1-Isopropyl-4-tosylpiperazin-1-ium trifluoroacetate

In the title compound, C14H23N2O2S+·C2F3O2 −, the piperazine ring adopts a chair conformation. The crystal packing is stabilized by C—H⋯O and N—H⋯O hydrogen bonds between the cation and anion. The F atoms are disordered over two positions; the site occupancy factors are 0.55 (2) and 0.45 (2).


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In the title compound ( Fig. 1) both N atoms have a pyramidal arrangement, but the pyramid of the amide is somewhat shallower than that of the protonated N. The protonated piperazin ring adopts a chair conformation.
The crystal packing is stabilized by C-H···O and N-H···O hydrogen bonds (Table 1) between the cation and anion.
Weak intermolecular C-H···O hydrogen bonds involving an S=O group as acceptor play an important role in the moleclular packing.

S2. Experimental
A solution of 4-methylbenzenesulfonyl chloride (3.28 g, 17 mmol) in CH 2 Cl 2 was added dropwise to a mixture of 1-isopropylpiperazine (2.23 g, 82%, 0.14 mmol) and sodium biscarbonate (3.36 g, 40 mmol) in CH 2 Cl 2 (30 ml) at room temperature with stirring. After stirring for 4 h followed by filtration, the organic filtrate was rotoevaporated under vacuum. The resulting solid, in a yield of 53.8%, was purified by recrystallization from methanol. Crystals in the form of colourless blocks were grown by evaporation of a trifluoroacetic solution.

S3. Refinement
The N-bound H atoms were refined freely with the restraint of 0.90 (1) Å, while the other H atoms were positioned geometrically (C-H = 0.93, 0.96 and 0.97 Å) and refined as riding with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). The three F atoms are disordered over two site occupancy of 0.55 (2): 0.45 (2). The C-F distances were restrained to 1.36 (1) Å and their displacement parameters were restrained to be isotropic by means of the instruction ISOR (tolerance

Figure 1
The molecular structure of (I) with the atom-numbering scheme and 30% probability displacement ellipsoids. Only one component of the disordered CF 3 group is shown.  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.