cis-Amminedichloro­isopropyl­amine­platinum(II) by X-ray powder diffraction analysis

The title compound, [PtCl₂(C₃H₉N)(NH₃)], was obtained from potassium tetra­chloro­platinate(II) by a two-step route. Ab initio crystal structure determination was carried out using X-­ray powder diffraction techniques. Patterson and Fourier syntheses were used for the atom locations and the Rietveld technique for the final structure refinement. The Pt coordination is close to planar, with Cl atoms in a cis orientation. Mol­ecules are combined into groups of two mol­ecules, with anti­parallel PtN₂Cl₂ planes and a shortest Pt...Pt distance of 3.42 Å. The mol­ecule groups are packed in a parquet motif into corrugated layers parallel to ab. The mol­ecules in the layers are linked by H—N...Cl hydrogen bonds.

S1. Comment

Asymmetric diamminedichloroplatinum(II) complexes exhibit high anticancer activity. Such activity is also observed in cis-amminedichloroisopropylamineplatinum(II) (Bradner et al., 1980; Hydes, 1981). The first evidence of asymmetric complex formation with amines was presented by Grinberg & Smolenskay (1961). The synthesis of cis-amminedichloroisopropylamineplatinum(II) has been described by several workers (Hydes, 1981; Zhelegovskay & Fat'kin, 1986; Zhelegovskay et al., 1991). It consists of the chemical reaction of potassium tetrachloroplatinate(II) with isopropylamine, followed by the refinement of the target product. The main synthetic difficulty stems from a requirement for a low level of impurities. High purity is important for medical applications, as well as for the measurement of the various physico-chemical properties of the substance. Successful investigation of the compound is strongly dependent upon reliable methods of identification; the purity of cis-amminedichloroisopropylamineplatinum(II) has been estimated by elemental chemical analysis, IR spectroscopy, chromatography and conductometry and, since these are not direct methods of identification, errors are possible. An attempt to use X-ray diffraction for cis-amminedichloroisopropylamineplatinum(II) was described by Zhelegovskay et al. (1991). However, the X-ray reference diffraction data they obtained were of low reliability because of the absence of crystallographic data. With regard to the problem of crystallographic investigation of ammine halogen platinates, it is pertinent to mention that the structure of trans-dichlorodiammineplatinum was defined by Porai-Koshits (1954) and redefined by Milburn & Truter (1966). These last authors also determined the structure of α-cis-dichlorodiammineplatinum (Milburn & Truter, 1966). However, β-cis-dichlorodiammineplatinum, the well known pharmaceutical preparation cisplatin, has not been structurally described to date (ICSD, 2005). In the present paper, the results of a crystal structure determination of cis-amminedichloroisopropylamineplatinum(II), (I), performed using the X-ray powder diffraction method, are presented.

The powder pattern of (I) is presented in Fig. 1. The crystal structure of (I) is of the molecular type. The geometry of the molecule is presented in Fig. 2. Atoms N1, N2,Cl1, Cl2 and Pt form a slightly distorted plane. The distances Pt—N and Pt—Cl (Table 2) agree with known values from the literature (Wells, 1984; Allen, 2002; ICSD, 2005). The isopropylamine ligand induces a more distorted square-planar Pt coordination than ammine (Milburn & Truter, 1966). Isopropylamine does not connect to other molecules by hydrogen bonds. Thus, the distortion is a result of the difference in volume of ammine and isopropylamine.

Molecules of (I) are combined into groups of two with antiparallel PtN₂Cl₂ planes. The shortest Pt···Pt distance in the group is 3.42 Å (Fig. 3), which is very close to the value observed in cis-dichlorodiammineplatinum (3.41 Å; Milburn & Truter, 1966). However, the overall molecular arrangements in these structures are different. In contrast with the columnar packed structure observed in the flat cis-diamminedichloroplatinum(II) complex [Pt(NH₃)₂Cl₂], in the structure of (I) the groups of two molecules are packed in a parquet motif into a corrugated layer parallel to ab (Fig. 3).

The molecules of (I) are linked into layers by hydrogen bonds of the N—H···Cl type. The probable candidates for hydrogen bonds, with Cl···N distances of 3.13 and 3.53 Å, are shown in Fig. 3. The arrangement of the layers in the structure is shown in Fig. 4. Bulk isopropylamine ligands project above and below each layer. There are no hydrogen bonds between layers.

S2. Experimental

The synthesis of cis-amminedichloroisopropylamineplatinum(II) involves the reaction of potassium tetrachloroplatinate(II) with ammonium oxalate, followed by addition of a solution of isopropylamine in hydrochloric acid (Kazbanov et al., 1997). The yellow substance which precipitated was refined according to the method of Kazbanov et al. (2002), then filtered, washed and dried in air. [Please give brief details here of synthesis and purification, specifying quantities, solvents, etc.]

S3. Refinement

X-ray powder diffraction data have been deposited in the JCPDS-ICDD PDF2 database. Cell parameters were obtained from d spacings by indexing and refining using programs described in Visser (1969) and Kirik et al. (1979). The space group was determined from the analysis of systematic absences. The structural investigations were carried out using a full-profile structure analysis package based on a modified version of the Rietveld refinement program DBWS-9006PC [DBWM below?] (Wiles & Young, 1981). The intensities of 80 reflections were estimated from the powder pattern by means of the full-profile fitting procedure (Le Bail et al., 1988) and used in the Patterson synthesis. Pt and Cl atoms were located directly from the Patterson map. Positions of light atoms N and C were defined from Fourier synthesis. H atoms were not located, but they were included in the refined structure models and rigidly connected to their C and N atoms. The final refinement was carried out using the Rietveld method (Rietveld, 1969). The crystal structure data are presented in Tables 1 and 2.

Computing details

Data collection: DRON-4 data collection software; cell refinement: POWDER (Kirik et al., 1979); data reduction: [Please provide missing details]; program(s) used to solve structure: DBWM (Wiles & Young, 1981), modified; program(s) used to refine structure: DBWM, modified; molecular graphics: XP (Siemens, 1989); software used to prepare material for publication: [Please provide missing details].

Figures

	Fig. 1. Observed (dots), calculated (superimposed solid) and difference profiles for (I), after the Rietveld refinement. The reflection positions are marked underneath.
	Fig. 2. The molecular complex of (I). Displacement ellipsoids are drawn at the ??% probability level [Please complete] and H atoms are shown as small spheres of arbitrary radii.
	Fig. 3. The arrangement of the complexes in the layer.
	Fig. 4. The arrangement of the layers in the crystal structure.

cis-Amminedichloroisopropylamineplatinum(II)

Crystal data

[PtCl2(C3H9N)(NH3)]	F(000) = 624.0
Mr = 342.14	Cell parameters were obtained from the Rietveld refinement
Monoclinic, P21/a	Dx = 2.647 Mg m^−3
Hall symbol: -P 2yab	Cu Kα radiation, λ = 1.54056 Å
a = 10.3661 (2) Å	T = 293 K
b = 9.5622 (2) Å	Particle morphology: thin powder
c = 9.1261 (2) Å	yellow
β = 108.386 (1)°	flat sheet, 20.0 × 20.0 mm
V = 858.43 (3) Å^3	Specimen preparation: Prepared at 293 K and 101 kPa, cooled at 0 K min^−1
Z = 4

Data collection

DRON-4 powder diffractometer	Data collection mode: reflection
Radiation source: conventional sealed tube	Scan method: step
Graphite monochromator	2θmin = 8.0°, 2θmax = 90.0°, 2θstep = 0.02°
Specimen mounting: packed powder pellet

Refinement

Refinement on F^2	Excluded region(s): none
Least-squares matrix: full	Profile function: Pearson VII
Rp = 0.083	58 parameters
Rwp = 0.111	0 restraints
Rexp = 0.086	0 constraints
RBragg = 0.051	H-atom parameters constrained
R(F^2) = 0.040	Weighting scheme based on measured s.u.'s
χ^2 = 1.664	(Δ/σ)max = 0.1
? data points	Preferred orientation correction: March-Dollase correction

Special details

Experimental. The structure determination was carried out by X-ray powder diffraction. The experimental data were collected on a DRON-4 automatic diffractometer, equipped with a secondary flat graphite monochromator in conjunction with a scintillation detector. Cu Kα radiation was used (λ₁ = 1.54056 Å, λ₂ = 1.54439 Å). The sample was prepared by top-loading the standard quartz sample holder with cutting the excess of well grained substance. The diffraction pattern was scanned with a step of 0.02° 2θ and counting time of 10 sec per step in the most informative angular range from 8° to 90% 2θ at ambient temperature. Corundum was used as the external standard.

Refinement. R_prof-backgr = 0.106

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

	x	y	z	Uiso*/Ueq
Pt	0.8741 (2)	0.1189 (2)	0.9212 (2)	0.0121*
Cl1	0.7855 (3)	−0.0658 (3)	0.7508 (3)	0.0202*
Cl2	0.7244 (3)	0.0566 (3)	1.0548 (3)	0.0152*
C1	1.0593 (6)	0.2042 (5)	0.5908 (5)	0.0256*
HC1A	1.0342 (6)	0.2305 (5)	0.4839 (5)	0.1267*
HC1B	1.1374 (6)	0.2572 (5)	0.6487 (5)	0.1267*
HC1C	1.0806 (6)	0.1063 (5)	0.6009 (5)	0.1267*
C2	0.9405 (6)	0.2343 (5)	0.6529 (5)	0.0393*
HC2A	0.8582 (6)	0.1849 (5)	0.6006 (5)	0.1267*
C3	0.9203 (6)	0.3892 (5)	0.6858 (6)	0.0316*
HC3A	0.8742 (6)	0.4361 (5)	0.5907 (6)	0.1267*
HC3B	0.8669 (6)	0.3959 (5)	0.7544 (6)	0.1267*
HC3C	1.0073 (6)	0.4322 (5)	0.7328 (6)	0.1267*
N1	0.9425 (7)	0.2832 (5)	1.0638 (6)	0.0519*
HN1A	0.8896 (7)	0.3592 (5)	1.0568 (6)	0.1267*
HN1B	1.0250 (7)	0.3305 (5)	1.0752 (6)	0.1267*
HN1C	0.9759 (7)	0.2505 (5)	1.1641 (6)	0.1267*
N2	1.0153 (7)	0.1812 (4)	0.8198 (6)	0.0345*
HN2A	1.0920 (7)	0.2220 (4)	0.8800 (6)	0.1267*
HN2B	1.0500 (7)	0.0950 (4)	0.7980 (6)	0.1267*

Geometric parameters (Å, º)

Pt—N2	2.051 (7)	N1—HN1A	0.90 (1)
Pt—N1	2.021 (3)	N1—HN1B	0.94 (1)
Pt—Cl1	2.341 (3)	C3—HC3A	0.96 (1)
Pt—Cl2	2.333 (3)	C3—HC3B	0.96 (1)
C1—C2	1.537 (9)	C3—HC3C	0.96 (1)
C2—C3	1.539 (7)	C1—HC1A	0.96 (1)
C2—N2	1.560 (7)	C1—HC1B	0.96 (1)
Pt—Pt^i	3.418 (3)	C1—HC1C	0.96 (1)
N1—HN1C	0.93 (1)	C2—HC2A	0.96 (1)
Cl1—Pt—Cl2	88.18 (9)	HC1C—C1—C2	109.5 (5)
N1—Pt—N2	84.8 (1)	HC1A—C1—C2	109.5 (6)
Cl1—Pt—N2	96.1 (1)	HC1B—C1—C2	109.4 (6)
Cl2—Pt—N1	91.0 (1)	C2—C3—HC3A	109.5 (5)
C1—C2—C3	115.3 (5)	C2—C3—HC3C	109.4 (6)
Pt—N1—HN1A	120.0 (6)	C2—C3—HC3B	109.4 (5)
Pt—N1—HN1B	124.4 (6)	HC2A—C2—C3	114.6 (6)
Pt—N1—HN1C	108.7 (5)

Symmetry code: (i) −x+2, −y, −z+2.