(12) 2.03(2)

2.637(2) 2.637(2) 2.898(2)

133(2) 123(8) 170(2)

79/21

1/2 - x, 1/2 þ y, 1/2 - z

0.92(3) 0.88(9) 0.87(2)

1cb 1.86(3) 2.02(16) 1.99(2)

2.630(2) 2.630(2) 2.910(2)

137(2) 114(9) 172(2)

85/15

3/2 - x, y - 1/2, 3/2 - z

0.94(3) 1.04(12) 0.92(2)

1d 1.90(2) 2.10(12) 2.06/2)

2.627(2) 2.627(2) 2.955(2)

134(2) 116(8) 170(2)

82/18

1/2 - x, 1/2 þ y, 1/2 - z

0.93(3) 0.91(9) 0.90(2)

1e 1.93(2) 2.12(13) 2.01(2)

2.632(2) 2.632(2) 2.910(1)

134(2) 119(8) 173(2)

85/15

1/2 - x, 1/2 þ y, 1/2 - z

0.90(2) 0.84(9) 0.91(2)

b

See Figure 3. Ref 14.

crystallographic data of crystals of compound 1 without solvent molecules (1a) as well as with benzene (1b), toluene (1c), p-xylene (1d), and chlorobenzene (1e) molecules are presented in Table 1. Selected bond lengths and bond angles and other parameters are given in Table S1, and parameters of both intra- and intermolecular hydrogen bonds are given in Table 2. Compound 1a in crystals is a mixture of tautomeric aminodiazenyl H2N3-C2dC1-N2dN1 and imino-hydrazone HN3=C2-C1dN2-N1-H forms with the former tautomer predominating (Scheme 1). Its behavior, when solvated with toluene (1c), was described elsewhere together with information about the effects of this tautomerism upon the bond lengths and bond angles.14 The intramolecular hydrogen bonds N3-H 3 3 3 N1 and N1-H 3 3 3 N3 in both tautomers are of resonance-assisted hydrogen bond (RAHB) nature and display, in the present

Scheme 1. The Tautomeric Equilibrium of the Compound 1

crystals, short distances between the donor and the acceptor nitrogen atoms in the range 2.627(2)-2.637(2) A˚ (Table 2).15 The tautomeric system represents a double minimum low barrier hydrogen bond (LBHB),16 in which the proton is transferred from one nitrogen atom to the other by means of a strong hydrogen bond. The tautomeric behavior of the compound 1 was studied both in CDCl3 solution by means of

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Table 3. Host-Guest Interactionsa

C2a-H2a 3 3 3 O1 C1a-H1a 3 3 3 Cpb C2a-H2a 3 3 3 O1 C1a-H1a 3 3 3 Cpb C2a-H2a 3 3 3 O1 C1a-H1a 3 3 3 Cpb C2a-H2a 3 3 3 O1 C1a-H1a 3 3 3 Cpb C7-H7 3 3 3 Cl1a

1b 1cc 1d 1e

Hydrogen Bonds (A˚ and ) symm. op. D-H H 3 3 3 A 1b 1.04(3) 2.57(4) 0.97(4) 2.75(3) 1cc 0.99(3) 2.72(3) 0.98(4) 2.78(3) 1d 1.01(2) 2.77(3) 1.03(3) 3.07(3) 1e 1.00(2) 2.62(2) 0.96(3) 2.80(3) -x, y, 0.95(2) 2.81(2) -z - 1/2

D3 3 3A

87

D-H 3 3 3 A

3.328(3) 129(3) 3.683(3) 161(3) 3.384(3) 125(3) 3.727(3) 162(3) 3.441(2) 124(2) 3.903(3) 138(3) 3.326(2) 128(2) 3.694(3) 156(3) 3.368(2) 119(1)

dihedral angle () C1a-C2a-C3a/ C5--C10

Vh (A˚3)d

Vg (A˚3)e

55.0(1) 54.3(1) 54.8(1) 55.3(1)

728.9 748.0 796.6 704.9

182.2 187.0 199.2 176.2

N NMR spectroscopy and in a solid phase in crystals by means of X-ray analysis.14 In CDCl3 solution, the ratio of tautomers azo/hydrazone is 83:17; in the crystals, the ratio is similar and almost independent of the presence or absence of the solvent and the type of aromatic compound, and it varies from 79:21 to 86:14 (Table 2). An ORTEP17 view of nonsolvated molecule 1a is shown in Figure 1. The crystal packing is dominated by chains of molecules linked by N-H 3 3 3 O hydrogen bonds running along a screw axis parallel to b. The hydrogen atom forming this H-bond is the aminic one that is not involved in the tautomeric azo-hydrazone system. When crystallized from aromatic solvents (benzene, toluene, p-xylene, chlorobenzene), compound 1 is combined with the solvent molecules in the stoichiometric ratio of 2:1. The single crystal X-ray analysis shows that the asymmetric unit of the cell (space group C2/c) contains a complex consisting of a molecule of 1 and one-half of an aromatic molecule of solvent situated around an inversion center.

a See Figure 5. b Cp = centroid of C5--C10 phenyl ring. c Ref 14. d Vh = volume of the host cavity per unit cell. e Vg = volume per guest molecule.

Figure 1. ORTEP view of 1a showing the thermal ellipsoids at 30% probability. Both tautomeric hydrogens linked to N1 and N3 atoms are displayed.

Figure 3. Hydrogen-bonded chain formed by molecules of 1 running along a screw axis parallel to b for the nonsolvated crystal 1a. The same arrangement is observed in the crystals of inclusion compounds 1b, 1c, 1d, and 1e (see the figures in the Supporting Information).

Figure 2. ORTEP views of 1b, 1d, and 1e showing the thermal ellipsoids at 40% probability. Both tautomeric hydrogens linked to N1 and N3 atoms are displayed.

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Figure 4. (a) A space filling representation of crystal packing of host-guest complex 1b as viewed down the crystallographic c axis. The guest molecules of benzene included in the channels formed by molecules of compound 1 are shown using the stick representation. (The other crystal packings are shown in the Supporting Information). (b) Part of the host fragment of 1b along with guest molecules of benzene. Components of the host and guest are shown using wireframe and space filling models, respectively.

There is no substantial difference at the molecular level between geometrical parameters of the molecule of the compound 1 in crystals of nonsolvated and solvated forms (Tables 2 and S1). ORTEP views of the inclusion compounds 1b, 1d, and 1e are shown in Figure 2. In all crystals, the molecular conformations of compound 1 are very similar, regardless of the structure of solvating aromatic molecule, displaying the p-dimethylaminophenyl group roughly coplanar with the tautomeric system but making an angle of about 65 with the phenyl ring of the benzoyl moiety. All the crystals 1b, 1c, 1d, and 1e are isostructural18 and, as in the nonsolvated crystal 1a, the crystal packing is dominated by host framework built up by catemers of hydrogenbonded molecules linked by N-H 3 3 3 O short hydrogen bonds around screw axes parallel to b (Figure 3). The mutual orientation of the molecules in the chains are almost identical in all crystals, but the catemers in 1a are packed in a monoclinic primitive P cell, while those in 1b, 1c, 1d, and 1e are arranged in a centered cell C allowing the inclusion of small aromatic solvent molecules situated on crystallographic centers of symmetry.

Because toluene and chlorobenzene are not centrosymmetric molecules, the methyl group and chlorine atom in 1c and 1e are disordered, 50:50, over two opposite positions on the phenyl group. The molecules of 1 in the solvated crystals form a threedimensional supramolecular network with two nanochannels per unit cell in the direction of the c axis situated around the inversion centers at (0, 0, 0) and (1/2, 1/2, 0) (Figure 4a,b). In the unit cell each channel contains two aromatic guest molecules that are sustained by two C-H 3 3 3 π interactions between the hydrogen atoms in mutual para positions and π systems of two centrosymmetric benzoyl groups, and by C-H 3 3 3 O hydrogen bonds between two more H atoms of the aromatic molecules (again in para positions) and two carbonyl groups. In the inclusion compound 1e the disordered Cl substituent is involved in further C-H 3 3 3 Cl interactions with C(sp2)-H groups of the benzoyl moiety. The supramolecular motifs shown in Figure 5 are thus primarly characterized by chains of the guest molecules 1 and by supramolecular synthons19 where two molecules of 1 and one molecule of aromatic guest form a stable trimeric system. A space filling

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Figure 6. Spacefill model of interaction of benzene molecule with benzoyl groups in the crystal of 1b.

Figure 5. Supramolecular synthons formed by trimers built up by two molecules of 1 and a molecule of aromatic solvent, for the inclusion compounds 1b, 1c, and 1d. For 1e, there are further C-H 3 3 3 Cl interactions involving the benzoyl groups of other two molecules of 1.

representation of the trimeric synthon of 1b is shown in Figure 6. The trimer in the compound 1e is accompanied by other two molecules of 1 that further contribute to recognize the aromatic guest molecules by means of C-H 3 3 3 Cl interactions. The planes of the aromatic solvent molecules, making angles in the range 54.3(1)-55.3(1) with the C5--C10 phenyl ring, allow optimal cooperative C-H 3 3 3 π and C-H 3 3 3 O interactions. The channels have approximately cylindrical shape with a diameter of ca. 10 A˚. The volumes of the host channels per unit cell, in the range 704.9-796.6 A˚3, correspond to volumes per guest molecule from 176.2 to 199.2 A˚3, comparable to

those, between 150 and 200 A˚3, for crystals of inclusion compounds built up by bile acids and their derivatives with monosubstituted benzenes.20 Purely organic structures with channels that measure ca. 10 A˚ are relatively rare.2b Compound 1d, containing the p-xylene as the guest molecule, displays the greatest volume of crystal cell as well as the greatest volume of the host cavity per unit cell and the greatest volume per guest molecule of 3922.4(2), 796.6, and 199.2 A˚3, respectively. Therefore, the p-xylene (a disubstituted benzene) induces an increase of the cavity in the crystal structure of 1d, with respect to those of 1b, 1c, and 1e containing unsubstituted or monosubstituted benzenes. This variation is accompanied by a weakening of both the C-H 3 3 3 π and C-H 3 3 3 O interactions within the channels of 1d (Table 3). Accordingly, the shape of the molecular channel adapts to the shape of the aromatic molecules deposited, which is manifested by small changes of the geometry parameters of the network. We also were able to prepare crystals of the inclusion compound with m-xylene 1f. The crystals turned out to be still isostructural with the previous ones 1b-1e displaying a cell volume of 4051.8(3) A˚ that is about 5%, on average, greater than the volumes observed in crystals 1b-1e. It was even possible to determine the crystal structure, but, while the amino-diazenyl derivative was well-defined without disorder, the channels were larger than in previous structures and filled with guest molecules of solvent so disordered, across centers of inversion, that it was impossible to find a comprehensible structural form. Differential Scanning Calorimetry. Thermal stability of the inclusion compounds 1b-1d and 1f has been studied by means of DSC. The dependences of heat flow on temperature are presented in Figure 7. In all the cases, there are two distinct endotherms in the records: the first corresponding to the guest loss followed by the second, which is very close in all the records and corresponds to the melting point of the compound 1 that has been rid of the solvent molecules. The melting point determined by means of DSC is 162 C (ref 14 gives mp 160-163 C). The temperatures at which the guest molecules start to be released from the inclusion compound (Ton)21,22 are given in Table 4. In the case of the inclusion compounds with p-xylene (1d), m-xylene (1f), and toluene (1c), the Ton are lower than bp (Tb) of these compounds. The molecules of these guests are bound in the channels of the lattice by very weak forces: the energy of interactions with the lattice is smaller than the energy of mutual interactions between these molecules in a liquid state. On the contrary, benzene has a lower bp than Ton, which means that the benzene molecule interacts with the lattice more strongly than with other benzene molecules in a liquid phase.

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correspond the loss of weight 17.21%). The order of stability of the solvates (Figure 8) is in accordance with the order found by means of DSC. The most stable solvate is formed with benzene. Conclusions

Figure 7. DSC analysis of the inclusion compounds 1b-d, f.

In summary, a new host framework based on tautomeric molecules forming isostructural solvates with solvent molecules located on common centers of inversion has been described. The unusual feature in this system is the retention of the host conformation in both the unsolvated and solvated crystals. The crystal packings of host molecules of 1 and guest aromatic solvents (benzene, toluene, p-xylene, chlorobenzene) are primarly governed by intermolecular N-H 3 3 3 O hydrogen bonds forming very similar catemers regardless of the presence or absence of the guest molecules. The inclusion complexes are stabilized by additional C-H 3 3 3 π and CH 3 3 3 O interactions between the benzene derivatives and two centrosymmetric benzoyl moieties. The guest molecules are included in tunable channels parallel to the c axis and fill similar volumes except for p-xylene, a disubstitued benzene, which occupies a slightly greater volume associated with weaker interactions. The m-xylene guest molecules, in crystals 1f, display heavy disorder and seem to be included in even larger channels. The results of the DSC analysis indicate a certain ability of compound 1 to bind m-xylene, probably involving the weakest host-guest interactions with respect to those of the other isostructural complexes. By means of TGA analysis of the inclusion compounds, the forces binding the guest molecules in the channels were found to increase in the order m-xylene < p-xylene < toluene < benzene. Experimental Section

Figure 8. TGA curves for the decomposition of the inclusion compounds 1b-d, f. Table 4. Thermal Analysis Results for Inclusion Compoundsa inclusion compound 1 3 benzene, 1b 1 3 toluene, 1c 1 3 p-xylene, 1d 1 3 m-xylene, 1f a

ratio 1/guest from TGA 2.01:1 2.03:1 2.01:1 1.99:1

guest release Ton, C

bp of pure guest Tb, C

Ton - Tb

99 92 70 67

80 110 138 138

þ19 -18 -68 -71

See Figures 7 and 8.

On heating, all the compounds lose weight in two steps. The thermogravimetric curves are shown in Figure 8. The first step belongs to the loss of the solvent, and the second one to the decomposition of the organic matrix. In the case of benzene, the loss in the weight of the sample in the temperature interval 100-170 C is 12.59% (to the assumed composition of the solvate C18H20N4O 3 0.5C6H6 would correspond to the value 12.66%). In the case of toluene, the loss in weight of the sample in the temperature interval 65-170 C was found to be 14.73%, (for C18H20N4O 3 0.5C6H5CH3 calculated 14.94%). In the cases of para and meta xylenes the losses of weights 17.13% and 17.32% were found in the temperature ranges 60-165 C and 55-165 C, respectively (to the solvate C18H20N4O 3 0.5H3CC6H4CH3 would

The synthesis of 1 by azo coupling reaction of 3-amino-1-phenylbut-2-en-1-one with 4-dimethylaminobenzenediazonium tetrafluoroborate and its identification are described in the literature.14 The solvates were prepared by crystallization of compound 1 from the respective solvents: benzene (1b), toluene (1c), p-xylene (1d), chlorobenzene (1e), and m-xylene (1f) from the hot saturated solutions being thermally insulated and allowed to evaporate freely. The crystal without solvent molecules, 1a, was prepared by crystallization of compound 1 from chloroform. Melting points were determined with a Kofler hot stage microscope and were not corrected. The elemental analyses were carried out with a Fisons EA 1108 automatic analyzer. Calcd C18H20N4O (1a): C, 70.11; H, 6.54; N, 18.17. Found: C, 70.18; H, 6.54; N, 18.09. Calcd C18H20N4O 3 0.5 C6H6 (1b): C, 72.60; H, 6.67; N, 16.13. Found: C, 72.65; H, 6.49; N, 16.31. Calcd C18H20N4O 3 0.5 C7H8 (1c): C, 72.86; H, 6.82; N, 15.81. Found: C, 73.17; H, 6.71; N, 16.19. Calcd C18H20N4O 3 0.5 p-C8H10 (1d): C, 73.10; H, 6.97; N, 15.50. Found: C, 73.42; H, 6.76; N, 15.96. Calcd C18H20N4O 3 0.5 m-C8H10 (1f): C, 73.10; H, 6.97; N, 15.50. Found: C, 73.12; H, 6.57; N, 15.81. Crystallography. Crystal data of compounds 1a, 1b, 1d, and 1e were collected on a Nonius Kappa CCD diffractometer using graphite monochromated Mo KR radiation (λ = 0.7107 A˚). Data sets were integrated with the Denzo-SMN package23 and corrected for Lorentz-polarization effects. The structures were solved by direct methods (SIR97)24 and refined by full-matrix least-squares methods with all non-hydrogen atoms refined anisotropically and hydrogens isotropically except the methylic hydrogens of compound 1a that were included on calculated positions, riding on their carrier atoms. In all compounds, the difference Fourier map showed diffuse electron density between N1 and N3 atoms with two maxima from which two proton positions could be identified. Refinement of the

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two tautomeric H atoms with partial occupancy factors and isotropic thermal parameters fixed at 1.2 times the average of those of the related nitrogen atoms was successfully attempted giving the final occupancy factors for H3 and H1 displayed in Table 3. The disordered Cl atom of chlorobenzene in compound 1e was refined over two sites with an occupancy of 0.5. All calculations were performed using SHELXL-97,25 PARST,26 and PLATON27 implemented in WINGX28 system of programs. Crystallographic data (excluding structure factors) have been deposited at the Cambridge Crystallographic Data Centre and allocated the deposition numbers CCDC 721560-721563. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/ retrieving.html or on application to CCDC, Union Road, Cambridge, CB2 1EZ, UK [fax: (þ44)1223-336033, e-mail: deposit@ ccdc.cam.ac.uk]. The thermal analyses were carried out on a differential scanning calorimeter Mettler DSC 12E. Instrument was calibrated with pure In. Measurements were performed in open aluminum pans in nonisothermal regime in the range of 25-300 C with heating rate 10 C min-1. Weight of samples was ∼3 mg. Pure R-Al2O3 was used as a standard. TGAs of the crystalline samples were performed using a homemade apparatus constructed of a computer-controlled oven and a Sartorius BP210 S balance. Samples (about 50 mg) were analyzed in an open quartz crucible in air from 25 to 300 C at a heating rate 1 C min-1.

 M.S.) thank the Acknowledgment. Authors (V.M., P.S., Ministry of Education, Youth and Sports of the Czech Republic (MSM 002167501) and Czech Science Foundation (Project No. 203/07/0469) for financial support. Supporting Information Available: Crystallographic data in .cif format. This information is available free of charge via the Internet at http://pubs.acs.org.

(5) (6)

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