THE PHENOMENON OF CONGLOMERATE CRYSTALLIZATION. PART 48. TWO POLYMORPHS OF RACEMIC TRANS-[CO(2,3,2-TET) (NO2)2]NO3 (I AND II)

Abstract

A racemic solution of trans-[Co(2,3,2-tet)(NO2)2]NO3(I), CoO7N7C7H20, crystallizes as a racemate in the centrosymmetric space group, P21/n with lattice constants: a=8.490(2)Å, b=8.884(2), c=18.580(2) Å and β=95.08(1)°; K=1395.89 Å3 and d(calc; M.W.=373.21, Z=4)=1.776 g-cm−3. A total of 3489 data were collected over the range of 4° ≤ 2θ ≤ 55°; of these, 2684 (independent and with 1 ≥ 3s(I)) were used in the structural analysis. Data were corrected for absorption (μ=12.732 cm−1) and the relative transmission coefficients ranged from 0.7721 to 0.9980. Refinement converged to final residuals of 0.0465 and 0.0541 for R(F) and R w(F), respectively. The mother liquor of the same compound, prepared by a different route, produced a second crystalline form of trans-[Co(2,3,2-tet)(NO2)2]NO3(II), CoO7N7C7H20, which crystallizes in space group Pn with lattice constants: a=6.493(5)Å, b=11.731(4), c=9.325(4) Å and b=100.13(9)°; V=699.21 Å3 and d(calc; M.W.=373.21, Z=2)=1.773 g-cm−3. A total of 2249 data were collected over the range of 4° ≤ 2θ ≤ 60°; of these, 2012 (independent and with I ≥ 2.5s(I)) were used in the structural analysis. Data were corrected for absorption (μ=12.732 cm−1) and the relative transmission coefficients ranged from 0.7892 to 0.9345. Refinement converged to final residuals of 0.0301 and 0.0308 for R(F) and Rw(F), respectively. For (I) and (II), the central six-membered ring has a chair conformation. The conformational chirality of the two five-membered, outer rings and the asymmetry at the secondary nitrogens, are internally compensated(meso) and, with the exception of small deviations at the -NO2 oxygens, the cation has a mirror plane which bisects the central ring. In both cases the asymmetric unit is an ion pair in which nitrate oxygens form bonds with the hydrogens of both terminal -NH2 moieties—the entire array resembling a macrocycle. The composition of both crystals is identical but while the lattice of both crystals contain racemic pairs, (I) is centrosymmetric, while crystals of (II) are polar.