Formation of a new 1D coordination polymer by in situ ligand reaction of 2,4,6-tris(pyrazol-1-yl)-1,3,5-s-triazine

Article abstract of DOI:10.3184/174751912X13469466943350

Solvothermal reactions of Zn(NO₃)2·6H₂O, 1,4-benzenedicarboxylic acid (H₂BDC) and 2,4,6-tris(pyrazol-1-yl)-1, 3,5- s-triazine, yielded a new coordination polymer [Zn(BDC)(pz) ·H ₂O]n (pz= pyrazole). The in situ methanolysis reaction of 2,4,6-tris(pyrazol-1-yl)-1,3,5-s-triazine with pyrazole and 2,4,6-trismethoxy-1, 3,5-triazine was confirmed by their single-crystal structures. [Zn(BDC)(pz)·H₂O]n was characterised by elemental analysis, IR, powder X-ray diffraction, photoluminescence and thermogravimetric analyses.

Full text of DOI:10.3184/174751912X13469466943350

648 RESEARCH PAPER
NOVEMBER, 648–651
JOURNAL OF CHEMICAL RESEARCH 2012
Formation of a new 1D coordination polymer by in situ ligand reaction of
2,4,6-tris(pyrazol-1-yl)-1,3,5-s-triazine
Qiang Cao*
College of Chemistry and Life Science, Weinan Normal University, Weinan 714000, Shaanxi, P. R. China
Solvothermal reactions of Zn(NO3)2·6H2O, 1,4-benzenedicarboxylic acid (H2BDC) and 2,4,6-tris(pyrazol-1-yl)-1,3,5-
s-triazine, yielded a new coordination polymer [Zn(BDC)(pz)·H2O]n (pz= pyrazole). The in situ methanolysis reaction
of 2,4,6-tris(pyrazol-1-yl)-1,3,5-s-triazine with pyrazole and 2,4,6-trismethoxy-1,3,5-triazine was confirmed by their
single-crystal structures. [Zn(BDC)(pz)·H2O]n was characterised by elemental analysis, IR, powder X-ray diffraction,
photoluminescence and thermogravimetric analyses.
Keywords: in situ ligand reaction, benzenedicarboxylic acid, crystal structure, 2,4,6-trismethoxy-1,3,5-triazine
Bruker Apex CCD area-detector diffractometer with Mo-Ka radiation
at 293(2) K. The structures were resolved by a direct method and
refined by full-matrix least-squares procedure on F2 using the
SHELXL-97 program.18 All hydrogen atoms were placed geometri-
cally and anisotropic thermal parameters were used to refine all non-
hydrogen atoms of the frameworks. Crystallographic parameters are
listed in Table 1.
Crystallographic data for the structural analysis of compound 1
have been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 866545. Copies of this information can be obtained
free of charge from The Director, CCDC, 12 Union road, Cambridge,
CB21EZ, UK(fax:+44 1223 336-033; E-mail: deposit@ccdc.cam.ac.
ukor www: http://www.ccdc.cam.ac.uk).
The design and construction of metal–organic frameworks
(MOFs) has attracted attention because of their applications in
gas storage and separation,1–3 catalysis,4–6 ion exchange7–9 and
sensors.10 Particularly, novel MOFs with in situ generated
ligands (especially those that are inaccessible by direct prepa-
ration) have attracted considerable attention both in coordina-
tion and organic chemistry. Many metal–ligand reactions have
been found and used to generate a large number of coordina-
tion polymers.11–15 We can obtain some unexpected structures
and explain some organic synthesis phenomenon directly by
solving their signal crystal structures. The triazine derivative
ligand can be easily substituted by the nucleopilic reagent.
Other papers have focused on MOFs based on the triazine
ligand.16
Here we report a new 1D coordination polymer [Zn(BDC)
(pz)·H2O]n constructed by the reactions of 1,4-benzenedicar-
boxylic acid and 2,4,6-tris(pyrazol-1-yl)-1,3,5-s-triazine with
Zn(NO3)2·6H2O. Interestingly, 2,4,6-tris(pyrazol-1-yl)-1,3,5-s-
triazine was found to be in the in situ methanolysis reaction to
pyrazole ligand. Fortunately, both of the two main productions
signal crystals [Zn(BDC)(pz)·H2O]n (1) (BDC= 1,4-benzenedi-
carboxylic acid, pz= pyrazole) and 2,4,6-trismethoxy-1,3,5-
triazine (2) were collected.
Table 1 Crystallographic data and collection parameters of
compounds 1 and 2
Compound
1
2
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C11H9N2O5Zn
314.57
C6H9N3O3
171.16
Orthorhombic
Pnma
8.4648(18)
6.7047(14)
14.373(3)
90
Monoclinic
P2(1)/n
8.2004(18)
9.065(2)
16.074(4)
90
b (Å)
c (Å)
Experimental
α (°)
β (°)
93.925(3)
90
90
90
IR spectra were measured from KBr pellets on a Nicolet Avatar 370
Fourier Transform IR spectrometer; Powder X-ray diffraction(PXRD)
on a Bruker AXS D8-Focus. C, H, N analyses were carried out with
a Finnigan EA1112 element analyser. Thermogravimetric analyse
(TGA) was carried out in a nitrogen stream using Seiko Extar 6000
TG/DTA equipment with a heating rate of 10 °C·min−1. All reagents
were purchased commercially and used without further purification.
2,4,6-Tris(pyrazol-1-yl)-1,3,5-s-triazine was prepared according the
literature,17 MS, m/z=280.10 (M+), m.p. 240–243 °C (lit.17 288–289 °C).
γ (°)
Volume (Å3)
Z
1192.1(5)
4
1.753
815.7(3)
4
1.394
Density (calculated)
(Mg m−3)
Absorption coefficient
(mm−1)
2.078
636
0.113
360
F(000)
Crystal size (mm3)
Theta range for data
collection (°)
Index ranges
0.20 x 0.10 x 0.10 0.28 x 0.27 x 0.26
2.54 to 26.00
2.79 to 25.99
Synthesis
A mixture of Zn(NO3)2·6H2O (0.1 mmol, 0.020 g), 1,4-benzenedicar-
boxylic acid (0.1 mmol, 0.015), 2,4,6-tris(pyrazol-1-yl)-1,3,5-s-
triazine (0.1 mmol, 0.047 g) and 12ml water/CH3OH (V/V=1:1) was
stirred for 20 min in air. The mixture was then transferred to a 23 mL
Teflon reactor and kept at 120°C for 3 days under autogenous
pressure, and then cooled to room temperature at a rate of 5 °C h−1.
Colourless crystals of 1 were obtained with a yield of 60% based on
Zn. IR spectrum (ν, cm–1): 3420 s, 3072 m, 1604 s, 1580 s, 1572 s,
1497 m, 1418 s, 1397 w, 1173 w, 1167 m, 1142s, 840 m, 779 s, 712 m.
Anal. Calcd for C11H9N2O5Zn: C, 42.00; H, 2.88; N, 8.90. Found: C,
41.59; H, 2.80; N, 9.01%. Crystals of compound 2 with different
shapes can be separated under a microscope, m.p. 90–93 °C, IR
spectrum (ν, cm–1): 1544, 1511, 1496, 1388, 1305, 1258.
–10<h<9,
–11<k<10,
–19<l<17
7517
–10<h<10,
–8<k<7,
–17<l<17
4314
Reflections collected
Independent reflections 2324 [R(int) =
0.0233]
Max. and min.
transmission
875 [R(int) =
0.0228]
0.8191 and 0.8191 0.9712 and 0.9690
Refinement method
Full-matrix least- Full-matrix least-
squares on F2
2324/3/179
squares on F2
875/0/75
Data/restraints/
parameters
Goodness-of-fit on F2
Final R indices
[I>2sigma(I)]
1.226
1.144
R1 = 0.0297,
wR2 = 0.0933
R1 = 0.0341,
wR2 = 0.1043
R1 = 0.0574,
wR2 = 0.1189
R1 = 0.0628,
wR2 = 0.1261
Crystallography
R indices (all data)
Suitable single crystal for 1 and 2 were selected for single-crystal
XRD analysis. All the single-crystal XRD data were collected on a
Largest diff. peak and
hole (e Å−3)
0.470 and –0.556 0.448 and –0.630
* Correspondent. E-mail: caoqiang123456@yeah.net

JOURNAL OF CHEMICAL RESEARCH 2012 649
Results and discussion
The presence of the characteristic absorptions at 1580 and
1397 cm−1; contribute to the COO− anti-stretching vibration
and stretching vibration. The ORTEP view of the compound 1
with the atomic numbering scheme is presented in Fig. 1. The
asymmetric unit of compound 1 consists of one independent
Zn centre, a BDC ligand, one pz ligand and one coordinate
Table 2 Selected bond lengths [Å] and angles [°] for compound
1
Zn(1)–O(3)
Zn(1)–N(1)
1.9617(19)
2.012(2)
Zn(1)–O(5)
Zn(1)–O(1)
O(3)–Zn(1)–O(1) 93.75(8)
O(5)–Zn(1)–O(1) 114.49(9)
N(1)–Zn(1)–O(1) 124.30(9)
1.981(2)
2.029(2)
O(3)–Zn(1)–O(5) 112.56(9)
O(3)–Zn(1)–N(1) 98.83(10)
O(5)–Zn(1)–N(1) 109.90(9)
Fig. 1 ORTEP view of 1 with the atomic numbering. (A: 1–x, 1–y, 2–z; AA: 2–x, –1–y, 2–z).
Fig. 2 1D chain structure of 1.
Fig. 3 Crystal packing of 1.

650 JOURNAL OF CHEMICAL RESEARCH 2012
water molecule. The Zn atom is four-coordinated by two
carboxylate oxygen atoms from two different BDC2− ligands,
one water oxygen atoms and one nitrogen atom from the pz
ligand with the distorted tetrahedral coordination geometry.
The distances between Zn atom and coordinated oxygen atoms
are in the range 1.9620–2.029 Å. Selected bond lengths and
bond angles are given in Table 2. Each BDC2− ligand connected
to two Zn atom in monodentate coordination or fashion, formed
a 1D zigzag chain (Fig. 2).
Zhou suggested that we must avoid using a nucleophilic
reagent (like methanol or alcohol) as the solvents. If the ligand
were a “slow release formulation”, small ligands could be
released slowly into the MOFs. Using pz and H2BDC with
Zn2+, it is not easy to obtain compound 1. Pz ligand will
coordinate to Zn2+ rapidly, so no other coordination site could
connect with BDC2−. This phenomenon demonstrates the
advantage of in situ ligand reactions in building some MOFs.
Hydrogen bonds displayed interesting interactions in the
compound. The neighbouring zigzag chains connect to each
other through the hydrogen bond, generated 2D layer. The 2D
layers are linked by hydrogen bonds to give rise to 3D struc-
ture through an ABAB model, which further stabilises this
supramolecular network (Fig. 3). PXRD is consistent with the
simulated pattern based on the XRD analysis. The experimen-
tal XRD patterns match with the calculated lines from the
crystal structure (Fig. 4).
Figure 5 is the ORTEP view of compound 2. Scheme 1
shows the possible mechanism of this reaction. Compound 2
was isolated in the mixed productions. Single-crystal X-ray
diffraction shows that the compound 2 is 2,4,6-trimethoxy-
1,3,5-triazine, the structure has been previously reported by
Krygowski19 and Zhou17. Compounds 2 indicate that Zn2+ can
act as a catalyst in certain nucleophilic substitution reactions.
Photoluminescence spectra and TG analysis
As compound 1 is a hybrid inorganic–organic coordination
polymer with d10 metal centres, the photoluminescence spectra
of the compound 1 in the solid state was measured at room
temperature (Fig. 6), absorptions were observed at 359 nm
may be tentatively assigned to a ligand-to-metal charge trans-
fer (LMCT) process. This phenomenon suggests that com-
pound 1 may be a new material which may have implications
for the design and implementation of fluorescent sensors for
studies of Zn2+.
Scheme 1 The mechanism of the reaction.
Fig. 4 PXRD of 1, black represent the simulated, red represent
the experiment.
Fig. 5 ORTEP view of 2 with the atomic numbering.
Fig. 6 Fluorescent emission spectra of compound 1.

JOURNAL OF CHEMICAL RESEARCH 2012 651
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Receieved 18 July 2012; accepted 30 August 2012
Paper 1201417 doi: 10.3184/174751912X13469466943350
Published online: 12 November 2012

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