Crystal structure of trans-di­chlorido­(4-nitro­aniline-κN¹)(piperidine-κN)platinum(II)

The packing of the title compound features N—H...Cl hydrogen bonds and π–π stacking inter­actions, which form one-dimensional chains of mol­ecules parallel to [001] further linked via N—H...O inter­actions.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.008 Å
• R factor = 0.032
• wR factor = 0.072
• Data-to-parameter ratio = 18.1

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT971_ALERT_2_B Check Calcd Residual Density  0.98A From     Pt1       2.69 eA-3

Alert level C
PLAT342_ALERT_3_C Low Bond Precision on  C-C Bonds ...............     0.0081 Ang.
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600         65 Report
PLAT971_ALERT_2_C Check Calcd Residual Density  0.93A From     Pt1       2.46 eA-3
PLAT971_ALERT_2_C Check Calcd Residual Density  0.98A From     Pt1       2.06 eA-3
PLAT971_ALERT_2_C Check Calcd Residual Density  0.99A From     Pt1       1.97 eA-3
PLAT972_ALERT_2_C Check Calcd Residual Density  0.87A From     Pt1      -1.90 eA-3
PLAT972_ALERT_2_C Check Calcd Residual Density  0.87A From     Pt1      -1.70 eA-3
PLAT972_ALERT_2_C Check Calcd Residual Density  0.91A From     Pt1      -1.55 eA-3

Alert level G
PLAT007_ALERT_5_G Number of Unrefined Donor-H Atoms ..............          3 Report
PLAT910_ALERT_3_G Missing # of FCF Reflection(s) Below Th(Min) ...          4 Report
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600         13 Note

   0 ALERT level A = Most likely a serious problem - resolve or explain
   1 ALERT level B = A potentially serious problem, consider carefully
   8 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   3 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   7 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. 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.

To explain this we suppose that p-nitro­aniline first coordinates with Pt^II 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.

S2. 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 Pt^II 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)°.

S3. 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+3/2; 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).

S4. 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 compounds), with the remaining 239 compounds 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.

S5. 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 (ν_NH); 3070, 2927, 2862 (ν_CH); 1596, 1525, 1479 (ν_{C═C arom}); 1342, 1325 (ν_NO); ¹H NMR (CDCl₃, 500 MHz): δ 8.21 (2H, d, ³J = 9.0 Hz, Ar-H), 7.47 (2H, d, ³J = 9.0 Hz, Ar-H), 5.49 (2H, br, O₂NC₆H₄NH₂), 3.66 (1H, br, C₅H₁₀NH), 3.26 (2H_α^e, d, ²J_ae = 13.0 Hz, C₅H₁₀NH), 2.99 (2H_α^a , q, ²J_ae, ³J_aa, ³J_aa(NH) = 13.0 Hz, C₅H₁₀NH), 1.69–1.43 (4H_β, 2H_γ, ov, C₅H₁₀NH). ¹³C{¹H} NMR (125 MHz, CDCl₃): δ 149.6, 125.1, 124.2 (O₂NC₆H₄NH₂), 54.0, 27.2, 24.3 (C₅H₁₀NH).

S6. Refinement

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).

Computing details

Data collection: CrysAlis PRO (Agilent, 2012); cell refinement: CrysAlis PRO (Agilent, 2012); data reduction: CrysAlis PRO (Agilent, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Figures

	Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level.
	Fig. 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).

trans-Dichlorido(4-nitroaniline-κN¹)(piperidine-\ κN)platinum(II)

Crystal data

[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) Å^3	, brown
Z = 8	0.35 × 0.15 × 0.1 mm

Data collection

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

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

Special details

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.

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

	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)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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)

Geometric parameters (Å, º)

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)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···O18^i	0.93	2.27	3.182 (6)	165
N10—H10A···Cl8^ii	0.92	2.32	3.198 (4)	158
N10—H10B···Cl9^iii	0.92	2.37	3.255 (4)	161

Symmetry codes: (i) x+1/2, −y+3/2, z−1/2; (ii) −x, −y+2, −z+1; (iii) −x, y, −z+1/2.