S. Ganta et al.
InorganicaChimicaActa484(2019)33–41
determined using Bruker X8 Kappa XRD instrument. Melting points
were determined using a CINTEX apparatus and were uncorrected. cis-
Protected palladium(II) components were obtained following well
(t, J = 1.6 Hz, 2H, Hf), 6.18 (s, 4H, Hg), and 3.25 (s, 4H, Hh). 13C NMR
(100 MHz, DMSO‑d6): δ = 137.3, 136.5, 131.8, 129.9, 120.5, 120.0,
114.6 and 46.9 ppm. Yield: (44 mg, 93%). MP – 235 °C (decomposed).
ESI-MS: m/z = 271 which correspond to [1 - 3NO3]3+
.
2: 1H NMR (400 MHz, DMSO‑d6): δ = 9.94 (s, 4H, Ha), 8. 64 (b, 6H,
Hb, Hc), 8.29–8.28 (m, 6H, Hd, He), 8.14 (s, Hf), 3.57 (s, 8H, Hi), 3.18 (s,
24H, Hj). 13C NMR (100 MHz, DMSO‑d6): δ = 137.2, 136.4, 131.7,
128.8, 120.1, 119.6, 113.6, 62.2 and 50.1 ppm. Yield: (48 mg, 93%).
MP – 240 °C (decomposed). ESI-MS: m/z = 307 which correspond to [2
2.2. Crystallographic data collection and refinement
X-ray data was collected with a Bruker AXS Kappa Apex II CCD
diffractometer equipped with graphite monochromated Mo(Kα) (λ =
0.7107 Ǻ) radiation. The crystal fixed at the tip of the glass fiber was
mounted on the Goniometer head and was optically cantered. The au-
tomatic cell determination routine, with 32 frames at three different
orientations of the detector, was employed to collect reflections, and
the APEXIISAINT program (Bruker, 2004) was used for finding the unit
cell parameters [10]. A 4-fold redundancy per reflection was utilized for
achieving good absorption correction using a multiscan procedure.
Besides absorption, Lorentz polarization and decay correction were
applied during data reduction. The SADABS program (Bruker 2004)
was used for absorption correction using a multiscan procedure. The
structures were solved by direct methods using SHELXL-97, [11] and
refined by full-matrix least-squares techniques using the APEXII
(Bruker, 2004) computer program. All hydrogen atoms were fixed at
chemically meaningful positions, and a riding model refinement was
applied. Molecular graphics were generated using Mercury programs.
The crystal data (CCDC numbers: 1851052–1851054) refinement de-
tails are summarized in the Table S1 of Supplementary Data.
– 3NO3]3+
.
3: 1H NMR (500 MHz, DMSO‑d6): δ = 9.84 (s, 4H, Ha), 9.142 (d,
J = 8 Hz, 4H, Hn), 8.94 (d, J = 7.5 Hz, 4H, Hm), 8.63 (b, 6H, Hb, Hc),
8.376 (b, 6H, He, Hk), 8.287 (s, 4H, Hf) and 8.23–8.22 (b, 8H, Hd, Hl).
13C NMR (100 MHz, DMSO‑d6): δ = 156.0, 150.5, 142.7, 137.9, 136.6,
131.6, 128.8, 128.4, 124.5, 121.7, 121.4 and 115.6 ppm. Yield: (53 mg,
94%). MP – 244 °C (decomposed). ESI-MS: m/z = 336, and 236 which
correspond to [3 – 3NO3]3+, [3 – 4NO3]4+ respectively.
4: 1H NMR (400 MHz, DMSO‑d6): δ = 10.08 (s, 4H, Ha), 9.65 (d,
J = 8.4 Hz, 4H, Hq), 8.95–8.89 (m, 10H, Hb, Hc, Ho), 8.74–8.72 (dd,
J = 4.4 Hr, Hc), 8.64–8.61 (m, 4H, Hp), 8.49–8.48 (m, 6H, Hd, He), 8.42
(t, J = 1.6 Hz, Hf). 13C NMR (100 MHz, DMSO‑d6): δ = 151.9, 146.6,
141.9, 138.7, 137.1, 132.2, 131.0, 129.7, 128.5, 127.1, 122.3, 122.0,
and 119.2 ppm. Yield: (55 mg, 95%). MP > 300 °C. ESI-MS: m/z = 248
which corresponding to [4 – 4NO3]4+
.
4′: 1H NMR (400 MHz, DMSO‑d6): δ = 10.07 (s, 4H, Ha), 9.67 (dd,
J = 7.2 Hz, 4H, Hq), 8.95–8.91 (m, 10H, Hb, Hc, Ho), 8.74–8.72 (dd,
J = 6.4 Hr, Hc), 8.65–8.62 (m, 4H, Hp), 8.49–8.48 (m, 6H, Hd, He), 8.42
(s, Hf). 13C NMR (100 MHz, DMSO‑d6): δ = 151.9, 146.6, 141.9, 138.7,
132.1, 131.0, 129.5, 128.5, 127.1, 122.7, 122.3, 119.5 and 118.6 ppm.
Yield: (70 mg, 95%). MP > 300 °C. ESI-MS: m/z = 1441, 646, 381, and
248, which corresponding to [4′ – CF3SO3]+, [4′ – 2CF3SO3]2+, [4′ –
2.3. Synthesis of the ligand
The ligand L was synthesized by a reported literature procedures
3CF3SO3]3+, and [4′ – 4CF3SO3]4+
3. Results and discussion
3.1. Ligand L
.
1,3-bis(1-imidazolyl)benzene, L:
A mixture of CuI (228 mg,
1.2 mmol), N,N-dimethylglycine (350 mg, 2.4 mmol), K2CO3 (4.2 g,
30 mmol), imidazole (1.24 g, 18 mmol), and 1,3-diiodobenzene (2 g,
6 mmol) in 50 mL DMSO was heated at 130 °C for 48 h under N2 at-
mosphere in a round bottom flask. Then the mixture was cooled down
to room temperature and partitioned between water (50 mL) and ethyl
acetate (100 mL). The organic layer was separated and the aqueous
fraction was extracted with ethyl acetate twice (2 x 50 mL). The com-
bined organic layers were washed with NaHCO3, dried over Na2SO4 and
concentrated in vacuum which leads to an off white powder of the li-
gand, L. Yield: (0.882 g, 70%) (based on 1,3-diiodobenzene).
In the present work, we have considered the π-surfaces located at
the ligand backbone and at the cis-protected palladium(II) unit of
Pd2L′2L2 type self-assembled complexes. The roles of the π-surfaces
towards self-assembly of already self-assembled complexes are ana-
lysed. The chosen bidentate non-chelating ligand, crafted with pheny-
lene as spacer moiety, was synthesized by the C-N bond formation be-
tween imidazole and benzene through general Ullmann coupling
procedure [12]. Ligand L can offer conformational isomerism, in which
the isomers differ only by a rotation about the C-N bond between the
benzene and imidazole moiety (Fig. 3).
2.4. Synthesis of the palladium(II) complexes
A common method for the synthesis of the complexes is described
below.
[Pd2(en)2(L)2](NO3)4, 1. The ligand L (20 mg, 0.093 mmol) was
added to the yellow-coloured solution of Pd(en)(NO3)2 (27 mg,
0.093 mmol) in acetonitrile–water (1:1) (5 mL). The resulting clear
solution was stirred for 8 h, followed by complete evaporation of the
solvent. The residual mass was dried under vacuum to afford the
complex 1 as an off-white powder.
The other complexes, [Pd2(tmeda)2(L)2](NO3)4, 2, [Pd2(bpy)2(L)2]
(NO3)4, 3, and [Pd2(phen)2(L)2](NO3)4, 4, were prepared in a similar
manner by using appropriate cis-protected palladium(II) components.
The complex [Pd2(phen)2(L)2](OTf)4, 4′ was prepared using Pd(phen)
(OTf)2 as the metal component. The reactions mixtures were stirred for
2 h to prepare the complex 2 and for 15 min to prepare the complexes 3,
4 and 4′.
3.2. Synthesis and characterization of self-assembled palladium(II)
complexes
The self-assembled coordination complexes [Pd2(L′)2(L)2](NO3)4,
1–4 were prepared by combination of ligand L with equimiolar
amounts of a cis-protected palladium(II) component i.e. cis-PdL′(NO3)2
where L′ stands for en, tmeda, bpy and phen, respectively (Scheme 1).
The complexation reactions were carried out in MeCN-H2O(1:1)
medium by stirring the reaction mixtures at room temperature and the
complexes were isolated by evaporation of the solvents. The ligand L is
soluble in CHCl3, and CH3CN; however, the polar complexes 1–4 are
insoluble in these solvents. The complexes are fairly soluble in DMSO,
and CH3CN-H2O (1:1) media.
The course of these self-assembly reactions were probed by re-
cording 1H NMR spectra of the samples prepared in CD3CN-D2O (1:1).
The spectra of the samples obtained as a function of time are provided
in the Supplementary Data (Figs. S32, S33, S34 and S35). During
synthesis of the complex 1 we detected another intermediate that
2.5. Analytical data
1: 1H NMR (400 MHz, DMSO‑d6): δ = 9.54 (s, 4H, Ha), 8.92 (s,2H,
Hb), 8.74 (t, J = 1.6 Hz, 2H, Hc), 8.36 (t, J = 5.2 Hz, 6H, Hd, He), 8.03
35