Crystal structure of di­chlorido­(1,2-phenyl­enedi­amine-κ² N,N′)platinum(II)

In the crystal structure of the title compound, almost planar [PtCl₂{(C₆H₄)(NH₂)₂}] mol­ecules are stacked into columns along the c axis, suggesting Pt⋯Pt inter­actions.

Abstract

The Pt^II atom in the title compound, [PtCl₂{(C₆H₄)(NH₂)₂}], lies on a twofold rotation axis and has a slightly distorted square-planar coordination environment defined by two N atoms of an 1,2-phenyl­enedi­amine ligand and two Cl⁻ ions. In the crystal, the planar complex mol­ecules are stacked parallel to the c axis, resulting in a columnar structure. In a column, an infinite almost straight Pt⋯Pt chain is formed, suggesting weak metal–metal inter­actions [Pt⋯Pt = 3.3475 (8) Å]. The crystal packing is stabilized by a three-dimensional N—H⋯Cl hydrogen-bonding network between the amino groups and the Cl ligands of adjacent mol­ecules.

Chemical context  

The title compound, di­chlorido­(1,2-phenyl­enedi­amine-κ² N,N′)platinum(II) [PtCl₂{(C₆H₄)(NH₂)₂}], (I), which was originally prepared by Connors et al. (1972 ▸), is a member of the family of derivatives of cis-diamminedi­chlorido­platinum(II), cis-[PtCl₂(NH₃)₂] (cis-platin). Since the discovery of the anti­tumor activity of cis-platin (Rosenberg et al., 1965 ▸), numerous derivatives and analogues of cis-platin have been prepared and investigated. However, reports on the corresponding crystal structures are rather scarce, probably because of the difficulty in obtaining crystals suitable for X-ray analysis, in part owing to poor solubility. Although the anti­tumor activity (Connors et al., 1972 ▸; Meischen et al., 1976 ▸) and the chemical stabilities (Köckerbauer & Bednarski, 1996 ▸) of the title compound have been reported, its crystal structure has not been determined so far. In the course of our study of the deprotonation and redox properties of a platinum complex with 1,2-phenyl­enedi­amine as a ligand (Konno & Matsushita, 2006a ▸,b ▸), we have successfully obtained single crystals of the title compound and report here its crystal structure.

Structural commentary  

The mol­ecular structure of (I) is displayed in Fig. 1 ▸. The platinum compound (I) is isostructural with the palladium compound [PdCl₂{(C₆H₄)(NH₂)₂}] reported previously (Konno & Matsushita, 2017 ▸). The Pt^II atom lies on a twofold rotation axis. Hence the asymmetric unit comprises half of a [PtCl₂{(C₆H₄)(NH₂)₂}] mol­ecule, the other half being completed by application of twofold rotation symmetry. The Pt^II atom is coordinated by two N atoms of an 1,2-phenyl­enedi­amine ligand and by two Cl⁻ ions in a slightly distorted square-planar configuration (Table 1 ▸). The r.m.s. deviation of the least-squares plane formed by atoms Pt1, N1, C1, C2 and C3 is 0.0121 Å. The structural parameters of the coordination sphere around Pt^II in the crystal of (I) (Table 1 ▸) are consistent with those found in cis-[PtCl₂(NH₃)₂] (Milburn & Truter, 1966 ▸), [PtCl₂(en)] (en is ethyl­enedi­amine; Iball et al., 1975 ▸), cis-[PtCl₂(L)₂] (L is cyclo­hexyl­amine; Lock et al., 1980 ▸), [PtCl₂(cis-dac)]·0.33-hydrate (dac is 1,2-di­amino­cyclo­hexane; Lock & Pilon, 1981 ▸), cis-[PtCl₂(L′)(NH₃)] (L′ is cyclo­butyl­amine; Rochon & Melanson, 1986 ▸), [PtCl₂(Me₂en)] (Me₂en is N,N-di­methyl­ethylenedi­amine; Melanson et al., 1987 ▸), [PtCl₂(tn)] (tn is 1,3-di­amino­propane; Odoko & Okabe, 2006 ▸), [PtCl₂(L′′)] (L′′ is 2-morpholino­ethyl­amine; Shi et al., 2006 ▸), [PtCl₂(Me₄en)] (Me₄en is N,N,N′,N′- tetra­methyl­ethylenedi­amine; Asiri et al., 2012 ▸). Bond lengths and angles of the 1,2-phenyl­enedi­amine moiety (Table 1 ▸) are not significantly different from those found in the bis­(1,2-phenyl­enedi­amine)­platinum(II) complex, [Pt(C₆H₈N₂)₂]Cl₂·2H₂O [N—C = 1.450 (2) Å, C—C = 1.365 (6)–1.389 (4) Å; Konno & Matsushita, 2006a ▸] or in isostructural di­chlorido­(1,2-phenyl­enedi­amine)­palladium(II) [N—C = 1.458 (2) Å, C—C = 1.371 (3)–1.416 (8) Å; Konno & Matsushita, 2017 ▸].

Figure 1.

A view of the mol­ecular structure of compound (I), showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level for non-H atoms. [Symmetry code: (i) −x + 1, y, −z + .]

Table 1. Selected geometric parameters (Å, °).

Pt1—N1	2.040 (4)	C1—C2	1.372 (6)
Pt1—Cl1	2.3213 (13)	C1—C1ii	1.386 (9)
Pt1—Pt1i	3.3475 (8)	C2—C3	1.377 (11)
N1—C1	1.445 (6)	C3—C3ii	1.38 (3)
N1—Pt1—N1ii	83.6 (3)	Pt1i—Pt1—Pt1iii	176.513 (11)
N1—Pt1—Cl1	91.39 (15)	C1—N1—Pt1	110.8 (3)
Cl1ii—Pt1—Cl1	93.69 (7)	C2—C1—C1ii	119.8 (3)
N1—Pt1—Pt1i	92.07 (14)	C2—C1—N1	122.7 (5)
Cl1—Pt1—Pt1i	93.80 (4)	C1ii—C1—N1	117.4 (2)
N1—Pt1—Pt1iii	85.32 (14)	C1—C2—C3	120.3 (8)
Cl1—Pt1—Pt1iii	88.59 (4)	C2—C3—C3ii	119.8 (6)

Symmetry codes: (i) ; (ii) ; (iii) .

Supra­molecular features  

As shown in Fig. 2 ▸, the neutral planar mol­ecules of (I) stack parallel to the c axis, resulting in a columnar structure. The planar [PtCl₂{(C₆H₄)(NH₂)₂}] units are arranged in parallel and the 1,2-phenyl­enedi­amine moieties alternate with each other as a result of the c-glide operation. In the column, an infinite, almost straight [Pt⋯Pt⋯Pt = 176.513 (11)°] platinum chain is formed with a short inter­atomic distance [Pt⋯Pt = 3.3475 (8) Å], suggesting weak metal–metal inter­actions. The infinite palladium chain of the isostructural Pd complex is straighter [Pd⋯Pd⋯Pd = 179.232 (7)°] than the platinum chain. The Pt⋯Pt distance in (I) is slightly shorter than those of cis-[PtCl₂(NH₃)₂] [3.372 (2) and 3.409 (2) Å; Milburn & Truter, 1966 ▸] or [PtCl₂(en)] [3.381 Å; Iball et al., 1975 ▸], and is considerably shorter than that of [PtCl₂(tn)] [3.646 Å; Odoko & Okabe, 2006 ▸], all of which have similar columnar structures.

Figure 2.

A view of the columnar structure of compound (I). Light-blue dashed lines represent hydrogen bonds between adjacent mol­ecules in the column. Yellow dashed lines indicate the short contact between Pt atoms in the column. [Symmetry codes: (i) −x + 1, −y + 1, −z; (ii) −x + 1, −y + 1, −z + 1; (iii) x, y, z + 1.]

The inter­molecular Pt⋯Pt distance of (I) suggests that the columnar structure is stabilized by weak metal–metal inter­actions. The columnar structure of (I) is further stabilized by inter­molecular N—H⋯Cl hydrogen bonds between adjacent mol­ecules in the column (Fig. 2 ▸ and Table 2 ▸). Inter­columnar hydrogen bonds also help to stabilize the crystal packing of the columns (Fig. 3 ▸, and Table 2 ▸).

Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯Cl1iv	0.90	2.57	3.353 (4)	146
N1—H1B⋯Cl1v	0.90	2.71	3.381 (4)	133
N1—H1B⋯Cl1vi	0.90	2.73	3.320 (5)	124

Symmetry codes: (iv) ; (v) ; (vi) .

Figure 3.

The crystal packing of compound (I), viewed along the c axis. Light-blue dashed lines represent inter­columnar hydrogen bonds. Solid orange lines indicate the unit cell.

Synthesis and crystallization  

Compound (I) was prepared using a method modified from that described by Connors et al. (1972 ▸) as follows. To an aqueous HCl solution (1.0 M, 15 ml) of K₂[PtCl₄] (0.241 mmol, 100 mg) was slowly added an aqueous HCl solution (1.0 M, 15 ml) of 1,2-phenyl­enedi­amine (0.241 mmol, 26 mg), and then the solution was sealed in a screw-cap vial and was kept at room temperature for one week in the dark. Pale-brown needle-like crystals suitable for X-ray analysis were obtained (yield 52%). Elemental analysis found: C 19.26, H 2.23, N 7.30%; calculated for C₆H₈Cl₂N₂Pt: C 19.26, H 2.16, N 7.49%. Elemental analysis was carried out by the Laboratory of Organic Elemental Analysis, Department of Chemistry, Graduate School of Science, The University of Tokyo.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. One reflection (010) was omitted in the final refinement because it was obstructed by the beam-stop. H atoms were placed in geometrically calculated positions and refined as riding, with C(aromatic)—H = 0.93 and N—H = 0.90 Å, and with U _iso(H) = 1.2U _eq(C,N). The maximum and minimum electron density peaks are located 0.80 and 0.74 Å, respectively, from atom Pt1.

Table 3. Experimental details.

Crystal data
Chemical formula	[PtCl2(C6H8N2)]
M r	374.13
Crystal system, space group	Monoclinic, P2/c
Temperature (K)	296
a, b, c (Å)	7.087 (2), 10.446 (3), 6.6920 (16)
β (°)	116.61 (2)
V (Å3)	442.9 (2)
Z	2
Radiation type	Mo Kα
μ (mm−1)	16.38
Crystal size (mm)	0.26 × 0.13 × 0.07
Data collection
Diffractometer	Rigaku R-AXIS RAPID imaging-plate
Absorption correction	Multi-scan (ABSCOR; Higashi, 1995 ▸)
T min, T max	0.116, 0.304
No. of measured, independent and observed [F 2 > 2σ(F 2)] reflections	10875, 1587, 1480
R int	0.030
(sin θ/λ)max (Å−1)	0.757
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.034, 0.099, 1.18
No. of reflections	1587
No. of parameters	52
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	4.62, −1.74

Computer programs: RAPID-AUTO (Rigaku, 1998 ▸), SIR92 (Altomare et al., 1994 ▸), DIAMOND (Brandenburg, 2017 ▸), SHELXL97 (Sheldrick, 2008 ▸) and publCIF (Westrip, 2010 ▸).

Supplementary Material

CCDC reference: 1055177

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

[PtCl2(C6H8N2)]	F(000) = 340
Mr = 374.13	Dx = 2.805 Mg m−3
Monoclinic, P2/c	Mo Kα radiation, λ = 0.71075 Å
Hall symbol: -P 2yc	Cell parameters from 12924 reflections
a = 7.087 (2) Å	θ = 2.0–32.6°
b = 10.446 (3) Å	µ = 16.38 mm−1
c = 6.6920 (16) Å	T = 296 K
β = 116.61 (2)°	Needle, pale brown
V = 442.9 (2) Å3	0.26 × 0.13 × 0.07 mm
Z = 2

Data collection

Rigaku R-AXIS RAPID imaging-plate diffractometer	1587 independent reflections
Radiation source: X-ray sealed tube	1480 reflections with F2 > 2σ(F2)
Graphite monochromator	Rint = 0.030
Detector resolution: 10.00 pixels mm-1	θmax = 32.6°, θmin = 3.2°
ω scans	h = −10→10
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −15→15
Tmin = 0.116, Tmax = 0.304	l = −10→8
10875 measured reflections

Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.034	H-atom parameters constrained
wR(F2) = 0.099	w = 1/[σ2(Fo2) + (0.0669P)2 + 0.3105P] where P = (Fo2 + 2Fc2)/3
S = 1.18	(Δ/σ)max = 0.001
1587 reflections	Δρmax = 4.62 e Å−3
52 parameters	Δρmin = −1.74 e Å−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0039 (12)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane) - 2.7022 (0.0123) x - 0.0000 (0.0000) y + 6.6740 (0.0026) z = 0.3174 (0.0059) * 0.0000 (0.0000) Pt1 * -0.0185 (0.0028) Cl1 * 0.0206 (0.0042) N1 * 0.0050 (0.0039) C1 * -0.0017 (0.0044) C2 * 0.0031 (0.0116) C3 * 0.0185 (0.0028) Cl1_$6 * -0.0206 (0.0042) N1_$6 * -0.0050 (0.0039) C1_$6 * 0.0017 (0.0044) C2_$6 * -0.0031 (0.0116) C3_$6 Rms deviation of fitted atoms = 0.0121

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
Pt1	0.5000	0.504875 (16)	0.2500	0.03029 (13)
Cl1	0.23327 (19)	0.65687 (13)	0.1392 (2)	0.0429 (3)
N1	0.2863 (7)	0.3592 (4)	0.1666 (8)	0.0407 (9)
H1A	0.2144	0.3653	0.2480	0.049*
H1B	0.1934	0.3657	0.0213	0.049*
C1	0.3910 (7)	0.2364 (4)	0.2066 (6)	0.0400 (8)
C2	0.2835 (10)	0.1225 (5)	0.1621 (9)	0.0563 (12)
H2	0.1370	0.1224	0.1016	0.068*
C3	0.391 (3)	0.0081 (5)	0.207 (2)	0.068 (3)
H3	0.3182	−0.0690	0.1780	0.082*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Pt1	0.02635 (17)	0.02835 (16)	0.03208 (18)	0.000	0.00944 (11)	0.000
Cl1	0.0335 (5)	0.0383 (5)	0.0513 (6)	0.0058 (4)	0.0140 (4)	0.0012 (4)
N1	0.0347 (18)	0.0371 (18)	0.043 (2)	−0.0017 (14)	0.0108 (16)	−0.0011 (15)
C1	0.050 (2)	0.0328 (18)	0.0365 (18)	−0.0028 (15)	0.0185 (17)	−0.0012 (14)
C2	0.067 (3)	0.046 (3)	0.054 (3)	−0.018 (2)	0.026 (2)	−0.005 (2)
C3	0.112 (10)	0.037 (3)	0.063 (6)	−0.017 (3)	0.047 (6)	−0.006 (2)

Geometric parameters (Å, º)

Pt1—N1	2.040 (4)	N1—H1B	0.9000
Pt1—N1i	2.040 (4)	C1—C2	1.372 (6)
Pt1—Cl1i	2.3213 (13)	C1—C1i	1.386 (9)
Pt1—Cl1	2.3213 (13)	C2—C3	1.377 (11)
Pt1—Pt1ii	3.3475 (8)	C2—H2	0.9300
Pt1—Pt1iii	3.3475 (8)	C3—C3i	1.38 (3)
N1—C1	1.445 (6)	C3—H3	0.9300
N1—H1A	0.9000
N1—Pt1—N1i	83.6 (3)	C1—N1—Pt1	110.8 (3)
N1—Pt1—Cl1i	174.82 (12)	C1—N1—H1A	109.5
N1i—Pt1—Cl1i	91.39 (15)	Pt1—N1—H1A	109.5
N1—Pt1—Cl1	91.39 (15)	C1—N1—H1B	109.5
N1i—Pt1—Cl1	174.82 (12)	Pt1—N1—H1B	109.5
Cl1i—Pt1—Cl1	93.69 (7)	H1A—N1—H1B	108.1
N1—Pt1—Pt1ii	92.07 (14)	C2—C1—C1i	119.8 (3)
N1i—Pt1—Pt1ii	85.32 (14)	C2—C1—N1	122.7 (5)
Cl1i—Pt1—Pt1ii	88.59 (4)	C1i—C1—N1	117.4 (2)
Cl1—Pt1—Pt1ii	93.80 (4)	C1—C2—C3	120.3 (8)
N1—Pt1—Pt1iii	85.32 (14)	C1—C2—H2	119.8
N1i—Pt1—Pt1iii	92.07 (14)	C3—C2—H2	119.8
Cl1i—Pt1—Pt1iii	93.80 (4)	C2—C3—C3i	119.8 (6)
Cl1—Pt1—Pt1iii	88.59 (4)	C2—C3—H3	120.1
Pt1ii—Pt1—Pt1iii	176.513 (11)	C3i—C3—H3	120.1
Pt1ii—Pt1—N1—C1	84.8 (3)	Pt1iii—Pt1—N1—C1	−92.9 (3)

Symmetry codes: (i) −x+1, y, −z+1/2; (ii) −x+1, −y+1, −z; (iii) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Cl1iv	0.90	2.57	3.353 (4)	146
N1—H1B···Cl1v	0.90	2.71	3.381 (4)	133
N1—H1B···Cl1vi	0.90	2.73	3.320 (5)	124

Symmetry codes: (iv) x, −y+1, z+1/2; (v) x, −y+1, z−1/2; (vi) −x, −y+1, −z.

Funding Statement

This work was funded by Ministry of Education, Culture, Sports, Science and Technology, MEXT-Supported Program for the Strategic Research Foundation at Private Universities grant S1311027.