Complexes in the Solid State: From Polymorphism to Isostructurality

ARTICLE pubs.acs.org/crystal

Conformational Diversity of Thiosemicarbazonatovanadium(V) Complexes in the Solid State: From Polymorphism to Isostructurality Mirta Rubcic,*,† Dalibor Milic,† Gordana Pavlovic,‡ and Marina Cindric† †

Laboratory of General and Inorganic Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia ‡ Laboratory of General Chemistry, Department of Applied Chemistry, Faculty of Textile Technology, University of Zagreb, Prilaz baruna Filipovica 28a, HR-10000 Zagreb, Croatia

bS Supporting Information ABSTRACT: New alkoxooxovanadium(V) complexes, [VO(L)(OR)] (OR = OMe (1), OEt (2), OPr (3)), were synthesized by the reaction of assorted vanadium precursors and 4-methoxysalicylaldehyde 4-phenylthiosemicarbazone (H2L) in appropriate alcohols. Complexes 2 and 3 crystallized each in two polymorphic forms, which can be selectively prepared by using either a vanadium(IV) or a vanadium(V) precursor. The conformational flexibility of these complexes manifests itself in conformational polymorphism (2a and 2b, 3a, and 3b), conformational isomorphism (2b, 3a, and 3b), and conformational synmorphism (3a and 3b). The largest conformational differences are found in the spatial arrangements of the coordinated alkoxo groups and the phenyl rings of the ligand. The isostructurality of complexes 2b and 3a reflects, on the other hand, their conformational similarity, with nearly the same pattern of intermolecular interactions dominating within their crystal architectures. However, unlike the case in 3a, the structure of 2b exhibits disorder in the stacking of molecular layers, which can be tentatively correlated with the crystallization rate. All compounds were thoroughly investigated by various solid-state methods, while the thermodynamic relation of polymorphs 2 and 3 was assessed via competitive slurry and thermal experiments.

’ INTRODUCTION Metal complexes, as any other chemical substances, can experience polymorphism, a phenomenon where the same chemical entity adopts two or more diverse solid-state arrangements.1 Polymorphs can arise from different intermolecular interactions of rigid structural units but can also originate from different conformations of flexible entities. In the latter case, such diversity in the crystalline state can result in conformational isomorphism, the occurrence of different conformers in the same crystal structure; conformational polymorphism, the occurrence of diverse conformers in different polymorphic forms; and conformational synmorphism, which refers to a random distribution of different conformers within the crystal structure.1b,2 As a consequence of diverse solid-state architectures, polymorphs can differ dramatically in their physicochemical properties, which is an especially important issue in the design of solid materials.3 Naturally, the need to control formation of the specific polymorph has been one of the key aspects of solid-state chemistry during last several decades.4 In this context, every opportunity to study the phenomenon is valuable because only through a detailed knowledge about shape, conformation, and overall arrangement of building blocks within a crystal can one comprehend the delicate structure property relationship. Isostructurality, on the other hand, can be considered as opposite of polymorphism and refers to identical or nearly identical crystal r 2011 American Chemical Society

structures displayed by different chemical compounds. Usually, the phenomenon is expected to be pronounced if the related molecules are isometric, i.e. vary only in the substituent (e.g., CH3 versus H), in the chirality, or in one or more atoms whose atomic radii do not differ substantially (e.g., Si and Ge).5 Interestingly, however, it has been recently demonstrated that even larger dissimilarities, such as differences in molecular shape and in functional groups, can be overcome via cocrystallization, affording in return isostructural materials.6 One of the interesting opportunities of isostructurality is utilization of this structural similarity as a templating tool during the crystal growth.7 For the system of two isostructural metal complexes, it was shown possible to epitaxially grow one of the components on the seed of another, creating thus composite crystals.8 Such an approach opens numerous possibilities, as one can easily tune the desired characteristics of the final material by varying the components and their ratio. As a continuation of our research on the chemistry of vanadium species with thiosemicarbazone ligands,9 we herein present several synthetic approaches which have successfully yielded novel alkoxooxo(thiosemicarbazonato)vanadium(V) complexes [VO(L)(OR)] Received: April 13, 2011 Revised: September 20, 2011 Published: October 05, 2011 5227

dx.doi.org/10.1021/cg200466b | Cryst. Growth Des. 2011, 11, 5227–5240

Crystal Growth & Design

ARTICLE

Scheme 1a

a

OR = OMe (1), OEt (2), OPr (3). A detailed synthetic and crystallographic discussion for the compound HL(acac)cycl (4) is given in the Supporting Information.

Figure 1. Polymorphic forms of complexes [VO(L)(OEt)] (2) and [VO(L)(OPr)] (3): (a) 2a, (b) 2b, (c) 3a, (d) 3b.

(OR = OMe (1), OEt (2), OPr (3)). In addition, when acetylacetonato precursors were employed, besides vanadium(V) complexes, an intermolecular cyclization reaction between H2L and acetylacetone lead to the isolation of small amounts of a byproduct, HL(acac)cycl (4) (Scheme 1). In the course of this investigation, it was observed that each of the complexes [VO(L)(OEt)] (2) and [VO(L)(OPr)] (3) crystallized as dimorphs. In both cases, efficient control over polymorphic appearance was achieved by utilizing either the vanadium(IV) or vanadium(V) precursor. The conformational flexibility of complexes 2 and 3 is evident through the occurrence of two almost opposite phenomena: (a) the existence of various conformers of the same compound within both the same (conformational isomorphism and conformational synmorphism) and different crystal structures (conformational polymorphism) and (b) isostructurality. Moreover, the detailed inspection of the crystal structure of [VO(L)(OEt)] (2b) and the associated experimental data revealed the disorder in stacking of the ordered molecular layers. Different solid-state methods (IR spectroscopy, TG/DSC analysis, hot stage microscopy, and X-ray diffraction) were employed in investigation of all reaction products, particularly focusing on the characterization of polymorphic forms and investigation of their potential (inter)conversion conditions.

’ EXPERIMENTAL SECTION Materials. 4-Methoxysalicylaldehyde, acetylacetone, 4-phenylthiosemicarbazide, V2O5, and NaVO3 were commercially available and used without further purification. The ligand H2L (4-methoxysalicylaldehyde 4-phenylthiosemicarbazone), [VO(OAc)2], and [V2O4(acac)2] were prepared according to the literature procedures.10 12 [VO(acac)2] was

prepared by slight modification of a well-established method, using triethylamine instead of Na2CO3.13 The solvents were of reagent grade and distilled before use.

Syntheses of [VO(L)(OMe)] (1), [VO(L)(OEt)] (2a and 2b), [VO(L)(OPr)] (3a and 3b), and HL(acac)cycl (4). General Method

A: Syntheses of 1, 2a, 3a, and 4 from [VO(acac)2]. A stoichiometric amount of [VO(acac)2] (0.18 g, 0.66 mmol) was added to an alcoholic solution (20 mL) of H2L (0.20 g, 0.66 mmol). The solution almost immediately changed color to dark brown and was heated under reflux for 2 h. In the case of methanol as a solvent, compound 1 and small quantities of compound 4 crystallized on cooling of the reaction mixture. The methanolic mother liquid was allowed to stand at room temperature overnight, during which more yellow-brown crystals of 4 were obtained. In the case of ethanol and propanol as a solvent, compound 4 crystallized on cooling of the reaction mixture. The remaining mother liquids, for ethanolic and propanolic solutions, yielded within a day or two redbrown platelike crystals of 2a and black prismatic crystals of 3a (Figure 1). In each case, the products were filtered off and washed with a small amount of the corresponding alcohol. [VO(L)(OMe)] (1). Yield: 0.15 g (57%). Anal. Calcd for C16H16N3O4SV: C, 48.37; H, 4.06; N, 10.57; S, 8.07; V, 12.82. Found: C, 48.30; H, 4.02; N, 10.40; S, 7.98; V, 12.84. IR (KBr, cm 1): 3367 (υN H); 1605 (υCdN); 1285, 760 (υC S); 1227 (υC Ophen); 982 (υVdO). Melting point: 168 C. [VO(L)(OEt)] (2a). Yield: 0.11 g (41%). Anal. Calcd for C17H18N3O4SV: C, 49.64; H, 4.41; N, 10.22; S, 7.80; V, 12.38. Found: C, 49.51; H, 4.30; N, 10.17; S, 7.69; V, 12.40. IR (KBr, cm 1): 3419 (υN H); 1606 (υCdN); 1289, 762 (υC S); 1229 (υC Ophen); 992 (υVdO). Melting point: 142 C. [VO(L)(OPr)] (3a). Yield: 0.12 g (43%). Anal. Calcd, for C18H20N3O4SV: C, 50.82; H, 4.74; N, 9.88; S, 7.54; V, 11.98. Found: C, 50.58; H, 4.66; 5228

dx.doi.org/10.1021/cg200466b |Cryst. Growth Des. 2011, 11, 5227–5240

Crystal Growth & Design N, 10.15; S, 7.87; V, 11.79. IR (KBr, cm 1): 3343 (υN H); 1605 (υCdN); 1288, 759 (υC S); 1229 (υC Ophen); 988 (υVdO). Melting point: 136 C. HL(acac)cycl (4). Yield: 10 25 mg (4 10%). Anal. Calcd for C20H19N3O3S: C, 62.97; H, 5.02; N, 11.02; S, 8.41. Found: C, 62.88; H, 4.93; N, 11.06; S, 8.30. IR (KBr, cm 1): 1618, 1608, 1574, 1550 (υCdN/υCdO); 1320, 756 (υC S). Melting point: 246 C. The yield of 4 depended on the alcohol used, being the lowest for methanol and the highest for propanol. General Method B. Syntheses of 1, 2a, and 3a from [VO(OAc)2]. The syntheses were performed by a procedure similar to that described for method A, using [VO(OAc)2] (0.12 g, 0.67 mmol) instead of [VO(acac)2]. Reaction mixtures were refluxed for 4 h due to the poor solubility of [VO(OAc)2] in alcohols. After 1 2 days, crystals of 1, 2a, and 3a deposited, and were filtered off and dried. [VO(L)(OMe)] (1). Yield: 0.15 g (57%). [VO(L)(OEt)] (2a). Yield: 0.11 g (41%). [VO(L)(OPr)] (3a). Yield: 0.10 g (36%). General Method C. Syntheses of 1, 2b, 3b, and 4 from [V2O4(acac)2]. H2L (0.10 g, 0.33 mmol) was added to an alcoholic solution (10 mL) of [V2O4(acac)2] (60 mg, 0.17 mmol). The solution rapidly changed color to dark brown and was heated under reflux for 2 h. On cooling, reaction mixtures yielded black prismatic crystals of 1, black prismatic crystals of 2b, and red-brown platelike crystals of 3b, respectively (Figure 1). The crystals were filtered off, washed with a small amount of cold alcohol, and dried. Mother liquids were allowed to stand at room temperature, and after a few days yellow-brown crystals of compound 4 deposited. The crystals of 4 were filtered off, washed with a small amount of appropriate alcohol, and dried. [VO(L)(OMe)] (1). Yield: 0.11 g (84%). [VO(L)(OEt)] (2b). Yield: 0.09 g (66%). Anal. Calcd for C17H18N3O4SV: C, 49.64; H, 4.41; N, 10.22; S, 7.80; V, 12.38. Found: C, 49.72; H, 4.20; N, 10.37; S, 7.69; V, 11.87. IR (KBr, cm 1): 3344 (υN H); 1606 (υCdN); 1288, 756 (υC S); 1230 (υC Ophen); 988 (υVdO). Melting point: 143 C. [VO(L)(OPr)] (3b). Yield: 0.09 g (64%). Anal. Calcd for C18H20N3O4SV: C, 50.82; H, 4.74; N, 9.88; S, 7.54; V, 11.98. Found: C, 51.04; H, 4.53; N, 9.64; S, 7.81; V, 12.00. IR (KBr, cm 1): 3343 (υN H); 1603 (υCdN); 1284, 760 (υC S); 1225 (υC Ophen); 974 (υVdO). Melting point: 117 C. HL(acac)cycl (4). Yield: 10 25 mg (4 8%). Analytical and spectral data for compounds 1 and 4 obtained by methods B and C were in agreement with those prepared according to method A. Likewise, spectral and analytical data for compounds 2a and 3a obtained by method A were compatible with those prepared by method B. The structural identity of the compounds prepared by different methods was additionally confirmed by X-ray powder diffraction (PXRD) experiments (Figures S1 S3 of the Supporting Information). This method was also used, when possible, for the determination of the purity of bulk samples (Figures S1 S3 of the Supporting Information). The resulting crystals of 3b were very thin plates which, in most cases, diffracted only to the resolution limits not higher than 1.4 Å and produced weak, diffuse, and elongated diffraction maxima (as illustrated also by the powder diffraction pattern of the bulk sample, Figure S1(e) of the Supporting Information). After testing dozens of crystal specimens, finally a crystal of somewhat improved diffraction quality was luckily chosen. The crystal structure of 3b was then, at last, solved and refined against the diffraction data collected from a pseudomerohedric twin, as detailed in the Experimental Section. The structural model of 3b was confirmed through the correspondence between the calculated and the experimental powder patterns (Figure S3(c) of the Supporting Information). Since we had severe difficulties in obtaining the structural data on 3b by using the X-ray diffraction experiments, additional structural information

ARTICLE

Scheme 2.

*Recrystallization from diluted solutions. **Recrystallization from concentrated solutions. on the compound was obtained via solution NMR spectroscopy (for details see Supporting Information). Recrystallization Experiments. Upon recrystallization, compounds 2 and 3 were obtained either as polymorphic mixtures or, under certain conditions, as pure polymorphic phases (Scheme 2). All recrystallization experiments were performed in an identical way, by dissolving a certain amount of compound (2 or 3) in the corresponding alcohol (ethanol or propanol), under reflux and below the boiling point of the alcohol used. It was observed that the crystallization outcome depended on the solutions’ concentration, i.e. fast crystallization from concentrated solutions favored phases 2b and 3b, while diluted solutions yielded forms 2a and 3a, if not exclusively then predominantly (Scheme 2). The recrystallization outcome did not, however, depend on the initial polymorphic phase used. Pure form 2b was obtained from the following procedure: 100 mg of [VO(L)(OEt)] was dissolved in 7 mL of ethanol, under reflux, and the resulting solution was heated for 1 h. The solution was filtered, and its volume was then slightly reduced under vacuum. During such treatment, crystals of 2b started to form. In a similar fashion pure 3b was obtained, i.e. by dissolving 100 mg of [VO(L)(OPr)] in 4 mL of n-propanol, and then somewhat reducing the volume of the solution, thus inducing immediate crystallization. On the other hand, when the batches, approximately three or more times more diluted, were left to crystallize via slow evaporation overnight (or longer), pure forms 2a and 3a were obtained. Solutions having concentration within the above-mentioned range yielded generally a mixture of polymorphs. However, a higher fraction of forms 2a and 3a was obtained from more diluted solutions. Seeding as well as heteroseeding experiments have not revealed preferences toward any particular polymorphic phase. Competitive Slurry Experiments. In order to assess the thermodynamic relation between the polymorphs of 2 and 3, competitive slurry experiments were performed. For such experiments, a mixture of polymorphs 2 and 3 along with their mother liquids were exploited. First, each polymorphic mixture was isolated, dried, and then carefully grounded and subjected to PXRD analysis. The solid phase was then returned to its saturated solution (mother liquid) and stirred at room temperature. After 5 h, small amounts of solid phases were removed from the slurry and analyzed by PXRD. It was established that only one phase remained in both cases, 2a for 2, and 3a in the case of 3 (Figure S4 of the Supporting Information). Methods. Elemental analyses (C, H, N, and S) were provided by the Analytical Services Laboratory of the Rudjer Boskovic Institute, Zagreb, Croatia. Infrared spectra were recorded as KBr pellets using a PerkinElmer Fourier-transform spectrum RX1 spectrophotometer in the 4500 450 cm 1 region. Thermogravimetric analyses were performed 5229


Crystal Growth & Design on a Mettler-Toledo TGA/SDTA851e thermobalance using aluminum crucibles under oxygen atmosphere with the heating rate 5 C min 1. In all experiments the temperature ranged from 25 to 600 C. The results were processed with the Mettler STARe 9.01 software. DSC measurements were performed on the Mettler-Toledo DSC823e calorimeter with STARe SW 9.01 in the range from 25 to 200 C (5 C min 1) under the nitrogen stream. The one- and two-dimensional 1H and 13C NMR spectra of complexes 3 were recorded in methanol-d4 with a Bruker AV-600 spectrometer, operating at 600.13 MHz for 1H spectra and at 150.90 MHz for 13C spectra. The 1H 1H COSY spectra were obtained in the magnitude mode with 2048 points in the F2 dimension and 512 increments in the F1 dimension. The 1H 13C HMQC spectra were measured with the one-bond C,H coupling value set to 145 Hz, using 2048 points in the F2 dimension and 256 increments in the F1 dimension. The 1H 13C HMBC spectra were measured with the C,H coupling value set to 145 and 8 Hz using 2048 points in the F2 dimension and 256 increments in the F1 dimension. All two-dimensional experiments were performed by standard pulse sequences using Bruker XWIN-NMR software Version 3.5. Hot-stage microscopy was performed on a Linkam hot stage Olympus BX51 optical microscope with magnification 20. The sample of 3b was heated in the temperature range 25 130 C, with the heating rate 5 C/min on a glass plate sample holder (15 mm diameter). X-ray powder diffraction experiments were performed on a Philips PW 3710 diffractometer, Cu Kα radiation, flat plate sample on a zero background sample holder in the Bragg Brentano geometry (40 kV and 40 mA). The patterns were collected in the angle region between 4 and 50 (2θ) with a step size of 0.02 and 1.5 s per step. Single-Crystal X-ray Diffraction Experiments. Selected crystallographic and refinement data for structures 1, 2a, 2b, 3a, 3b, and 4, obtained by the single-crystal X-ray diffraction experiments, are reported in Table 1. The data for all structures were collected by ω-scans on an Oxford Xcalibur diffractometer equipped with a four-circle k geometry goniometer, a CCD Sapphire 3 detector, and graphite-monochromated Mo Ka radiation (λ = 0.71073 Å). The data reduction, including the empirical absorption correction, as well as reconstruction of the precession images were performed using the CrysAlis software package.14 Structures were solved by direct methods and refined on F2 by a weighted full-matrix least-squares method. The programs SHELXS9715 and SHELXL-9715 integrated in the WinGX software system16 were used to solve and refine the structures. All non-hydrogen atoms were refined anisotropically. The significant discrepancy in the maximal and minimal residual electron densities (1.63 and 0.30 e Å 3) for the preliminary model of 2b, which contained only the major disorder component, alerted us to carefully check the corresponding difference Fourier map. Peaks in the difference Fourier map analyzed in Coot17 revealed an additional, significantly less occupied position of the two crystallographically independent molecules [refined population parameter = 0.0373(5)] (Figure S5 of the Supporting Information). Molecules in the minor position were refined by using very strict restraints on the molecular geometry (instructions NCSY and SAME related to the molecular geometry for the major site with the effective standard deviations of 0.0001) and with ADPs exactly identical to the corresponding ones in the major site (EADP). The structure of 3b was refined in the triclinic space group P1 as twinned by pseudomerohedry with the twin law (1 0 0/0 1 0/1 0 1) and the twin-scale factor 0.307(2). The twin law corresponds to a 2-fold rotation around the a axis of the triclinic unit cell (Table 1). Namely, the triclinic unit cell of 3b can be transformed to the metrically equivalent C-centered monoclinic one with the unique b axis being the same as the triclinic a axis, which explains the observed pseudomerohedric twinning. The restraints on geometrical and displacement parameters (SAME, DELU, ISOR, and SIMU) were applied for the disordered propoxo residues in 3a and 3b. Hydrogen atoms attached to carbon atoms were placed in geometrically idealized positions and refined using the riding model. In the structures of

ARTICLE

vanadium complexes, the hydrogen atom attached to the amino N1 atom was located in the difference Fourier maps at the final stages of the refinement procedure and its coordinates were refined freely but with the restrained N H distance of 0.87 and 0.88 Å for the data collected at 296 K (1 and 2a) and 120 K (2b and 3a), respectively, except for 3b, where N1 bounded hydrogen atoms were refined using the riding model. The geometrical calculations and structural analyses were done using PLATON18 and CrystalExplorer.19 Drawings were made by ORTEP3,20 POV-Ray,21 PLATON18, and Mercury.22 The main geometrical features (selected bond distances and angles, dihedral angles) along with the hydrogen bond geometry for all examined structures are given in Tables S1 S6 of the Supporting Information.

’ RESULTS AND DISCUSSION The alkoxooxovanadium(V) complexes of general formula [VO(L)(OR)] (1 3) were prepared by the reaction of 4-methoxysalicylaldehyde 4-phenylthiosemicarbazone (H2L) and selected vanadium(IV) and vanadium(V) precursors ([VO(acac)2], [VO(OAc)2], [V2O4(acac)2]) as presented in Scheme 1. All synthetic procedures were performed in alcohols (methanol, ethanol, and propanol), with allowed access of air. In all isolated complexes, vanadium is present as vanadium(V), which illustrates its well pronounced tendency to undergo rather slow oxidation in alcoholic solutions by molecular oxygen.23 Moreover, all complexes [VO(L)(OR)] (1 3) were obtained in substantially higher yields when synthesized from [V2O4(acac)2] than from vanadium(IV) precursors, which is likely due to retention of the vanadium oxidation state.9c When [VO(acac)2] or [V2O4(acac)2] was employed as the starting materials, reactions also yielded thiazoline compound HL(acac)cycl (4) (Scheme 1). During this work it was observed that complexes [VO(L)(OEt)] (2) and [VO(L)(OPr)] (3), unlike [VO(L)(OMe)] (1), crystallize in two different forms (Figure 1, Scheme 2). Interestingly, we became aware that, by utilizing either the vanadium(IV) or vanadium(V) precursor, the occurrence of targeted polymorph(s) can be controlled (Figures S1 and S2 of the Supporting Information). In particular, when [VO(acac)2] or [VO(OAc)2] was used, reaction mixtures yielded exclusively reddish-brown platelike crystals of 2a (ethanolic solution; Figure 1a) and black prismatic crystals of 3a (propanolic solution, Figure 1c). On the contrary, when [V2O4(acac)2] was utilized for the synthesis, black prismatic crystals of 2b (Figure 1b), morphologically fairly similar to those of 3a, and brown platelike crystals of 3b (Figure 1d), of poor diffraction quality, were isolated. Furthermore, when reactions were performed with [VO(acac)2] or [VO(OAc)2], compounds 2 and 3, i.e. polymorphs 2a and 3a, crystallized much more slowly. It is important to note that in the case of [VO(acac)2] or [VO(OAc)2] vanadium ions are oxidized during the reaction, whereas in the case of the vanadium(V) precursor, the same oxidation state is retained in the final product, [VO(L)(OR)]. To inspect further the occurrence conditions for each polymorphic phase, a number of recrystallization experiments were performed. It was observed that immediate crystallization from concentrated solutions (Experimental Section) yielded, regardless of the starting polymorph used, pure forms 2b and 3b. On the other hand, as the solution concentration was lowered, polymorphic mixtures were obtained. Finally, when slow crystallization was allowed from rather diluted solutions, regardless of the initial form used (Experimental Section), we were able to obtain pure forms of 2a and 3a. On the basis of these results, the 5230


397.32

monoclinic, black prism

crystal system,

0.30,

0.97

0.0765 0.27

0.0279 0.0487, 0.00

(0.022), 5210

17982, 7047

632/241

1.512

1696

120(2) 0.692

3613.64(16)

90

96.51(1)

90

18.5559(5)

15.7746(4)

12.4255(3)

a R = ∑ Fo| |Fc /∑|Fo|. b w = 1/[σ2(Fo2) + (g1P)2 + g2P], where P = (Fo2 + 2Fc2)/3. c wR = {∑[w(Fo2 independent reflections, Np = number of refined parameters.

density (e Å 3)

0.39

0.45,

0.33,

0.27

0.89

0.89

goodness of fit on F2, Sd

max., min electron

0.1303

0.0812

wR2c (all data)

(0.048), 2864

9134, 5152 0.0534 0.0672, 0.00

(0.038), 2358

0.0368 0.0395, 0.00

R1a [I g 2σ(I)] g1, g2 in wb

Rint, observed [I g 2σ(I)]

reflections collected, unique,

12518, 3688

240/1

231/1

no. refined parameters,

Np /restraints

1.517

1.554

)

)

5231

424

816

Dcalc (g cm 3)

296(2) 0.695

900.4(3)

71.45(2)

F(000)

1698.46(15)

V (Å3)

296(2) 0.734

90

γ (deg)

86.73(2)

87.32(2)

13.592(3)

9.693(2)

7.2239(11)

T (K) μ (mm 1)

90

16.3811(9)

c (Å)

125.60(1)

10.3757(4)

b (Å)

β (deg)

12.2897(5)

unit cell parameters: a (Å)

α (deg)

4

Z 8

P21/c

P1 2

0.46 0.44 0.10

0.40 0.20 0.08

0.18 0.14 0.10

P21/c

0.31,

1.06

0.0772 0.39

0.0284 0.0424, 0.606

(0.020), 6467

33918, 8127

508/129

1.504

1760

120(2) 0.669

3756.60(16)

90

97.975(2)

90

19.1848(5)

15.9862(4)

12.3684(3)

8

P21/c

0.40 0.30 0.15


425.37

C18H20N3O4SV

3a

3b

0.67,

0.99

0.2379

Fc2)2]/(Nr

0.83

0.0827 0.1152, 0.00

(0.068), 7002

26016, 12613

1022/108

1.484

1760

296(2) 0.660

3808.6(7)

89.875(9)

80.838(9)

88.183(8)

30.452(3)

12.9941(14)

9.7545(11)

8

P1

0.36 0.11 0.03

triclinic, red-brown plate

425.37

C18H20N3O4SV

Fc2)2]/∑[w(Fo2)2]}1/2. d S = {∑[w(Fo2


411.34

C17H18N3O4SV

2b

space group

triclinic, red-brown plate

411.34

C17H18N3O4SV

2a

crystal dimensions (mm3)

color and habit

C16H16N3O4SV

chemical formula

Mr

1

Table 1. Crystallographic Data for 1, 2a, 2b, 3a, 3b, and 4

0.22

Np)}1/2, where Nr = number of

0.23,

1.04

0.1393

0.0508 0.0596, 0.1063

(0.039), 2490

13922, 3954

248/0

1.358

400

296(2) 0.199

933.25(6)

95.380(4)

110.803(4)

95.346(3)

10.5474(3)

10.0727(4)

9.5269(4)

2

P1

0.22 0.10 0.03

triclinic, yellow-brown prism

381.44

C20H19N3O3S

4

Crystal Growth & Design ARTICLE



ARTICLE

Figure 2. ORTEP-POV-Ray rendered view of the compounds: (a) 1 and (b) 2a with atom labeling schemes. The displacement ellipsoids are drawn at the 50% probability level at 296 K. The full atom-numbering scheme for 1 and 2a is given in Figure S6 of the Supporting Information.

Figure 3. ORTEP-POV-Ray rendered view of the: (a) asymmetric unit of the major component of 2b [site occupancy factor 0.9627(5)]; (b) asymmetric units of both major (molecules A and B) and minor components (molecules C and D) of 2b with atom labeling schemes. The atoms of the minor component are presented in brighter colors, and bonds are drawn with dashed lines. The displacement ellipsoids are drawn at the 50% probability level at 120 K. The full atom-numbering scheme is given in Figure S6(d) of the Supporting Information.

occurrence of a particular polymorph via synthetic approaches using V(IV) or V(V) precursors can be tentatively associated with the additional oxidation step required in the case of vanadium(IV) compounds. Among different approaches to the polymorphic resolution, seeding experiments have recently drawn particular attention.1b,3c,24 Especially interesting are those employing heteromolecular seeds of isostructural or quasi-isostructural species.25 In some cases, such procedures have been used for the separation of concomitant polymorphs26 or, more interestingly, have led to crystallization of otherwise unyielding compounds.27 However, in our systems this approach has not resulted in the resolution between the polymorphic species, nor did it yield any new phases. Molecular Structures of Vanadium Complexes 1 3. The molecular structures of 1, 2a, 2b, 3a, and 3b are presented in Figures 2 5 and Figure S6 of the Supporting Information. The asymmetric units of 2b and 3a contain two crystallographically independent molecules depicted as A and B (Figure 3a and Figure 4). Due to the stacking disorder, which is discussed in

more detail later in the text, the two crystallographically independent molecules in 2b are also found at an additional position with 4% occupancy (molecules C and D; Figure 3b). Since the geometry of the minor component was held very strictly restrained during refinement, only the geometry of the major component (molecules A and B) is discussed. The asymmetric unit of 3b is composed of four molecules denoted as A, B, C, and D (Figure 5). In all complexes the vanadium(V) ion assumes a distorted tetragonal pyramidal environment with the VO3+ moiety serving as a main building unit. Such a VO3+ core accommodates the 4-salicylaldehyde 4-phenylthiosemicarbazonato ligand via an ONS-donor set and the alkoxo moiety through the (O4) oxygen atom (Figures 2 5). Bond distances within the ligand support the fact that the 4-phenylthiosemicarbazonato ligand acts in all complexes in the enthiolate form (Scheme S2, Table S1 of the Supporting Information) with the deprotonation at the sulfur S1 atom.28 More precisely, the ligand acts in an anionic, doubly deprotonated (at phenolic O1 atom and thiolato-sulfur S1 atom) 5232


Crystal Growth & Design tridentate form realizing bonds with vanadium ion through the phenolic-oxygen O1, imine-nitrogen N3, and thiolato-sulfur S1 atoms (Table S1 of the Supporting Information). In such a way, two chelate rings, five-membered and six-membered with the imine N3 atom acting as a common atom, form a bicyclic system slightly folded along the V1 N3 axis. Moreover, through the dianionic ONS coordination mode of the ligand, the N2 C1 bond becomes predominantly imine in character,28 while the N1 C1, N2 N3, and C4 O1 bonds remain mostly single in nature (Table S1 of the Supporting Information).29

Figure 4. ORTEP-POV-Ray rendered view of the asymmetric unit of 3a with atom labeling schemes. The displacement ellipsoids are drawn at the 50% probability level at 120 K. The full atom-numbering scheme is given in Figure S6(e) of the Supporting Information. The disordered alkoxo group in the position with lower occupancy [0.208(3)] is shown in light gray, and bonds are represented as dashed lines.

ARTICLE

The donor atoms of both thiosemicarbazonato and the alkoxo ligands (O1, N3, S1, and O4) are arranged in such a way to form a basal plane. The vanadium ion is shifted from such a plane toward the apical oxygen O3 atom by 0.519(1) Å (1), 0.550(1) Å (2a), 0.494(1) and 0.502(1) Å (2b), 0.501(1) and 0.490(1) Å (3a), and 0.516(2) 0.526(2) Å (3b). The τ-descriptor30 (Table S1 of the Supporting Information), being in the range 0.214 0.313, suggests the prevalence of the tetragonal pyramidal coordination environment, although a certain distortion toward a trigonal bipyramid exists. The similar τ-values (0.28 0.38) are found in the vanadium complexes with thiosemicarbazone derivatives.9,28,31 In all herein structurally investigated complexes the intramolecular hydrogen bond, C10 H10 3 3 3 N2, is found with similar geometrical parameters (Table 2, Figure S6 of the Supporting Information). Conformational Diversity of Vanadium Complexes 2 and 3. Overlapping diagrams for molecules comprising crystal structures of 2a, 2b, 3a, and 3b are shown in Figure 6. As expected, the largest differences in conformations among the investigated complexes are observed in the spatial position of the flexible alkoxo residues. Nonetheless, a noticeable degree of conformational variation is also observed in the arrangement of the aromatic rings of the coordinated ligand (rings I and II, Figure 6). Comparison of molecules A and B of 2b reveals a subtle dissimilarity in the spatial position of both aromatic rings and the ethoxo residues, whereas their arrangement in 2a is significantly different (Figure 6a, Tables S2 and S3 of the Supporting Information). In 3a, molecules A and B are similar with respect to the position of the aromatic rings, while the position of their propoxo residues significantly differs. In particular, the alkoxo moieties in 3a assume overall three conformations due to a discrete positional disorder of the propoxo residue of molecule B

Figure 5. ORTEP-POV-Ray rendered view of the crystallographically independent molecules A, B, C, and D in the structure of 3b with atom labeling schemes. Due to clarity, molecules B and D are not presented in their real positions relative to molecules A and C within the same asymmetric unit. The displacement ellipsoids are drawn at the 50% probability level at 296 K. The full atom-numbering scheme is given in Figure S6(f) of the Supporting Information. The disordered propoxo groups in the positions with lower occupancies [0.30(2) for molecule A; 0.22(2) for molecule B] are shown in light gray with the corresponding bonds represented as dashed lines. 5233



ARTICLE

Table 2. Hydrogen Bond Geometry (Å, deg) for Complexes 1 3 and Geometrical Parameters of C H 3 3 3 π Interactions (Å, deg) for 2b and 3a Compoundsa D H3 3 3A

D H

H3 3 3A

D3 3 3A

—D H 3 3 3 A

symmetry code

1 C10 H10 3 3 3 N2 N1 H1N 3 3 3 O3 C13 H13 3 3 3 O2

0.93

2.31

2.920(4)

122

0.83(2) 0.93

2.66(2) 2.63

3.479(2) 3.497(4)

167(1) 156(1)

2.898(3)

118

122

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

z

2a C10 H10 3 3 3 N2

0.93

2.34

C10A H10A 3 3 3 N2A C10B H10B 3 3 3 N2B

0.95

2.25

2.873(2)

0.95

2.25

2.868(2)

122

N1A H1NA 3 3 3 O3B N1B H1NB 3 3 3 O3A C15A H15C 3 3 3 O3B C15B H15E 3 3 3 O3A

0.81(2)

2.31(2)

3.091(2)

163(2)

0.83(2)

2.20 (2)

3.002(2)

161(2)

0.98 0.98

2.49 2.52

3.186(2) 3.193(2)

128 126

1 + x, y, z

C16A H16A 3 3 3 O4A

0.99

2.74

3.493(2)

133

1

x, 1

C10A H10A 3 3 3 N2A C10B H10B 3 3 3 N2B

0.95

2.27

2.883(2)

122

0.95

2.25

2.872(2)

122

N1A H1NA 3 3 3 O3B N1B H1NB 3 3 3 O3A

0.84(2)

2.24(2)

3.064(2)

164(2)

0.82(2)

2.22(2)

3.026(2)

166(2)

x

1, y, z

0.98

2.44

3.194(2)

134

1 + x, y, z

0.98 0.99

2.63 2.54

3.257(2) 3.451(2)

122 154

1

C10A H10A 3 3 3 N2A C10B H10B 3 3 3 N2B

0.93

2.36

2.914(15)

118

0.93

2.41

2.961(11)

118

C10D H10D 3 3 3 N2C C10D H10D 3 3 3 N2D N1A H1NA 3 3 3 O3B

0.93

2.33

2.927(15)

121

0.93

2.36

2.928(11)

119

0.86

2.26

3.104(9)

169

0.86 0.86

2.26 2.27

3.114(9) 3.125(10)

174 176

1 + x, y, z

0.86

2.27

3.122(9)

172

x

2b

x

1, y, z

y,

z

y,

z

3a

C15A H15C 3 3 3 O3B C15B H15E 3 3 3 O3A C16A H16A 3 3 3 O4A

x, 1

3b

N1B H1NB 3 3 3 O3A N1C H1NC 3 3 3 O3D N1D H1ND 3 3 3 O3C C H 3 3 3 Cg

C 3 3 3 Cg

C17A H17A 3 3 3 Cg(10)b, i

3.806(3)

C18A H18C 3 3 3 Cg(10)i

3.748(2)

C H3 3 3π H 3 3 3 Cg

1, y, z

— C H 3 3 3 Cg

βc

2.97

144

55

2.90

146

56

2b

3a a

Symmetry code: i = 1 + x, 1/2 y, z 1/2. b Cg(10) in 2b and 3a is defined by the N-phenyl atoms C9B, C10B, C11B, C12B, C13B, and C14B. The atoms C17A in 2b and C18A in 3a belong to the methyl groups of the ethoxo and propoxo residues in 2b and 3a, respectively. c Angle between a line through the C H bond and the ring plane.

(Figure 6b, Table S2 of the Supporting Information). The arrangements of both aromatic rings are almost identical for all four crystallographically independent molecules in 3b. Although the conformations of the propoxo residues in 3b are very similar to those observed in 3a, the positions of the aromatic rings I in 3b are significantly distinct from those in 3a (Figure 6c and d and Table S2 of the Supporting Information). On the basis of previous considerations, pairs 2a and 2b as well as 3a and 3b can be described as conformational polymorphs, while

the conformational differences among them can be best understood on the basis of the dissimilarities in the crystal environment (Table 2). On the other hand, the crystallographically independent molecules of 2b, 3a, and 3b display, as Corradini termed it, conformational isomorphism, due to the presence of different conformers in their crystal structure.1b,2 Moreover, since molecules in 3a and 3b exhibit a discrete positional disorder, it could also be stated that these particular structures exhibit a conformational synmorphism.1b,2 5234



ARTICLE

Figure 6. Mercury-POV-Ray rendered view of overlapping diagrams for: (a) 2a (dark gray) and 2b (orange, molecule A; red, molecule B); (b) 3a (purple, molecule A; blue, molecule B; the disordered alkoxo group of the molecule B in the position with lower occupancy, light gray); (c) 3b (red, molecule A; gold, molecule B; black, molecule C; green, molecule D; the disordered alkoxo group of the molecule A in the position with lower occupancy, dark gray; the disordered alkoxo group of the molecule B in the position with lower occupancy, light gray); (d) 3a and 3b (the coloring code is the same as in parts b and c). Diagrams were constructed by overlapping molecules through V1, O1, O4, N3, and S1 atoms. Dihedral angles between the planes of the N-phenyl (I; atoms C9 C14) and salicylidene (II; atoms C3 C8) rings are 25.79(15) (2a), 12.34(8) (2b, A), 13.18(8) (2b, B), 14.72(8) (3a, A), 12.65(8) (3a, B), 21.4(5) (3b, A), 23.3(5) (3b, B), 22.1(5) (3b, C), and 19.5(5) (3b, D).

Crystal Structures of Vanadium Complexes 1 3. Packing diagrams of the crystal structures of the complexes are presented in Figures S9 S12 of the Supporting Information. In the structure of 1 the relatively long N1 H1N 3 3 3 O3 interaction (Figure 7) has been revealed by carefully checking the intermolecular contacts. Its existence is additionally supported by the fingerprint plot derived from the Hirshfeld surface for 1 in comparison with the fingerprint plots for other vanadium complexes (Figure S12 of the Supporting Information). This particular interaction associates molecules of 1 into infinite chains which rise along the b axis. However, no further interactions except those of van der Waals type are found between chains (Figure S9 of the Supporting Information). Comparison of the crystal architectures of the polymorphs 2a and 2b reveals substantial differences between them (Table 2). Unlike the rest of the herein structurally investigated complexes, in the structure of 2a a good hydrogen bond donor (N1 H) remains unemployed, thus leaving the architecture stabilized exclusively through van der Waals’ interactions. Such an array of interactions in 2a can be at least partially related to the significantly different spatial arrangement of the ethoxo moiety in this structure, when compared to other complexes (Figure 6). On the contrary, the architecture of 2b is stabilized by a plethora of intermolecular interactions: N H 3 3 3 O, C H 3 3 3 O, and C H 3 3 3 π. More precisely, the two conformers of 2b (A and B) are alternately assembled via N1 H1N 3 3 3 O3 hydrogen bonds and C15 H15 3 3 3 O3 interactions into molecular chains which extend along the a axis (Figure S10 of the Supporting Information). Such chains are further arranged in the molecular layers parallel to the ab-plane. The van der Waals interactions along with the weak C H 3 3 3 π interactions,32,33 between the H atoms of the methyl groups of the ethoxo residuals in A molecules and the π system of the N-phenyl ring in B molecules,

Figure 7. Crystal packing in 1 showing two one-dimensional, infinite chains of molecules assembled via relatively long N1 H1N 3 3 3 O3 interactions along the b-axis. N1 H1N 3 3 3 O3 interactions are presented by yellow dashed lines. Molecules are viewed down the a-axis.

assemble the molecular layers into the final three-dimensional crystal architecture (Table 2). Several known examples of isostructurality with the alkoxo functional group exchange (e.g., methoxy ethoxy or ethoxy propoxy)34 and almost identical morphology of the 2b and 3a crystals led us to consider their possible isostructurality. The initial requirement in such considerations is the similarity of unit cells of the examined compounds, which can be easily tested by comparison of their powder patterns (Figure 8). However, more precise way of establishing the degree of similarity between the unit cells is by calculating the unit-cell similarity index (Π), which should be close to zero for similar unit cells.5b For herein inspected structures, 2b and 3a, the unit-cell similarity index (Π) was found to be 0.016. To achieve similar internal arrangement, besides unit cell similarity, molecules should not differ substantially in their structure, i.e. they should be isometric.5 2b and 3a fulfill such requirement, since their molecular structures differ only in one CH2 moiety. Finally, the two isostructural crystals should exhibit identical or quasi-identical packing motifs. Probably the 5235


Crystal Growth & Design best way of estimating the resemblance of packing patterns is achieved by overlapping the two structures. Such comparison revealed nearly the same solid-state architecture for 2b and 3a, thus affirming their isostructurality (Figure 9 and Figures S10 and S11 of the Supporting Information). The only difference in intermolecular interactions between 2b and 3a is the geometry of the C16A H16A 3 3 3 O4A hydrogen bond which mutually joins molecules A via an ethoxo (2b) or propoxo (3a) methylene group and the atom O4A of the adjacent A molecule (Table 2, Figure 9, and Figures S10 and S11 of the Supporting Information).

Figure 8. Comparison of powder patterns for compounds 2b (pink) and 3a (blue) indicating the similarity of their unit cells.

ARTICLE

Careful analysis of the initial structural model of 2b (containing only molecules A and B) revealed significant maxima in the corresponding difference electron density map (Figure S5 of the Supporting Information). These were ascribed to the alternative positions of the two crystallographically independent molecules with 4% occupancy (denoted as molecules C and D). The two disorder components are approximately related by the noncrystallographic inversion operator 1/2 x, 3/4 y, 1/2 z. The true nature of the disorder was revealed in the reconstructed layers of the reciprocal space. Streaks of diffuse scattering parallel to the c* reciprocal axis (Figure 10a) were a clear indicator of the stacking disorder along the crystallographic c axis.35 While the molecular ab-layers are ordered in two dimensions, 4% of them are stacked along the c axis in the alternative orientation, not related by the crystallographic symmetry to the major orientation (Figure 9b). As could be expected, all C H 3 3 3 π and van der Waals interactions between a properly stacked and the adjacent mis-stacked layer are almost the same as those between the two properly stacked layers, thus accounting for the observed disorder in the crystals of the polymorph 2b. More detailed characterization of the disorder in 2b would require more extensive analysis of the diffuse scattering profiles. In the structure of 3b, the N1 H1N 3 3 3 O3 hydrogen bonds (Table 2) link the molecules in the infinite chains parallel to the crystallographic a axis (Figure 11a). Such a one-dimensional molecular arrangement is very similar to the one found in the crystal architecture of 1 (Figure 7). The molecular chains in 3b

Figure 9. Packing similarities of the isostructural pair 2b and 3a. Molecules of 2b are presented as dark-red (molecule A) and orange (molecule B). Molecules of 3a are presented as dark-gray (molecule A) and light-gray (molecule B). Intermolecular interactions relevant for discussion are denoted as orange (between the molecules of 2b) and black (between the molecules of 3a) dashed lines. 5236


Crystal Growth & Design are further assembled in molecular layers parallel to the ab-plane. Interestingly, the two adjacent molecular layers are joined only by van der Waals’ interactions (Figure 11b). These weak and nonspecific interactions presumably allow the molecular layers in crystals of 3b to glide over each other. This induces disorder and defects in the crystal structure and ultimately results in the observed foliation of the platelike crystals and the reduced diffraction quality (Figure S1(e) of the Supporting Information). Thermal Analyses and IR Spectroscopy. The thermal analyses (TGA/SDTA experiment) of compounds 1 3 were conducted under the oxygen atmosphere in the temperature range between 25 and 600 C, and they revealed for all investigated vanadium complexes similar decomposition patterns (Supporting Information, Figure S13). The first peak (endothermic) observed on the SDTA curve, which was not followed by the weight loss according to TG analyses, was assigned to the melting point of the particular complex. Immediately after the melting, deterioration of the complexes began, as indicated by an exotherm on the SDTA curve and the first weight loss observed on the TGA curve. This step was assigned to loss of the alkoxo moieties and was immediately followed by the second thermic event. The second step was ascribed to decomposition of the thiosemicarbazonato ligand, which in all cases ended around 500 C. The remaining residues were found to be V2O5 (XRPD) and were used to establish the percentage of vanadium in the synthesized complexes (Experimental Section). DSC measurements (N2 atmosphere; temperature range between 25 and 200 C; Figure S14 of the Supporting Information) were additionally performed to establish more precisely the melting points of the investigated compounds as well as to explore the nature of the polymorphic systems 2 and 3. On the basis of these measurements, it was established that polymorph 2b (143 C) melts at only slightly higher temperature than 2a (142 C), which is particularly interesting, since a greater variety of intermolecular interactions is observed in the crystals of 2b. On the other hand, such a resemblance of melting points prompted us to investigate the possibility of a phase transition, although DSC curves have not revealed any peaks which could be correlated with such thermal events. Nonetheless, both samples were heated to 140 C, i.e. just before their melting points, and then cooled to room temperature (Supporting Information, Figures S15 S16). The powder patterns of samples, both 2a and 2b, before and after thermal treatment were the same, thus revealing that no phase transition occurred in either case. The melting points of 3a and 3b, on the other hand, differed by approximately 20 C, being higher for 3a (136 C). When assessing the relative thermodynamic stability between the polymorphs, several approaches can be used. For compounds that melt without decomposition, a thermodynamic relation is usually established upon melting points and heat of fusion data or several other Burger and Ramberger rules.1b,36 Otherwise, a simple technique, competitive slurry evaluation in combination with melting points, might be more appropriate for such an evaluation.36a,37 A typical procedure involves suspending the mixture of polymorphs in a solvent that is saturated with the investigated compound. The resulting slurry is then stirred, and the more stable polymorph, at a given temperature, should be the only remaining phase after a certain period. To establish if a system is enantiotropic or monotropic, such an evaluation is carried out at the lowest investigated temperature. If the polymorph that is stable at this lowest temperature has, at the same time, the highest melting point, the system is monotropic in this temperature range.36 Herein, such experiments were conducted

ARTICLE

Figure 10. Stacking disorder in 2b. (a) Detail of the reconstructed 5kl precession image. Diffuse scattering streaks are visible along c*. (b) Four percent of the molecular ab-layers are found in the different (minor) orientations randomly distributed throughout the crystal structure and not related by the crystallographic symmetry to the major orientation. The accompanying stacking faults do not significantly perturb the interactions between the layers. Molecules in the major orientation are denoted in purple (molecules A) and bluish-gray (molecules B), while those in the minor orientation are shown in brown (molecules C) and orange (molecules D).

at room temperature, and according to slurry evaluation, polymorphs 2a and 3a were established as more stable under these conditions (Figure S4 of the Supporting Information). Since 3a has at the same time a higher melting point, it can be concluded that dimorphs of 3 are monotropically related and 3a is thermodynamically stable. In the case of 2, such an assessment is rather delicate, since the polymorphs have fairly similar melting points. Although the results indicate that the system might be enantiotropic, since 2a has a somewhat lower melting point, in this particular case it is very hard to conclude such a relation with certainty. The IR spectra of complexes 1 3 are fairly similar and are characterized by a single strong band in the region between 3320 cm 1 and 3440 cm 1 due to the N1 H stretching, and the VdO stretch in the range 974 992 cm 1. The remaining features of their spectra are in agreement with the established enthiolate ONS coordinating mode of the ligand (Figures S19 and S20 of the Supporting Information). Although the spectra of the polymorphic complexes 2a and 2b, as well as 3a and 3b resemble each other, on close inspection some interesting dissimilarities are observed. Namely, complex 2a exhibits a band at 3419 cm 1 due to N1 H stretching (Figure S20(b) of the Supporting Information), whereas in the spectrum of 2b the same band is found at 3344 cm 1 (Figure S20(c) of the Supporting Information). Additionally, a band assigned to VdO stretching is observed at 992 cm 1 for 2a and at 988 cm 1 for 2b. Such dissimilarities account for different packing interactions in the solid state, in particular hydrogen bonding. As has been established, intermolecular hydrogen bonds of the N1 H 3 3 3 OdV type are not 5237



ARTICLE

Figure 11. Crystal packing in 3b showing: (a) two one-dimensional, infinite chains of molecules assembled along the a-axis via N1 H1N 3 3 3 O3 hydrogen bonds (presented by yellow dashed lines); the hydrogen atoms, except for H1N, are not presented for clarity); (b) the molecular layers parallel to the ab-plane which are mutually joined only by van der Waals’ interactions. Molecules in part b are viewed down the a-axis, and the crystallographically independent molecules are depicted in different colors.

present in the structure of 2a, whereas in 2b they represent dominant packing interactions. The difference for complexes 3 is observed only in the position of ν(VdO), which is found at 988 cm 1 for 3a and at 974 cm 1 for 3b (Figures S20(d) and S20(e) of the Supporting Information), which is indicative of the involvement of the VdO group in hydrogen bonding. On the other hand, being characterized by nearly the same solid-state architecture, complexes 2b and 3a display IR bands of the N1 H and VdO stretching at virtually the same wavenumbers, 3344/3343 cm 1 and 988 cm 1, respectively (Figures S20(c) and S20(d) of the Supporting Information).

’ CONCLUSIONS A series of new alkoxooxovanadium(V) complexes [VO(L)(OR)] (1 3) was prepared by the reaction of 4-methoxysalicylaldehyde 4-phenylthiosemicarbazone (H2L) and the selected vanadium precursors: [VO(acac)2], [VO(OAc)2], or [V2O4(acac)2]. Unlike [VO(L)(OMe)] (1), complexes [VO(L)(OEt)] (2) and [VO(L)(OPr)] (3) crystallized as dimorphs. In both cases, employment of vanadium precursors of the different oxidation states proved to be a rather simple routine for obtaining pure polymorphic phases. Namely, vanadium(IV) precursors yielded polymorphs 2a and 3a, whereas the use of [V2O4(acac)2] led to the isolation of forms 2b and 3b. Both 2 and 3 display conformational richness which is manifested in several phenomena: conformational isomorphism (2b, 3a, and 3b), conformational synmorphism (3a and 3b), conformational polymorphism (2a and 2b, 3a and 3b) and isostructurality (2b and 3a). The structure of 2b, in contrast to its isostructural 3a, is characterized by disorder in layer stacking which can be, at least partially, correlated with different crystallization conditions. Dimorphs of both 2 and 3 do not exhibit phase transitions upon heating. On the basis of the additional competitive slurry evaluation, polymorphs of 3 were found to constitute a monotropic system with 3a being thermodynamically stable. The thermodynamic relation between dimorphs of 2 could not be established with certainty due to too similar melting points. However, on the basis of the slurry experiment, 2a was found to be the stable form at room temperature.

This apparently simple system provided us with the opportunity to study a variety of solid-state phenomena, but also with the prospect of polymorph control through utilization of metal precursors differing in oxidation states. This approach thus seems to open novel possibilities for polymorph resolution but requires a detailed knowledge of solution chemistry, which is the subject of our current studies.

’ ASSOCIATED CONTENT

bS

Supporting Information. Detailed X-ray crystallography for vanadium complexes 1, 2a, 2b, 3a, and 3b: XRPD patterns and their comparison; selected geometrical parameters; packing diagrams; and stacking disorder in 2b. Thermal analyses and infrared spectra of vanadium complexes 1 3 as well as thiazoline compound HL(acac)cycl (4). Detailed synthetic and crystallographic discussion for compound 4. The CCDC reference numbers for compounds 1, 2a, 2b, 3a, 4, and 3b are 757678 757682 and 836818, respectively. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT This research was supported by the Ministry of Science, Education and Sports of the Republic of Croatia (Grant Nos. 119-1191342-1082, 098-1191344-2943, and 119-1193079-1084). We are thankful to Dr. Krunoslav Uzarevic and Dr. Ivica îlovic for preliminary X-ray crystallographic analyses of crystals of 2b and 1a, and 2a, respectively, as well as for the most helpful discussions. We are also grateful to Dr. Ivan Halasz for productive discussions and helpful suggestions. Moreover, we are grateful to dipl.ing. Marina Ratkaj, Mr. Edislav Leksic, and Prof. Ernest Mestrovic for hot stage microscopy. Finally, we would like to thank Dr. Laszlo Fabian and Prof. Alajos Kalman for providing us a source code for the L€owdin orthogonalization program. 5238



’ REFERENCES (1) (a) McCrone, W. C. In Physics and Chemistry of the Organic Solid State; Fox, D., Labes, M. M., Weissberger, A., Eds.; Interscience Publishers: New York, 1965; Vol. 2, pp 725 767. (b) Bernstein, J. Polymorphism in Molecular Crystals, 1st ed.; Oxford University Press Inc.: New York, 2002; pp 29 65. (c) Threlfall, T. L. Analyst 1995, 120, 2435–2460. (d) Jin, Y.; Lah, M. S. Eur. J. Inorg. Chem. 2005, 4944–4952. (e) Rath, N. P.; Kumar, V. S. S.; Janka, M.; Anderson, G. K. Inorg. Chim. Acta 2007, c, I.; Kokan, Z.; 360, 2997–3001. (f) Uzarevic, K.; Rubcic, M.; îlovi alogovic, D.; Cindric, M. Cryst. Growth Des. 2009, 9 (12), Matkovic-C 5327–5333. (g) Smyth, D. R.; Vincent, B. R.; Tiekink, E. R. T. Cryst. Growth Des. 2001, 1 (2), 113–117. (h) Chun, H.; Bernal, I. Cryst. Growth Des. 2001, 1 (1), 67–72. (i) Ramos Riesco, M.; Martínez Casado, F. J.; Lopez-Andres, S.; García Perez, M. V.; Redondo Yelamos, M. I.; Torres, M. R.; Garrido, L.; Rodríguez Cheda, J. A. Cryst. Growth Des. 2008, 8 (7), 2547–2554. (j) Ahmad, S.; Altaf, M.; Stoeckli-Evans, H.; R€uffer, T.; Lang, H.; Mufakkar, M.; Waheed, A. J. Chem. Crystallogr. 2010, 40 (8), 639–645. (2) (a) Corradini, P. Chim. Ind. (Milan) 1973, 55, 122–129. (b) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry, 2nd ed.; John Wiley & Sons: Chichester, U.K., 2009; pp 487 492. (c) Bilton, C.; Howard, J. A. K.; Laxmi Madhavi, N. N.; Nangia, A.; Desiraju, G. R.; Allenc, F. H.; Wilson, C. C. Chem. Commun. 1999, 1675–1676. (d) Nangia, A. Acc. Chem. Res. 2008, 41, 595–604. (3) (a) Bernstein, J. J. Phys. D: Appl. Phys. 1993, 26, 666–876. (b) Aaltonen, J.; Allesø, M.; Mirza, S.; Koradia, V.; Gordon, K. C.; Rantanen, J. Eur. J. Pharm. Biopharm. 2009, 71, 23–37. (c) Llinas, A.; Goodman, J. M. Drug Discovery Today 2008, 13, 198–210. (d) Brittain, H. G. Polymorphism in Pharmaceutical Solids, 2nd ed.; Informa Healthcare USA, Inc.: New York, 2009. (4) (a) Desiraju, G. Crystal Engineering: The Design of Organic Solids; Elsevier: Amsterdam, 1989. (b) Tiekink, E. R. T.; Vittal, J. J. Frontiers in Crystal Engineering; John Wiley & Sons, Ltd: Chichester, 2006. (c) Blagden, N.; Davey, R. J. Cryst. Growth Des. 2003, 3, 873–885. (d) Bernstein, J. Cryst. Growth Des. 2011, 11 (3), 632–650. (5) (a) Kalman, A.; Parkanyi, L.; Argay, G. Acta Crystallogr., Sect. B 1993, 49, 1039–1049. (b) Fabian, L.; Kalman, A. Acta Crystallogr., Sect. B 1999, 55, 1099–1108. (6) (a) Cincic, D.; Friscic, T.; Jones, W. Chem.—Eur. J. 2008, 14, 747–753. (b) Cincic, D.; Friscic, T.; Jones, W. New J. Chem. 2008, 32 (10), 1776–1781. (c) Cincic, D.; Friscic, T.; Jones, W. Chem. Mater. 2008, 20 (21), 6623–6626. (7) MacDonald, J. C.; Dorrestein, P. C.; Pilley, M. M.; Foote, M. M.; Lundburg, J. L.; Henning, R. W.; Schultz, A. J.; Manson, J. L. J. Am. Chem. Soc. 2000, 122, 11692–11702. (8) (a) Ferlay, S.; Hosseini, M. W. Chem. Commun. 2004, 788–789. (b) Dechambenoit, P.; Ferlay, S.; Kyritsakas, N.; Hosseini, M. W. Chem. Commun. 2009, 1559–1561. (9) (a) Cindric, M.; Rubcic, M.; îlovic, I.; Giester, G.; Kamenar, B. Croat. Chem. Acta 2007, 80, 583–590. (b) Rubcic, M.; Milic, D.; Kamenar, B.; Cindric, M. Acta Chim. Slov. 2008, 55, 810–814. (c) Rubcic, M.; Milic, D.; Horvat, G.; îlovic, I.; Galic, N.; Tomisic, V.; Cindric, M. Dalton Trans. 2009, 44, 9914–9923. alogovic, D. (10) Rubcic, M.; îlovic, I.; Cindric, M.; Matkovic-C Acta Crystallogr., Sect. C 2008, 64, o570–o573. (11) Cotton, F. A. Inorg. Synth. 1972, 13, 181–183. (12) Nawi, M. A.; Riechel, T. L. Inorg. Chem. 1982, 21, 2268–2271. (13) Rowe, R. A.; Jones, M. M. Inorg. Synth. 1957, 5, 113–115. (14) Xcalibur CCD system. CrysAlis Software system, Versions 1.171.32.24 and 1.171.33.41; Oxford Diffraction Ltd.: Abingdon, Oxfordshire, England, 2008. (15) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122. (16) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838. (17) Emsley, P.; Lohkamp, B.; Scott, W. G.; Cowtan, K. Acta Crystallogr., Sect. D 2010, 66, 486–501. (18) Spek, L. J. Appl. Crystallogr. 2003, 36, 7–13. (19) McKinnon, J. J.; Spackman, M. A.; Mitchell, A. S. Acta Crystallogr., Sect. B 2004, 60, 627–668.

ARTICLE

(20) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (21) http://www.povray.org/. (22) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P. A. J. Appl. Crystallogr. 2008, 41, 466–470. (23) Grybos, R.; Samotus, A.; Popova, N.; Bogolitsyn, K. Transition Met. Chem. 1997, 22, 61–64. (24) Braga, D.; Giaffreda, S. L.; Curzi, M.; Maini, L.; Polito, M.; Grepion, F. J. Therm. Anal. Calorim. 2007, 90, 115–123. (25) (a) Davey, R. J.; Blagden, N.; Potts, G. D.; Docherty, R. J. Am. Chem. Soc. 1997, 119, 1767–1772. (b) Koshima, H.; Miyauchi, M. Cryst. Growth Des. 2001, 1, 355–357. (26) Braga, D.; Cojazzi, G.; Paolucci, D.; Grepioni, F. CrystEngComm 2001, 3, 159–161. (27) (a) Nath, N. K.; Saha, B. K.; Nangia, A. New J. Chem. 2008, 32, 1693–1701. (b) Braga, D.; Grepioni, F.; Maini, L.; Polito, M.; Rubini, K.; Chierotti, M. R.; Gobetto, R. Chem.—Eur. J. 2009, 15, 1508–1515. (28) Wang, D.; Ebel, M.; Schulzke, C.; Gr€uning, C.; Hazari, S. K. S.; Rehder, D. Eur. J. Inorg. Chem. 2001, 935–942. (29) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1–S19. (30) Addison, A. W.; Rao, T. N.; Reedijk, J.; Van Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349–1356. (31) (a) Maia, P. I. da S.; Pavan, F. R.; Leite, C. Q. F.; Lemos, S. S.; de Sousa, G. F.; Batista, A. A.; Nascimento, O. R.; Ellena, J.; Castellano, E. E.; Niquet, E.; Deflon, V. M. Polyhedron 2009, 28, 398–406. (b) Philip, V.; Manoj, E.; Prathapachandra Kurup, M. R.; Nethaji, M. Acta Crystallogr., Sect. C 2005, 6, m488–m490. (32) Malone, J. F.; Murray, C. M.; Charlton, M. H.; Docherty, R.; Lavery, A. J. J. Chem. Soc., Faraday Trans. 1997, 93 (19), 3429–3436. (33) Nishio, M. CrystEngComm 2004, 6 (27), 130–158. (34) (a) McCleverty, J. A.; Rae, A. E.; Wolochowicz, I.; Bailey, N. A.; Smith, J. M. A. J. Organomet. Chem. 1979, 168, C1–C7. (b) McCleverty, J. A.; Rae, A. E.; Wolochowicz, I.; Bailey, N. A.; Smith, J. M. A. J. Chem. Soc., Dalton Trans. 1982, 951–965. (c) Winter, G.; Hartung, H.; Jaskolski, M. Mol. Cryst. Liq. Cryst. 1987, 149, 17–27. (d) Frydenvang, K.; Grønborg, L.; Jensen, B. Acta Crystallogr., Sect. C 1988, 44, 841–845. (e) Hounslow, A. M.; Lincoln, S. F.; Tiekink, E. R. T. J. Chem. Soc., Dalton Trans. 1989, 233–236. (f) Henderson, K. W.; Kennedy, A. R.; McKeown, A. E.; Strachan, D. J. Chem. Soc., Dalton Trans. 2000, 4348–4353. (g) Molek, C. D.; Halfen, J. A.; Loe, J. C.; McGaff, R. W. Chem. Commun. 2001, 2644–2645. (h) Liu, C.-W.; Hung, C.-M.; Wang, J.-C.; Keng, T.-C. J. Chem. Soc., Dalton Trans. 2002, 3482–3488. (i) Abourahma, H.; Bodwell, G. J.; Lu, J.; Moulton, B.; Pottie, I. R.; Walsh, R. B.; Zaworotko, M. J. Cryst. Growth Des. 2003, 3, 513–519. (j) John, G. H.; May, I.; Sharrad, C. A.; Sutton, A. D.; Collison, D.; Helliwell, M.; Sarsfield, M. J. Inorg. Chem. 2005, 44, 7606–7615. (k) Tyree, W. S.; Slebodnick, C.; Spencer, M. C.; Wang, G.; Merola, J. S.; Yee, G. T. Polyhedron 2005, 24, 2133–2140. (l) Ho, S. Y.; Tiekink, E. R. T. CrystEngComm 2007, 9, 368–378. (m) Ellis, C. A.; Miller, M. A.; Spencer, J.; ZukermanSchpector, J.; Tiekink, E. R. T. CrystEngComm 2009, 11, 1352–1361. (n) Ho, S. Y.; Tiekink, E. R. T. Acta Crystallogr., Sect. E 2009, 65, m1446–m1447. (35) (a) Jagodzinski, H.; Frey, F. Disorder diffuse scattering of X-rays and neutrons. In International Tables for Crystallography, Vol. B: Reciprocal Space; Shmueli, U., Ed.; Kluwer Academic Publishers: London, 2001; pp 407 442. (b) Schwarzenbach, D.; Schmelczer, R. Acta Crystallogr., Sect. B 1978, 34, 1827–1833. (c) Gardon, M.; Pinheiro, C. B.; Chapuis, G. Acta Crystallogr., Sect. B 2003, 59, 527–536. (d) Birkedal, H.; B€urgi, H. B.; Komatsu, K.; Schwarzenbach, D. J. Mol. Struct. 2003, 647, 233–242. (e) B€urgi, H.-B.; Hostettler, M.; Birkedal, H.; Schwarzenbach, D. Z. Kristallogr. 2005, 220, 1066– 1075. (f) Bond, A. D.; Boese, R.; Desiraju, G. R. Angew. Chem., Int. Ed. alogovic, 2007, 46, 618–622. (g) Milic, D.; Aleskovic, M.; Matkovic-C D.; Mlinaric-Majerski, K. Croat. Chem. Acta 2009, 82, 833–839. (h) Chan, E. J.; Welberry, T. R.; Heerdegen, A. P.; Goossens, D. J. Acta Crystallogr., Sect. B 2010, 66, 696–707. 5239



ARTICLE

(36) (a) Stahly, G. P. Cryst. Growth Des. 2007, 7 (6), 1007–1026. (b) Burger, A.; Ramberger, R. Mikrochim. Acta 1979, II, 259–272. (c) Burger, A.; Ramberger, R. Mikrochim. Acta 1979, II, 273–316. (37) (a) Jarring, K.; Larsson, T.; Stensland, B.; Ymen, I. J. Pharm. Sci. 2006, 95 (5), 1144–1161. (b) Storey, A.; Ymen, I. Solid State Characterization of Pharmaceuticals, 1st ed.; Blackwell Publishing Ltd., John Wiley & Sons: U.K., Chichester, 2011; pp 20 30.

5240


Complexes in the Solid State: From Polymorphism to Isostructurality

Recommend Documents