J Chem Crystallogr (2011) 41:747–750 DOI 10.1007/s10870-010-9967-4
ORIGINAL PAPER
Molecular Structure of an Unexpected Binuclear Salicylaldimine Semicarbazone Palladium(II) Complex Prinessa Chellan • Kelly Chibale • Gregory S. Smith
Received: 12 February 2010 / Accepted: 31 December 2010 / Published online: 21 January 2011 Ó Springer Science+Business Media, LLC 2011
Abstract Reaction of a salicylaldehyde semicarbazone ligand with PdCl2(PPh3)2 yields an unexpected binuclear Pd(II) complex, 2. The complex crystallizes in a triclinic system with a P-1 space group, with unit cell parameters ˚ , b = 15.2603(3) A ˚ , c = 18.7142(3) A ˚, a = 14.0283(3) A a = 66.662(10)°, b = 86.162(10)°, c = 76.265(10)°, Z = 2. The semicarbazone ligand acts as a tridentate chelating donor to one palladium metal centre, forming a five- and six- membered ring, and a monodentate donor to the second palladium centre. There are four molecules of solvent per complex molecule in the asymmetric unit. Each metal centre is contained within a slightly distorted square-planar environment. Keywords Semicarbazone Salicylaldehyde Binuclear Palladium(II) Molecular structure
Introduction Semicarbazones, a class of Schiff-base compounds which contain a urea moiety, are compounds well known for their pharmacological properties and have been screened for anticancer [1–3], anticonvulsant [4] and antimicrobial activity [5, 6]. Due to their inherent biological activity, there is growing interest in the use of transition metal
P. Chellan K. Chibale G. S. Smith (&) Department of Chemistry, University of Cape Town, Private Bag, Rondebosch 7701, South Africa e-mail:
[email protected] K. Chibale Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Rondebosch 7701, South Africa
complexes of semicarbazones as biological agents [7–11]. Semicarbazones are capable of acting as multidentate ligands toward metals. Ruthenium(II) [10], platinum(II) [9, 11], palladium(II) [9, 11], nickel(II) [8, 11] and titanium(IV) [7] complexes containing semicarbazone derivatives have been reported in the literature. One of the key research areas within our group is the synthesis and biological study of multidentate Schiff-base ligands and their transition metal complexes. Currently, we are interested in aryl semicarbazone and thiosemicarbazone compounds which coordinate to palladium(II) and platinum(II) in a tridentate fashion. In the case of salicylaldehyde derived semicarbazones, these compounds are reported to act as tridentate [O,N,O] donors to palladium via the phenolic oxygen, imine nitrogen and the enolate oxygen of the urea moiety [12, 13]. Thus, during the course of our investigations we expected to isolate similar Pd(II) complexes but, as attested by the solid state structure, this was not the case. Instead of the anticipated mononuclear complex, an unexpected binuclear complex was synthesized. In this paper, we report the synthesis and molecular structure of the binuclear palladium(II) complex synthesized from the salicylaldimine ligand, 2-hydroxy-3-methoxybenzaldehyde semicarbazone (1) where the semicarbazone ligand acts as a tridentate [O,N,N] donor to one metal centre and a monodentate donor to a second metal.
Experimental The salicylaldimine semicarbazone ligand (1), (2-hydroxy3-methoxy-benzaldehyde)semicarbazone [14, 15], and the metal precursor, PdCl2(PPh3)2 [16], were synthesized according to previously published methods.
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Table 1 Crystal data and refinement information for 2 CCDC deposit no.
719356
Empirical formula
C67 H53 Cl13 D4 N3 O3 P3 Pd2
Formula weight
1722.74
Temperature (K) ˚) Wavelength (A
173(2) K 0.71073 A
Crystal system
Triclinic
Space group
P-1
Unit cell dimensions ˚) a (A
14.0283(3)
˚) b (A ˚) c (A
15.2603(3)
a (°)
66.662(10)
b (°)
86.162(10)
c (°)
76.265(10)
˚ 3) Volume (A Z
3571.65(12) 2
18.7142(3)
Calculated density (Mg/m3)
1.602
Absorption coefficient (mm-1)
1.105
F(000)
1724
Crystal size (mm)
0.15 9 0.11 9 0.09
h Range for data collection (°)
2.24–25.68
Limiting indices -17 B h B 17 -18 B k B 18 -22 B l B 22 Reflections collected
Suitable crystals were grown from a 1:1 volume mixture of deuterated chloroform and hexane. X-ray single crystal intensity data were collected on a Nonius Kappa-CCD diffractometer using graphite monochromated Mo Ka radiation. Temperature was controlled by an Oxford Cryostream cooling system (Oxford Cryosystems). The strategy for the data collections was evaluated using the Bruker Nonius ‘‘Collect’’ program. Data were scaled and reduced using DENZO-SMN software [17]. A multiscan error correction using the program SADABS [18] was used. The structure was solved by direct methods and refined employing full-matrix least-squares with the program SHELXL-97 [19] refining on F2. Packing diagrams were produced using the program PovRay and graphic interface X-seed [20]. All non-H atoms were refined anisotropically. All the hydrogen atoms were placed in idealised positions on riding models with Uiso set at 1.2 or 1.5 times those of the parent atoms. The structure was refined successfully with R = 0.0412. The crystal and experimental data are listed in Table 1. Selected bond lengths and angles are shown in Table 2. Complete bond lengths and angles, calculated hydrogen coordinates and anisotropic thermal coordinates are given in the supplementary information. Molecular structure of complex 2 is given in Fig. 1.
115616
Reflections independent
13536, R(int) = 0.0535
Goodness-of-fit on F2
1.042
Final R indices [I [ 2r(I)]
R1 = 0.0412, wR2 = 0.0990
R indices (all data)
R1 = 0.0590, wR2 = 0.1094
˚ -3) 1.052 and -1.094 Largest diff. peak and hole (e A
Synthesis of (2-Hydroxy-3-methoxy-benzaldehydesemicarbazone)Pd2(PPh3)3Cl (2-Hydroxy-3-methoxy-benzaldehyde)semicarbazone (0.162 g, 0.775 mmol) was added to dry ethanol (40 cm3) under argon gas. The solution was heated to 60 °C with stirring to facilitate dissolution of the ligand. Triethylamine (0.220 cm3, 1.563 mmol) was then added followed by PdCl2(PPh3)2 (0.533 g, 0.760 mmol). The mixture was refluxed under argon for 5 h before it was cooled to room temperature. The crude product was isolated via filtration and washed with ethanol (10 cm3) and diethyl ether (10 cm3). The crude solid was recrystallised from a 1:1 volume mixture of dichloromethane and hexane to give the pure product (2) as red crystals (0.4101 g, 86%). Composition for C63H53ClN3O3P3Pd2: Found (Calculated) C: 59.21 (60.96); H: 4.56 (4.30); N: 2.88 (3.39), ESI–MS: m/z 1243 [M ? H]?, 50%.
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Structure Determination and Refinement
Results and Discussion The salicylaldimine ligand (1), 3-methoxy-2-hydroxybenzaldehyde semicarbazone, was reacted with dichlorobis(triphenylphosphine)palladium(II) in the presence of triethylamine (Scheme 1). Rather than the expected mononuclear complex 3, where the ligand acts as a tridentate [O,N,O] donor to palladium, complex 2 was isolated as red crystals. Coordination of the semicarbazone ligand (1) to palladium in an [O,N,N] fashion rather than [O,N,O] may be explained by Pearson’s concept of hard and soft acids and bases [21]. Palladium is a soft acid and so would prefer to bond to soft or borderline bases such as nitrogen compared to the harder base oxygen. Additionally, chlorine is termed a hard base and thus loss of one chlorine ion from a second molecule of the palladium precursor followed by coordination of the metal to the preferred hydrazinic nitrogen occurs. The presence of the base triethylamine may also play a role. The weak base promotes deprotonation not only of the phenolic oxygen but the terminal nitrogen as well. The molecular structure (Fig. 1) clearly shows the semicarbazone ligand coordinating to Pd1 via the phenolic oxygen (O1), the imine nitrogen (N3) and the nitrogen (N1)
J Chem Crystallogr (2011) 41:747–750 Table 2 Selected bond lengths and angles for 2
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Pd(1)–N(1)
1.966(3)
Pd(2)–N(2)
2.020(3)
Pd(1)–O(1)
2.008(2)
Pd(2)–P(3)
2.3194(9)
Pd(1)–N(3)
2.014(3)
Pd(2)–Cl(1)
2.3207(9)
Pd(1)–P(1) O(3)–C(1)
2.2796(9) 1.251(4)
Pd(2)––P(2) N(2)–N(3)
2.3248(10) 1.361(4)
N(1)–C(1)
1.343(5)
N(2)–C(1)
1.379(5)
N(3)–C(2)
1.290(5)
N(1)–Pd(1)–O(1)
171.97(11)
N(2)–Pd(2)–P(3)
90.36(8)
N(1)–Pd(1)–N(3)
78.94(12)
N(2)–Pd(2)–Cl(1)
176.71(9)
O(1)–Pd(1)–N(3)
93.05(11)
P(3)–Pd(2)–Cl(1)
89.35(3)
N(1)–Pd(1)–P(1)
93.67(9)
N(2)–Pd(2)–P(2)
91.56(9)
O(1)––Pd(1)–P(1)
94.32(7)
P(3)–Pd(2)–P(2)
174.13(3)
N(3)–Pd(1)–P(1)
172.52(8)
Cl(1)–Pd(2)–P(2)
88.42(3) -171.8(6)
N(1)–Pd(1)–P(1)–C(10)
-162.81(17)
N(3)––Pd(1)–P(1)–C(10)
P(1)–Pd(1)–O(1)–C(4)
-179.0(3)
Cl(1)–Pd(2)–P(2)–C(28)
-178.53(15)
Cl(1)–Pd(2)–N(2)–N(3)
-179(100)
Cl(1)–Pd(2)–P(3)–C(46)
176.18(14)
NH2
N N
O H N
Pd PPh3
OMe
NH2
O
3
N
PdCl2(PPh3)2 / Et3N Ethanol / reflux OH
Cl
O Ph3P
OMe
1
Pd
PPh3 O
N N
O
OMe
Pd
NH
PPh3
2
Scheme 1 Synthetic route to complex 2
of the terminal amine upon loss of one proton; forming a five- and six-membered ring with Pd1. The phosphorus atom, P1, coordinates to Pd1 trans to the imine nitrogen, N3. The hydrazinic nitrogen (N2) coordinates to Pd2 with the chloride ion (Cl1) trans to nitrogen. Each metal ion is contained within a close to square-planar environment. Table 1 shows the crystal and experimental data for 2 and selected bond lengths and angles as well as torsion angles are listed in Table 2. The complex crystallizes in a triclinic system with a P-1 space group. The bond lengths and angles observed around each metal centre are similar to those observed for other palladium(II) square–planar complexes containing a tridentate ligand [22–24]. The bond lengths for Pd(1)–N(1),
Pd(1)–O(1), Pd(1)–N(3) and Pd(1)–P(1) are similar to each other with the longest bond being observed between Pd(1)–P(1) suggesting a strong trans influence exerted by the triphenylphosphine ligand. There is no intermolecular hydrogen bonding observed either between complex molecule or between solvent and complex molecules. The bond lengths observed around Pd(2), Pd(2)–N(2), Pd(2)–P(3), Pd(2)–Cl(1) and Pd(2)–P(2), are slightly longer than those observed around Pd(1). The shorter bond lengths observed around Pd(1) may be attributed to the highly conjugated system of the semicarbazone ligand leading to greater electron density donation to the metal centre. The bond lengths observed for N(1)–C(1) and N(2)–C(1) are close to the length of the imine bond
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Center, CCDC: 719356. Copies of this information may be obtained from the the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ (fax: ?44-1223-336033; email:
[email protected] or at: http://www.ccdc.cam.ac.uk). Acknowledgments Financial support from the University of Cape Town, the National Research Foundation (NRF) of South Africa, and Anglo Platinum Corporation are gratefully acknowledged.
References
Fig. 1 Molecular structure of 2 with ellipsoidal model of probability level = 50%. All hydrogen atoms and four solvent molecules of CDCl3 are omitted for clarity
N(3)–C(2) suggesting increased double bond character in these bonds. The bond angles O(1)–Pd(1)–N(3), N(1)–Pd(1)–P(1) and O(1)–Pd(1)–P(1) are close to 90° suggesting that these atoms are almost coplanar [22]; the N(1)–Pd(1)–N(3) angle has the greatest deviation from 90° leading to an overall slightly distorted square–planar geometry around the Pd(1) metal centre. The bond angles formed between Pd(2) and its coordinated atoms are closer to 90° compared to Pd(1) illustrating that the geometry around Pd(2) is closer to square–planar than around Pd(1). This is further supported by the bond angles, N(2)–Pd(2)–Cl(1) and P(3)–Pd(2)–P(2) which are closer to linearity (180°) than the angles N(1)– Pd(1)–O(1) and N(3)–Pd(1)–P(1). The torsion angles, P(1)–Pd(1)–O(1)–C(4), N(3)–Pd(1)–P(1)–C(10) and N(1)– Pd(1)–P(1)–C(10) also illustrate the slightly distorted square planar geometry around Pd(1). Similar torsion angles are observed for Pd(2), although the deviation from planarity is not as large as for Pd(1).
Supplementary Information X-ray crystallographic files for the structure analysis of (2) been deposited with the Cambridge Crystallographic Date
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1. Asis SE, Bruno AM, Molina DA, Conti GM, Gaozza CH (1996) Farmaco 51:419 2. Pandeya SN, Yogeeswari P, Sausville EA, Mauger AB, Narayanan VL (2000) Sci Pharm 68:369 3. Dutta S, Padhye S, Priyadarsini KI, Newton C (2005) Bioorg Med Chem Lett 15:2738 4. Yogeeswari P, Sriram D, Veena V, Kavya R, Rakhra K, Ragavendran JV, Mehta S, Thirumurugan R, Stables JP (2005) Biomed Pharmacother 59:51 5. Joshi S, Das MA, Tiwari P (2009) Int J Chem Sci 7:869 6. Gupta BD (2008) Pak J Sci Ind Res 51:124 7. Singh D, Singh R (1994) Trans Met Chem 19:347 8. Rodriguez-Argueelles MC, Mosquera-Vazquez S, SanmartinMatalobos J, Garcia-Deibe AM, Pelizzi C, Zani F (2010) Polyhedron 29:864 9. Sharma K, Singh R, Fahmi N, Singh RV (2010) Spectrochim Acta Part A Mol Biomol Spec 75:422 10. Mahalingam V, Chitrapriya N, Fronczek FR, Natarajan K (2008) Polyhedron 27:2743 11. Chandra S, Tyagi M (2008) J Serb Chem Soc 73:727 12. Yadav JS, Gayathri KU, Ather H, ur Rehman H, Prasad AR (2007) J Mol Cat A Chem 271:25 13. Hingorani S, Singh K, Agarwala BV (1994) J Indian Chem Soc 71:183 14. James AR, Heilbron I, Henderson M (1915) J Chem Soc Trans 107:1740 15. Mishra V, Pandeya SN, Singh PN, Rupainwar DC (1998) Pharmaco Res 37:17 16. Herrmann WA, Slazer A (1996) Synthetic methods of organometallic and inorganic chemistry, vol 1. Thieme, Stuttgart, p 160 17. Otwinowski Z, Minor W (1997) Methods in enzymology, vol 276, macromolecular crystallography. Academic Press, New York, p 307 18. Sheldrick GM (1996) SADABS. University of Go¨ttingen, Germany 19. Sheldrick GM (1997) SHELXL-97 and SHELXS-97, Program for crystal structure refinement. University of Go¨ttingen, Germany 20. Barbour LJ (2001) J Supramol Chem 1:189 21. Pearson RG (1963) J Am Chem Soc 85:3533 22. Patil SA, Weng C-M, Huang P-C, Hong FE (2009) Tetrahedron 65:2889 23. Halder S, Peng S-M, Lee G-H, Chatterjee T, Mukherjee A, Dutta S, Sanyal U, Bhattacharya S (2008) New J Chem 32:105 24. Kumar A, Agarwal M, Singh AK, Butcher RJ (2009) Inorg Chim Acta 362:3208
