2,2′-(1,3-Diazinane-1,3-diyl)diacetonitrile: a second monoclinic polymorph

A new monoclinic polymorph of the title compound, C8H12N4, in the space group P21/n (Z = 4) is reported. The previously known form was also monoclinic, P21 /c (Z = 4), but the unit-cell parameters and crystal packing were different [Shoja & Saba (1993 ▶). Acta Cryst. C49, 354–355]. The hexahydropyrimidine ring of the title compound adopts a chair conformation with a diequatorial substitution and with the CH2-C N groups oriented nearly parallel and in the same direction [NC—CH2⋯CH2—CN pseudo torsion angle = −6.27 (18)°]. In the crystal, intermolecular C—H⋯ N hydrogen bonds connects the molecules into a chain along the b axis.

A new monoclinic polymorph of the title compound, C 8 H 12 N 4 , in the space group P2 1 /n (Z = 4) is reported. The previously known form was also monoclinic, P2 1 /c (Z = 4), but the unitcell parameters and crystal packing were different [Shoja & Saba (1993). Acta Cryst. C49, [354][355]. The hexahydropyrimidine ring of the title compound adopts a chair conformation with a diequatorial substitution and with the CH 2 -C N groups oriented nearly parallel and in the same direction [NC-CH 2 Á Á ÁCH 2 -CN pseudo torsion angle = À6. 27 (18) ]. In the crystal, intermolecular C-HÁ Á Á N hydrogen bonds connects the molecules into a chain along the b axis.

Comment
Nitriles are widely used starting materials and intermediates in organic synthesis. For instance, hydration of nitriles to corresponding carboxamides is an important reaction in nature and organic synthesis (Prasad & Bhalla, 2010). The title compound (I) was synthesized by one-step reaction between the macrocyclic aminal 1, 3,7,9,13,15,19,21-octaazapentacyclo-[19.3.1.1 3,7 .1 9,13 .1 15,19 ]octacosane and hydrocyanic acid according to a methodology previously published (Rivera, et al. 2004). Single crystals of title compound were obtained by recrystallization from EtOH solution. An alternative synthetic method for the preparation of title compound involves the substitution of benzotriazolyl groups by cyano anion from the (Katritzky et al., 1990) The molecular structure and atom-numbering scheme for (I) are shown in

Experimental
For the originally reported synthesis, see: Rivera et al. (2004). Single crystals of the title compound were obtained by recrystallization from EtOH solution (m.p. 340 K).

Refinement
Hydrogen atoms were added in calculated positions and refined as riding with C-H distance of 0.96 Å The isotropic atomic displacement parameters of hydrogen atoms were evaluated as 1.2×U eq of the parent atom.

Special details
Refinement. The refinement was carried out against all reflections. The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F 2 for refinement carried out on F and F 2 , respectively. The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement.
The program used for refinement, Jana2006, uses the weighting scheme based on the experimental expectations, see _refine_ls_weighting_details, that does not force S to be one. Therefore the values of S are usually larger than the ones from the SHELX program.