Polymorphism and isomorphism in trans-bis(2,5-diiodopyridine)dihalocopper(ii) complexes: theoretical and crystallographic studies

Abstract

Two polymorphs of each of the complexes, [Cu((25dIpy)2Cl2] and [Cu(25dIpy)2Br2], (where 25dIpy = 2,5-diiodopyridine) have been prepared and characterized by single and powder X-ray diffraction. The two polymorphs of [Cu(25dIpy)2Cl2]...

Halogen bond and polymorphism in trans-bis(2-iodo-5-halopyridine)dihalocopper(ii) complexes: crystallographic, theoretical and magnetic studies

“…69 Recently, both conformers of Cu(2I5IP) 2 Cl 2 have been characterized, which indicates that the presence of a halogen atom on position 5 of the pyridine will support crystallization of both conformers. 40 The syn-conformer crystallizes from acetonitrile at 60 °C, whereas, both conformers crystallize concomitantly at lower temperatures. Only the anti-conformer crystallizes from 2-propanol.…”

“…Cu(2ClP) 2 X 2 crystallizes as syn-conformer whereas Cu(2BrP) 2 X 2 and Cu(2IP) 2 X 2 crystallize as anti-conformers. 19,64,67,68 All our attempts to crystallize syn-conformers from either Cu(2BrP) 2 X 2 or Cu(2IP) 2 X 2 have been unsuccessful, 40 even though calculations indicated that the syn-conformer is more stable than the anti-conformer. Cu(2Br5MP) 2 X 2 crystallize as anti-conformers (2Br5MP = 2-bromo-5-methylpyridine).…”

“…18 Different polymorphs have different physical properties (optical, magnetic, solubility… etc.). [40][41][42] Different polymorphs of pharmaceutically active ingredients may have different solubility, and hence different pharmacokinetics and activity. 43,44 Different solid state polymorphs may crystallize concomitantly or as pure phases under different experimental conditions.…”

“…Different experimental factors may enhance formation of different polymorphs such as temperature, pressure, solution pH, and auxiliary substances, however, none of these conditions guarantee the formation of different polymorphs. 37,40,[45][46][47] Crystallization of different polymorphs is due to the presence of several local energy minima on the potential energy surface, which may arise due to differences in molecular and (or) supramolecular structure. Hence, the possibility of formation of different polymorphs is enhanced in flexible molecules due to the presence of more than one local energy minimum upon rotation or flipping of molecular units.…”

“…[48][49][50][51][52][53][54][55][56][57][58] The geometry around Cu(II) ion in copper(II) halide complexes is also flexible; it varies between tetrahedral, distorted tetrahedral with D2/d geometry, square planar, octahedral with Jahn-Teller effect, square pyramidal and trigonal bipyramidal, which enhances the possibility of formation of different conformational polymorphs in copper(II) complexes. 37,38,40,[59][60][61][62][63] Complexes of the general formula Cu(2ZP) 2 X 2 where 2ZP = 2-halopyridine and X = Cl or Br are flexible due to rotation around the N-Cu bond of the C2-N-Cu-N torsion angle (Scheme 1), two local energy minima are identified in these molecules, [64][65][66] hence they may crystallize as two different conformational polymorphic phases. The first conformer arises when the halogen atoms on position 2 of the pyridine ring are located on the same side of the coordination sphere (henceforth; syn-conformer) and when the substituents are located on opposite sides of the coordination sphere (henceforth anti-conformer) (Scheme 2).…”