A new polymorph of dichlorido(1,10-phenanthroline)platinum(II)

Inorganica Chimica Acta 366 (2011) 384–387

Contents lists available at ScienceDirect

Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica

Note

A new polymorph of dichlorido(1,10-phenanthroline)platinum(II) Carmen R. Barone, Luciana Maresca ⇑, Giovanni Natile, Concetta Pacifico Dipartimento Farmaco-Chimico, Università degli Studi di Bari Aldo Moro, via E. Orabona 4, 70125 Bari, Italy

a r t i c l e

i n f o

Article history: Received 29 September 2010 Accepted 2 November 2010 Available online 8 December 2010 Keywords: Platinum complexes Polymorphism 1,10-Phenanthroline X-ray crystal structure

a b s t r a c t A yet unreported polymorph of [PtCl2(1,10-phenanthroline)] was obtained by slow decomposition, in CH2Cl2 solution, of [Pt{CH2CH2N(CH2CH3)2-jC,jN}(1,10-phenanthroline)](ClO4). The structure of the new orthorhombic form, III, (space group Pna21), is described and compared to those of the two already reported forms, I and II, which are monoclinic (space group P21/c) and orthorhombic (space group Pca21), respectively [21]. Polymorph III appears to be the least stable of the three. Ó 2010 Elsevier B.V. All rights reserved.

1. Introduction Polymorphism, that is the ability of a given molecular species to form in the solid state different crystalline edifices, is relevant to many fields spanning from pharmaceutical chemistry to material science. Differences in the crystalline arrangement can affect the solubility or the bioavailability of a drug [1–4]; moreover, the least stable phase, at room temperature, generally coincides with the most efficient pharmaceutical form. Polymorphs are present in explosives [5,6] and in pigments; in the latter substances the different solid phases may differ in resistance to heat and light irradiation with severe effects on the commercial value of one phase over the other [7]. In the case of metal complexes, polymorphism (or pseudopolymorphism) can be related to phenomena of vapo-chromism [striking color changes obtained on exposing a crystalline phase to volatile organic compounds (VOC)] [8–10] and, under these circumstances, polymorphs may have potential applications as photosensitizers and chemical sensors [11–13]. Chromatic differences, present in metal based polymorphs, are related to metal– metal interactions and different crystallization conditions, or incorporation of small molecules into a solid phase, may lead to crystalline edifices having significantly different intermetallic distances [14]. A historical example of polymorphism in metal complexes is given by [PtCl2(2,20 -bipyridine)]. This compound, isolated in 1934 [15] and studied for decades, has a red and a yellow form that,

starting from the 1970s, have been object of several X-ray investigations [16–19]. In the red polymorph, which also exhibits luminescent properties, the Pt  Pt distance is 3.45 Å, while in the yellow form the intermetallic distance stretches to 4.52 Å (the quoted values both refer to r.t. data collections). Several other examples have been reported over the years and, limiting the discussion to platinum chemistry, there are a number of dimorphic complexes in which color differences are related to the Pt  Pt intermolecular distances [20]. In a quite recent study [21] the selective crystallization of either the yellow or the red form of [PtCl2(2,20 -bipyridine)] was achieved by polymer induced heteronucleation (PIHn). The authors, using the same experimental tools, were able to obtain crystals, suitable for X-ray analysis, also for the well known platinum complex [PtCl2(1,10-phenanthroline)] [22], which, up to the mentioned study, had eluded a crystallographic analysis. Also [PtCl2(1,10-phenanthroline)], in complete analogy with [PtCl2(2,20 -bipyridine)], was found to exist in two polymorphic structures: a monoclinic yellow form (I) with a Pt  Pt distance of 4.83 Å and an orthorhombic orange one (II) with a Pt  Pt distance of 3.45 Å. We have now found the existence of a third polymorph, III, for [PtCl2(1,10-phenanthroline)] and its structure is described and compared to the already reported forms [21].

2. Experimental 2.1. Materials and methods

⇑ Corresponding author. Tel.: +39 0805442759; fax: +39 0805442230. E-mail addresses: [email protected] (C.R. Barone), maresca@ farmchim.uniba.it (L. Maresca), [email protected] (G. Natile), pacifico@ farmchim.uniba.it (C. Pacifico). 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.11.001

Solvents and reagents were commercially available and used as received. All other quoted platinum complexes are described in Ref. [22].

385

C.R. Barone et al. / Inorganica Chimica Acta 366 (2011) 384–387 Table 1 Crystal data and structure refinement data for polymorph III. Formula Formula weight Temperature (K) Wavelength (Å) Crystal system Space group a (Å) b (Å) c (Å) V (Å3) Z Density (calculated) (Mg/m3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm3) h range for data collection (°) Index ranges

Table 2 Selected bonds and angles (Å, °) for III (this work), I, and II (Ref. [1]).

C12H8Cl2N2Pt 446.19 292(2) 0.71073 orthorhombic Pna21 7.2727(5) 17.3087(12) 9.3258(6) 1173.9(1) 4 2.525 12.382 824 0.500  0.150  0.10 2.35–26.26 9 6 h 6 9, 21 6 k 6 21, 11 6 l 6 11 20 428 2373 (0.1171) full-matrix least-squares on F2 2373/15/154 0.956 R1 = 0.0334, wR2 = 0.0656 R1 = 0.0549, wR2 = 0.0711 0.969 and 1.033

Reflections collected Independent reflections (Rint) Refinement method Data/restraints/parameters Goodness-of-fit (GOF) on F2 Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)

Polymorph

III

I

II

Pt–Cl1 Pt–Cl2 Pt–N1 Pt–N2 N1–C1 N1–C12 N2–C10 N2–C11 N1–Pt–N2 N1–Pt–Cl1 N1–Pt–Cl2 N2–Pt–Cl1 N2–Pt–Cl2 Cl1–Pt–Cl2 C1–N1–Pt C12–N1–Pt C10–N2–Pt C11–N2–Pt

2.311(3) 2.305(3) 2.045(9) 2.046(9) 1.29(2) 1.43(2) 1.32(2) 1.37(2) 83.1(4) 92.6(3) 176.5(3) 175.6(3) 93.6(2) 90.8(1) 132.8(10) 110.4(8) 128.2(8) 112.0(7)

2.288(3) 2.292(2) 2.024(5) 2.006(5) 1.323(7) 1.365(7) 1.342(7) 1.373(6) 81.5(2) 94.4(1) 174.9(1) 175.6(1) 93.4(1) 90.73(6) 128.4(4) 112.7(3) 129.5(4) 113.1(3)

2.320(2) 2.310(2) 2.021(5) 2.031(5) 1.331(7) 1.363(7) 1.343(8) 1.368(8) 80.9(2) 94.2(1) 175.1(1) 174.9(2) 94.3(2) 90.63(6) 128.2(4) 112.8(4) 128.0(5) 113.4(4)

C5

C6

C4

C7 C8

2.2. Crystallization of polymorph III

C9

Bright yellow crystals of [PtCl2(1,10-phenanthroline)] were obtained in an unexpected way by slow crystallization from a solution of [Pt{CH2CH2N(CH2CH3)2-jC,jN}(1,10-phenanthroline)](ClO4) in CH2Cl2 kept at 298 K for ca. 6 weeks. The crystals, subjected to X-ray analysis, revealed to be a yet unknown polymorph of [PtCl2(1,10-phenanthroline)], which formed through a decomposition process.

C3 C11

C2

C12

C10

C1 N1

N2

Pt 2.3. X-ray crystallography Selected crystals of obtained compound were mounted on a Bruker AXS X8 APEX CCD system equipped with a four-circle Kappa goniometer and a 4 K CCD detector (radiation Mo Ka). For data reduction and unit cell refinement the SAINT-IRIX package was employed [24]. A total of 20 428 reflections (Hmax = 26.26°) were

Fig. 1. Molecular structure of [PtCl2(1,10-phenanthroline)] in polymorph III showing the atom-numbering scheme. Displacement ellipsoids are drawn at 30% probability level.

+

Et

+

HCl

Cl

N

Pt N

HCl

Cl

N

Pt N

A

+

Et N

N

Cl1

Cl2

+

Pt NHEt2

N

B

C Cl−

Cl

N

+

Pt N

Scheme 1.

Cl

(NH2Et2)Cl

386

C.R. Barone et al. / Inorganica Chimica Acta 366 (2011) 384–387

Fig. 2. Packing diagrams for III (view along the [1 0 0], a, and [0 1 0] direction, a0 ) (this work), I (view along the [0 0 1], b, and [0 1 0] direction, b0 ), and II (view along the [0 0 1], c, and [1 0 0] direction, c0 ) (see Ref. [21]).

collected. All reflections were indexed, integrated, and corrected for Lorentz, polarization, and absorption effects using the program SADABS [25]. The unit cell dimensions were calculated from all reflections and the structures were solved using direct methods technique in the Pna21 space group. The model was refined by full-matrix least-square methods. All non-hydrogen atoms were refined anisotropically. The Flack parameter [26] was 0.014(16) from 1111 Friedel pairs. Hydrogen atoms were placed at calculated positions and refined, giving isotropic parameters equivalent to 1.2 times those of the atom to which they are attached. Rigid bond restraints were applied to carbon anisotropic displacement parameters. All calculations and molecular graphics were carried out using SIR2002 [27], SHELXL97 [28], PARST97 [29,30], WINGX [31], and ORTEP-3 for Windows packages [32]. Details of the crystal data are listed in Table 1. Selected bond lengths and angles are listed in Table 2. 3. Results and discussion Bright yellow crystals of [PtCl2(1,10-phenanthroline)] were serendipitously obtained through the slow decomposition, in un-dried dichloromethane, of the complex [Pt{CH2CH2N(CH2CH3)2jC,jN}(1,10-phenanthroline)]+, A, isolated as perchlorate salt. The involved reaction steps are presumably those depicted in Scheme 1. Traces of HCl, released from the solvent [33], reverse the reaction sequence that, starting from the cationic complex [PtCl(g2-C2H4)(1,10-phenanthroline)]+, C, and the secondary amine NHEt2 leads to A [23]. Thus HCl promotes the opening of the azaplatinacyclobutane ring in A and favors the regression of the open chain complex B (through protonation of the freed amine) to the g2-C2H4 complex C [34]. Cationic C readily reacts with chlorido ions (that can also be formed, in the un-dried solvent, by hydrolysis of any platinum coordinated chlorido) to give the neutral dichlorido species, [PtCl2(1,10-phenanthroline)], which crystallises in a yet unreported polymorphic form (III). [PtCl2(1,10-phenanthroline)], probably because of its extremely low solubility (hampering crystallization processes), has eluded a crystallographic characterization until recently, when a polymer induced heteronucleation

allowed the growth of suitable crystals of polymorphs I and II [21]. Polymorph III (Fig. 1) crystallizes in the orthorhombic space group Pna21. Cell dimensions (Table 1 1) and bond lengths within the molecule (Table 2) are similar to those of forms I and II of Ref. [21]. The supramolecular aggregation pattern of III consists of columnar stacks of nearly planar [PtCl2(1,10-phenanthroline)] molecules related by glide planes (Fig. 2a). Within a column, extending along the [1 0 0] direction, p–p and d–p interactions are present between contiguous molecules. The inter-planar distances are in the range 3.4–3.6 Å. The closest contact distances are 3.47(2) Å for N1  C10, and 3.52(2) Å for both C1  C7 and C2  C5; the shortest contact involving the metal atom is 3.52(2) Å for Pt  C10. The Pt  Pt distance is 4.82(1) Å. The molecular planes of adjacent columns form a dihedral angle of 31.5° (Fig. 2a0 ); weak C–H  Cl contacts between columns are also present (shortest H  Cl distances of ca. 3.00 Å). Polymorph III exhibits similarities and differences with respect to forms I and II [21]. III is orthorhombic, like II, but its Pt  Pt distance (4.82 Å) is very similar to that of the monoclinic form I (4.83 Å). Looking at a single column of III along the [1 0 0] direction (Fig 2a), the disposition of contiguous molecules resembles that of I seen along the [0 0 1] direction (Fig 2b), with about 50% overlap of the phenanthroline ligands, the two chlorides of one complex overlapping the phenanthroline C1–C3 region of the contiguous complex, and the closest contact involving platinum featuring a Pt  N distance of 3.86 Å. Differently from polymorphs III and I, in the case of polymorph II, within the column extending along the [0 0 1] direction (Fig. 2c), there is practically no overlap between phenanthroline ligands of contiguous complex molecules; but the two chlorides of each platinum unit overlap the C1–N1– C12 region of the contiguous complex with C  Cl contacts of 3.37 and 3.43 Å. The closest contact involving the metal features

1 Polymorph I: space group P21/c; a = 9.602(10) Å, b = 17.119(5) Å, c = 7.339(5) Å, b = 109.437(13)°, V = 1137.6(15) Å 3 . Polymorph II: space group Pca2 1 ; a = 18.257(10) Å, b = 9.167(5) Å, c = 6.866(4) Å, V = 1149.0(10) Å3. For polymorph III see Table 1.

C.R. Barone et al. / Inorganica Chimica Acta 366 (2011) 384–387

a Pt  Pt distance of 3.52(2) Å. In all three polymorphs there are weak C–H  Cl interactions between columns (H  Cl distances of ca. 3.00, 2.83, and 2.71 Å for polymorphs III, I, and II, respectively). The dihedral angle between molecular planes of adjacent columnar stacks is quite similar for orthorhombic III (31.5°) and II (24.7°) (Fig. 2a0 and c0 , respectively); in contrast, the dihedral angle for I is close to zero (Fig. 2b0 ). As far as the density of polymorphs is concerned, a direct comparison can only be made between III (2.524 g/cm3) and I (2.605 g/cm3) for which data collection was performed at room temperature. For II (2.579 g/cm3) the data were collected at 123 K and, particularly for stacking planar molecules, as the temperature goes down there could be a shrinking of the intermolecular distances (with the overall structure becoming more densely packed) [19,20]. In the case of polymorph I a lowering of temperature from 293 to 123 K causes an increase of density from 2.605 g/cm3 to 2.627 g/cm3. Assuming a similar increase of density also for polymorph III (which is similar to I in the mutual disposition of contiguous molecules), the value at 123 K should probably be 2.546 g/cm3 and, though, still lower than that of II at the same temperature. Stable crystalline forms tend to minimize the free volume unless the energy loss, due to a less packed structure, is compensated by other inter-atomic interactions such as those between contiguous metal atoms [20]. On the basis of the principle of close packing [35], the presently isolated polymorph III would appear to be the least stable having the lowest density and no inter-metallic interactions; the rather high kinetic barrier to transformation between polymorphs of [PtCl2(1,10-phenanthroline)] [21] can account for its formation. 4. Conclusions Through the slow decomposition of [Pt{CH2CH2N(CH2CH3)2-

jC,jN}(1,10-phenanthroline)](ClO4) in CH2Cl2 solution and a subsequent classical crystallization process, a yet unreported polymorph of [PtCl2(1,10-phenanthroline)] (III) has been obtained. The other two known polymorphs (I and II) had to be obtained by using polymer induced heteronucleation. It has been found that columnar stacks with similar disposition of contiguous molecules can give rise to different crystal systems (III and I), while columnar stacks with different disposition of contiguous molecules can share the same crystal system (III and II). The obtained new polymorph appears to be the least dense and, probably, it is the least stable. Acknowledgements The authors gratefully acknowledge Profs Ernesto Mesto and Ferdinando Scordari (University of Bari) for data collection and the University of Bari for financial support.

387

Appendix A. Supplementary material CCDC 783996 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2010. 11.001. References [1] A.J. Aguiar, J. Krc, A.W. Kinkel, J.C. Samyn, J. Pharm. Sci. 56 (1967) 847. [2] A. Foppoli, M.E. Sangalli, A. Maroni, A. Gazzaniga, M.R. Caira, G. Giordano, J. Pharm. Sci. 93 (2003) 521. [3] R. Kaliszan, J. Pharm. Sci. 75 (1986) 187. [4] S. Roy, P.M. Bhatt, A. Nangia, G.J. Kruger, Cryst. Growth Des. 7 (2007) 477. [5] N.B. Bolotina, M.J. Hardie, R.L. Jr Speer, A.A. Pinkerton, J. Appl. Crystallogr. 37 (2004) 808. [6] Y. Hu, P. Huang, L. Guo, X. Wang, C. Zhang, Phys. Lett. A 359 (2006) 728. [7] T. Senju, N. Nishimura, J. Mizuguchi, J. Phys. Chem. A 111 (2007) 2966. [8] T. Abe, T. Suzuki, K. Shinozaki, Inorg. Chem. 49 (2010) 1794. [9] M. Kato, S. Kishi, Y. Wakamatsu, Y. Sugi, Y. Osamura, T. Koshiyama, M. Hasegawa, Chem. Lett. 34 (2005) 1368. [10] J. Ni, Y.-H. Wu, X. Zhang, B. Li, L.-Y. Zhang, Z.-N. Chen, Inorg. Chem. 48 (2009) 10202. [11] A. Flamini, G. Mattei, A. Pausa, J. Inclusion Phenom. Macrocyclic Chem. 33 (1999) 377. [12] M.H. Keefe, K.D. Benkstein, J.T. Hupp, Coord. Chem. Rev. 205 (2000) 201. [13] M. Kato, Bull. Chem. Soc. Jpn. 89 (2007) 287. [14] T.J. Wadas, Q.-M. Wang, Y.-J. Kim, C. Fleischenreim, T.N. Blanton, R. Eisenberg, J. Am. Chem. Soc. 126 (2004) 16841. [15] G.T. Morgan, F.H.J. Burstall, J. Chem. Soc. (1934) 965. [16] R.S. Osborn, D.J. Rogers, J. Chem. Soc., Dalton Trans. (1974) 1002. [17] E. Bielli, P.M. Gidney, R.D. Gillard, B.T.J. Heaton, J. Chem. Soc., Dalton Trans. (1974) 2133. [18] A.J. Canty, B.W. Skelton, P.R. Traill, A.H. White, Aust. J. Chem. 45 (1992) 417. [19] W.B. Connick, L.M. Henling, R.E. Marsh, H.B. Gray, Inorg. Chem. 35 (1996) 6261. [20] W.B. Connick, R.E. Marsh, W.P. Schaefer, H.B. Gray, Inorg. Chem. 36 (1997) 913. [21] A.L. Grzeziak, A.J. Matzger, Inorg. Chem. 46 (2007) 453. [22] F.A. Palocsay, J.V. Rund, Inorg. Chem. 8 (1969) 524. [23] C.R. Barone, M. Benedetti, V.M. Vecchio, F.P. Fanizzi, L. Maresca, G. Natile, Dalton Trans. (2008) 5313. [24] C.O.S.M.O. Bruker, APEX2, BIS and SAINTIRIX, Bruker AXS Inc., Madison, Wisconsin, USA, 2004. [25] G.M. Sheldrick, SADABS, Program for Empirical Absorption Correction of Area Detector Data, University of Göttingen, Germany, 1996. [26] H.D. Flack, Acta Crystallogr., Sect. A 39 (1983) 876. [27] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L. De Caro, C. Giacovazzo, G. Polidori, R. Spagna, J. Appl. Crystallogr. 38 (2005) 381. [28] G.M. Sheldrick, Institüt für Anorganische Chemie der Universität, Tammanstrasse 4, D-3400 Göttingen, Germany, 1998. [29] M. Nardelli, Comput. Chem. 7 (1983) 95. [30] M. Nardelli, J. Appl. Crystallogr. 28 (1995) 659. [31] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837. [32] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565. [33] (In CH2Cl2, notwithstanding the use of preservatives, traces of HCl can develop with time especially by exposure to light. The presence in solution of metal containing species may favour decomposition processes; e.g. see) K.J. Doyle, H. Tran, M. Baldoni-Olivencia, M. Karabulut, P.E. Hoggard, Inorg. Chem. 47 (2008) 7029. [34] L. Maresca, G. Natile, J. Chem. Soc., Dalton Trans. (1982) 1903. [35] C.P. Brock, J.D. Dunitz, Chem. Mater. 6 (1994) 1118.