X.-F. Yang et al. / Polyhedron 128 (2017) 18–29
19
10 °C/min. Powder X-ray diffraction (PXRD) data were recorded
on XRD diffractometer (Ultima IV, Rigaku Corporation) with
Cu-Ka radiation (k = 1.54056 Å).
2.2. Synthesis of H3Lws ligand
2.2.1. Synthesis of intermediate a
Into a 250 ml round-bottom flask was charged 5-bromosalicylic
acid (20 g, 92.16 mmol), methanol (110 ml) and concentrated
H2SO4 (12 ml). The mixture was stirred under reflux for 22 h. Upon
cooled to room temperature, the precipitated white solid, viz.
methyl 5-bromosalicylate, was filtered by suction, and washed
with cold methanol solvent, which was directly used for the next
step without further purification (18.0 g, 84.7%).
Into a 250 ml round-bottom flask was charged methyl 5-bro-
mosalicylate
(7 g,
30.30 mmol),
4-(Methoxycarbonyl)ben-
Scheme 1. Schematic showing of H3Lws ligand.
zeneboronic Acid (6.54 g, 36.36 mmol), Pd(PPh3)2Cl2 (1.91 g,
0.09 mmol), 20 ml of H2O and 150 ml of 1,2-Dimethoxyethane in
sequence. Under a nitrogen atmosphere the reaction mixture was
stirred under reflux for 5 h. After cooled to room temperature,
the reaction mixture was filtered to remove insoluble catalyst
and inorganic salts, and poured into 200 ml of EtOAc-H2O (1:1)
mixed solvent. The organic phase was separated and washed by
saturated NaCl solution. After removal of solvent by rotary evapo-
ration, the key intermediate of a was obtained by flash chromatog-
raphy. White solid, 4.6 g, yield 53%. 1H NMR (300 MHz, CDCl3, d,
ppm): 3.94 (s, 3H) , 3.99(s, 3H), 7.09(d, 1H, J = 8.7 Hz), 7.62(d, 2H,
J = 7.8 Hz), 7.74(d, 1H, J = 8.4 Hz), 8.10(d, 3H, J = 9.0 Hz), 10.82(s,
1H) (Fig. S1).
still to be less explored probably because of critical demand for
hydrolytic stability [36–42]. For practical in-field use in soil and
ground water, nonetheless, it urgently calls for the pursuit of
water-stable luminescent sensors that can efficiently work in
aqueous phase [43].
As a starting point of our program towards water-stable CPs or
MOFs, we have designed and synthesized a new biphenyl-based
polytopic organic ligand H3Lws that combines two rigid aromatic
carboxylate groups and one flexible ether-linked aliphatic carboxy-
late moiety (Scheme 1). Prior to our report, the coordination chem-
istry of few organic ligands carrying both aromatic and aliphatic
carboxylate groups have been described in literatures, which high-
light the great conformational freedom and the strong inclination
to form polynuclear metal clusters [44–51]. We conjectured that
the ease of polynuclear cluster formation with such type of ligand
might be utilized to access water-stable CPs or MOFs on the basis
of two considerations. On the one hand, the polynuclear cluster
formation is expected to enforce the metal–ligand coordination
interactions. On the other hand, the steric hindrance around the
metal ion caused by cluster is anticipated to hamper the water
approaching. In this work, solvothermal reactions between H3Lws
ligand and transition metal ions (Co2+, Ni2+ and Cd2+) resulted in
three coordination polymers of 1–3. Compound 1 features a one-
dimensional (1-D) Co(II)-based chain structure, whereas com-
pound 2 is composed of a two-dimensional (2-D) wave-like sheet
based on Ni4O6 clusters. Compound 3 shows a three-dimensional
(3-D) Cd(II)-based coordination network constructed by 2-D Cd/
O-based layers pillared by H3Lws ligands. Compounds 1–3 demon-
strate excellent hydrolytic stabilities even under heating condi-
tions. Particularly, through luminescence quenching compound 3
is capable of detecting those NACs with phenolic group (TNP, 2,
4-DNP and PNP) with higher sensitivity in an aquatic environment.
2.2.2. Synthesis of intermediate b
Into a 250 ml round-bottom flask equipped with an addition
funnel was charged
a (5.33 g, 18.62 mmol), K2CO3(8.24 g,
59.58 mmol) and acetone (120 ml). At room temperature, ethyl
bromoacetate (3.11 g, 18.62 mmol) was added dropwise into the
above homogeneous solution. After the addition was completed,
the reaction was heated to reflux under stirring for 5 h. Upon
cooled to room temperature, the reaction was filtered and reduced
under vacuum to give a colorless viscous liquid, which solidified
into white solid upon treatment with 50 ml of petroleum. The
white solid of b was collected by filtration and dried at 45 °C under
vacuum for 8 h (6.71 g, 96.8% yield).
2.2.3. Synthesis of H3Lws
Into a 500 ml round-bottom flask was charged b (7.15 g,
19.21 mmol), NaOH(7.68 g, 192.1 mmol), THF (200 ml) and H2O
(140 ml) in turn. The resultant turbid solution was heated to reflux
for 12 h. After cooled to room temperature, the reaction mixture
was partially concentrated by rotary evaporation to remove the
THF solvent followed by addition of 2 M HCl solution to adjust
pH in the range of 2–3. The precipitated white solid of H3Lws was
filtered by suction, and dried at 65 °C under vacuum for 12 h.
White solid, 5.77 g, 95.0% yield. 1H NMR (300 MHz, DMSO-d6, d,
2. Experimental
2.1. Materials and methods
ppm): 4.85 (s, 2H) , 7.14 (d, 1H, J = 8.7 Hz) , 7.78(d, 2H,
J = 8.1 Hz), 7.86(d, 1H, J = 8.6 Hz), 7.74(d, 1H, J = 8.4 Hz), 8.01(d,
3H, J = 8.2 Hz), 12.97(s, 3H) (Fig. S2).
All reagents and solvents were commercially available and used
as received. FT-IR spectra were recorded with a Thermo Scientific
Nicolet 5700 FT-IR spectrophotometer with KBr pellets in the
400–3600 cmꢀ1 region. Elemental analyses for C and H were per-
formed on a CHN-O-Rapid analyzer or an Elementar Vario MICRO
analyzer. The fluorescent spectra were collected on a Horiba Flu-
oroMax 4 spectrometer. UV–vis absorption spectra were recorded
on a Shimadzu UV-2450 spectrophotometer. Thermogravimetric
2.3. Synthesis of complexes 1–3
2.3.1. [Co(HLws)](H2O)2]n (1)
A
mixture of Co(NO3)2ꢂ6H2O (58.2 mg, 0.2 mmol), H3Lws
(31.6 mg, 0.1 mmol) and 1.0 ml of KOH solution (0.2 mol/L) were
dissolved in 14 ml of H2O, and sealed in a Parr Teflon-lined stain-
less steel vessel (25 ml). The mixture was heated at 160 °C for
3 days. Upon cooled to room temperature at a rate of 5 °C /h, deep
analyses were carried out on
a TA Instruments SDT-Q600
simultaneous DTA-TGA under N2 atmosphere at a heating rate of