A nearly planar arrangement of ions in 4,4′-bipiperidinium tetracyanidoplatinate(II) monohydrate

The title compound, (C10H22N2)[Pt(CN)4]·H2O, was isolated from solution as a molecular salt. The compound contains discrete 4,4′-bipiperidinium cations and tetracyanoplatinate(II) anions that are involved in a hydrogen-bonding network with one water molecule of hydration. The structure differs from that of the similar acetonitrile solvate, (C10H22N2)[Pt(CN)4]·2CH3CN, in the orientation of the ions relative to one another. The hydrate reported here contains layers of nearly parallel cations and anions with an angle between their mean planes of only 4.35 (11)°, while in the acetonitrile solvate the cations and anions are nearly perpendicular to one another (86.1° between mean planes). The crystal showed partial inversion twinning.


Related literature
Organic dications such as 4,4 0 -bipyridinium and 4,4 0 -bipiperidinium have been shown to be successful in crystallizing a number of square-planar metallate anions, and a large number of salts containing these two ions have been reported (Lewis & Orpen, 1998;Angeloni & Orpen, 2001;Crawford et al., 2004). For the acetonitrile solvate, with a contrasting arrangement of the ions, see Crawford et al. (2004).

Comment
The title compound, (C 10 H 22 N 2 )Pt(CN) 4 ·H 2 O, was obtained as an unexpected product during a reaction that attempted to prepare a praseodymium tetracyanoplatinate incorporating 4,4'-bipiperidine.
The structure of (I) consists of separated 4,4'-bipiperidinium dications and tetracyanoplatinate anions, additionally one water molecule of crystallization is also present. Fig. 1 shows an illustration of the units of the structure along with the atomic labeling scheme. The 4,4'-bipiperidinium cations and tetracyanoplatinate anions lie in approximately the ab crystallographic planes and contain multiple hydrogen bonding interactions as can be seen in Fig. 2. Each of the approximately square planar anions is hydrogen bonded to four cations and each cation is also hydrogen bonded to four anions. See Table 1 for bond distances and angles of these hydrogen bonding interactions. The mean plane that passes through the 4,4'-bipiperidinium cation makes an angle of 4.35 (11)° with the mean plane of the tetracyanoplatinate anion in the structure, illustrating the nearly parallel nature of these groups relative to one another. Small cavities in these two dimensional planes are filled with water molecules that hydrogen bond within the plane to N1 and N3 atoms of the tetracyanoplatinate anions. Additional hydrogen bonding interactions are also present between the water molecules in one plane and H5A atoms of neighboring planes. See Table 1 for details of these H-bonding interactions.
Several major structural differences exist between I and the previously reported (C 10 H 22 N 2 )Pt(CN) 4 ·2CH 3 CN, II (Crawford et al., 2004). While compound I contains a nearly parallel arrangement of the cations and anions, the 4,4'-bipiperidinium cations in II are nearly perpendicular to the tetracyanoplatinate anions. The angle between the mean planes formed by the two groups in II is 86.1°. This packing arrangement of the cations and anions in II leaves relatively large holes in the structure that accommodate acetonitrile solvate molecules. In I, the smallercavities contain water molecules.

Refinement
H atoms of the 4,4'-bipiperidinium cation were placed in calculated positions and allowed to ride during subsequent refinement, with U iso (H) = 1.2U eq (C) and C-H distances of 0.97 Å for H atoms bonded to the C atoms and U iso (H) = 1.2U eq (N) and N-H distances of 0.90 Å for the H atoms bonded to the N atoms. The H atoms on the water molecule were not located in the difference map, but were placed in calculated positions with O-H distances of 0.85 Å and U iso (H) = 1.2U eq (O). The H atoms were not allowed to move during refinement. The crystal of I that was used for the diffraction study was found to be a racemic twin and therefore the refinement was carried out taking into account the inverted component. Fig. 1. The molecular structure of (I), with the atom-numbering scheme. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level. Fig. 2. A representation of two-dimensional layers of 4,4'-bipiperidinium cations, tetracyanoplatinate anions and water molecules found in the ab plane of (I).