Crystal structure of chlorido{4,5-dimethoxy-2-[(2,3-η)-2-prop-2-en-1-yl]phenyl-κC 1}(piperidine-κN)platinum(II) ethanol monosolvate

The title platinum(II) complex shows a trigonal–bipyramidal coordination and intermolecular C—H⋯Cl, C—H⋯π and (C/O)—H⋯O hydrogen bonds.

In the title compound, [Pt(C 11 H 13 O 2 )Cl(C 5 H 11 N)]ÁC 2 H 5 OH, the Pt II cation is pentacoordinated in a distorted square-planar geometry. In the crystal, inversion dimers showing C-HÁ Á ÁCl and C-HÁ Á Á interactions are further stacked in columns along the a axis via C-HÁ Á Á interactions. The ethanol solvate molecule interacts with neighbouring methoxy groups of methyleugenol through O-HÁ Á ÁO hydrogen bonds.

Chemical context
Methyleugenol or 4-allyl-1,2-dimethoxybenzene (Meug, C 11 H 14 O 2 ) is a natural product occurring in a number of plants such as fennel, pimento, lemongrass and nutmeg, and frequently used in perfumery and as flavouring agent (Ford et al., 2000). Methyleugenol is used as a fruit-fly attractant in agriculture (Todd et al., 2008) and in the formulation of UV absorbers, analgesics, and psychotropic drugs in medicine (Darshan & Doreswamy, 2004;Freeman & Alder, 2002). Platinum(II) complexes containing methyleugenol of formula [PtCl 2 (Meug)(Amine)] and deprotonated methyleugenol of formula [PtCl(Meug-1H)(Amine)] have been described in very few works (Da et al., 2007(Da et al., , 2010(Da et al., , 2015. It is interesting that some of these complexes exhibit strong activities on human cancer cells KB with IC 50 = 3.2-3.7 mg/mL (Da et al., 2015). Based on these observations and prompted by the fact that one of our research areas focuses on the design and synthesis of compounds with high biological activity starting from inexpensive natural products, we have prepared the title compound [PtCl(Meug-1H)(Piperidine)] and determined its crystal structure.

Structural commentary
In [PtCl(Meug-1H)(piperidine)], the Pt II cation is pentacoordinated with Pt II at the centre of a distorted square-planar geometry. The methyleugenol is bound with the Pt II cation both at the ethylenic double bond and at a deprotonated benzene carbon atom (Fig. 1). The two methoxy groups of the methyleugenol part are almost in the phenyl plane, as illustrated by the torsion angles C2-C3-O1-C7 [À7.9 (6) ] and C5-C4-O2-C8 [À4.0 (6) ]. The piperidine is in the cis position with respect to the ethylenic double bond. The piperidine ring occurs in the usual chair conformation with the N1-Pt1 bond in the equatorial position. The best planes through the two six-membered rings make a dihedral angle of 24.6 (2) . In order to avoid steric hindrance between Cl1 and the two ring systems, especially atoms C2 and C12, both rings rotate along their bond with Pt1. This is easier for the piper-idine ring [resulting in a C12-N1-Pt1-Cl1 torsion angle of 70.7 (2) ] than for the phenyl ring [C2-C1-Pt1-Cl1 torsion angle of only À25.0 (4) ]. As a consequence the H12BÁ Á ÁCl1 distance (2.831 Å ) is larger than the H2Á Á ÁCl1 distance (2.789 Å ).

Supramolecular features
In the crystal packing ( Fig. 2), the complex forms inversion dimers by pairs of C-HÁ Á ÁCl and C-HÁ Á Á interactions (C10-H10Á Á ÁCl1 and C15-H15AÁ Á ÁCg1 interactions, Cg1 is the centroid of the C1-C6 aromatic ring, see Table 1). These dimers are stacked in columns along [100] by C12-H12AÁ Á ÁCg1 interactions. The ethanol molecule interacts by bifurcated O-HÁ Á ÁO hydrogen bonds with both methoxy groups of methyleugenol and further on by C-HÁ Á ÁO interactions to a neighboring methoxy group. No voids are present in the crystal packing.

Database survey
The Cambridge Structural Database (CSD, Version 5.35, May 2014; Groom & Allen, 2014) contains 52 1,2-dimethoxyphenyl fragments in which the methoxy oxygen atoms interact simultaneously with a third oxygen atom (OÁ Á ÁO distance less than the sum of the van der Waals radii). The third oxygen atom belongs in descending order to a water, alcohol, oxime or carboxylic acid, and the mean OÁ Á ÁO distance is 2.916 Å . In the 690 4-substituted 1,2-dimethoxyphenyl fragments present in the CSD, the majority of the C-C-O-CH 3 torsion angles vary between À28 and +32 (only 11 torsion angles are outside this region).
The title compound was synthesized by adding a solution of 1 mmol of piperidine in 3 ml of acetone to a mixture of 408 mg (0.5 mmol) of [Pt 2 Cl 2 (Meug-1H) 2 ] and 6ml of acetone. The reaction mixture was stirred at room temperature for 30 min. The obtained solution was cooled to 255 K after which the precipitate was collected and washed with Et 2 O. The yield was Molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level and the O-HÁ Á ÁO interactions shown as dashed lines. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
View of the crystal packing for the title compound, with O-HÁ Á ÁO, C-HÁ Á ÁCl and C-HÁ Á Á hydrogen bonds shown as red, green and blue dashed lines, respectively. Cg1 is the centroid of the C1-C6 ring.