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: jiehuiyu@yahoo.com.cn; xjq@mail.jlu.edu.cnbState 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

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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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