Synthesis, characterization, photoluminescent and thermal properties of zinc(ii) 4′-phenyl-terpyridine compounds

Article abstract of DOI:10.1039/c3nj41176a

Reactions between 4′-phenyl-terpyridine (L) and several Zn(ii) salts (trifluoromethane sulfonate, p-toluenesulfonate, benzoate, p-hydroxybenzoate, o-hydroxybenzoate or m-hydroxybenzoate) led to the formation of the complexes [Zn(OSO₂CF₃)₂L(H₂O)] (1), [Zn(p-OSO₂PhCH₃)₂L] (2), [Zn(OCOPh) ₂L] (3), [Zn(p-OCOPhOH)₂L] (4), [Zn(o-OCOPhOH) ₂L] (5) and [Zn(m-OCOPhOH)₂L] (6), which were characterized by elemental analysis, ¹H NMR, ¹³C NMR, IR, single crystal X-ray diffraction and fluorescence spectroscopies. In 1, the Zn atom is hexacoordinated, with a N₃O₃ coordination environment, whereas in the remaining structures the metal atom is envisaged as possessing distorted N₃O₂ irregular trigonal bipyramidal coordination geometries. All the compounds show interesting photo-luminescent properties in solid and solution states in DMF, DMSO and methanol, which are reported along with their TG-DTA thermal decomposition processes.

Full text of DOI:10.1039/c3nj41176a

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Graphical abstract
The zinc(II)
mononuclear complexes [Zn(OR)2L] were obtained by reaction of several zinc salts
(trifluoromethane sulfonate, p-toluenesulfonate, benzoate and p-, o-and m-derivatives) with 4′-phenyl-terpyridine
(L). Their photoluminescent and thermal properties were studied.

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Synthesis, Characterization, Photoluminescent and Thermal Properties of Zinc(II)
4′-phenyl-terpyridine Compounds
Zhen Ma a,b*, Wanbing Lu a, Baohuan Liang a and Armando J.L. Pombeiro b*
a Guangxi Key Laboratory of Petrochemical Resource Processing and Process Intensification Technology, School
of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, P. R. China; E-mail:
mzmz2009@sohu.com
b Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av.
Rovisco Pais, 1049-001, Lisbon, Portugal, E-mail: pombeiro@ist.utl.pt
Abstract
Reactions between 4′-phenyl-terpyridine (L) and several Zn(II) salts (trifluoromethane sulfonate,
p-toluenesulfonate, benzoinate, p-hydroxybenzoinate, o-hydroxybenzoinate or m-hydroxybenzoinate)
led to the formation of the complexes [Zn(OSO2CF3)2L(H2O)] (1), [Zn(p-OSO2PhCH3)2L] (2),
[Zn(OCOPh)2L]
(3),
[Zn(p-OCOPhOH)2L]
(4),
[Zn(o-OCOPhOH)2L]
(5)
and
[Zn(m-OCOPhOH)2L] (6), which were characterized by elemental analysis, 1H NMR, 13C NMR, IR,
single crystal X-ray diffraction and fluorescence spectroscopies. In 1, the Zn atom is hexacoordinated,
with a N3O3 coordination environment, whereas in the remaining structures the metal atom is
envisaged as possessing distorted N3O2 irregular trigonal bipyramidal coordination geometries. All
the compounds show interesting photo-luminescent properties in solid and solution states in DMF,
DMSO and methanol, which are reported along with their TG-DTA thermal decomposition
processes.
Introduction
Characterized by featuring three distinct pyridyl groups, terpyridine ligands behave as suitable hosts
for transition metal ions.1-17 They provide impetus for chemists to design a large number of
coordination compounds for use in many fields, namely in material and medicinal chemistries.9-16
Since the work of Constable et al., many new terpyridine compounds, which show special
coordinative abilities towards transition metal elements, have been synthesized by condensation of
the respective aldehydes and 2-acetonepyridine followed by oxidation, in simple and high yield
processes.18-22 Other terpyridine-like ligands were also reported.23 Combining these ligands with
transition metal ions leads to a diversity of complexes with interesting properties,1-22 in particular

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12,13,16
showing photoluminescence
and antitumor activities.16a For the general [n:n] type of
terpyridine compounds (mainly 2:2 or 1:1), the photoluminescence and antitumor activities are
known to depend not only on the terpyridine ligands and metal ion, but also on the anionic co-ligands
and counterions. Hence, to investigate the effects of the auxiliary ligands on the structural and
photo-luminescent properties of zinc terpyridine complexes, we synthesized a series of six novel
complexes of this metal with a multi-pyridyl ligand (4′-phenyl-terpyridine), and bearing, as anionic
-
-
ligands, trifluoromethane sulfonate (OSO2CF3 ), p-tolylsulfonate (p-CH3PhSO3 ), benzoate (PhCOO-),
or p-, o, m-hydroxyl substituted benzoate. They were characterized by elemental analysis, NMR, IR,
X-ray structural analysis, and their photoluminescence in solid state or solutions of DMF, DMSO
and methanol was studied.
2. Results and discussion
2.1. Syntheses and characterization of the complexes
17
4′-phenyl-terpyridine (L) was obtained according to a literature procedure,
complexes [Zn(OSO2CF3)2L(H2O)] (1), [Zn(p-OSO2PhCH3)2L] (2),
[Zn(p-OCOPhOH)2L] (4), [Zn(o-OCOPhOH)2L] (5) and [Zn(m-OCOPhOH)2L] (6) were
synthesized (Scheme 1) by reaction of L with the appropriate Zn(II) salt added in stoichiometric
amounts, i.e. Zn(SO3CF3)2, Zn(p-SO3PhCH3)2·6H2O, Zn(OCOPh)2,
Zn(p-OCOPhOH)2·3MeOH·1.5H2O, Zn(o-OCOPhOH)2·2H2O or Zn(m-OCOPhOH)2·2H2O,
and the Zn(II)
[Zn(OCOPh)2L] (3),
respectively, in a methanol - CH2Cl2 solution. The reactions usually proceeded smoothly at room
temperature and the complexes were isolated after 24 h, in good to high yields (50 – 90 %). In the
case of 3, the conditions were harsher (hydrothermal synthesis at 120 °C for two days).

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O2
S
CF3
CF3
O
N
Zn(SO3CF3)2
Zn OH2
N
MeOH:CH2Cl2
N
O
S
(1)
O2
O2
S
O
N
Zn(p-SO3PhCH3)2·6H2O
Zn
O
N
MeOH:CH2Cl2
N
S
(2)
O2
O
OC
N
Zn(OCOPh)2
Zn
N
O
Hydrothermal synthesis
N
OC
(3)
N
N
N
O
OC
OH
OH
N
N
Zn(p-OCOPhOH)2·3MeOH·1.5H2O
Zn
N
O
MeOH:CH2Cl2
OC
(4)
HO
O
OC
N
Zn(o-OCOPhOH)2·2H2O
Zn
N
O
MeOH:CH2Cl2
N
OC
(5)
HO
OH
O
OC
N
Zn(m-OCOPhOH)2·2H2O
Zn
N
O
MeOH:CH2Cl2
N
OC
(6)
OH
Scheme 1
2.2. Elucidation of the structures of the compounds
The six complexes were isolated as white solids which were characterized (see experimental) by

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elemental analysis, 1H NMR, 13C NMR (e.g., the protons of the –OH group in 4, 5 and 6 resonate at
δ 9.79, 13.22 and 9.34, respectively, whereas the carboxylate carbons of the corresponding ligands
appear at δ 170.5 – 173.1), IR and fluorescence spectroscopies, as well as by X-ray diffraction.
Suitable crystals of all the complexes for X-ray analysis were obtained upon crystallization from
methanol solution or the mother liquor solution by diffusion of diethyl ether (1, 2, 4 and 5),
hydrothermal method (3) or slow evaporation of the mother liquor solution (6). Compound 4
crystallizes with one molecule of methanol.
[Zn(OSO2CF3)2L(H2O)] 1 is a mononuclear neutral di-trifluoromethanesulfonate complex (Fig.
1). The zinc ion is coordinated with six atoms, three nitrogen atoms from the terpyridine ligand, two
oxygen atoms from the two anionic ligands and one oxygen atom from water, involved in a distorted
-
ZnN3O3 octahedral geometry with the coordinated oxygen atoms of the two ligated CF3SO3
occupying the apical positions [bond angles range from 83.32(6) to 97.04(6)º between the apical
atoms and the equatorial positions]. This type of geometry is that usually reported for related Zn(II)
compounds, e.g. [Zn2(ꢀ-O2SO2)2L2(CH3OH)2] (L =
4′-phenyl-2,2’:6’,2”-terpyridyl),16a or
[Zn(OSO2CF3)2L(H2O)] [L = 12,12- dimethyl-7,10,14,17-tetraoxa-1(3,6),3(2,5),2(2,6)- tripyridina-
-11,13(1,4)-dibenzenacycloicosaphane].24 Several intermolecular hydrogen bonds exist in the
structure, and two of them are worth to be mentioned. They involve the coordinated water molecule
-
and the O2 and O6 oxygen atoms from the two CF3SO3 ligands, along with several others involving
-
the other oxygen atoms or a fluorine atom of CF3SO3 with hydrogen atoms at the carbon atoms of
phenyl or pyridyl groups of the terpyridine ligand. In its structure, the terpy group in the ligand is
nearly planar (with an RMS deviation of 0.0585 Å). Moreover, the phenyl ring is twisted (17.82(14)º)
with the connecting pyridyl or (20.08(12)º) relative to the plane containing N1, N2, N3 and Zn1. Due
to the position and orientation of the trifluoromethanesulfonate in 1, the Zn complex molecules are
too far apart for any convenient π-π interaction, a situation that contrasts with the structures of other
terpyridine-type complexes.12,16 However, several π-ring interactions (Y-X...Cg) exist in the structure,
within the range of 3.039 - 3.762 Å.
The asymmetric unit of compound 2 (Fig. 2) comprises half of the molecule because of the
symmetry of the compound. The mononuclear complex crystallized in a centrosymmetric space
group and the atoms Zn1, N2, C8, C9 and C12 are located on the twofold axis. Each zinc ion is
coordinated by the three N atoms of the 4′-Ph-terpy (L) ligand and two oxygen atoms from two

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-
SO3PhCH3 ions, therefore forming an irregular N3O2 trigonal bipyramidal coordination environment
(Fig. 2). The three pyridyl units of the ligand are almost perfectly flat (with an RMS deviation of
0.0225 Å) and the phenyl group in complex 2 is folded and twisted, as revealed by the angle between
the phenyl ring and the connected pyridyl (18.57(7)º) and the plane formed by Zn, N1, N2 N1A
(16.47(6)º). The Zn1─N2 bond distance of 2.052(2) Å for the central pyridyl ring is shorter than that
for the terminal ones, Zn1─N1 and Zn1─N1A bonds [2.1570(19), 2.1570(19) Å, respectively], what
is also shown by all the complexes of this study. The structure presents no intermolecular π-π
interactions but two π-ring (Y-X...Cg) interactions between two oxygen atoms at the sulfonates and
two neighbouring rings constituted by Zn1-N1-C5-C6-N2 with an atom-centroid distance (X..Cg) of
3.5076 Å. Further stabilization, by several intermolecular hydrogen bonds, can also be found,
involving the O2 sulfonate oxygen and the hydrogens at carbon atoms of the ligand, although no
classic hydrogen bond is present in the structure.
Like 2, compounds 3, 4, 5 and 6 (Figs. 3 - 6) are also mononuclear species crystallized in
centrosymmetric space groups. The asymmetric units of the compounds present half of the molecule
in 3 and 6, one molecule in 4, and two molecules in 5, respectively, because of the symmetry of the
molecule. The atoms Zn1, N2, C8, C9 and C12 are also located on the twofold axis in 3 and 6. The
coordination environment around the zinc ion in these compounds displays an irregular trigonal
bipyramidal geometry, as in complex 2 and other related compounds [12, 16], which results from the
coordination of zinc by three nitrogen atoms from the terpyridine ligand and two oxygen atoms from
the auxiliary ligands in a monodentate mode. The average contacts between the central metal ion and
the oxygen atoms (Zn–O) is 1.957 Å in 3, which has no hydroxyl group at its auxiliary ligands, being
shorter than those in 4 (1.984 Å), 5 (1.974 Å) and 6 (1.971 Å). This is indicative that the hydroxyl
substituent has an elongating effect on the Zn-O bond lengths. However, these bond lengths do not
follow the sequence of pKa values of the conjugated acids of the anions, the latter being 2.98 (for o-),
4.08 (for m-), 4.17 (for benzoic acid) and 4.58 (for p-hydroxyl benzoic acid). Such bond lengths are
not only affected by the basicity of the anions but also by other factors, including hydrogen bonds, or
even spatial environments determined by the positions of the hydroxyl groups at the phenyl rings.
The three pyridyl units of L in these complexes are planar (with an RMS deviation of 0.0668 Å
for 3, 0.1685 Å for 4, 0.0741 and 0.0527 Å in 5, and 0.0185 Å in 6). The angles between the pendent
phenyl rings and the connected pyridyls and the attached N-N-N-Zn planes are 18.97 (9) and

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21.08(9)º in 3, 33.81(11) and 36.91(11)º in 4, 9.02º (3.81(6)º in one molecule and 14.23(5)º in the
other) and 11.00º (7.50(7) and 14.50(7)º for the respective two molecules) in 5, and 5.82(15) and
4.81(15)º in 6, respectively, showing that there is not a great effect of the hydroxyl substituent on
these angles. No classic hydrogen bond is found in the structure of 3 but two other kinds of
intermolecular hydrogen bonds can be found in the structure, involving the O2 oxygen of the
benzoate and the hydrogens at carbon atoms of the terpyridine ligand. Intermolecular hydrogen
bonds exist in the structures of 4, 5, and 6, which are in the range of 2.50 – 3.50 Å. Unlike 4 and 6,
which only shows intermolecular hydrogen bonds, intramolecular hydrogen bonds also exist in the
structure of 5 because of the ortho-position of the hydroxyl substituent, thus further consolidating the
structure.
Several π-ring interactions exist in each structure of the complexes between oxygen or H atoms
and their neighbouring rings. The structure of 3 presents two kinds of π-ring (Y-X...Cg) interactions:
one is between one hydrogen at C3 and a neighbouring phenyl ring of a benzoate with an
atom-centroid distance (X..Cg) of 2.660 Å; the other one is between one oxygen atom (O2) of a
benzoate and two neighbouring rings constituted by Zn1-N1-C5-C6-N2 or by Zn1-N2-C6-C5A-N1A
with the atom-centroid distances (X…Cg) of 3.398 and 3.398 Å, respectively. In 4, several π-ring
interactions are present (Y-X...Cg is 2.868 Å and H-X...Cg are in the range of 2.74 – 2.95 Å)
between one oxygen atom (O2) at a benzoate ligand or several H atoms and their neighbouring rings,
which are in the range of 2.79 – 2.96 Å for X-H...Cg and 3.076 – 3.333 Å for Y-X...Cg in 5, and
3.039 – 3.763 Å for Y-X...Cg in 6.
2.3. TG-DTA properties of the complexes
The TG properties of the six complexes were studied and the results for the sulfonated
compounds 1 and 2 are shown in Fig 7, whereas the others are deposited as supporting material.
Fig. 7(a) shows the TG and DTA curves for complex 1. There are three major decomposition
steps corresponding to loss of the solvent and two decomposition processes of the molecules. The
first loss is in the range of 139-185 °C (centred at 162 °C) and it concerns the loss of the coordinated
water molecule. The weight loss in this step is 2.51 % (calc. 2.61 %). The second decomposition
occurs in the temperature range of 369 - 541 °C (centred at 455 °C) and corresponds to a 45.5 % loss
of weight. The loss in the final decomposition process is 8.88 mg within the temperature range of

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541 – 743 °C (centred at 642 °C) with the percentage of 38.8 %. The final product is ZnO and its
weight is 2.99 mg with the percentage of 13.1, which matches with the calculated value of 11.8 %.
The TG and DTA curves of compound 2 are shown in Fig. 7(b). It has three major weight
losses corresponding to a gradual loss of two methyl groups and two decomposition steps. The first
loss, in the range of 180 – 306 °C (centred at 243 °C) can possibly be accounted for by the loss of the
two methyl groups at the two p-toluene sulfonate ligands. The total loss is 3.80 % (calc. 4.19 %). The
second decomposition step is in the range of 389 – 507 °C (centred at 448 °C) and the total loss is
21.5 %, and the next one occurs in the range of 507 - 891 °C (centred at 699 °C). The percentage of
lost weight in this step is 61.2 %. The final product is ZnO and its percentage is 13.0 %, which is
comparable to the calc. value of 11.4 %. The results show that compound 2 is more thermal stable
than 1. The final stable temperature in the case of 2 is 891 °C, much higher than that (743 °C) of 1.
The decomposition processes for the two compounds are different. By comparison with the thermal
decompositions of ZnSO4·7H2O and a Zn cyclic dithiocarbamate compound,[25, 26] complex 2 appears
to lead to the formation of ZnSO4 and then ZnO, whereas 1 undergoes conversion to [ZnOL] on the
way to ZnO.
The TG-DTA properties of the benzoate complexes 3, 4, 5 and 6 were also studied and their
decomposition processes are summarized in Table 2. The final product of thermal decomposition of
the four complexes is also ZnO, what corresponds to 14.1 % for 3, 11.2 % for 4, 13.7 % for 5 and
13.2 % for 6, complying with the theoretical value of 13.2 % (3), 11.8 % (4), 12.5 % (5), and 12.5 %
(6), respectively.
The results are indicative that the decomposition processes and the final stable temperatures
greatly depend on the auxiliary ligands. In comparison with complexes 1 and 2 bearing the
substituted sulfonate ligands, the final stable temperatures of the benzoate complexes 3 - 6 are lower.
Complex 4, with the hydroxyl substituent in para position, displays the lowest final state temperature
(491 °C), being easier to decompose than the others. Complex 6, with the meta-OH substituent, is the
benzoate complex with the highest final state temperature (700 °C). Differences in hydrogen-bonds
(which in the case of the ortho-OH complex 5 can be intramolecular) are expected to play a role in
the decomposition processes.
Table 2 Decomposition processes in TG-DTA of the benzoate complexes 3 - 6

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Complex
Step 1
Step 2
Step 3
Step 4
3
322 – 428
59.8
4
5
275 – 321
21.7
6
333-405
27.9
a, °C
b, %
a, °C
b, %
a, °C
b, %
a, °C
b, %
70-106
4.80
463 – 651
26.1
260 – 341
23.2
349 – 383
12.4
431 – 528
28.8
376 – 458
52.6
383 - 420
8.0
528 – 700
30.0
458 – 491
8.2
420 - 655
32.9
a. Temperature range of decomposition in TG-DTA of the complex;
b. Percentage of weight loss in every decomposition process of the complex.
2.4. Photoluminescent properties
All the compounds 1 – 6 show interesting photoluminescent properties in the solid state at room
temperature, and their emission spectra are presented in Fig 8. The sulfonate compounds 1 and 2
show very strong photoluminescent bands in their spectra (the determinations were run with a small
amount of samples, a few mg, and under conditions of the narrowest slits of emission and excitation,
see experimental section). Compound 1, excited at 300 nm, has one band in its emission spectra at ca.
394 nm, which is similar to the photoluminescent band in the emission spectrum of compound 2
(excited at 300 nm), which appears at ca. 386 nm. These results are indicative that the organic parts
of the sulfonate ligands have no marked effects on the photoluminescence of the complexes. In
comparison with the already reported photoluminescence of the free ligand L,13 the bands of 1 and 2
can tentatively be assigned to an intraligand charge transfer (ILCT).
In the benzoate complex 3, two bands are clearly detected, one at 387 nm with a high intensity
and the other at 524 nm with a medium intensity. A related zinc complex bearing acetate instead of
benzoate displays two bands in its photoluminescent spectrum at 381 (high intensity) and 500 nm
(low intensity) [16a]. The first peaks, at the higher energy, are very close and with similar intensity
(also for complex 1), being assigned (see above) to an ILCT band. The second peaks differ by 24 nm
for the benzoate (3) and acetate complexes. This is attributed mainly to the different electronic
properties of their anionic ligands. The phenyl group at benzoate has a positive induction effect,
whereas the methyl group at acetate has a negative one, and the band undergoes a blue-shift from
524 to 500 nm, being tentatively assigned to a MLCT band. 27, 28

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The benzoate compounds 4, 5 and 6, with the hydroxyl substituent, show also interesting
photoluminescent properties, the positions and intensities of their bands depending on the position of
the hydroxyl group at the benzoate ligand. In the spectrum of 4, excited at 390 nm, a band with
medium intensity is observed at 530 nm, whereas a strong peak at 553 nm is displayed by the
spectrum of 5. When excited at 300 nm, both compounds show their emission bands at 413 and
411nm, respectively. As for the complexes 1 and 2, the band is assigned to a MLCT. 12,16,27,28 It is an
interesting result that the band at ca. 390 nm, observed in 1-3 and in some Zn and Cd
4′-phenyl-terpyridine compounds,12,16 is not exhibited by 4 and 5. The behaviour of 6 is unique in
comparison with 4 and 5, since the peak at 390 nm is observed, although with a very low intensity.
However, a clear rationale for the overall effect of the position of the hydroxyl substituent in the
phenyl ring cannot be established, conceivably depending on inductive and resonance effects,
hydrogen bonds, interaction with the neighbouring molecules or packing of the molecules in the
solid state. The bands of photoluminescence in these compounds do not follow the sequence of pKa
values of the conjugated acids of the anions. Although compound 5, bearing the carboxylate ligand
with the lowest pKa value of the conjugated acid, shows the lowest energy of the emission band, the
other compounds do not follow such a sequence.
The photoluminescent properties of the complexes were also studied in solution. On account of
their solubility in DMSO, DMF and methanol, these were the selected solvents (Table 3).
Table 3 Photoluminescent properties of the complexes in solution
Complex Bands, nm
DMSOa
DMFa
Methanola
Exmax
378, 478
379, 478
252
366
252
367
255
366
300
367
362, 434
1
Emmax
518
519
513
Exmax
379, 478
443, 513
375, 479
443, 508
375, 479
512
378, 480
449, 518
376, 479
508
361, 434
513
2
Emmax
Exmax
3b
Emmax
Exmax
375, 480
510
364, 433
509
4
Emmax

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Exmax
Emmax
Exmax
Emmax
376, 479
397, 515
375, 479
445, 511
376, 483
512
264
368
259
366
365, 434
511
5
6
375, 480
439, 510
359, 434
510
a. The concentrations of the six complexes prepared in the tests are 1 mmol/L in DMSO, and 0.5
mmol/L in DMF and methanol.
b. In a 1:1 mixture of DMSO and methanol, a weak band appears at 438 nm (when 3 is excited at 382
nm) or at 513 nm (when 3 is excited at 371 or 453 nm).
The six complexes show a strong photoluminescence at ca. 515 nm both in DMSO and DMF
with the two Exmax at ca. 378 and 479 nm. 1 and 4 show only one emission band in DMSO and DMF.
2 and 6 display two bands in both solvents. 3 and 5 exhibit two bands in DMSO, but only one in
DMF.
In methanol, a new emission band appears at ca. 366 nm in the spectra of all the six complexes.
Strong emission bands are also observed in methanol at ca. 510 nm, except for 3 which does not
show such an emission band in this solvent. In a 1:1 solution of DMSO and methanol, complex 3
shows a weak band at 438 nm (when excited at 382 nm) or at 513 nm (when excited at 371 or 453
nm). The results are indicative that DMSO enhances the band at ca. 513 nm but quenches the band at
ca. 365 nm, whereas methanol has the opposite effect. The combined effects of the two solvents
results in the appearance of the two weak bands of 3 in their mixture.
From the results obtained in the photoluminescent studies, the three peaks appearing at ca. 366,
445 and 515 nm are tentatively assigned to ILCT, LMCT and MLCT, respectively. 12,16,27,28 The
results also show that these charge transfers are affected by the anionic auxiliary ligands and the
solvents used in the tests.
Conclusion
4′-phenyl-terpyridine appears as a convenient N,N,N-tripodal ligand source towards the easy
synthesis of zinc complexes with interesting photoluminescence.
Six Zn(II) complexes with such a ligand were obtained (usually in good yields) by a simple
reaction with an appropriate zinc salt, and, in their composition, the auxiliary anionic ligand was

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determined by the nature of the salt. The zinc complexes thus prepared show photoluminescence in
the solid state and in solution (in DMSO, DMF and methanol) at room temperature and the
photoluminescent properties (namely the energy and intensity of the emission bands) are markedly
dependent on the anionic auxiliary ligands and on the solvents used in the tests. In particular,
compounds 1 and 2 show a very strong photoluminescence at the high energy region, indicating that
a sulfonate is a much better auxiliary ligand in these terpyridine compounds, concerning the
photoluminescent properties, than a carboxylate ligand in that energy region. Moreover, these
properties are easily turned upon variation of the organic group of the sulfonate ligand. Within the
carboxylate complexes, the position of the hydroxyl group substituent at the aromatic ring also has a
marked effect, and, e.g., the ortho position (complex 5) results in an enhancement of the intensity of
the low energy band, whereas the meta position (complex 6) does not show that band but enhances
the high energy one, in the solid.
The thermal properties of the complexes are also greatly affected by the auxiliary ligands. The
sulfonate complexes display a higher final stable temperature than the carboxylate ones. Within the
latter, the meta position of the hydroxyl group (compound 6) results in the highest thermal stability.
However, a clear rationale for the overall effect of the position of the hydroxyl substituent in the
phenyl ring cannot be established, conceivably depending on inductive and resonance effects,
hydrogen bonds interaction with the neighbouring molecules or packing styles of the molecules in
the solid state.
Nevertheless, the recognition of the above types of effects can be of significance towards further
design of photoluminescent materials. The work provides good candidates for further
photoluminescent studies and deserves to be extended to other substituted terpyridine zinc complexes
on attempting to study substituent effects and to establish relationships.
3. Experimental
3.1. Instrumentation and reagentes
1H NMR spectra were run on a Varian Unity 400 spectrometer. Elemental analyses were
determined with an Elementar Vario EL III Elemental Analyser. IR spectra were measured with a
Perkin–Elmer Spectrum 2000 or a Magna750 FT-IR spectrophotometer, in KBr pellets. Emission

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and excitation spectra were recorded on a Perkin–Elmer LS 55 luminescence spectrometer with a
red-sensitive photomultiplier type R928. TG-DTA data were collected with a Perkin Elmer STA6000
Simultaneous Thermal Analyzer at a heating rate of 10 K min-1 under an air atmosphere. All reagents
used in the experiments were of analytical grade or purified by standard methods. The amounts of the
solid state samples used in the photoluminescent studies are as follows: 3 mg for compounds 1 and 2,
and 25 mg for compounds 3 - 6. For 1 and 2, the photoluminescent experiments were undertaken with the
narrowest slits (2.5) of excitation and emission.
3.2 Synthesis
4′-Ph-terpy (L) was prepared by following a reported procedure. 17 Zn(SO3CF3)2 is a product of
Fluka. Zn(OCOPh)2 was synthesized by the reaction of Zn(NO)2·6H2O and NaCOOPh in water.
Other salts were prepared by the reaction of Zn(OH)2 and the respective acids.
[Zn(OSO2CF3)2L(H2O)] (1)
A 15 mL dichloromethane solution of L (0.31 g, 1.0 mmol) was added dropwise to a 15 mL
methanol solution of Zn2(SO3CF3)2 (0.36 g, 1.0 mmol) and the system was stirred for 24 h. After
filtration, a pale yellow solution was obtained. Slow diffusion into the mother solution of diethyl
ether led to colourless crystals which were suitable for X-ray analysis (0.33 g, 49 % based on the
salt). Anal. calcd for C23F6H17N3O7S2Zn: C 39.98; H 2.48; N 6.08. Found: C 39.98; H 2.35; N 5.95.
TG-DTA determination: H2O % = 2.55, ZnO % = 13.1; Calc by formula C23F6H17N3O7S2Zn: H2O %
= 2.61, ZnO % = 11.8. 1H NMR (400 MHz, DMSO-d6): δ 7.51 (m, 1.3H), 7.68 ~ 7.78 (m, 3H), 7.97
(s, 2H), 8.29 (s, 2H), 8.44 (d, 2H, J = 6.4 Hz), 8.91 (s, 0.7H), 9.08 (d, 0.7H, J = 7.2 Hz), 9.16 (s, 2H),
9.40 (s, 1.3H). 13C NMR (100 MHz, DMSO-d6): δ 115.92, 119.12, 120.53, 121.19, 122.33, 123.58,
125.53, 127.70, 128.09, 128.23, 129.44, 130.95, 131.16, 135.60, 141.31, 147.38, 147.73, 147.84,
148.80, 149.51, 154.52, 155.24. IR (KBr disc) (cm-1): 3503 (vs), 3062 (w), 1613 (s, νpyridyl-H), 1552
(m, νaryl-H), 1476 (m, νpyridyl-H), 1415 (m), 1262 (vs), 1174 (s), 1036 (s), 886 (w), 795 (w), 767 (m),
644 (s).
[Zn(OSO2PhCH3)2L] (2)
40 mL of a dichloromethane solution of L (0.31 g, 1.0 mmol) were added dropwise to 40 mL of

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a methanol solution of Zn(p-SO3PhCH3)2·6H2O (0.52 g, 1.0 mmol) and the system was stirred for 24 h.
The pale yellow solution thus formed was concentrated and a solid of 2 was obtained by adding 20
mL of diethyl ether. It was separated by filtration, washed with dichloromethane and diethyl ether
and dried under vacuum (0.65 g, 90 % yield based on L). Anal. calcd for C35H29N3O6S2Zn·2.5H2O: C
1
55.15, H 4.50, N 5.51. Found: C 55.29; H 4.32; N 5.65. H NMR (400 MHz, DMSO-d6): δ 2.26 (s,
6H), 7.07 (d, 4H, J = 8.0 Hz), 7.43 (d, 4H, J = 8.0 Hz), 7.50 (t, 1H, J = 6.2 Hz), 7.67 - 7.76 (m, 3H),
7.90 - 7.98 (m, 2H), 8.27 (t, 2H, J = 7.6 Hz), 8.38 - 8.45 (m, 2H), 8.90 (d, 1H, J = 4.4 Hz), 9.02 (d,
1H, J = 7.6 Hz), 9.07 (s, 1H), 9.18 (d, 1H, J = 8.0 Hz), 9.42 (s, 1H). 13C NMR (100 MHz, DMSO-d6):
δ 20.79, 120.30, 121.17, 123.46, 123.61, 125.46, 127.49, 127.74, 128.26, 129.36, 129.47, 130.89,
131.20, 135.54, 135.64, 137.70, 141.10, 141.36, 145.55, 147.41, 147.73, 147.85, 148.78, 149.51,
154.23, 155.16. IR (KBr disc) (cm-1): 3069 (m), 2924, 1603 (s, νpyridyl-H), 1549 (m, νaryl-H), 1475 (m),
1415 (m, νpyridyl-H), 1263 (s), 1165 (s), 1110 (s), 1207 (w), 1005 (s), 812 (w), 793 (m), 767 (m), 733
(w), 684 (s), 569 (s). Suitable crystals for X-ray analysis were obtained upon dissolution of the white
solid in methanol and slow diffusion of diethyl ether. TG-DTA determination of the crystals: ZnO %
= 13.1; Calc by formula C35H29N3O6S2Zn: ZnO % = 11.4.
[Zn(OCOPh)2L] (3)
A mixture of Zn(OCOPh)2 (0.049 g，0.16 mmol), L (0.050 g, 0.16 mmol) and 20 mL distilled
water was sealed in a 25 mL stainless reactor with a Teflon liner and heated at 120 ºC for two days.
Colorless crystals of 3 were obtained (0.051 g, 52 % yield based on L). Anal. calcd for
C35H25N3O4Zn: C 68.13; H 4.08; N 6.81. Found: C 68.30; H 4.06; N 6.80. TG-DTA determination:
1
ZnO % = 14.1; Calc by formula C35H25N3O4Zn: ZnO % = 13.2;. H NMR (400 MHz, DMSO-d6): δ
7.31 (m, 4H), 7.39 (m, 2H), 7.66 (m, 3H), (t, 2H), 7.76 (t, 2H, J = 6.0 Hz), 7.83 (d, 4H, J = 6.8 Hz),
8.27 (m, 4H), 8.89 (d, 2H, J = 3.6 Hz), 8.96 (d, 2H, J = 7.6 Hz), 9.11 (s, 2H). IR (KBr disc) (cm-1):
3059 (m), 1609 (vs, νpyridyl-H), 1570 (s, νaryl-H), 1477 (m, νpyridyl-H), 1414 (s, νpyridyl-H), 1372 (vs), 1252
(m), 1167 (w), 1018 (m), 836 (m, δAr-H), 796 (m, δAr-H), 720 (s), 681 (m).
[Zn(p-OCOPhOH)2L] (4)
20 mL of a dichloromethane solution of L (0.12 g, 0.39 mmol) were added dropwise to 20 mL
of a methanol solution of Zn(p-OCOPhOH)2·3MeOH·1.5H2O (0.18 g, 0.39 mmol) in a 100 mL flask

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and the mixture was stirred for 24 h. Filtration led to the separation of a white powder of 4 from the
mother solution, which was dried in a desiccator (0.14 g, 52 % yield based on L). Anal. calcd for
ZnC35H25N3O6·2.4H2O: C 60.72; H 4.34; N 6.07. Found: C 60.84; H 4.17; N 6.26. TG-DTA: Calc by
formula ZnC35H29.8N3O8.4: H2O % = 6.3, ZnO % = 11.8; Determined: H2O % = 4.8, ZnO % = 11.2.
1H NMR (400 MHz, DMSO-d6): δ 6.68 (d, 4H, J = 8.4 Hz), 7.14 (t, 2H, J = 6.8 Hz), 7.29 (t, 1H, J =
6.8 Hz), 7.56 (t, 2H, J = 6.0 Hz), 7.73 - 7.75 (m, 6H), 7.97 (d, 2H, J = 6.8 Hz), 8.46 (d, 2H, J = 6.0
Hz), 8.69 (s, 2H). 8.77 (d, 2H, J = 3.6 Hz), 9.79 (s, 2H, -OH). 13C NMR (100 MHz, DMSO-d6): δ
114.36, 119.20, 122.22, 126.53, 127.56, 128.85, 130.40, 131.28, 135.01, 139.70, 147.79, 148.54,
148.83, 152.90, 159.79, 170.46, 170.87. IR (KBr disc) (cm-1): 3655 (m, νOH), 3402 (br, w, νOH), 3128
(s), 2927 (w, νCH3), 1602 (vs, br, νpyridyl-H), 1554 (vs, νaryl-H), 1474 (w, νpyridyl-H), 1442 (w, νpyridyl-H),
1378 (vs), 1284 (s), 1243 (s), 1162 (m), 1097 (w), 1015 (m), 859 (m, δAr-H), 791 (s, δAr-H), 763 (m,
δAr-H), 698 (m), 633 (s). Suitable crystals for X-ray analysis were obtained upon diffusion of the
filtrate by diethyl ether.
[Zn(o-OCOPhOH)2L] (5)
20 mL of a dichloromethane solution of L (0.12 g, 0.39 mmol) were added dropwise to 20 mL
of a methanol solution of Zn(o-OCOPhOH)2·2H2O (0.15 g, 0.39 mmol) in a 100 mL flask and the
mixture was stirred for 24 h. Filtration led to the separation of a white powder of 5 from its mother
solution, which was dried in a desiccator (0.19 g, 73 % yield based on L). Anal. calcd for
ZnC35H25N3O6: C 64.77; H 3.88; N 6.47. Found: C 64.91; H 3.80; N 6.50. TG-DTA: Calc by formula
1
ZnC35H25N3O6: ZnO % = 12.5; Determined ZnO % = 13.7. H NMR (400 MHz, DMSO-d6): δ 6.75
(d, 4H, J = 7.6 Hz), 7.28 (t, 2H, J = 7.4 Hz), 7.64 (s, 3H), 7.79 (m, 4H), 8.31 (m, 4H), 8.97 (m, 4H),
9.11 (s, 2H), 13.22 (s, br, 2H, -OH). 13C NMR (100 MHz, DMSO-d6): δ 116.18, 117.44, 117.72,
120.30, 122.86, 127.32, 128.06, 129.26, 130.61, 130.78, 133.19, 135.66, 140.74, 147.68, 148.68,
148.86, 154.28, 161.15, 173.05. IR (KBr disc) (cm-1): 3749 (w, νOH), 3446 (br, w, νOH), 3063 (w),
1602 (vs, br, νpyridyl-H), 1483 (s, νpyridyl-H), 1413 (w, νpyridyl-H), 1390 (s), 1331 (m), 1254 (s), 1159 (m),
1018 (m), 863 (m, δAr-H), 795 (w, δAr-H), 765 (s, δAr-H), 671 (m), 641 (w). Suitable crystals for X-ray
analysis were obtained upon diffusion of the filtrate by diethyl ether.
[Zn(m-OCOPhOH)2L] (6)

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20 mL of a dichloromethane solution of L (0.12 g, 0.39 mmol) were added dropwise to 20 mL
of a methanol solution of Zn(m-OCOPhOH)2·2H2O (0.15 g, 0.39 mmol) in a 100 mL flask and the
mixture was stirred for 24 h. Filtration led to the separation of a white powder of 6 from its mother
solution, which was dried in a desiccator (0.22 g, 85 % yield based on L). Anal. calcd for
1
ZnC35H25N3O6·0.5H2O: C 63.89; H 3.98; N 6.39. Found: C 64.18; H 3.70; N 6.49. H NMR (400
MHz, DMSO-d6): δ 6.77 (d, 2H, J = 7.2 Hz), 7.10 (t, 2H, J = 7.6 Hz), 7.31 (m, 4H), 7.43 (m, 3H),
7.68 (s, 2H), 8.08 (d, 4H, J = 28.4 Hz), 8.82 (t, 6H, J = 37.6 Hz), 9.34 (s, 2H, -OH). 13C NMR (100
MHz, DMSO-d6): δ 116.22, 117.25, 119.58, 120.13, 122.36, 126.75, 127.78, 128.56, 129.07, 130.58,
135.34, 137.77, 140.01, 147.86, 148.69, 148.93, 153.36, 156.86, 170.60. IR (KBr disc) (cm-1): 3402
(m, br, νOH), 3254 (vs, br, νOH), 1619 (s, νpyridyl-H), 1565 (vs, νaryl-H), 1476 (w, νpyridyl-H), 1443 (s,
ν
pyridyl-H), 1398 (vs), 1350 (s), 1250 (s), 1157 (m), 1113 (m), 1069 (m), 1016 (m), 933 (m), 884 (m,
δAr-H), 798 (s, δAr-H), 772 (s, δAr-H), 689 (m), 622 (m), 539 (m), 455 (m). Suitable crystals for X-ray
analysis were obtained upon evaporation of the filtrate naturally. Determination of the crystals by
TG-DTA: Calc by formula ZnC35H25N3O6: ZnO % = 12.5; Determined: ZnO % = 13.2.
3.3. Crystal structure determinations
Single crystals of 1-6 were obtained as indicated above. Intensity data were collected using a
Bruker AXS-KAPPA APEX II diffractometer with graphite monochromated Mo-Kα (λ 0.71073)
radiation. Data were collected using omega scans of 0.5º per frame and full sphere of data were
obtained. Cell parameters were retrieved using Bruker SMART software and refined using Bruker
29
SAINT on all the observed reflections. Absorption corrections were applied using SADABS.29
30
Structures were solved by direct methods by using the SHELXS–97 package and refined with
SHELXL–97.31 Calculations were performed using the WinGX System–Version 1.80.03.32 All
hydrogens were inserted in calculated positions. Least square refinements with anisotropic thermal
motion parameters for all the non–hydrogen atoms and isotropic for the remaining atoms were
employed. CCDC 831974, 831975, 831976, 916058, 916059 and 916060 contain the supplementary
crystallographic data for this paper. These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via w.ccdc.cam.ac.uk/data_request/cif.

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Acknowledgements
The authors are grateful for the financial support from the Foundation for Science and Technology
(FCT), Portugal, and its programs (POCI, FEDER funded, Grant No. SFRH/BPD/24691/2005 and
Project PEst-OE/QUI/UI0100/2011), the Science Foundation of China (21261002), the Scientific
Fund of Guangxi University (X061144) and the Opening Project of Guangxi Key Laboratory of
Petrochemical Resource Processing and Process Intensification Technology (K008).
.
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Fig. 1: Thermal ellipsoid plot, drawn at the 30% probability level, of [Zn(OSO2CF3)2L(H2O)] (1) with atomic
numbering scheme. Selected bond lengths (Å) and angles (°): Zn1−N1 2.1506(17), Zn1−N2 2.0488(17),
Zn1−N3 2.1524(18), Zn1−O1 2.1814(16), Zn1−O4 2.1705(16), Zn1−O7 2.0054(15); N2−Zn1−N1 76.87(6),
N2−Zn1−N3 76.48(6), N1−Zn1−N3 153.35(7), O1−Zn1−O4 167.59(6), O1−Zn1−O7 84.28(6), O4−Zn1−O7
83.32(6).
Fig. 2: Thermal ellipsoid plot, drawn at the 30% probability level, of [Zn(OSO2PhCH3)2L] (2) with atomic
numbering scheme. Symmetry codes: A 1-x, y, 1/2-z. Selected bond lengths (Å) and angles (°): Zn1−N1
2.1570(19), Zn1−N2 2.050(2), Zn1−O1 1.9586(17); N2−Zn1−N1 76.17(5), N1−Zn1−N1A 152.35(10),

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O1−Zn1−O1A 98.07(13), O1−Zn1−N1 103.28(8), O1A−Zn1−N1 94.79(8).
Fig. 3: Thermal ellipsoid plot, drawn at the 30% probability level, of [Zn(OCOPh)2L] (3) with atomic
numbering scheme. Symmetry codes: A -x, y, 3/2-z. Selected bond lengths (Å) and angles (°): Zn1−N1
2.1780(19), Zn1−N2 2.078(2), Zn1−O1 1.9569(14); N2−Zn1−N1 75.09(4), N1−Zn1−N1A 150.17(9),
O1−Zn1−O1A 97.27(8), O1−Zn1−N1 95.60(7), O1−Zn1−N2 131.36(4), O1A−Zn1−N1 104.04(7).
Fig. 4: Thermal ellipsoid plot, drawn at the 30% probability level, of [Zn(p-OCOPhOH)2L]·CH3OH
(4·CH3OH) with atomic numbering scheme. Selected bond lengths (Å) and angles (°): Zn1−N1 2.164(2),
Zn1−N2 2.080(2), Zn1−N3 2.202(2), Zn1−O1 1.983(2), Zn1−O4 1.9855(18); N1−Zn1−N2 75.59(8),
N1−Zn1−N3 149.01(8), N2−Zn1−N3 74.85(8), O1−Zn1−O4 100.73(8), O1−Zn1−N1 108.85(8), O1−Zn1−N2
119.44(8), O1−Zn1−N3 93.71(9). H atoms at all carbon atoms of the two ligands have been omitted for
clarity.

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Fig. 5: Thermal ellipsoid plot, drawn at the 30% probability level, of one of the molecules of
[Zn(o-OCOPhOH)2L] (5) with atomic numbering scheme. Selected bond lengths (Å) and angles (°): Zn1−N1
2.210(2), Zn1−N2 2.075(2), Zn1−N3 2.166(2), Zn1−O1 1.990(2), Zn1−O2 1.9841(19); Zn2−N4 2.186(2),
Zn2−N5 2.059(2), Zn2−N6 2.171(2), Zn2−O7 1.972(2), Zn2−O10 1.948(2); N1−Zn1−N2 74.70(8),
N1−Zn1−N3 148.69(8), N2−Zn1−N3 75.16(8), O1−Zn1−O2 115.48(9), O1−Zn1−N1 93.53(9), O1−Zn1−N2
105.36(9), O1−Zn1−N3 102.40(9), O2−Zn1−N1 93.61(9), O2−Zn1−N2 138.18(8), O2−Zn1−N3 103.28(9). H
atoms at all carbon atoms of the two ligands have been omitted for clarity.
Fig. 6: Thermal ellipsoid plot, drawn at the 30% probability level, of one of the molecules of
[Zn(m-OCOPhOH)2L] (6) with atomic numbering scheme. Symmetry codes: A -x, y, 1/2-z. Selected bond
lengths (Å) and angles (°): Zn1−N1 2.1979(16), Zn1−N2 2.0735(17), Zn1−O1 1.9708(12); N1−Zn1−N2
75.35(4), N1−Zn1−N1A 150.70(8), O1−Zn1−O1A 99.54(7), O1−Zn1−N1 106.55(5), O1−Zn1−N2 130.23(3),
O1−Zn1−N1A 92.40(5). H atoms at all carbon atoms of the two ligands have been omitted for clarity.

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25
20
15
10
5
1
0
-1
-2
-3
0
100
200
300
400
500
600
700
800
Temperature,°C
20
18
16
14
12
10
8
2
0
-2
-4
-6
-8
6
4
-10
-12
2
100
200
300
400
500
600
700
800
900
Temperature,°C
Fig. 7: Thermal analyses (TG and DTA plots) of complexes 1 (a) and 2 (b).

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Fig. 8: Solid state emission spectra (excitation at 300 nm for 1, 2, 3 and 6, excitation at 390 nm for 4 and
excitation at 410 nm for 5) of complexes 1 – 6 at room temperature. Sample amounts: 3 mg (1, 2), 25 mg (3 -
6).

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Table 1 Relevant crystal data for complexes 1 – 6.
Compounds
Formula
Formula
Weight
1
2
3
4·CH3OH
5
6
C23H17F6N3O7S2Zn
690.93
C35H29N3O6S2Zn C35H25N3O4Zn C36H29N3O7Zn C35H25N3O6Zn C35H25N3O6Zn
717.14
616.97
681.01
648.97
648.97
Crystal system Monoclinic
Monoclinic
C2/c
Monoclinic
C2/c
Monoclinic
P2(1)/c
13.007(3)
9.863(2)
26.388(8)
90
Triclinic
P-1
Monoclinic
C2/c
Space group
a(Å)
P2(1)/c
11.0686(7)
22.0148(13)
12.9592(9)
90
20.389(4)
13.924(3)
12.196(2)
90
19.352(4)
13.626(3)
11.721(2)
90
13.998(2)
14.822(2)
15.489(2)
106.615(7)
103.451(7)
91.595(7)
2979.6(7)
4
16.503(3)
17.021(3)
10.663(2)
90
b (Å)
c (Å)
α
β
(°)
(°)
117.908(4)
90
113.21(3)
90
107.01(3)
90
110.93(3)
90
99.67(3)
90
γ (°)
V (Å3)
Z
2790.6(3)
3182.2(11)
4
2955.5(10)
4
3161.9(14)
4
2952.7(9)
4
4
Dcalc (Mg m-3) 1.645
1.497
1.387
1.431
1.447
1.460
1.117
0.955
0.875
0.832
0.877
0.885
ꢀ
(mm-1)
F(000)
θmax min (°)
1392
1480
1272
1408
1336
1336
28.31, 2.57
-12→14
-29→29
-17→17
6919
28.39, 1.82
-27→24
-17→18
-14→16
3914
28.37, 1.86
-18→25
-16→17
-15→15
3646
27.21, 2.22
-16→16
-9→12
-33→33
6956
28.47, 1.97
-18→18
-18→19
-20→20
14722
28.29, 1.73
-22→21
-22→22
-14→14
3637
,
θ
Index range h
k
l
Independent
reflections
Observed
reflections
Rint
5801
3104
2949
5248
10316
3096
0.0261
0.0371
0.0945
1.005
0.0269
0.0372
0.1126
1.029
0.0302
0.0362
0.0953
1.000
0.0322
0.0408
0.1048
1.036
0.0297
0.0476
0.1144
1.014
0.0204
0.0305
0.0883
1.024
R
wR
GOF