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Synthesis, structural characterization and photoluminescence property of fourdi(mono)acylhydrazidate-coordinated Cd2+ and Zn2+ compounds{
Juan Jin,a Fu-Quan Bai,b Guang-Hua Li,a Ming-Jun Jia,b Jin-Jing Zhao,a Hong-Li Jia,a Jie-Hui Yu*a and
Ji-Qing Xu*a
Received 8th August 2012, Accepted 17th September 2012
DOI: 10.1039/c2ce26263k
Under hydrothermal conditions, the simple reactions between metal salts, aromatic polycarboxylic
acids (4,49-diphthalic anhydride ketone, dphahk; 4,49-sulfoyldiphthalic anhydride, sdpha; pyridine-
2,3-dicarboxylic acid, pdca) and N2H4?H2O with or without the presence of phenanthroline?H2O
(phen) yielded four di(mono)acylhydrazidate-coordinated Cd2+/Zn2+ compounds as
[Cd(DPHKH)(phen)]?1.75H2O 1, [Zn3(DPHKH)2(HDPHKH)2(phen)2]?8H2O 2,
[Cd(SDPTH)(phen)(H2O)]?H2O 3 and [Zn(PDH)2(H2O)2] 4 (DPHKH =
4,49-diphthalhydrazidatoketone hydrazone; SDPTH = 4,49-sulfoyldiphthalhydrazidate; PDH =
pyridine-2,3-dicarboxylhydrazidate). The di(mono)acylhydrazide molecules in the title compounds
originated from the hydrothermal in situ acylation reactions of aromatic polycarboxylic acids with
N2H4?H2O. It is noteworthy that another kind of hydrothermal in situ reaction was also observed
when preparing compounds 1 and 2, namely the nucleophilic addition reaction between the keto
group (of dphahk) and N2H4. The photoluminescence analysis indicates that the compounds in the
different states (in the solid state or in aqueous solution) may exhibit different emission behaviors.
Introduction
In the past decade, the study of the design and synthesis of novel
coordination polymers has attracted considerable attention
owing to their structural diversity1 and the potential applications
in adsorption,2 optics3 and magnetism.4 To date, many
coordination polymers with interesting structures and useful
properties have been obtained by the simple self-assemblies
between metal centers and organic molecules. Various organic
bridging-type molecules have been applied as the building
blocks, and typical examples contain N-heterocyclic ligands,
polycarboxylic acids, pyridinepolycarboxylic acids and similar
species. However, the organic acylhydrazide molecules are less
well developed.5 In 2004, Xu first reported three examples of
PMDH/CPTH-bridged Co2+ compounds with magnetic proper-
ties by applying the hydrothermal in situ acylation reactions
between pyromellitic acid/benzene-1,2,4-tricarboxylic acid and
N2H4?H2O (PMDH = pyromellitdihydrazidate; CPTH = 4-car-
boxylphthalhydrazidate).6 Subsequently, Xu reported four
examples of PMDH-extended Zn2+/Cd2+ compounds and their
luminescence properties again.7 Based on the following con-
siderations, one of our current interests is focused on the
investigation of the structural characterization of a series of
metal-acylhydrazidate coordination polymers: (i) the diversity of
the acylhydrazide molecule. The organic polycarboxylic acids
containing at least a pair of neighboring carboxyls all possess the
potential to hydrothermally acylate in situ with N2H4?H2O into
the acylhydrazide molecules, so the acylhydrazide molecule has a
large family; (ii) the diversity of the coordination mode for the
acylhydrazide molecule. The N and O atoms in the acylhydrazide
molecule can all act as donors to coordinate to metal centers.
Moreover, these N and O atoms can also act as the hydrogen-
bonded donors/acceptors, extending the molecular units into
supramolecular networks; (iii) the potential presence of multiple
kinds of charge-transfer paths in acylhydrazidate-containing
complexes. To date, some metal-acylhydrazidate compounds
have been obtained such as the zero-dimensional (0D) [Cd2
(APTH)4(phen)2]?2H2O,8 [Pb2(DPHKH)2(phen)2]?2H2O,9 one-
dimensional (1D) [Cd(BPTH)(phen)]?3.75H2O,10 [Mn(MPDH)2],11
two-dimensional (2D) [Cu(PTH)],12 [Mn(APTH)2(H2O)], [Pb
(APTH)2]?0.25H2O,13 [Pb4(OH)2(CPTH)3(H2O)3]?2H2O14 and the
three-dimensional (3D) [Pb(3,4-PDH)2] (PTH = phthalhydrazidate;
APTH = 3-aminophthalhydrazidate; BPTH = biphthalhydrazi-
date; 3,4-PDH = pyridine-3,4-dicarboxylhydrazidate; MPDH =
6-methylpyridine-2,3-dicarboxylhydrazidate; DPHKH = 4,49-
diphthalhydrazidatoketone hydrazone).12 Some of these com-
pounds show photoluminescence properties, and emit the different
light upon excitation: red light for [Cu(PTH)] (lem = 636 nm);12
aCollege of Chemistry and State Key Laboratory of Inorganic Synthesisand Preparative Chemistry, Jilin University, Changchun, Jilin, 130023,China. E-mail: [email protected]; [email protected] Key Laboratory of Theoretical and Computational Chemistry,Institute of Theoretical Chemistry, Jilin University, Changchun, Jilin,130023, China{ Electronic supplementary information (ESI) available. CCDC 890597–890600. For ESI and crystallographic data in CIF or other electronicformat see DOI: 10.1039/c2ce26263k
CrystEngComm Dynamic Article Links
Cite this: CrystEngComm, 2012, 14, 8162–8172
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8162 | CrystEngComm, 2012, 14, 8162–8172 This journal is � The Royal Society of Chemistry 2012
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yellow for [Pb(MPDH)] (lem = 600 nm); green for [Pb2(EPDH)4
(H2O)] (EPDH = 5-ethylpyridine-2,3-dicarboxylhydrazidate) (lem
= 531 nm);13 blue for [H(DCPTH)] (DCPTH = 4,5-dichlorophthal-
hydrazidate) (lem = 460 nm).15 In this article, we report the
structural characterization of four acylhydrazidate-coordinated
Cd2+ and Zn2+ compounds as the chained [Cd(DPHKH)(phen)]?
1.75H2O 1, [Zn3(DPHKH)2(HDPHKH)2(phen)2]?8H2O 2, [Cd
(SDPTH)(phen)(H2O)]?H2O 3 and the mononuclear [Zn(PDH)2
(H2O)2] 4 (SDPTH = 4,49-sulfoyldiphthalhydrazidate; PDH =
pyridine-2,3-dicarboxylhydrazidate). Note that two types of
hydrothermal in situ reactions are involved in the formation
process of the acylhydrazide molecules in compounds 1–4: the
acylation reaction between the carboxyl and N2H4; the nucleophilic
addition reaction between the keto and N2H4.
Experimental
All chemicals were of reagent grade quality, obtained from
commercial sources without further purification. Elemental
analysis (C, H and N) was performed on a Perkin-Elmer
2400LS II elemental analyzer. Infrared (IR) spectra were recorded
on a Perkin-Elmer Spectrum 1 spectrophotometer in the 4000–400
cm21 region using a powdered sample on a KBr plate. Powder
X-ray diffraction (XRD) data were collected on a Rigaku/max-
2550 diffractometer with Cu Ka radiation (l = 1.5418 A).
Thermogravimetric (TG) behavior was investigated on a Perkin-
Elmer TGA-7 instrument with a heating rate of 10 uC min21 in air.
Fluorescence spectrum was obtained on a LS 55 fluorescence/
phosphorescence spectrophotometer at room temperature.
Synthesis of the title compounds
The reactions were carried out in 30 mL Teflon-lined stainless
steel vessels under autogenous pressure. The single crystals were
collected by filtration, washed with distilled water and dried in
air at ambient temperature.
[Cd(DPHKH)(phen)]?1.75H2O 1. The brown block crystals of
1 were obtained by a simple hydrothermal self-assembly of
Cd(CH3COO)2?3H2O (134 mg, 0.5 mmol), 4,49-diphthalic
anhydride ketone (dphahk) (161 mg, 0.5 mmol), N2H4?H2O
(0.16 mL) and phen (99 mg, 0.5 mmol) in a 15 mL aqueous
solution (pH = 4 adjusted by saturated H2C2O4) at 170 uC for
4 days. Yield: ca. 35% based on Cd(II). Anal. Calcd
C29H22.50N8O5.75Cd 1: C 50.67, H 3.30, N 16.30. Found: C
50.77, H 3.06, N 15.51%. IR (cm21): 1635 s, 1573 s, 1492 s, 1427
m, 1382 s, 1342 m, 1206 m, 1144 m, 1069 m, 852 m, 725 s.
[Zn3(DPHKH)2(HDPHKH)2(phen)2]?8H2O 2. The brown
block crystals of 2 were obtained by a similar hydrothermal
self-assembly to that of 1 except that Zn(CH3COO)2?2H2O (110
mg, 0.5 mmol) replaced Cd(CH3COO)2?3H2O. Yield: ca. 30%
based on Zn(II). Anal. Calcd C92H74N28O24Zn3 2: C 51.35, H
3.47, N 18.23. Found: C 50.91, H 3.51, N 17.39%. IR (cm21):
1642 s, 1570 s, 1490 s, 1472 s, 1451 s, 1387 m, 1295 m, 1239 m,
1159 m, 837 m, 816 m, 725 m.
[Cd(SDPTH)(phen)(H2O)]?H2O 3. The yellow block crystals
of 3 were obtained by a simple hydrothermal self-assembly of
Cd(CH3COO)2?3H2O (134 mg, 0.5 mmol), 4,49-sulfoyldiphthalic
anhydride (sdpha) (179 mg, 0.5 mmol), N2H4?H2O (0.19 mL)
and phen (99 mg, 0.5 mmol) in a 15 mL aqueous solution (pH =
8 adjusted by N2H4) at 170 uC for 4 days. Yield: ca. 40% based
on Cd(II). Anal. Calcd C28H20N6O8SCd 3: C 47.17, H 2.83, N
11.79. Found: C 47.02, H 2.69, N 11.60%. IR (cm21): 1647 s,
1570 s, 1488 s, 1429 m, 1369 m, 1325 m, 1243 m, 1213 m, 1172 m,
1144 m, 1103 m, 1062 s, 859 m, 823 s, 727 m, 656 m, 573 m.
[Zn(PDH)2(H2O)2] 4. The yellow block crystals of 4 were
obtained by a similar hydrothermal self-assembly of
Zn(CH3COO)2?2H2O (110 mg, 0.5 mmol), pyridine-2,3-dicar-
boxylic acid (pdca) (84 mg, 0.5 mmol) and N2H4?H2O (0.09 mL)
in a 15 mL aqueous solution (pH = 7 adjusted by N2H4) at 170
uC for 4 days. Yield: ca. 30% based on Zn(II). Anal. Calcd
C14H12N6O6Zn 4: C 39.50, H 2.84, N 19.74. Found: C 38.90, H
2.74, N 19.10%. IR (cm21): 1680 s, 1599 s, 1542 s, 1467 s, 1427
m, 1394 m, 1338 s 1206 s, 1114 m, 845 m, 778 s, 648 m.
X-ray crystallography
The data were collected with Mo Ka radiation (l = 0.71073 A)
on a Rigaku R-AXIS RAPID IP diffractometer. With the
SHELXTL program, the title compounds were solved using
direct methods except compound 3 solved using heavy-atom
methods.16 The non-hydrogen atoms were assigned anisotropic
displacement parameters in the refinement. The hydrogen atoms
attached to C and N atoms except N3 in compound 2 were
treated using a riding model. The water H atoms for compound 4
were obtained from the difference Fourier maps. The water H
atoms for compounds 1–3 were not located. The H atoms on O7
and N3 in compound 2 were also not located. Only 4.5 water
molecules in compound 2 were found in the difference Fourier
maps. The others were not found. The structures were then
refined on F2 using SHELXL-97.16 CCDC numbers of the title
compounds are 890597–890600, respectively.{ The crystallo-
graphic data are summarized in Table 1. The C–O distances for
the acylhydrazidate ring moieties are listed in Table S1, ESI.{
Results and discussion
Synthetic analysis
All of the title compounds were obtained by simple hydro-
thermal self-assemblies between the metal salts, aromatic
polycarboxylic acids, N2H4?H2O with or without the presence
of phen. The di(mono)acylhydrazidate molecules in the title
compounds were derived from the hydrothermal in situ reactions
of aromatic polycarboxylic acids with N2H4?H2O. Between the
polycarboxylic acids and N2H4?H2O, two types of hydrothermal
in situ reactions occurred: one is the acylation reaction between
the carboxyl and N2H4; the other is the nucleophilic addition
reaction between the keto and N2H4. Eqn (a)–(c) (see Scheme 1)
show the formation process of the di(mono)acylhydrazidate
molecules in the title compounds. For each phthalic acid moiety
of dphahk/sdpha or pdca, two neighbouring carboxyls in situ
acylate to one N2H4 into the monoacylhydrazide moiety,
simultaneously losing two H2O molecules. Eqn (d) in Scheme 1
shows the details of the nucleophilic addition reaction. One
N2H4 H atom combined with the carboxyl O atom to form a
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hydroxyl group. Simultaneously, the remaining NHNH22 group
connected with the carboxyl C atom, forming an intermediate.
This tetrahedral intermediate is unstable. After losing one water
molecule, it transformed into the stable ketone hydrazone
(–C=NNH2). According to the acylation reaction equations,
the acylhydrazide molecule should exist in the diketo form.
However, X-ray analysis revealed that the acylhydrazide
molecule in the compound actually exists in the keto-hydroxyl
form. The diketo form is not the stable form for the
acylhydrazide molecules. This is directly confirmed by two C–
O distances for each monoacylhydrazide moiety. As shown in
Table S1, ESI,{ one C–O distance (CLO) is apparently shorter
than the other (C–O2), suggesting that the isomerization for the
acylhydrazide molecule has occurred. Eqn (a)–(c) also show the
isomerization reactions. Eqn (a) indicates that the metal ion
influences the isomerized position of the acylamino group. For
DPHKH, the acylamino group above on the left together with
the acylamino group on the bottom on the right isomerized when
interacting with the Cd2+ ion, while either two acylamino groups
above or two acylamino groups bottom isomerized when
reacting with the Zn2+ ion. This is due to the coordination of
the acylhydrazide molecule to the metal ion. For SDPTH, the
isomerized situation is the same as that of DPHKH in compound
1 (see Eqn (b)). For PDH, the acylamino group close to pyridyl
N atom isomerized (see Eqn (c)). It is noteworthy that only one
acylamino group for each monoacylhydrazide moiety isomerized
into the hydroxylimino group, the other did not.
Structural description
[Cd(DPHKH)(phen)]?1.75H2O 1. Compound 1 is a DPHKH-
propagated chained Cd2+ compound with an auxiliary phen
molecule. It crystallizes in space group P1, and the asymmetric
unit is found to be composed of one Cd2+ ion (Cd1), one
DPHKH molecule, one phen molecule as well as 1.75 lattice
water molecules. Fig. 1 displays the 1D chain structure of
compound 1. The 5-fold coordinated Cd1 center is surrounded
by one hydroxylimino O atom (O3b), two hydroxylimino N
atoms (N1, N3a) and two phen N atoms (N7, N8). The Cd1–
O3b distance of 2.319(3) A is normal. The average Cd1–Nphen
distance of 2.337 A is comparable with that of the Cd1–N1
(2.330(4) A), but somewhat longer than that of Cd1–N3a
(2.244(4) A). As shown in Scheme 2, DPHKH exhibits a m3
coordination mode. The left phthalhydrazidate ring for DPHKH
only with the hydroxylimino N atom acts as the donor, while the
right one with the hydroxylimino N and O atoms bidentately
binds to two Cd(II) centers. With ancillary phen molecule, the
triple-bridged DPHKH molecules connect the Cd(II) centers into
a 1D chain structure based on two types of loops. As shown in
Fig. S1, ESI,{ the alternate linkage of two Cd(II) centers and two
hydroxylimino groups creates an eight-membered small loop,
whereas the alternate arrangement of two Cd(II) centers and two
DPHKH molecules creates a 26-membered large loop. For these
two DPHKH molecules, only one pair of phthalhydrazidate
rings form the weak p…p stacking with a contact of ca. 3.80 A.
The remaining phthalhydrazidate ring for each DPHKH forms
the p…p stacking with the adjacent phen molecule. So the large
loop shows a rectangle with the size of 8.6 6 5.3 A2. The shortest
Cd…Cd contact in the chain is Cd1…Cd1d = 4.300 A.
[Zn3(DPHKH)2(HDPHKH)2(phen)2]?8H2O 2
Compound 2 is a DPHKH-extended Zn2+ compound. It
crystallizes in space group P2/n, and the asymmetric unit is
found to be composed of two types of Zn(II) ions (occupancy
ratio: 1 for Zn1; 0.5 for Zn2), two types of DPHKH molecules (I,
II), one phen molecule together with six lattice water molecules
(occupancy ratio: 0.5 for Ow1, Ow2, Ow3; 0.25 for Ow4, Ow5,
Ow6). As shown in Fig. 2a, compound 2 also possesses a 1D
chain structure. Two types of Zn(II) centers in the chain are
involved in the different sites. Zn1 with a tetrahedral geometry is
surrounded by four DPHKH molecules. Two use the hydro-
xylimino O atoms (O1b, O4a) to act as the donors, while the
other two use the hydroxylimino N atoms (N1, N9) to act as the
donors. Zn2 in an octahedral site is coordinated by two
acylamino O atoms (O2, O2c) and four phen N atoms (N7,
Table 1 Crystallographic data for the title compounds
1 2 3 4
Formula C29H22.5N8O5.75Cd C92H74N28O24Zn3 C28H20N6O8SCd C14H12N6O6ZnM 687.46 2151.90 712.98 425.67T (K) 293(2) 293(2) 293(2) 293(2)Crystal system Triclinic Monoclinic Triclinic MonoclinicSpace group P1 P2/n P1 P21/ca (A) 10.487(2) 17.194(3) 10.346(2) 12.805(3)b (A) 11.160(2) 12.050(2) 11.139(2) 5.3901(11)c (A) 12.296(3) 22.453(5) 13.478(3) 10.848(2)a (u) 99.54(3) 66.01(3)b (u) 98.62(3) 95.42(3) 84.96(3) 100.58(3)c (u) 90.56(3) 76.27(3)V (A3) 1402.2(6) 4630.9(16) 1378.5(5) 736.0(3)Z 2 2 2 2Dc (g cm23) 1.628 1.543 1.718 1.921m (mm21) 0.837 0.864 0.932 1.723Reflections collected 13 624 35 567 13 520 6802Unique reflections 6303 8150 6239 1667Rint 0.0286 0.0746 0.0237 0.0286GOF 1.089 1.064 1.198 1.060R1, I . 2s(I) 0.0538 0.0793 0.0321 0.0249wR2, all data 0.1810 0.2495 0.1032 0.0597
8164 | CrystEngComm, 2012, 14, 8162–8172 This journal is � The Royal Society of Chemistry 2012
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N8, N7c, N8c). The Zn–Ohydroxylimino distance (Zn1–O1b =
1.979(4) A, Zn1–O4a = 1.935(4) A) is somewhat shorter than
that of the Zn–Oacylamino (Zn2–O2 = 2.170(4) A), whereas the
Zn–Nphen bond length (Zn2–N7 = 2.124(6) A, Zn2–N8 =
2.122(6) A) is slightly longer than that of the Zn–Nhydroxylimino
(Zn1–N1 = 2.030(5) A, Zn1–N9 = 2.039(5) A). Also as shown in
Scheme 2, two types of DPHKH molecules exhibit two kinds of
new coordination modes, different from that observed in
compound 1. DPHKH I with only one hydroxylimino N atom
acts as the donor. The remaining phthalhydrazidate ring for
DPHKH I is uncoordinated. DPHKH II adopts a tetra-bridged
coordination mode: the right phthalhydrazidate ring only with
the hydroxylimino O atom acts as the donor, while the left one
with the hydroxylimino group and the acylamino O atom
Scheme 1 The detailed formation process of the di(mono)acylhydrazidate molecules in the title compounds.
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tridentately bridges three Cd(II) centers. To the chain formation,
Zn1 and DPHKH II play the key role. The DPHKH II
molecules link the Zn1 centers into the 1D chain structure of
compound 2. This chain can also be described as an alternate
arrangement of small loops and large loops (see Fig. S2, ESI,{for better understanding). The small loop is the same as that
observed in compound 1. But note that the large loop shows the
difference. The large loop is composed of 30 members. Eight
water molecules in the formula of compound 2 were determined
by CHN and TG analyses. For the two DPHKH molecules
which construct the large loop, two pairs of phthalhydrazidate
rings are both parallel to each other via the p…p interactions.
Due to their close array, two neighboring acylamino O atoms for
these two DPHKH molecules bind to another Zn(II) ion (Zn2).
The phen molecule is used mainly to satisfy the coordination of
Zn2. The shortest Zn…Zn contact in the chain is Zn1…Zn1b =
3.706 A. DPHKH I chiefly satisfies the coordination of Zn1. The
adjacent uncoordinated phthalhydrazidate rings for DPHKH I
form the p…p stacking. Through this kind of weak interaction,
the 1D chain self-assembles into a 2D supramolecular layer as
shown in Fig. 2b.
[Cd(SDPTH)(phen)(H2O)]?H2O 3. Compound 3 is a SDPTH-
extended Cd2+ compound. It crystallizes in space group P1, and
Fig. 1 The 1D chain structure of compound 1, running down the c axial direction.
Scheme 2 Three coordination modes for the di(mono)acylhydrazidate molecules in the title compounds.
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the asymmetric unit is found to be composed of one Cd2+ ion
(Cd1), one SDPTH molecule, one phen molecule, one coordina-
tion water molecule (Ow1) and one lattice water molecule (Ow2).
As shown in Fig. 3, compound 3 possesses a similar structure to
that of compound:1: (i) SDPTH adopts the same triple-bridged
coordination mode as that of DPHKH in compound 1 (see
Scheme 2); (ii) the m3-mode SDPTH molecules bridge the Cd(II)
centers into a 1D endless structure; (iii) the chain is composed of
large loops and small loops by the alternate arrangement; (iv) the
Cd1–Nphen and Cd1–Nhydroxylimino distances are comparable with
the corresponding ones in compound 1; (v) the member number
of the loops as well as the shape for the small loop are the same
as those found in compound 1; (vi) the phen molecule acts as the
auxiliary ligand. However, note that there are differences
between both chains: (i) in compound 3, the Cd1 center is
involved in a six-coordinate site. Around Cd1, there exists one
additional coordinated water molecule with Cd1–Ow1 = 2.395(2)
A; (ii) the Cd1–Ohydroxylimino distance of 2.443(2) A is slightly
longer than the corresponding one in compound 1 (2.319(3) A);
(iii) in compound 3, the large loop shows a square shape with a
size of 9.0 6 9.0 A2. For two pairs of phthalhydrazidate rings in
the large loop, none of them form p…p stacking.
Fig. 2 The 1D chain structure (part of DPHKH I is omitted for clarity) (a) and the interactions between the chains (Zn2 and phen are omitted for
clarity) (b) for compound 2.
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[Zn(PDH)2(H2O)2] 4. Compound 4 is a PDH-coordinated
mononuclear Zn2+ compound.5h It crystallizes in space group
P21/c, and the asymmetric unit is found to be composed of one
Zn2+ ion (Zn1), one PDH molecule and one coordinated water
molecule (Ow1). As shown in Fig. 4, the octahedral Zn(II) center
is completed by two PDH molecules and two H2O molecules.
Two PDH molecules with the pyridyl N atoms and the
hydroxylimino O atoms as the donors are located at the
equatorial plane (Zn1–O1 = 2.0934(12), Zn1–N1 = 2.0966(15)
A). Two H2O molecules lie on the axial positions (Zn1–Ow1 =
2.1739(15) A). Between the molecular units, two types of
hydrogen-bonded interactions are found: (i) the coordinated
H2O molecule (Ow1) as the acceptor forms the hydrogen bond to
the hydroxylimino O atom (O1b) with the Ow1…O1b contact of
2.799(2) A (b: 2x, 2y 2 1, 2z); (ii) via the N–H…O interaction,
the adjacent uncoordinated acylamino groups form a dimer with
a separation of N3…O2c = 2.866(2) A (c: 2x + 1, 2y 2 1, 2z).
Through these weak interactions, compound 4 self-assembles
Fig. 3 The 1D infinite chain structure of compound 3 (part of phen is omitted for clarity).
Fig. 4 The 2D supramolecular sheet structure of compound 4.
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into a 2D supramolecular layer in the ab plane. Note that the six-
membered Zn2Ow2O2 loop adopts the chair-shape configuration,
stabilizing the supramolecular layer structure.
In the past three years, our group has obtained two series
of monoacylhydrazidate-coordinated compounds including
the phthalhydrazide series (substituent: –H,12 –CH3,9 –Cl,15
–NH28,13 and –COOH)14 and the pyridine-monoacylhydrazide
series (substituent: –H,12 –CH311,13 and –C2H5).11,13 However,
the obtained complexes with diacylhydrazide molecules are
limited. Only four examples were obtained in our lab.8–10 The
title compounds 1–3 are three examples of new diacylhydrazi-
date-coordinated compounds. Compounds 1 and 2 are the
PDHKH-extended compounds. They show different chain
structures, which should be ascribed to the difference of the
metal centers used (Cd2+ for compound 1; Zn2+ for compound
2). In both compounds, the metal centers adopt different
geometric configurations: five-fold coordination for Cd1 in
compound 1; tetrahedron for Zn1 in compound 2 (Zn2 has no
contribution to the extension of the chain). The 5-fold
coordinated Cd1 in compound 1 is completed by an addition
bidentate liagnd (phen), while the 4-fold coordinated Zn1 in
compound 2 is completed by an additional monodentate ligand
(DPHKH I). In compound 1, owing to formation of p…p
stacking with the adjacent phthalhydrazidate ring, phen influ-
ences the arrangement of two DPHKH molecules in a large loop:
only one pair of phthalhydrazidate rings form the p…p stacking.
In compound 2, the monodentate DPHKH I does not form the
p…p stacking with the adjacent DPHKH molecule, so two
DPHKH molecules in the large loop show the closer arrange-
ment: two pairs of phthalhydrazidate rings form the p…p
stacking. Due to the closer stacking: (i) DPHKH II shows a new
coordination mode, and the members of the large loop increases
to 30; (ii) two acylamino O atoms further bind to another Zn2+
ion (Zn2), which makes the chain structure of compound 2 more
complex. Compounds 1 and 3 are the diacylhydrazidate-
coordinated Cd2+ compounds. The diacylhydrazidate ligands
DPHKH in compound 1 and SDPTH in compound 3 have
similar structures, so compounds 1 and 3 show similar chain
structures. However, since the spacers for two diacylhydrazide
molecules are different (–C=N–NH2 in compound 1, –SO2 in
compound 3), especially the centric atoms adopt different
geometric configurations (trigonal for C17 in compound 1;
tetrahedral for S1 in compound 3), the large loops show different
shapes: rectangle in compound 1, square for compound 3.
Compound 4 is a pyridine-monoacylhydrazidate-coordinated
complex. Based on the structural information, two conclusions
could be drawn: (i) the coordination ability of the pyridyl N
atom is stronger than that of the hydroxylimino N atom; (ii) the
intermolecular uncoordinated acylamino groups could form the
hydrogen-bonded dimer. This is an interesting hydrogen-bonded
synthon, via which the compounds could be propagated into the
high-dimensional supramolecular networks. The acylhydrazidate
molecule is a good bridging-type ligand, and could exhibit
multiple types of bridging modes in the complex. For example,
DPHKH exhibit three types of coordination manners in two
compounds. As shown in Scheme 2, only the hydroxylimino N
and O atoms and the acylamino O atom can act as donors to
coordinate to the metal centers. No examples show that the
acylamino N atom could also participate in the coordination to
the metal center. When the di(mono)acylhydrazidate molecule
coordinates to the metal center, the hydroxyl group deprotonates
to balance the metal charge. So the monoacylhydrazidate
molecule as PDH generally shows a 21 oxidation state and the
diacylhydrazidate molecule as DPHKH and SDPTH show a 22
oxidation state. Note DPHKH I in compound 2 differs. Since
one hydroxylimino group is uncoordinated, DPHKH I shows a
21 oxidation state in compound 2.
IR and powder XRD analyses
The n(COO) peaks for the polycarboxylic acid molecules are
generally either larger than 1680 cm21 or smaller than 1610
cm21, whereas the n(CONH) peaks for the acylhydrazidate-
coordinated compounds generally appear in the range of 1625–
1675 cm21.15 Based on this, the strong peaks appearing at 1635
cm21 for 1, 1642 cm21 for 2, 1647 cm21 for 3 and 1680 cm21 for
4 indicate that the acylation reaction for polycarboxylic acid has
occurred (see Fig. S3, ESI{). The IR spectra of the poly-
carboxylic acid molecules used in this article were also given in
Fig. S3, ESI{ (nCOO: 1775 cm21 for dphahk, 1777 cm21 for
sdpha and 1604 cm21 for pdca). In the range of 1625–1675 cm21,
no peak is observed. Fig. S4, ESI,{ presents the experimental and
simulated XRD patterns for the compounds. The simulated
XRD pattern is generated on the basis of the structural data. For
each compound, the experimental and simulated powder XRD
patterns are in accord with each other, confirming that the as-
synthesized product is pure phase.
TG analysis
The TG behaviors of compounds 1–4 were investigated, and
Fig. 5 presents the corresponding TG curves. Based on the TG
curves, some information can be obtained: (i) the initial minor
weight losses for all should be assigned as the decomposition of
the coordinated and lattice H2O molecules (calcd: 4.5%, found:
4.0% for 1; calcd: 6.7%, found: 5.7% for 2; calcd: 5.0%, found:
4.5% for 3; calcd: 8.5%, found: 8.8% for 4); (ii) in the
temperature range of 350–600 uC, the organic molecules in the
compounds gradually departed; (iii) the organic acylhydrazidate
and phen molecules were lost synchronously; (iv) the residuals
are proved to be metal oxides (CdO, calcd: 18.7%, found: 18.5%
for 1; ZnO, calcd: 11.3%, found: 10.4% for 2; CdO, calcd: 18.1%,
found: 19.0% for 3; ZnO, calcd: 19.1%, found: 18.7% for 4).
Fig. 5 The TG curves for compounds 1–4.
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Solid state photoluminescence property
In the introduction, we mentioned that some obtained metal-
acylhydrazidate compounds emit light, so the photoluminescence
properties of the title compounds in the solid state were
investigated. Fig. 6 gives the corresponding excitation and
emission spectra. Obviously, compounds 3 and 4 possess
photoluminescence properties. They emit green light with a
maximum at 513 nm for 3 and 520 nm for 4 upon excitation (lex
= 420 nm for 3, lex = 400 nm for 4). In order to understand the
emission mechanism, density functional theory (DFT) calcula-
tions were carried out on the excited electronic states of the
molecular unit for compound 4. The DFT calculation results
indicate that the effective emission appears at 490 nm, which is
comparable with that observed (520 nm). The calculations also
indicate that the HOMO ( highest occupied molecular orbital) is
composed of orbital 98 and orbital 99. They possess the
approximate energies. The LUMO ( lowest unoccupied mole-
cular orbital) is also composed of two orbitals with similar
energies: orbital 100 and orbital 101. The emission mainly
corresponds to the electronic transitions from orbital 100 to
orbital 98 as well as from orbital 101 to orbital 99 (E = 2.53 eV).
Fig. 7 exhibits the characteristics of orbitals 98–101. Orbitals 98
and 99 (HOMO) have similar compositions, which are located
on the p orbitals of the acylhydrazidate ring moiety for PDH.
Two LUMOs possess comparable compositions, which are
chiefly distributed on the p* orbitals of the pyridine ring moiety
for PDH. So the photoluminescence emission of compound 4
should be attributed to the charge transfer within the PDH
molecule. The charge transfer from the p orbitals of the
acylhydrazidate ring moiety to the p* orbitals of the pyridine
ring moiety should be responsible for the green light emission of
compound 4. Compound 3 shows a similar emission to that of
compound 4, so the emission of compound 3 should be assigned
as a similar attribution. Compounds 1 and 2 do not emit light.
This may be due to the close arrangement of the chain structures.
In compounds 1 and 2, the adjacent DPHKH molecules in the
chain form p…p packing, which may lead to fluorescence
quenching. However in compound 3, the adjacent SDPTH
molecules in the chain do not form p…p stacking, so it emits
light.
Photoluminescence property in aqueous solution
The photoluminescence properties of the title compounds in the
aqueous solutions were also studied. As shown in Fig. 8, in
aqueous solutions, all of the title compounds emit light.
Compounds 1–3 emit violet light with the maximum at 390 nm
for 1 (lex = 293 nm), 369 nm for 2 (lex = 260 nm) and 366 nm for 3
(lex = 268 nm). Compound 4 emits green light with the maximum
at 505 nm when excited at 340 nm. The emission of compounds 1–
3 should be ascribed as the charge transfer within the phen
molecule, because the phen molecule in aqueous solution shows a
similar emission (lem = 360 nm) upon excitation at 330 nm. In
aqueous solution, compound 4 shows a similar emission to that in
the solid state, so it should have a similar attribution. Compared
with the solid state emission behaviors, compounds 1–3 show
differences in aqueous solutions. This is due to the changes of the
Fig. 6 The fluorescence excitation (a) and emission (b) spectra for compounds 3–4 in the solid state.
Fig. 7 The surfaces of HOMO (orbitals 98, 99) and LUMO (orbitals 100, 101) of the molecular unit for compound 4 obtained at the B3LYP level.
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existing form for the compound. In the aqueous solutions, the
compounds generally exist in the molecular form. The weak
intermolecular interactions such as the p…p packing will
disappear. So some compounds in the aqueous solutions can emit
light, or emit light of different wavelength.
Conclusion
In short, we reported the syntheses, structures and photolumines-
cence properties of four di(mono)acylhydrazidate-coordinated
Cd2+/Zn2+ compounds. They were prepared by the simple
hydrothermal self-assemblies between Cd2+/Zn2+ salts, organic
polycarboxylic acids and N2H4?H2O with or without the presence
of phen. The di(mono)acylhydrazidate molecules as DPHKH,
SDPTH and PDH were obtained by two types of in situ ligand
reactions: the acylation reaction between the carboxyl and N2H4
and the nucleophilic addition reaction between the keto and
N2H4. Compounds 1 and 2 are DPHKH-extended compounds
and show different chain structures. The geometric configuration
for the metal center plays a key role. The difference for the chain
structure of compounds 1 and 3 is due to the distinctness of the
spacers used for the diacylhydrazidate molecules. The nature of
the acylhydrazidate molecule is further known: the acylhydrazide
molecule is an interesting bridging-type ligand; they generally exist
in the keto-hydroxyl form in the complex; only the hydroxylimino
N and O atoms as well as the acylamino O atom can act as the
donors, and the acylamino N atom does not interact directly with
the metal center; the hydroxyl group deprotonates to balance the
metal charge. In the solid state, compounds 3 and 4 emit green
light. DFT calculations indicate that the emission should be
attributed to the charge transfer from the p orbitals of the
acylhydrazidate ring moiety for PDH to the p* orbitals of the
pyridine ring moiety for PDH. In the aqueous solutions,
compounds 1–3 exhibit similar violet light emissions, different
from their corresponding emission behaviors in the solid state.
Acknowledgements
This research was supported by the National Natural Science
Foundation of China (No. 21271083), the Corporation
Coordination Project (No. 3R111N651412) and the Graduate
Innovation Fund of Jilin University (No. 20121038).
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