POLYMORPHISM IN COORDINATION CHEMISTRY - SELECTIVE SYNTHESES AND AB-INITIO X-RAY-POWDER DIFFRACTION CHARACTERIZATION OF 2 NEW CRYSTALLINE PHASES OF SOLID [PD(DMPZ)(2)(HDMPZ)(2)](2) (HDMPZ=3,5-DIMETHYLPYRAZOLE)
N. Masciocchi et al., POLYMORPHISM IN COORDINATION CHEMISTRY - SELECTIVE SYNTHESES AND AB-INITIO X-RAY-POWDER DIFFRACTION CHARACTERIZATION OF 2 NEW CRYSTALLINE PHASES OF SOLID [PD(DMPZ)(2)(HDMPZ)(2)](2) (HDMPZ=3,5-DIMETHYLPYRAZOLE), Inorganic chemistry, 36(3), 1997, pp. 449-454
[Pd(dmpz)(2)(Hdmpz)(2)](2), which is known to crystallize in the monoc
linic system (alpha phase), possesses two polymorphs which could only
be produced as microcrystalline powders. Selective syntheses of these
new (beta and gamma) polymorphs and their structural characterization
from X-ray powder diffraction data have been successfully accomplished
by ab initio methods and Rietveld refinement. beta-[Pd(dmpz)(2)(Hdmpz
)(2)](2) is tetragonal, space group I422, a = 13.1342(7) Angstrom, c =
13.7920(9) Angstrom, Z = 2; R(p), R(wp) and R(F) being 0.106, 0.143,
and 0.075, respectively, gamma-[Pd-(dmpz)(2)(Hdmpz)(2)](2) is triclini
c, space group <P(1)over bar>, a = 11.470(1) Angstrom, b = 11.619(2) A
ngstrom, c = 19.221(2) Angstrom, alpha 80.928(6)degrees, beta = 81.434
(7)degrees, and gamma = 69.033(5)degrees, Z = 2; R(p), R(wp), and R(F)
being 0.104, 0.136, and 0.085, respectively. In all three phases the
identity of the [Pd(dmpz)(2)(Hdmpz)(2)](2) dimer, containing four stro
ng intramolecular N-H ... N bonds, is retained. The alpha and gamma ph
ases are a racemate of chiral molecules, while during the formation of
the beta phase, spontaneous resolution of chiral molecules occurs, th
us generating a conglomerate of enantiomeric crystals.