Crystal structure of trans-di-chlorido-(4-nitro-aniline-κN (1))(piperidine-κN)platinum(II).

In the title complex, [PtCl2(C5H11N)(C6H6N2O2)], the Pt(II) metal atom displays a slightly distorted trans-PtN2Cl2 square-planar coordination geometry. The dihedral angle between the mean plane of the benzene and piperidine rings is 89.03 (3)°. In the crystal structure, inversion dimers are formed via N-H⋯Cl hydrogen-bond inter-actions, resulting in chains parallel to the [001] direction. The benzene rings within the chains show π-π stacking inter-actions [centroid-to-centroid distances of 3.801 (3) Å] and neighbouring chains inter-act via N-H⋯O hydrogen bonds.

Chemical context

The title compound is one of many complexes which have been synthesized for the purpose of potential medical applications (Klein & Hambley, 2009 ▸; Wilson & Lippard, 2014 ▸; Peng et al., 2014 ▸). It is notable that according to the procedure used for the synthesis of complexes of the type cis-[PtCl2(piperidine)(another amine)] (piperidine hereafter denoted Pip) (Dinh & Da, 2003 ▸; Nguyen Thi Thanh et al., 2014 ▸), the reaction between K[PtCl3(Pip)] and p-nitro­aniline under appropriate conditions gave no cis complex, as expected, but instead gave the trans-[PtCl2(p-nitro­aniline)(Pip)] derivative, (I).

To explain this we suppose that p-nitro­aniline first coordinates with PtII via the N atom of the amino group to form cis-[PtCl2(p-nitro­aniline)(Pip)] based on the trans effect. Then, in the reaction solution, the cis complex converts into the trans complex and the thermodynamics of this conversion are currently under investigation by us.

The anti­cancer activity of the title compound was tested according to the method described by Skehan et al. (1990 ▸) against four human cancer cell lines (HepG2, RD, MCF7 and Fl). The IC50 values calculated based on OD values taken on an Elisa instrument at 515–540 nm are >10, 4.86, >10 and 8.25 µg ml−1, respectively.

Structural commentary

The mol­ecular structure of the title compound is illustrated in Fig. 1 ▸ and surprisingly shows a trans arrangement of the two Cl atoms [Cl8—Pt1—Cl9 = 177.84 (4)°]. The piperidine ring adopts the usual chair conformation, with the N2—Pt1 bond in the equatorial position. The piperidine ring is oriented nearly perpendicular to the coordination plane of the PtII atom, thereby reducing the van der Waals repulsion; the dihedral angle between the least-squares mean planes through the piperdine ring and the four atoms coordinated to the Pt atom is 89.6 (2)°. One short intra­molecular contact is observed, i.e. H7B⋯Cl8 = 2.83 Å. The mean planes through the piperidine ring and the benzene ring make a dihedral angle of 89.0 (3)°. The dihedral angle between the mean planes of the nitro substituent and the benzene ring is 16.6 (3)°.

Figure 1

The mol­ecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level.

Supra­molecular features

In the crystal, inversion dimers are formed via N—H⋯Cl inter­actions between the aniline N atom and both Cl atoms, resulting in chains of mol­ecules along the [001] direction (Fig. 2 ▸ and Table 1 ▸). Within these chains, π–π inter­actions occur between the aromatic rings [Cg⋯Cg iv = 3.801 (3) Å; Cg is the centroid of the C11–C16 ring; symmetry code: (iv) −x, y, −z + ; Fig. 2 ▸]. Neighbouring chains are linked via N—H⋯O hydrogen bonds between the piperidine N atom and a nitro O atom (Fig. 2 ▸ and Table 1 ▸).

Figure 2

Partial packing diagram of the title compound, showing a chain of mol­ecules formed parallel to the [001] direction via N—H⋯Cl inter­actions (green dotted lines) and π–π inter­actions (grey dotted line). Neighbouring chains inter­act via N—H⋯O hydrogen bonds (red dotted line).

Table 1

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
N2H2O18i	0.93	2.27	3.182(6)	165
N10H10ACl8ii	0.92	2.32	3.198(4)	158
N10H10BCl9iii	0.92	2.37	3.255(4)	161

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

Database survey

A search of the Cambridge Structural Database (Version 5.36; last update February 2015; Groom & Allen, 2014 ▸) for Pt complexes with Pt coordinated to exactly two Cl atoms and two N atoms gave 713 hits. The majority of these Pt complexes display a cis coordination of the Cl atoms (474 structures), with the remaining 239 structures showing a trans coordination. There is no difference in the Pt—Cl distances between both configurations. The average Pt—Cl distances are 2.300 (15) and 2.299 (12) Å for the cis and trans arrangements, respectively, and correspond to the observed distances of 2.3039 (11) and 2.2917 (12) Å for Pt1—Cl8 and Pt1—Cl9, respectively.

Synthesis and crystallization

The starting complex K[PtCl3(piperidine)] (0.425 g, 1 mmol), prepared according to the synthetic procedure of Da et al. (2001 ▸) with slight modifications, was dissolved in water (10 ml) and filtered to afford a clear solution. To this solution, p-nitro­aniline (1 mmol) in ethanol (10 ml) was added gradually while stirring at 413–318 K. After 1 h, a brown powder appeared and the reaction mixture was then stirred further for 24 h until all the precipitate was completely dissolved. The solvent was removed in vacuo to give a brown–yellow product. The product was washed consecutively with a 0.1 M HCl solution (2 × 2 ml), warm water (2 × 2 ml) and diethyl ether (2 × 2 ml). The yield was 80%. Single crystals suitable for X-ray determination were obtained by slow evaporation within 12 h from an acetone solution at room temperature. IR (KBr, cm−1): 3199, 3113 (νNH); 3070, 2927, 2862 (νCH); 1596, 1525, 1479 (νC=C arom); 1342, 1325 (νNO); 1H NMR (CDCl3, 500 MHz): δ 8.21 (2H, d, 3 J = 9.0 Hz, Ar-H), 7.47 (2H, d, 3 J = 9.0 Hz, Ar-H), 5.49 (2H, br, O2NC6H4NH), 3.66 (1H, br, C5H10NH), 3.26 (2Hα e, d, 2 J ae = 13.0 Hz, C5 HNH), 2.99 (2Hα a, q, 2 J ae, 3 J aa, 3 J aa(NH) = 13.0 Hz, C5 HNH), 1.69–1.43 (4Hβ, 2Hγ, ov, C5 HNH). 13C{1H} NMR (125 MHz, CDCl3): δ 149.6, 125.1, 124.2 (O2NCH4NH2), 54.0, 27.2, 24.3 (CH10NH).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All H atoms were placed at idealized positions and refined in riding mode, with U iso(H) values assigned as 1.2U eq of the parent atoms, with C—H distances of 0.95 (aromatic) and 0.99 Å (methyl­ene), and N—H distances of 0.93 (NH) and 0.92 Å (NH2).

Table 2

Experimental details

Crystal data
Chemical formula	[PtCl2(C5H11N)(C6H6N2O2)]
M r	489.27
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	100
a, b, c ()	15.8763(11), 18.5394(11), 10.8707(6)
()	103.119(7)
V (3)	3116.1(3)
Z	8
Radiation type	Mo K
(mm1)	9.35
Crystal size (mm)	0.35 0.15 0.1
Data collection
Diffractometer	Agilent SuperNova (single source at offset, Eos detector)
Absorption correction	Multi-scan (CrysAlis PRO; Agilent, 2012 ▸)
T min, T max	0.538, 1.000
No. of measured, independent and observed [I > 2(I)] reflections	8156, 3109, 2713
R int	0.044
(sin /)max (1)	0.625
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.032, 0.072, 1.10
No. of reflections	3109
No. of parameters	172
H-atom treatment	H-atom parameters constrained
max, min (e 3)	2.75, 1.82

Computer programs: CrysAlis PRO (Agilent, 2012 ▸), SHELXS97 and SHELXL97 (Sheldrick, 2008 ▸) and OLEX2 (Dolomanov et al., 2009 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989015009196/rz5159sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015009196/rz5159Isup2.hkl

CCDC reference: 1400786

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

[PtCl2(C5H11N)(C6H6N2O2)]	F(000) = 1856
Mr = 489.27	Dx = 2.086 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 15.8763 (11) Å	Cell parameters from 3549 reflections
b = 18.5394 (11) Å	θ = 3.4–28.8°
c = 10.8707 (6) Å	µ = 9.35 mm−1
β = 103.119 (7)°	T = 100 K
V = 3116.1 (3) Å3	, brown
Z = 8	0.35 × 0.15 × 0.1 mm

Agilent SuperNova (single source at offset, Eos detector) diffractometer	3109 independent reflections
Radiation source: SuperNova (Mo) X-ray Source	2713 reflections with I > 2σ(I)
Mirror monochromator	Rint = 0.044
Detector resolution: 15.9631 pixels mm-1	θmax = 26.4°, θmin = 2.8°
ω scans	h = −19→15
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2012)	k = −17→23
Tmin = 0.538, Tmax = 1.000	l = −13→13
8156 measured reflections

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.072	H-atom parameters constrained
S = 1.10	w = 1/[σ2(Fo2) + (0.0296P)2 + 0.5839P] where P = (Fo2 + 2Fc2)/3
3109 reflections	(Δ/σ)max = 0.003
172 parameters	Δρmax = 2.75 e Å−3
0 restraints	Δρmin = −1.82 e Å−3

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

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 > σ(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.

	x	y	z	Uiso*/Ueq
C3	0.2646 (4)	0.9772 (3)	0.4633 (5)	0.0233 (13)
H3A	0.2439	1.0130	0.5173	0.028*
H3B	0.2335	0.9859	0.3748	0.028*
C4	0.3620 (4)	0.9877 (3)	0.4750 (5)	0.0243 (13)
H4A	0.3815	0.9562	0.4132	0.029*
H4B	0.3734	1.0383	0.4551	0.029*
C5	0.4128 (4)	0.9694 (3)	0.6083 (5)	0.0267 (13)
H5A	0.4755	0.9727	0.6122	0.032*
H5B	0.3985	1.0045	0.6691	0.032*
C6	0.3905 (4)	0.8933 (3)	0.6443 (6)	0.0255 (14)
H6A	0.4109	0.8580	0.5892	0.031*
H6B	0.4210	0.8833	0.7326	0.031*
C7	0.2938 (4)	0.8839 (3)	0.6313 (5)	0.0220 (13)
H7A	0.2816	0.8332	0.6501	0.026*
H7B	0.2746	0.9151	0.6937	0.026*
C11	−0.0526 (3)	0.8256 (3)	0.5180 (4)	0.0175 (11)
C12	−0.0838 (4)	0.8538 (3)	0.6181 (5)	0.0193 (11)
H12	−0.0832	0.9044	0.6328	0.023*
C13	−0.1159 (3)	0.8069 (3)	0.6957 (5)	0.0205 (12)
H13	−0.1370	0.8248	0.7649	0.025*
C14	−0.1167 (4)	0.7338 (3)	0.6710 (5)	0.0225 (12)
C15	−0.0857 (4)	0.7057 (3)	0.5722 (5)	0.0266 (14)
H15	−0.0870	0.6552	0.5571	0.032*
C16	−0.0528 (4)	0.7522 (3)	0.4957 (5)	0.0218 (12)
H16	−0.0303	0.7339	0.4280	0.026*
Cl8	0.10439 (9)	0.97037 (6)	0.62798 (11)	0.0190 (3)
Cl9	0.12310 (9)	0.80109 (7)	0.32660 (11)	0.0212 (3)
N2	0.2441 (3)	0.9028 (2)	0.5016 (4)	0.0160 (9)
H2	0.2629	0.8713	0.4469	0.019*
N10	−0.0192 (3)	0.8739 (2)	0.4368 (4)	0.0157 (9)
H10A	−0.0439	0.9185	0.4409	0.019*
H10B	−0.0373	0.8576	0.3552	0.019*
N17	−0.1522 (3)	0.6855 (3)	0.7523 (4)	0.0294 (12)
O18	−0.1616 (3)	0.7083 (2)	0.8546 (3)	0.0316 (10)
O19	−0.1721 (4)	0.6237 (2)	0.7150 (4)	0.0464 (14)
Pt1	0.113556 (13)	0.887195 (10)	0.474086 (16)	0.01473 (9)

	U11	U22	U33	U12	U13	U23
C3	0.021 (3)	0.032 (3)	0.019 (3)	−0.008 (2)	0.007 (2)	0.001 (2)
C4	0.024 (4)	0.030 (3)	0.022 (3)	−0.003 (2)	0.010 (2)	0.000 (2)
C5	0.021 (3)	0.031 (3)	0.029 (3)	−0.001 (3)	0.007 (3)	−0.003 (3)
C6	0.022 (4)	0.026 (3)	0.028 (3)	0.000 (2)	0.005 (3)	0.000 (2)
C7	0.018 (3)	0.026 (3)	0.022 (3)	−0.001 (2)	0.003 (2)	0.003 (2)
C11	0.013 (3)	0.022 (3)	0.016 (2)	−0.002 (2)	0.000 (2)	0.000 (2)
C12	0.019 (3)	0.019 (3)	0.020 (3)	−0.001 (2)	0.006 (2)	−0.004 (2)
C13	0.013 (3)	0.034 (3)	0.014 (2)	−0.003 (2)	0.004 (2)	−0.002 (2)
C14	0.025 (3)	0.024 (3)	0.021 (3)	−0.004 (2)	0.010 (2)	0.005 (2)
C15	0.040 (4)	0.017 (3)	0.021 (3)	−0.001 (3)	0.004 (3)	−0.002 (2)
C16	0.025 (3)	0.021 (3)	0.020 (3)	−0.001 (2)	0.008 (2)	0.001 (2)
Cl8	0.0217 (8)	0.0195 (6)	0.0164 (6)	0.0017 (5)	0.0054 (5)	−0.0009 (5)
Cl9	0.0220 (8)	0.0239 (6)	0.0174 (6)	0.0023 (6)	0.0039 (5)	−0.0042 (5)
N2	0.012 (3)	0.020 (2)	0.016 (2)	−0.0003 (18)	0.0033 (18)	−0.0026 (18)
N10	0.013 (3)	0.019 (2)	0.015 (2)	0.0011 (18)	0.0022 (19)	−0.0009 (18)
N17	0.031 (3)	0.030 (3)	0.028 (3)	−0.003 (2)	0.009 (2)	0.006 (2)
O18	0.035 (3)	0.044 (2)	0.021 (2)	−0.007 (2)	0.0163 (18)	0.0022 (19)
O19	0.077 (4)	0.026 (2)	0.046 (3)	−0.006 (2)	0.034 (3)	0.003 (2)
Pt1	0.01469 (15)	0.01670 (13)	0.01350 (12)	0.00081 (7)	0.00464 (9)	0.00004 (7)

C3—H3A	0.9900	C12—H12	0.9500
C3—H3B	0.9900	C12—C13	1.387 (7)
C3—C4	1.535 (8)	C13—H13	0.9500
C3—N2	1.497 (6)	C13—C14	1.381 (7)
C4—H4A	0.9900	C14—C15	1.382 (7)
C4—H4B	0.9900	C14—N17	1.458 (7)
C4—C5	1.528 (8)	C15—H15	0.9500
C5—H5A	0.9900	C15—C16	1.380 (7)
C5—H5B	0.9900	C16—H16	0.9500
C5—C6	1.526 (7)	Cl8—Pt1	2.3039 (11)
C6—H6A	0.9900	Cl9—Pt1	2.2917 (12)
C6—H6B	0.9900	N2—H2	0.9300
C6—C7	1.520 (8)	N2—Pt1	2.046 (4)
C7—H7A	0.9900	N10—H10A	0.9200
C7—H7B	0.9900	N10—H10B	0.9200
C7—N2	1.492 (7)	N10—Pt1	2.068 (4)
C11—C12	1.396 (7)	N17—O18	1.231 (5)
C11—C16	1.382 (7)	N17—O19	1.232 (6)
C11—N10	1.440 (6)
H3A—C3—H3B	107.9	C13—C12—H12	120.5
C4—C3—H3A	109.3	C12—C13—H13	120.5
C4—C3—H3B	109.3	C14—C13—C12	119.0 (5)
N2—C3—H3A	109.3	C14—C13—H13	120.5
N2—C3—H3B	109.3	C13—C14—C15	122.2 (5)
N2—C3—C4	111.8 (4)	C13—C14—N17	118.2 (5)
C3—C4—H4A	109.5	C15—C14—N17	119.6 (5)
C3—C4—H4B	109.5	C14—C15—H15	120.6
H4A—C4—H4B	108.1	C16—C15—C14	118.9 (5)
C5—C4—C3	110.8 (4)	C16—C15—H15	120.6
C5—C4—H4A	109.5	C11—C16—H16	120.1
C5—C4—H4B	109.5	C15—C16—C11	119.7 (5)
C4—C5—H5A	109.6	C15—C16—H16	120.1
C4—C5—H5B	109.6	C3—N2—H2	106.2
H5A—C5—H5B	108.1	C3—N2—Pt1	111.5 (3)
C6—C5—C4	110.2 (5)	C7—N2—C3	112.2 (4)
C6—C5—H5A	109.6	C7—N2—H2	106.2
C6—C5—H5B	109.6	C7—N2—Pt1	113.9 (3)
C5—C6—H6A	109.3	Pt1—N2—H2	106.2
C5—C6—H6B	109.3	C11—N10—H10A	108.0
H6A—C6—H6B	107.9	C11—N10—H10B	108.0
C7—C6—C5	111.7 (5)	C11—N10—Pt1	117.0 (3)
C7—C6—H6A	109.3	H10A—N10—H10B	107.3
C7—C6—H6B	109.3	Pt1—N10—H10A	108.0
C6—C7—H7A	109.3	Pt1—N10—H10B	108.0
C6—C7—H7B	109.3	O18—N17—C14	118.7 (4)
H7A—C7—H7B	108.0	O18—N17—O19	122.8 (5)
N2—C7—C6	111.5 (4)	O19—N17—C14	118.5 (5)
N2—C7—H7A	109.3	Cl9—Pt1—Cl8	177.84 (4)
N2—C7—H7B	109.3	N2—Pt1—Cl8	91.59 (12)
C12—C11—N10	119.4 (4)	N2—Pt1—Cl9	88.59 (12)
C16—C11—C12	121.2 (5)	N2—Pt1—N10	176.94 (15)
C16—C11—N10	119.4 (4)	N10—Pt1—Cl8	89.56 (12)
C11—C12—H12	120.5	N10—Pt1—Cl9	90.37 (12)
C13—C12—C11	119.0 (5)
C3—C4—C5—C6	54.8 (6)	C12—C11—N10—Pt1	97.9 (5)
C3—N2—Pt1—Cl8	−66.5 (3)	C12—C13—C14—C15	0.7 (9)
C3—N2—Pt1—Cl9	115.7 (3)	C12—C13—C14—N17	−178.9 (5)
C4—C3—N2—C7	54.8 (6)	C13—C14—C15—C16	0.0 (9)
C4—C3—N2—Pt1	−176.0 (3)	C13—C14—N17—O18	−16.4 (8)
C4—C5—C6—C7	−55.5 (6)	C13—C14—N17—O19	163.1 (6)
C5—C6—C7—N2	55.4 (6)	C14—C15—C16—C11	−0.9 (8)
C6—C7—N2—C3	−54.8 (6)	C15—C14—N17—O18	164.0 (5)
C6—C7—N2—Pt1	177.4 (3)	C15—C14—N17—O19	−16.5 (8)
C7—N2—Pt1—Cl8	61.7 (3)	C16—C11—C12—C13	−0.3 (8)
C7—N2—Pt1—Cl9	−116.1 (3)	C16—C11—N10—Pt1	−81.8 (5)
C11—C12—C13—C14	−0.6 (8)	N2—C3—C4—C5	−54.9 (6)
C11—N10—Pt1—Cl8	−82.4 (3)	N10—C11—C12—C13	180.0 (5)
C11—N10—Pt1—Cl9	95.5 (3)	N10—C11—C16—C15	−179.2 (5)
C12—C11—C16—C15	1.1 (8)	N17—C14—C15—C16	179.6 (5)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···O18i	0.93	2.27	3.182 (6)	165
N10—H10A···Cl8ii	0.92	2.32	3.198 (4)	158
N10—H10B···Cl9iii	0.92	2.37	3.255 (4)	161