metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
There is a correlation between the shielding ability and the
metal–Npz distance. The shielding is expressed by the
percentage of the metal coordination sphere blocked by the
ligand from molecular attack. Tables 2 and 3 compile the data
of the shielding percentage (Guzei & Wendt, 2006) and the
metal–Npz distance for (I), literature data and other related
compounds in the Cambridge Structural Database (see
Scheme; Allen, 2002) (Ojwach et al., 2009; Segapelo et al.,
2009; Balamurugan et al., 2004; Benade et al., 2011; Kilpin &
Crowley, 2010; Allen, 2002).
ISSN 0108-2701
Dichlorido{2-[(3,5-diphenyl-1H-pyra-
zol-1-yl-jN2)methyl]pyridine-jN}-
palladium(II)
Lara C. Spencer,a Ilia A. Guzei,a* Tebogo V. Segapelob
and James Darkwab
aDepartment of Chemistry, University of Wisconsin–Madison, 1101 University
Avenue, Madison, WI 53706, USA, and bDepartment of Chemistry, University of
Johannesburg, Auckland Park Kingsway Campus, Johannesburg 2006, South Africa
Received 25 July 2012
Accepted 16 October 2012
Online 30 October 2012
The title compound, [PdCl2(C21H17N3)], is a member of a
sequence of Pd, Pt and Co dichloride complexes bearing
polysubstituted (pyrazol-1-ylmethyl)pyridine ligands. It is
shown that there is a correlation between the steric bulkiness
of the bidentate (pyrazol-1-ylmethyl)pyridine ligands and the
Pd—Npyrazole distances, i.e. the larger the ligand, the longer the
bond. In contrast, no trend is observed between the steric
properties of the ligand and the Pd—Npyridine bond lengths.
Comment
(Pyrazol-1-ylmethyl)pyridine ligands have been used to
prepare platinum(II) and gold(III) complexes that were
investigated as potential anticancer agents (Segapelo et al.,
2009). (Pyrazol-1-ylmethyl)pyridine palladium(II) complexes
with 3,5-dimethyl- and 3,5-di-tert-butyl- substitutents have also
been investigated as catalysts for ethylene polymerization
reactions (House et al., 1986; Mohlala et al., 2005; Ojwach et
al., 2007, 2009). In the course of this experimental work,
the palladium 3,5-diphenyl- analogue, namely dichlorido{2-
[(3,5-diphenyl-1H-pyrazol-1-yl-ꢀN2)methyl]pyridine-ꢀN}palla-
dium(II), (I), was synthesized.
Compound (I) (Fig. 1) has a slightly distorted square-planar
geometry, with a bidentate ligand bite angle of 87.04 (4)ꢀ. The
six-membered heterocycle is in the boat conformation which is
common for metal compounds with this family of ligands
(Ojwach et al., 2009). The geometric parameters (Table 1)
agree well with those of the 3,5-dimethyl- and 3,5-tert-butyl-
analogues, as well as with those of {2-[(4-phenyl-1H-1,2,3-
triazol-4-yl)methyl]pyridine}palladium(II) chloride (Ojwach
et al., 2009; Kilpin & Crowley, 2010).
The 2-[(4-phenyl-1H-1,2,3-triazol-1-yl)methyl]pyridine lig-
and (L1), with only one phenyl substituent on the triazole ring,
is the least sterically demanding among the ligands in Table 2
(Kilpin & Crowley, 2010). Therefore it shields the metal
coordination sphere in PdCl2(L1) and PtCl2(L1) to the least
extent, resulting in the shortest metal–Npz distance. This trend
continues for the Pd and Pt complexes with the 3,5-di-
methylpyrazole (L2), 3,5-diphenylpyrazole (L3) and 3,5-di-
tert-butylpyrazole (L4) ligands. Interestingly, the cobalt
analogues do not adhere to this trend. While the L2 analogue
shields a smaller percentage of the metal than the L3
analogue, it is CoCl2(L2) that has a longer metal–Npz distance
than CoCl2(L3) (Balamurugan et al., 2004; Benade et al.,
2011). Steric effects alone cannot explain the latter observa-
tions for a metal with different electronic properties; thus,
electronic effects must contribute to the solid-state geometry
of the Co complexes.
The metal–Npy distances (py is pyridine) for the Pd, Pt and
Co compounds are presented in Table 4. There are no
consistent trends found between the ligand shielding percen-
tage and this distance. Table 5 tabulates the ligand folding
angle along the metal–methylene C atom. The folding angle is
defined as a dihedral angle between two planes defined by
It has been established in previous work with similar
compounds that the metal–Npz distance (pz is pyrazole) is
dependent on the steric size of the pz ligand and its ability to
shield the metal coordination sphere (Ojwach et al., 2009).
Acta Cryst. (2012). C68, m317–m319
doi:10.1107/S0108270112043119
# 2012 International Union of Crystallography m317