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Scheme 2. Synthesis of the complexes 1, 1a and 2.
nated by L and also bears one terminal and two bridging chloride
ions (CuNOCl3 coordination unit). Coordination unit of the complex
1a, CuNO2Cl2, includes one bidentate ligand L, one water molecule,
and two chloride ions, each coordinated to the Cu2+ ion. Finally, the
combination of Cu:L = 1:2 stoichiometry and slow crystallization of
the resulting solution led to the formation of the double complex
salt 2. The cationic part of 2 consists of the Cu2+ ion bidentately
coordinated by two L molecules and one chloride ion (CuN2O2Cl
coordination unit). The anionic part of 2 includes the Cu2+ ion coor-
dinated by one L molecule and three chloride ions; coordination
unit CuNOCl3. The nontrivial composition of 2 most likely indicates
the competition between ligands having a comparably strong
metal-coordination ability. On the other hand, the presence of
the 6-methyl group on the pyridine ring of L presumably prevents
the formation of the complexes trans-[CuL2Cl2], which were
reported previously for both unsubstituted 2-(N-acetylamino)pyr-
idine and its 4-methyl derivative. By this reason, at the Cu:L = 1:2
ratio the common distorted octahedral coordination with two
nearly coplanar L ligands is not possible; it rearranges into a trigo-
nal bipyramid with large (>50°) dihedral angles between the ligand
planes. Thus, although the cationic part of 2 includes two L mole-
cules per metal ion (i.e. the 1:2 stoichiometry is formally met),
the overall Cu:L ratio in the entire complex is lower, being 1:1.5,
which can be attributed to the steric hindrance provided by the
6-methyl group.
Fig. 1. Thermal ellipsoid representation (at the 30% probability level) of the
binuclear complex [Cu2L2Cl4]. Only the asymmetric unit is numbered. Unnumbered
atoms are related to numbered ones by an inversion center midway between the
bridging chloride ligands.
hydrogen bonds of 3.29 Å in such a way as to give infinite one-
dimensional ribbons parallel to the a axis (Fig. 2). Only non-bridg-
ing chloride ligands are involved in hydrogen bonding. The ribbons
are packed in the crystal lattice without any significant interac-
tions between them other than van der Waals forces.
3.2. Description of crystal structures
The crystals of compound 1 are triclinic; space group P–1 and
the unit cell contains 1 formula unit. The asymmetric unit consists
only half of the binuclear complex [Cu2L2Cl4] with all atoms occu-
pying general positions. The entire [Cu2L2Cl4] molecule is gener-
ated by the inversion center located at (1/2, 1/2, 1/2). The
coordination environment of the Cu2+ ion includes N and O atoms
of the bidentate ligand L, and three chloride ions, two of which are
The compound 1a crystallizes in the monoclinic space group
P21/n with 4 formula units per unit cell. All atoms comprising the
asymmetric unit, [CuL(H2O)Cl2] neutral complex and uncoordi-
nated L molecule, are located in general positions. The coordination
environment of the Cu2+ ion in the [CuL(H2O)Cl2] complex includes
N and O atoms of the bidentate ligand L, two chloride ions, and O
atom of the water molecule. It can be described as either a dis-
torted trigonal bipyramid with the equatorial plane defined by
O(1), Cl(1), and Cl(2) atoms, or as a distorted tetragonal pyramid
with the basal plane defined by N(1), O(1W), Cl(1), and Cl(2) atoms
(Fig. 3). The latter representation is more appropriate since the Cl–
Cu–Cl angle is rather wide, 157.54(4)°, while both Ow–Cu–Cl angles
are close to 90° (Table 3). The Cu–N, Cu–O, Cu–Ow and two Cu–Cl
bond lengths are 2.006(3), 2.112(2), 1.957(3), and 2.3629(10) and
2.2794(10) Å, respectively, which are in good agreement with the
l2-bridging (Fig. 1). These atoms form a distorted tetragonal pyr-
amid with the basal plane defined by N(1), Cl(1), Cl(2), and symme-
try-generated Cl(2)i atoms ((i): 1 – x, 1 – y, 1 – z). The Cu–N and
Cu–O distances are 2.0038(15) and 2.1228(15) Å, respectively.
Three Cu–Cl bond lengths are 2.2809(6), 2.2814(5) and
2.3677(6) Å; there is no clear dependence on the coordination
mode of the particular chloride ion. The CuÁ Á ÁCu separation within
the binuclear unit is 3.4356(5) Å. Each binuclear unit is further
connected to two adjacent units through pairs of Namide–HÁ Á ÁCl