ADDENDA AND ERRATA

A correction has been published for this article. To view the correction, click here.

Synthesis and structural characterization of a new dinuclear platinum(III) complex, [Pt₂Cl₄(NH₃)₂{μ-HN=C(O)Bu^t}₂]

Cisplatin plays an important role in treating many tumors. However, its pharmacological potential is limited by several side effects (nephrotoxicity, neurotoxicity, hair loss) and the resistance of many cancer types. In the effort of overcome resistance to cisplatin, more than 3000 platinum complexes have been synthesized in the past 45 years, but only about 30 have demonstrated adequate pharmacological platinum(III) complexes have been synthesized and their structure determined, because some of these exhibit antitumor and catalytic activity for the oxidation of olefins. Herein the synthesis of a new dinuclear platinum(III) complex with two butyl­(amidato) bridging ligands, namely [Pt₂Cl₄(NH₃)₂{μ-HN=C(O)Bu^t}₂], is reported. The complex was characterized by means of nuclear magnetic resonance (¹H and ¹⁹⁵Pt NMR) and infrared spectroscopy, and the crystal structure determined using X-ray single-crystal diffraction. This complex, to the best of our knowledge, is the first dinuclear complex of Pt^III with two butyl­(amidato) bridging ligands with a head-to-tail configuration.

1. Introduction

The interest in platinum complexes arises from their anti­cancer and catalytic activities for the oxidation of olefins. The discovery of the anticancer properties of cisplatin and its clinical introduction in the 1970s represent an important milestone in the history of effective anticancer drugs. Cisplatin, cis-diamminedi­chloro­platinum(II), was discovered by Rosenberg et al. (1965) during their experiments on the effect of electric fields on the cell division of bacteria. Cisplatin plays a significant role in the treatment of epithelial malignancies and in the cure of testicular cancer. It is used also as a principal component for the treatment of ovarian, head-and-neck, esophagus, stomach, colon, bladder, cervix and uterus cancers and as second-line treatment against most other advanced cancers including breast, pancreas, liver, kidney and prostate cancers. The primary cellular target of cisplatin is DNA, and the antitumor effects of platinum complexes are expected to arise from their ability to form several adducts with DNA, blocking its replication and transcription, and inducing cell death. The antitumor properties of cisplatin are attributed to the kinetics of the aqua­tion reactions of its chloride ligands leading to DNA crosslinking activities. This process is responsible of DNA bending, interferes with DNA replication, transcription and other nuclear functions, and blocks cancer cell proliferation and tumor growth (Boulikas et al., 2007). However, its pharmacological potential is limited by its side effects (nephrotoxicity, neurotoxicity, hair loss), and the resistance of many cancer types (O'Dwyer et al., 1999; Von Hoff et al., 1979). In the past 45 years over 3000 platinum complexes have been synthesized in the effort of overcoming cisplatin limitations, but not more than 30 of them exhibited adequate pharmacological advantages over cisplatin. Only five of these latter complexes have been used in clinical applications, three FDA-approved (cisplatin, carboplatin and oxaliplatin), one used in Japan (nedaplatin) and one in China (lobaplatin). For a long time, the cisplatin geometry has been retained as a necessary requisite for a platinum complex to exhibit antitumoral activity (Kelland, 2007). Indeed, the trans-geometry of the platin complex and other transplatin analogs do not exhibit antitumor activity because of their kinetic instability which renders the complex unable to bind the target in the active form (Cornacchia et al., 2009). More recently, however, several researchers have reported that the trans-isomer can gain cytotoxicity comparable to that of the cis-isomer and even of cisplatin (Farrell et al., 1992; Natile & Coluccia, 2001; Montero et al., 1999; Kasparkova et al., 2003a,b).

On the other hand, the number of dinuclear Pt^III complexes containing a metal–metal single bond is steadily increasing as well (O'Halloran & Lippard, 1985; Matsumoto & Sakai, 1999; González et al., 2000; Saeki et al., 2003). Dinuclear Pt^III complexes are interesting for their potential use in catalysis and biomedicine, and their chemistry and reactivity has not yet been explored to the same extent as for Pt^II and Pt^IV species. The majority of Pt^III complexes include a metal–metal single bond supported by two (Matsumoto & Sakai, 1999; Chen & Matsumoto, 2003; Lippert, 1999) or four (Fedotova et al., 1997; Dolmella et al., 2002; Bandoli et al., 2003) bridging ligands (Fig. 1), namely `platinum blues'-derived and `lantern-type', respectively. Dinuclear platinum complexes with three bridging ligands (Fig. 1) (Abe et al., 1991) or unsupported by covalent bridges (Matsumoto et al., 1996; Lippert et al., 1983) are rare. The chelating chain usually consists of three atoms of the type OXO (X = C,S,P), NCO, NCS, SCS or PXP (X = C,O) resulting in an overall five-membered ring including the platinum–platinum interaction (Cornacchia et al., 2009; Goodgame et al., 1986; Umakoshi et al., 1987; Cotton et al., 1997; Bellitto et al., 1983; Usón et al., 1994). In addition to the bridging ligands, dinuclear Pt^III complexes also have equatorial and axial ligands (Matsumoto, 2003). A characteristic feature of dinuclear Pt^III complexes is an unusually long bond distance between the platinum and the axial ligands, which is 10% longer than the corresponding distances in square-planar Pt^II and octahedral Pt^IV coordinations (O'Dwyer et al., 1999). Therefore, axial ligands are weaker bound, due to the strong trans labialization influence exerted by the intermetallic bond (Kuo et al., 2007; Hartmann & Lipp, 2003; Dolmella et al., 2002), and this characteristic feature may increase the reactivity toward the guanine bases of the DNA. The two-bridge Pt^III complexes are characterized by a tilting of the two platinum coordination planes of 25° and a twist about the platinum–platinum vector averaging a torsion angle of 25° (O'Halloran & Lippard, 1985). These distortions are due to the steric interactions between the non-bridging equatorial ligands.

Figure 1 (a) `Lantern-type' diplatinum(III) complex, (b) dinuclear Pt^III with three bridging ligands and (c) a `platinum blues' derivate (this work). In this study, YZX = OCN, axial L = Cl, HHT is head-head-to-tail and HT is head-to-tail.

In recent decades, the chemistry of dinuclear platinum complexes has attracted an increasing interest (O'Halloran & Lippard, 1985; Matsumoto & Sakai, 1999), because it has been demonstrated that some of these dinuclear Pt^III complexes exhibit antitumor (Cervantes et al., 1997) and catalytic activities for the oxidation of olefins (Matsumoto & Sakai, 1999; Saeki et al., 2003; Ochiai et al., 2004). From this perspective, our research efforts have focused on the synthesis and the structural determination of a new head-to-tail (HT) dinuclear Pt^III complex (Fig. 1), with chemical formula [Pt₂Cl₄(NH₃)₂{μ-HN=C(O)Bu^t}₂]. The complex has been characterized by means of NMR and IR spectroscopies, while the structure was determined using X-ray single-crystal diffraction.

2. Experimental

2.1. Synthesis

(i) K₂PtCl₄ (2.1641 g, 5.21 mmol, M_r = 415.06 g mol⁻¹) and KI (4.3874 g, 26.4 mmol, M_r = 165.99 g mol⁻¹) were dissolved in water (15 ml). The solution was stirred at 55°C until a brown suspension consistent with the formation of the tetra­iodo salt, having formula K₂PtI₄, was observed. To this aqueous dispersion of potassium salt, an aqueous solution of NH₄OH was added dropwise and the pH was controlled to not exceed 7.5 during the addition. The obtained solution was warmed at 55°C under stirring for 20 min to allow the formation of a yellow precipitate of cis-[PtI₂(NH₃)₂].

(ii) cis-[PtI₂(NH₃)₂] (1.5229 g, 3.15 mmol, M_r = 482.92 g mol⁻¹) was dissolved in water (20 ml), stirred with AgNO₃ (1.0713 g, 6.31 mmol, M_r = 169.88 g mol⁻¹) at 70°C for 20 min in the dark, and AgI was then removed by filtration from the yellowish suspension. The mother liquor was treated with NCBu^t (2 ml) and stirred at 70°C for 1 h, affording a blue solution of cis-[Pt(NH₃)₂(NCBu^t)₂]. The resulting nitrile complex was stirred at room temperature for 1 h with KI (2.6192 g, 17.78 mmol) to give a green precipitate of trans-[PtI₂(NH₃)(NCBu^t)].

(iii) trans-[PtI₂(NH₃)(NCBu^t)] (0.9457 g, 1.72 mmol, M_r = 549 g mol⁻¹), dissolved in acetone (20 ml), was first stirred at 60°C to give a yellow solution, and then stirred with AgNO₃ (0.5859 g, 3.45 mmol) at 70°C for 20 min in the dark, affording a green solution that was filtered. The mother solution was treated with KCl (1.2892 g, 17.3 mmol, M_r = 74.56 g mol⁻¹) and then taken to dryness by evaporation of the solvent under reduced pressure. The solid residue was dissolved in water (20 ml), stirred at 50°C for 1 h, and dried in vacuum to obtain the formation of a green precipitate of trans-[PtCl₂(NH₃)(NCBu^t)] .

(iv) trans-[PtCl₂(NH₃)(NCBu^t)] (0.1780 g, 0.49 mmol, M_r = 366 g mol⁻¹) dissolved in chloro­form (30 ml) and Cl₂ (2 ml) was stirred at room temperature for 30 min. The solvent was then evaporated under vacuum, forming a yellow precipitate of trans-[PtCl₄(NH₃)(NCBu^t)].

(v) The novel binuclear Pt^III complex can be prepared by the reaction of trans-[PtCl₄(NH₃)(NCBu^t)] and trans-[PtI₂(NH₃)(NCBu^t)] in water solution: trans-[PtCl₄(NH₃)(NCBu^t)] (0.0335 g, 76.8 µmol, M_r = 436 g mol⁻¹) and trans-[PtI₂(NH₃)(NCBu^t)] (0.0415 g, 75.6 µmol) were first stirred at 60°C for 6 h in a water solution (10 ml), giving a brown suspension, and then heated for 20 h at 60°C. The solid residue was separated from the solution and crystallized in water by slow evaporation at room temperature. After three days, red crystals were formed (Fig. 2). It is worth noting that in the final complex only chlorine ligands are in the equatorial and axial positions. This can be explained by assuming that the iodide anion (from the Pt^II complex) is a stronger base with respect to chlorine, and as a consequence exhibits a larger reactivity with H₃O⁺ cations (water after reacting with the platinum precursors releases hydrogen ions).

Figure 2 Single crystal selected for the X-ray diffraction characterization.

2.2. X-ray structure determination

The selected crystal (Fig. 1) was mounted on a Bruker AXS X8 APEX CCD diffractometer equipped with a four-circle Kappa goniometer and a 4 K CCD detector (radiation Mo Kα). Data reduction and unit-cell refinement were carried out with the SAINT package (Bruker, 2003). A total of 29306 reflections (θ_max = 20.28°) was collected. The reflections were indexed, integrated and corrected for Lorentz, polarization and absorption effects with the program SADABS (Sheldrick, 2010). The unit-cell parameters were calculated from all reflections. The structure was solved using direct methods in space group C2/c and the model refined using full-matrix least-squares. The ADPs of non-hydrogen atoms were refined anisotropically, while hydrogen atoms were located by Fourier difference, except for those of the tert-butyl group which have been placed at calculated positions, and ADPs refined isotropically. All calculations and molecular graphics were carried out with SIR92 (Altomare et al., 1993), PARST97 (Nardelli, 1995), WinGX (Ferrugia, 1999), CRYSTALS (Betteridge et al., 2003), MERCURY (Macrae et al., 2020) and ORTEP-3 for Windows packages (Ferrugia, 2012). Details of the experiment and crystal data are listed in Table 1. Atomic positions are listed in Table 2. Selected bond lengths, bond angles and atomic displacement parameters are given in the CIF (see supporting information). The CIF file has been deposited in the Crystallography Open Database (Gražulis et al., 2009; ref. 3000395).

Table 1
Experimental details

Crystal data
Chemical formula	[Pt2Cl4(NH3)2{μ-HN=C(O)Bu^t}2]
Mr	766.33
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	293
a, b, c (Å)	19.3247 (3), 8.8795 (1), 12.7062 (2)
β (°)	108.332 (1)
V (Å^3)	2069.65 (5)
Z	4
Radiation type	Mo Kα
μ (mm^−1)	14.03
Crystal size (mm)	0.77 × 0.24 × 0.21
Data collection
Diffractometer	Nonius KappaCCD
Absorption correction	Multi-scan (SADABS)
Tmin, Tmax	0.03, 0.05
No. of measured, independent and observed [I > 2.0σ(I)] reflections	29306, 6496, 4944
Rint	0.027
(sin θ/λ)max (Å^−1)	0.910
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.022, 0.017, 1.12
No. of reflections	4707
No. of parameters	100
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å^−3)	1.30, −1.30
Computer programs: COLLECT (Nonius, 2001), CrysAlis (Oxford Diffraction, 2002), SIR92 (Altomare et al., 1993), CRYSTALS (Betteridge et al., 2003), CAMERON (Watkin et al., 1996).

Table 2
Selected geometric parameters (Å, °)

Pt1—Pt1^i	2.5661 (2)	Pt1—N2^i	1.9989 (18)
Pt1—Cl1	2.3214 (6)	Pt1—O1	2.0243 (16)
Pt1—Cl2	2.4282 (6)	C1—O1	1.293 (3)
Pt1—N1	2.0576 (19)	C1—N2	1.294 (3)
Pt1^i—Pt1—Cl2	170.852 (16)	Cl1—Pt1—N1	90.92 (6)
Pt1^i—Pt1—O1	85.94 (5)	N2^i—Pt1—O1	93.18 (8)
Pt1^i—Pt1—N1	99.37 (6)	N2^i—Pt1—Cl2	90.82 (6)
O1—C1—N2	121.65 (19)	N2^i—Pt1—Cl1	87.80 (6)
Cl2—Pt1—O1	88.46 (5)	N2^i—Pt1—N1	177.99 (9)
Cl2—Pt1—N1	87.66 (7)	N2^i—Pt1—Pt1^i	82.28 (6)
Cl1—Pt1—O1	179.02 (5)
Symmetry code: (i) 1 − x, y, −z + ½.

3. Results and discussion

NMR and IR characterization. The ¹H-NMR spectrum at 295 K in DMSO-d₆ (Fig. S1) exhibits signals at frequencies ∼1.20, ∼5.00 and ∼6.70 ppm assigned to the tert-butyl [—C(CH₃)₃], ammine (—NH₃) and amidate [—N(H)CO] protons, respectively. The [¹H-¹⁹⁵Pt] HSQC–NMR heterocorrelate spectrum (Fig. S2) recorded in DMSO-d₆, exhibits two NH signals at 5.01 and 6.74 ppm correlated with the platinum signal at −347 ppm, indicative of a Pt^III cation in a N₂Cl₂OPt coordination environment. The occurrence of the tert-butyl and ammine ligands in the complex is coherent with the IR spectrum with bands at 2964–2918 and 3283–3405 cm⁻¹, respectively (Fig. S2).

X-ray diffraction analysis. The asymmetric unit comprises half a molecule of the [Pt₂Cl₄(NH₃)₂{μ-HN=C(O)Bu^t}₂] complex and the structure is generated by the twofold axis at the midpoint of the Pt–Pt bond (Fig. 3). The coordination geometry of each Pt^III atom (Fig. 3) can be considered a distorted octahedron, with one chlorine, one oxygen and two nitro­gen atoms in equatorial positions, and one chlorine and one platinum of the second subunit in axial positions. The Pt–Pt bond distance [2.5661 (2) Å] is larger than that observed for four-bridge complexes with the same amidate bridge {e.g. [Pt₂{HN=C(Bu^t)O}₄(9-EtG)₂](NO₃)₂, 2.4512 (5) Å (Pacifico et al., 2010)}, and in the range of `platinum blue'-derivates with the head-to-tail configuration [2.582 (1)–2.547 (1) Å range given by O'Halloran & Lippard (1985)]. This behavior indicates that the Pt–Pt distance is influenced by the number of bridging ligands. The equatorial Pt1—Cl1 [2.3214 (6) Å], Pt1—N1 [2.0576 (19) Å] and Pt—O1 [2.0243 (16) Å] bond distances are within the range of those reported for doubly and quadruply bridged dinuclear Pt^III (Fedotova et al., 1997; Dolmella et al., 2002; Hollis et al., 1983), as well as for Pt^II and Pt^IV complexes (Erxleben et al., 2002; Lippert et al., 1984; Ali et al., 2005; Sigel et al., 1999; Shamsuddin et al., 2007). Instead, the axial Pt1−Cl2 bond distance [2.4282 (6) Å] is longer than those reported in the literature (Fedotova et al., 1997; Dolmella et al., 2002; Hollis et al., 1983; Erxleben et al., 2002; Lippert et al., 1984, 1986; Ali et al., 2005; Sigel et al., 1999; Shamsuddin et al., 2007), possibly because of the strong trans influence exerted by the Pt—Pt bond. The doubly-bridged Pt^III molecule is characterized by a twist around the platinum–platinum vector [N2—Pt1—Pt1—O2] with an average torsion angle of 19.58°. The steric interactions between the ammine (bound to the first platinum) and the chloride (bound to the platinum in the second subunit) ligands are responsible for these distortions. In the amidate moiety, the C—X distances are 1.294 (3) Å and 1.293 (3) Å for the C1—N2 and C1—O1 bonds, respectively, in accordance with an extensive π-bond delocalization over the O—C—N moiety. The complex exhibits an intramolecular hydrogen bond involving the ammine hydrogen and the chlorine ligand (Fig. 4)

Figure 3 ORTEP drawing of the final structure model of the [Pt2Cl4(NH3)2{μ-HN=C(O)Bu^t}] complex. Symmetry code: (i) 1 − x, y, ½ − z. Ellipsoids drawn at the 30% probability level. Atom color coding: white for hydrogen, green for chlorine, blue for nitrogen, gray for carbon and red for oxygen.

Figure 4 MERCURY drawing of [Pt2Cl4(NH3)2{μ-HN=C(O)Bu^t}2] showing the intra­molecular hydrogen bond interaction [N1⋯Cl1^i 3.176 (3) Å, (N1)H12⋯Cl1^i 2.46 Å, N1—H12⋯Cl1^i 140°; symmetry code: (i) 1 − x, y, −z + ½]. Ellipsoids drawn at the 30% probability level. Atom color coding: white for hydrogen, green for chlorine, blue for nitrogen, gray for carbon and red for oxygen.

The molecular packing (Fig. 5) is governed by intermolecular hydrogen bonds (Table 3) and van der Waals interactions. (i) Intermolecular hydrogen bonds occur between the N(H) hydrogen of the ammine group and the chlorine ligand (see Fig. 6); and between the axial chlorine and the N(H) hydrogen of the amidate chelating group (see Fig. 7). (ii) van der Waals intermolecular forces involve chlorine and ammine ligands in equatorial position (see Fig. 8).

Table 3
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
Intramolecular
N1—H11⋯Cl2^i	0.89	2.464	3.176 (3)	140
Intermolecular
N1—H11⋯Cl2^ii	0.89	2.541	3.406 (2)	166
N2—H21⋯Cl2^iii	0.87	2.669	3.361 (2)	138
Symmetry codes: (i) 1 + x, y, −z + ½; (ii) 1 − x, −y, 1 − z; (iii) x, 1 − y, z + ½.

Figure 5 Crystal packing of [Pt2Cl4(NH3)2{μ-HN=C(O)Bu^t}2], viewed along [010]. Ellipsoids drawn at the 30% probability level. Atom color coding: white for hydrogen, green for chlorine, blue for nitrogen, gray for carbon and red for oxygen.

Figure 6 MERCURY drawing of two molecules of [Pt2Cl4(NH3)2{μ-HN=C(O)Bu^t}2] linked by an intermolecular hydrogen bond [N1⋯Cl2^i 3.406 (2) Å, (N1)H11⋯Cl2^i 2.54 Å, N1—H1⋯Cl2^i 166°; symmetry code: (i) 1 − x, −y, 1 − z]. Ellipsoids drawn at the 30% probability level. Atom color coding: white for hydrogen, green for chlorine, blue for nitrogen, gray for carbon and red for oxygen.

Figure 7 MERCURY drawing of two molecules of [Pt2Cl4(NH3)2{μ-HN=C(O)Bu^t}2] linked by an intermolecular hydrogen bond [N2⋯Cl2^i 3.361 (2) Å, (N2)H21⋯Cl2^i 2.67 Å, N2—H21⋯Cl2^i 138°; symmetry code: (i) x, 1 − y, z + ½]. Ellipsoids drawn at the 30% probability level. Atom color coding: white for hydrogen, green for chlorine, blue for nitrogen, gray for carbon and red for oxygen.

Figure 8 MERCURY drawing of two molecules of [Pt2Cl4(NH3)2{μ-HN=C(O)Bu^t}2] linked by van der Waals intermolecular interactions [N1⋯Cl1^i 3.496 (2) Å, (N1)H13⋯Cl1^i 2.86 Å, N1—H13⋯Cl1^i 130°; symmetry code: (i) 1 − x, −y, 1 − z]. Ellipsoids drawn at the 30% probability level. Atom color coding: white for hydrogen, green for chlorine, blue for nitrogen, gray for carbon and red for oxygen.

The structural results from the spectroscopic and diffraction analyses confirm that we have successfully designed the synthesis of the expected complex, and the absence of iodine ligands as hypothesized.

4. Conclusion

The necessity to overcome the limitations associated with the use of cisplatin, such as the occurrence of toxic side effects and drug-resistance behaviors, has led to the synthesis of new complexes with higher pharmacological properties. In this study, we have identified a strategy for synthesizing a novel dinuclear Pt^III complex from the pivalo­nitrile derivatives of Pt^II and Pt^IV as precursors. The complex has been characterized by NMR (¹H and ¹⁹⁵Pt) and IR spectroscopies. The crystal structure was determined by X-ray crystallography. To our knowledge this complex is the first example of dinuclear Pt^III species with two bridging ligands in HT configuration. Since it has been demonstrated that `lantern-shaped' Pt^III complexes exhibit antitumor activity, it will be interesting to investigate the activity of our complex with biological assays.

Supporting information

Computing details

Data collection: COLLECT (Nonius, 2001).; cell refinement: DENZO/SCALEPACK (Otwinowski & Minor, 1997); data reduction: CrysAlis, (Oxford Diffraction, 2002); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS (Betteridge et al., 2003).

{2-amino-2-[mu-butyl(amidate)]-4-clhoride}diplatinum(III)

Crystal data

C10H26Cl4N4O2Pt2	F(000) = 1416
Mr = 766.33	Dx = 2.459 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 19.3247 (3) Å	Cell parameters from 9905 reflections
b = 8.8795 (1) Å	θ = 3–40°
c = 12.7062 (2) Å	µ = 14.03 mm^−1
β = 108.332 (1)°	T = 293 K
V = 2069.65 (5) Å^3	Tabular, orange
Z = 4	0.77 × 0.24 × 0.21 mm

Data collection

Nonius KappaCCD diffractometer	4944 reflections with I > 2.0σ(I)
Graphite monochromator	Rint = 0.027
φ & ω scans	θmax = 40.3°, θmin = 3.3°
Absorption correction: multi-scan SADABS	h = −34→34
Tmin = 0.03, Tmax = 0.05	k = −16→16
29306 measured reflections	l = −22→23
6496 independent reflections

Refinement

Refinement on F	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.022	H-atom parameters constrained
wR(F^2) = 0.017
S = 1.12	(Δ/σ)max = 0.003
4707 reflections	Δρmax = 1.30 e Å^−3
100 parameters	Δρmin = −1.30 e Å^−3
0 restraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.39504 (12)	0.4284 (2)	0.70417 (18)	0.0252
C2	0.33011 (13)	0.5356 (3)	0.6762 (2)	0.0328
C3	0.3542 (2)	0.6860 (4)	0.6415 (5)	0.0736
C4	0.26775 (19)	0.4685 (5)	0.5828 (3)	0.0604
C5	0.3040 (2)	0.5602 (5)	0.7774 (3)	0.0615
Pt1	0.496514 (4)	0.231576 (8)	0.647481 (7)	0.0213
Cl2	0.48843 (4)	0.27493 (7)	0.45529 (5)	0.0362
Cl1	0.60019 (3)	0.08476 (7)	0.67596 (5)	0.0328
N1	0.43076 (12)	0.0464 (2)	0.59437 (19)	0.0321
O1	0.40504 (9)	0.35648 (18)	0.62161 (14)	0.0292
N2	0.43773 (11)	0.4095 (2)	0.80464 (16)	0.0281
H33	0.3159	0.7596	0.6298	0.1098*
H32	0.3965	0.7232	0.6981	0.1102*
H31	0.3662	0.6740	0.5739	0.1097*
H43	0.2260	0.5350	0.5667	0.0900*
H42	0.2546	0.3716	0.6055	0.0900*
H41	0.2821	0.4581	0.5169	0.0899*
H53	0.2617	0.6241	0.7577	0.0917*
H52	0.3416	0.6095	0.8348	0.0921*
H51	0.2923	0.4629	0.8041	0.0924*
H21	0.4322	0.4680	0.8560	0.0346*
H12	0.4038	0.0293	0.6360	0.0492*
H11	0.4571	−0.0353	0.5945	0.0494*
H13	0.4017	0.0619	0.5253	0.0497*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0222 (8)	0.0235 (8)	0.0276 (9)	0.0025 (6)	0.0046 (7)	0.0002 (7)
C2	0.0248 (10)	0.0331 (11)	0.0390 (12)	0.0070 (8)	0.0078 (9)	0.0013 (9)
C3	0.056 (2)	0.0418 (17)	0.126 (4)	0.0180 (15)	0.032 (2)	0.033 (2)
C4	0.0328 (14)	0.080 (2)	0.055 (2)	0.0133 (15)	−0.0056 (13)	−0.0156 (17)
C5	0.0392 (16)	0.095 (3)	0.0502 (19)	0.0221 (17)	0.0139 (14)	−0.0106 (18)
Pt1	0.02004 (3)	0.02133 (3)	0.02118 (3)	−0.00012 (3)	0.004499 (19)	−0.00125 (3)
Cl2	0.0471 (3)	0.0360 (3)	0.0259 (2)	0.0030 (3)	0.0119 (2)	0.0024 (2)
Cl1	0.0290 (2)	0.0361 (3)	0.0340 (3)	0.0074 (2)	0.0107 (2)	−0.0035 (2)
N1	0.0307 (9)	0.0298 (9)	0.0342 (10)	−0.0058 (7)	0.0081 (8)	−0.0074 (7)
O1	0.0271 (7)	0.0315 (8)	0.0254 (7)	0.0071 (6)	0.0029 (6)	−0.0019 (6)
N2	0.0286 (9)	0.0270 (8)	0.0264 (8)	0.0072 (7)	0.0053 (7)	−0.0015 (6)

Geometric parameters (Å, º)

C1—C2	1.526 (3)	C5—H52	0.959
C1—O1	1.293 (3)	C5—H51	0.980
C1—N2	1.294 (3)	Pt1—N2^i	1.9989 (18)
C2—C3	1.524 (4)	Pt1—Pt1^i	2.5661 (2)
C2—C4	1.522 (4)	Pt1—Cl2	2.4282 (6)
C2—C5	1.538 (5)	Pt1—Cl1	2.3214 (6)
C3—H33	0.963	Pt1—N1	2.0576 (19)
C3—H32	0.961	Pt1—O1	2.0243 (16)
C3—H31	0.964	N1—H12	0.864
C4—H43	0.969	N1—H11	0.886
C4—H42	0.966	N1—H13	0.891
C4—H41	0.965	N2—H21	0.867
C5—H53	0.962
C2—C1—O1	116.14 (19)	H52—C5—H51	110.0
C2—C1—N2	122.2 (2)	N2^i—Pt1—Pt1^i	82.28 (6)
O1—C1—N2	121.65 (19)	N2^i—Pt1—Cl2	90.82 (6)
C1—C2—C3	108.1 (2)	Pt1^i—Pt1—Cl2	170.852 (16)
C1—C2—C4	109.2 (2)	N2^i—Pt1—Cl1	87.80 (6)
C3—C2—C4	110.9 (3)	Pt1^i—Pt1—Cl1	94.280 (16)
C1—C2—C5	110.8 (2)	Cl2—Pt1—Cl1	91.44 (2)
C3—C2—C5	109.1 (3)	N2^i—Pt1—N1	177.99 (9)
C4—C2—C5	108.7 (3)	Pt1^i—Pt1—N1	99.37 (6)
C2—C3—H33	110.5	Cl2—Pt1—N1	87.66 (7)
C2—C3—H32	110.5	Cl1—Pt1—N1	90.92 (6)
H33—C3—H32	108.3	N2^i—Pt1—O1	93.18 (8)
C2—C3—H31	110.0	Pt1^i—Pt1—O1	85.94 (5)
H33—C3—H31	109.1	Cl2—Pt1—O1	88.46 (5)
H32—C3—H31	108.4	Cl1—Pt1—O1	179.02 (5)
C2—C4—H43	109.2	N1—Pt1—O1	88.10 (8)
C2—C4—H42	109.5	Pt1—N1—H12	111.6
H43—C4—H42	109.0	Pt1—N1—H11	111.0
C2—C4—H41	109.9	H12—N1—H11	108.1
H43—C4—H41	108.8	Pt1—N1—H13	109.5
H42—C4—H41	110.4	H12—N1—H13	108.4
C2—C5—H53	110.0	H11—N1—H13	108.2
C2—C5—H52	109.4	C1—O1—Pt1	118.96 (13)
H53—C5—H52	107.9	C1—N2—Pt1^i	123.31 (15)
C2—C5—H51	109.7	C1—N2—H21	118.4
H53—C5—H51	109.9	Pt1^i—N2—H21	117.4

Symmetry code: (i) −x+1, y, −z+3/2.