cis-Diamminedichloridoplatinum(II) N,N-dimethylformamide monosolvate

In the title compound, cis-[PtCl2(NH3)2]·C3H7NO, the metal complex molecules are stacked parallel to the b axis, forming close Pt⋯Pt interactions of 3.4071 (7) and 3.5534 (8) Å and weak N—H⋯Cl hydrogen bonds between the ammine ligand and the Cl atoms of the neighboring complex. Conventional N—H⋯O hydrogen bonds are formed between ammine ligands and the O atom of adjacent N,N-dimethylformamide molecules. The crystal was found to be a split crystal and was analyzed using two domains related by a rotation of ca 4.4° about the reciprocal axis (−0.351 1.000 0.742) and refined to give a minor component fraction of 0.084 (6).

This work was supported in part by the National Science Foundation through grant DUE-0942850.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: PK2417). metal-organic compounds crystallographically characterized (Alston et al., 1985).
The title compound has a square-planar geometry ( Fig. 1) and forms stacked chains along the crystallographic b axis with Pt-Pt distances of 3.4071 (7) and 3.5534 (8) Å and Pt-Pt-Pt angle of 156.90 (2) degrees as shown in Figures 2 and 3. Formation of extended platinum chains through stacking is a common motif in square-planar platinum compounds (Connick et al., 1997). Hydrogen bonds are formed between the ammine hydrogen atoms and the chlorine atoms on the closer of the two neighboring complexes. This type of hydrogen bonding has been proposed or observed in previous studies on cisplatin and related complexes (Milburn & Truter, 1966;Brammer et al., 1987;Ting et al., 2010).
Additional hydrogen bonds are formed between the ammine hydrogen atoms and the oxygen atom of the N,N-dimethylformamide as illustrated in Figure 4. Similar interactions are seen in the DMF-solvated cisplatin structure previously described (Raudaschl et al., 1983, Raudaschl et al., 1985, Raudaschl-Sieber et al., 1986. Interestingly, the previously described DMF solvate of cisplatin does not display stacking of the metal complexes seen in the title compound.

Experimental
The title complex was prepared by refluxing 2.00 g (4.82 mmol) of K 2 [PtCl 4 ] with 1.60 g (20.8 mmol) of ammonium acetate and 2.0 g (26.8 mol) of KCl in 25 ml of water for two hours, during which the solution changed from a dark red to green. The solution was hot filtered and a greenish-yellow powder formed on cooling. The powder was recrystallized by vapor diffusion of diethylether into a DMF solution of the complex yielding yellow-orange crystals. Infrared spectra were in agreement with literature values (Nakamoto et al., 1965) Data sets on multiple crystals showed evidence of at least two independent domains, either from agglomeration or from the crystal being cracked or split, perhaps during rapid cooling to 200 K.

Refinement
The matrix relating the two domains, Refinement produced a minor component fraction of 0.084 (6). All hydrogen atoms were positioned geometrically and refined with the atom positions constrained to appropriate positions with N-H distances of 0.91 Å and C-H distances of either 0.95 Å (amide) or 0.98 Å (methyl groups). A riding model was used for all H atoms with U iso (H) = 1.2 times U iso (amine, amide) or 1.5 times U iso (methyl carbon atoms).

Figure 1
The molecular structure of the title compound drawn with 50% probability displacement ellipsoids for non-H atoms.  The packing of the title compound viewed along the b axis drawn with 50% probability displacement ellipsoids for non-H atoms.  An illustration of the hydrogen bond interactions between the ammine ligands and the N,N-dimethylformamide solvent molecules. Additional donor/acceptor distances and angles are listed in Table 1. [Symmetry codes: (ii) -x + 2, -y + 2, -z + 2; (iii) x -1, y, z -1; (v) -x + 1, -y + 2, -z + 1.] Special details Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.