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Inorganica Chimica Acta 360 (2007) 2638–2646

Syntheses, crystal structures and thermal behaviors of threecomplexes with 4-acyl pyrazolone derivatives

Yun Yang, Li Zhang, Lang Liu, Guangfei Liu, Jixi Guo, Dianzeng Jia *

Institute of Applied Chemistry, Xinjiang University, Urumqi, Xinjiang Province 830046, PR China

Received 23 October 2006; received in revised form 11 January 2007; accepted 14 January 2007Available online 18 January 2007

Abstract

Three new complexes, [Zn(PPePeP–PNH)(CH3OH)]2(CH3OH) [PPePeP–PHN = N-(1-phenyl-3-phenylethyl-4-phenylethylene-5-pyr-azolone) p-nitrobenzoylhydrazide] (1), [Mn(PPePeP–PNH)(CH3OH)2]2(CH3OH) (2), [Mn(PM4MbP–PNH)(C2H5OH)3] [PM4MbP–PHN = N-(1-phenyl-3-methyl-4-(p-methylbenzoylene)-5-pyrazolone) p-nitrobenzoylhydrazide] (3), have been prepared and characterizedby elemental analyses, IR spectra, UV–Vis absorption spectra, thermal-analyses and X-ray diffraction studies. The structural analysesshow that the N(2) atoms of the pyrazolyl heterocycles play an important role in building the N–H� � �O hydrogen bonds of 1, 2, 3 and1, 2 formed 2D networks and 3 formed 1D chain linked by hydrogen bonds, respectively.� 2007 Elsevier B.V. All rights reserved.

Keywords: 4-Acyl pyrazolone derivatives; Crystal structures; Thermal-analyses; UV–Vis spectra; Fluorescent properties

1. Introduction

The design of new coordination supramolecules andpolymers based on transition metal compounds and multid-entate organic ligands has attracted much interest in recentyears [1,2]. Dependent on the nature of the metal and thecoordination behavior of the ligand one can develop syn-thetic strategies to influence the one, two or three-dimen-sional arrangement in the crystal in a more directed way[3]. Furthermore, it is now realized that weak hydrogenbonds that involve N–H� � �O and/or O–H� � �O hydrogenbonds stacking interactions also play a significant and pre-dictable structure determining role. Their representing reli-able and ubiquitous supramolecules show that they alreadyhave been applied in a broad range of systems and haveanalogues in the context of coordination supramoleculesand polymers [1a,1b]. One major goal in this area is thepreparation of new compounds with interesting propertiessuch as functional materials in molecular magnetism [4],catalysis [5], optoelectronic devices and gas sorption [6].

0020-1693/$ - see front matter � 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2007.01.009

* Corresponding author. Tel./fax: +86 991 8580032.E-mail address: jdz@xju.edu.cn (D. Jia).

4-Acyl pyrazolones are efficient extractants of metalions, and they have potential to form different types ofcoordination compounds due to tautomeric effect of enolform and keto form [7]. In addition, 4-acyl pyrazolonescan form a variety of Schiff bases and are reported to besuperior reagents in biological, clinical and analyticalapplications [8]. Meanwhile, compounds containing hydra-zide and acylhydrazone moieties and their complexes alsopossess biological activities, especially as potential inhibi-tors for many enzymes [7b,9,10]. Previously, we have syn-thesized a series of 4-acyl pyrazolone derivatives withmethyl or phenyl in position 3 of pyrazole [11] and reportedseveral transition metal complexes [12]. Among these com-pound, mononuclear mixed-ligand nickel complex [Ni-(PMBP–PNH)(Py)3] has been reported [12c], and anothertwo dinuclear complexes [Cu(PMBP–PNH)(CH3OH)]2-(CH3OH)2, [Mn(PMBP–PNH)(CH3OH)2]2(CH3OH)2 (CCDCNos. 614329 and 614330) have been prepared. An interest-ing feature of these compounds is that, the structures of[Cu(PMBP–PNH)(CH3OH)]2(CH3OH)2 and [Mn(PMBP–PNH)(CH3OH)2]2(CH3OH)2 are obviously different fromthe structure of [Ni(PMBP–PNH)(Py)3]. What’s more,in the two dinuclear complexes, the hydrogen bonds

Y. Yang et al. / Inorganica Chimica Acta 360 (2007) 2638–2646 2639

(N–H� � �O) formed by N(2) atoms of the pyrazolyl hetero-cycles contribute to form the better packing format. Thisencourages us to extend our research by using transitionmetal ions and pyrazoline ligands to synthesize novelaggregates, since these assemblies may have potential inter-est. In this paper, three new coordination supramoleculesbased on transition metals of Zn(II) and Mn(II) with mul-tidentate Schiff base ligands N-(1-phenyl-3-phenylethyl-4-phenylethylene-5-pyrazolone) p-nitrobenzoylhydrazideand N-(1-phenyl-3-methyl-4-(p-methylbenzoylene)-5-pyr-azolone) p-nitrobenzoylhydrazide have been synthesized.Crystal structures, fluorescent properties, UV–Vis spectraand thermal behaviors of them are also reported.

2. Experimental

2.1. Physical measurements and materials

IR spectra were recorded on BRUKER EQUINOX-55spectrophotometer within 400–4000 cm�1 using the samplesprepared as pellets with KBr. The fluorescence behavior ofligand and its zinc(II) complex 1 have been studied usingHitachi F-4500 Fluorescence Spectrophotometer with aXe arc lamp as the light source at room temperature.UV–Vis measurements were performed on a HitachiU-3010 Spectrophotometer at room temperature. Thermalanalyses were carried out on NETZSCH STA 449C instru-ment at a temperature range of 30–900 �C with a heatingrate of 20 �C min�1 in an atmosphere of flowing air. XRDwere taken on a DX-1000 X-ray diffractometer with graph-ite-monochromatized Cu Ka radiation (k = 1.54056 A),with a step size of 0.12�. The crystal structures were per-formed using Rigaku R-axis Spider IP diffractometer. Allreagents purchased from commercial sources were used asreceived. PPePeP, PM4MbP and PNH (p-nitrobenzoylhyd-razide) were prepared according to the literature method[7a,13–15]. The elemental analyses, solutions of synthesesand the yields for ligands and complexes are in Table 1.

2.2. Preparation of the ligands [16]

Ligands were prepared by mixing equimolar amounts ofPPePeP (PM4MbP) and PNH in ethanol solutions. The

Table 1Elemental analyses for ligands and complexes 1–3

Compound Solution Yield (%)

PPePeP–PNH ethanol 81.12

PM4MbP–PNH ethanol 78.57

1 methanol 86.32

2 methanol 81.69

3 ethanol 57.12

mixture was refluxed with oil bath at 80 �C for 3 h. Uponcooling, the yellow precipitate was formed and collectedby filtrating, washing and purifying with ethanol, and driedin oven.

2.3. Preparation of complexes

To a solution of the ligands in 50 mL of methanol orethanol was added a solution of equimolar amounts ofZn(OAc)2 Æ 2H2O or Mn(OAc)2 Æ 4H2O in 5 mL of solutionat 60 �C with continuous stirring for 3 h. The resultingsolution was allowed to cool in room temperature, andthe precipitate was collected by filtration, washed with cor-responding solution and dried in air. The filtrate wasallowed to stand in an open beaker for several days underambient conditions to produce the corresponding crystals.

2.4. X-ray crystallography

Crystal data for the complexes were collected at293(2) K on Rigaku R-axis Spider diffractometer usingMo Ka radiation (k = 0.71073 A). Data reductions andabsorption corrections were performed with the SAINT

and SADABS software packages, respectively. The structureswere solved by direct methods using SHELXS-97 [17], andwere refined by full matrix least-squares methods usingSHELXL-97 [17]. Anisotropic displacement parameters wererefined for all non-hydrogen atoms except for the disor-dered atoms. The hydrogen atoms were generated geomet-rically and refined using a riding model. Crystallographicdata and other pertinent information are summarized inTable 3. Selected bond lengths and bond angles are listedin Table 4. Summary for hydrogen bond data is listed inTable 5.

3. Results and discussion

3.1. IR spectra

The most important IR absorption bands of the ligandsand complexes are listed in Table 2. Of the ligands, thebroad peaks in the range 3023–3128 cm�1 correspond tothe t(NH) stretching vibration [18]. And the strong bands

Color Found (Calc.) (%)

C H N

yellow 69.87 4.81 13.69(70.1) (4.56) (13.20)

yellow 65.82 4.83 15.67(66.07) (4.44) (15.41)

red 60.62 4.53 10.88(61.30) (4.34) (11.17)

black 61.55 4.53 10.59(61.21) (4.67) (10.81)

black 57.45 4.81 10.92(57.67) (5.62) (10.85)

Table 2Some prominent IR bands for ligands and complexes 1–3 (cm�1)

Compounds mNH mC@O mC–O mC@N mM–O mM–N

PPePeP–PNH 3023 1620, 1589PM4MbP–PNH 3128 1645, 15951 1339 1484 460 4252 1385 1567 468 4753 1335 1562 451 429

Table 4Selected bond distances (A) and angles (�) for 1–3

Compound 1

Zn(1)–O(1) 1.9591(14) Zn(1)–O(5) 2.009(2)Zn(1)–O(2) 2.0347(13) Zn(1)–N(3) 2.0382(16)Zn(1)–O(2)A 2.1080(14)

O(1)–Zn(1)–O(5) 89.76(8) O(5)–Zn(1)–O(2) 103.11(7)O(5)–Zn(1)–O(2)A 97.56(8) O(5)–Zn(1)–N(3) 124.56(9)N(3)–Zn(1)–O(2)A 77.49(6) O(1)–Zn(1)–N(3) 92.87(6)O(1)–Zn(1)–O(2) 104.49(6) O(2)–Zn(1)–O(2)A 80.41(6)O(1)–Zn(1)–O(2)A 170.09(6) O(2)–Zn(1)–N(3) 129.31(7)

Compound 2

Mn(1)–O(1) 1.8982(18) Mn(1)–O(2) 1.9089(18)Mn(1)–O(3) 1.8840(18) Mn(1)–O(4) 2.272(2)Mn(1)–O(3)A 2.2245(18) Mn(1)–N(3) 2.014(2)Mn(1)A–O(3) 2.2245(18)

O(1)–Mn(1)–O(2) 168.95(8) O(3)–Mn(1)–N(3) 172.35(8)O(3)A–Mn(1)–O(4) 172.91(8) O(3)–Mn(1)–O(4) 94.30(9)O(1)–Mn(1)–O(4) 85.74(9) O(2)–Mn(1)–O(4) 86.18(9)N(3)–Mn(1)–O(4) 90.84(9) O(3)–Mn(1)–O(3)A 80.17(8)N(3)–Mn(1)–O(3)A 94.24(8) O(2)–Mn(1)–O(3)A 89.79(8)O(1)–Mn(1)–O(3)A 98.99(8) Mn(1)–O(3)–Mn(1)A 99.83(8)

Compound 3

Mn(1)–O(5) 1.8408(19) Mn(1)–O(2) 1.9218(18)Mn(1)–O(1) 1.9321(18) Mn(1)–N(3) 2.016(2)Mn(1)–O(3) 2.247(2) Mn(1)–O(4) 2.277(2)

O(5)–Mn(1)–O(2) 90.71(8) O(5)–Mn(1)–O(1) 98.00(8)O(2)–Mn(1)–O(1) 171.28(7) O(5)–Mn(1)–N(3) 170.56(8)O(2)–Mn(1)–N(3) 79.87(8) O(1)–Mn(1)–N(3) 91.42(8)O(5)–Mn(1)–O(3) 91.89(9) O(2)–Mn(1)–O(3) 90.83(9)O(1)–Mn(1)–O(3) 88.41(9) N(3)–Mn(1)–O(3) 87.66(9)O(5)–Mn(1)–O(4) 91.66(9) O(2)–Mn(1)–O(4) 92.49(8)O(1)–Mn(1)–O(4) 87.76(8) N(3)–Mn(1)–O(4) 89.38(9)

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in 1589 and 1645 cm�1 range are assigned to t(C@O) of thepyrazolone-ring and t(C@O) of the lateral chain, respec-tively [19]. All these suggest that structure of the ligandsin the solid state are the keto form.

The infrared spectra of complexes exhibit new bands atabout 1335–1339 cm�1 due to t(C–O). Meanwhile, thereare new bands between 1484 and 1567 cm�1 in the complexes,which are assigned to t(–C@N–N@C–) of hydrazones[12c,12d,20]. The weak bands in the region 425–475 cm�1

are due to M–N and M–O stretching vibrations. From theseobservations, it is concluded that the ligands react in the enolform with prototropy, which incorporates into two protontransfers, and then lose the enolic protons and coordinatesto the central metal atoms in the complexes.

3.2. Description of the crystal structures

Complex 1 crystallized in the monoclinic space groupP21/n with Z = 2. Fig. 1 illustrates the single crystal struc-ture of 1, which shows a centrosymmetric binuclear dimer,in which each Zn(II) atoms are linked by carbonyl oxygenatom from one of the carbonyl oxygen of each PPePeP–

Table 3Crystal and structure refinement data for complexes 1–3

1 2 3

Empiricalformula

C64H54N10O10Zn2 C34H34N5O7Mn C31H36N5O7Mn

Formulaweight

1318.00 679.60 645.59

Crystal system monoclinic monoclinic triclinicSpace group P21/n P21/n P�1T (K) 293(2) 293(2) 293(2)k (A) 0.71073 0.71073 0.71073a (A) 13.470(3) 12.899(3) 10.149(2)b (A) 23.095(5) 23.824(5) 12.901(3)c (A) 1.0229(2) 11.154(2) 13.528(3)b (�) 18.13(3) 102.60(3) 108.72(3)V (A3) 3150.1(11) 3345.3(12) 1621.7(6)Z 2 4 2F(000) 1368 1416 676dcalc (g/cm3) 1.390 1.349 1.332l (mm�1) 0.832 0.449 0.459Reflections

collected29339 31575 16114

Uniquereflections[Rint]

7218 [0.0289] 7657 [0.0491] 7374 [0.0242]

R1,awR2,b (%) 0.0341, 0.0892 0.0574, 0.1527 0.0486, 0.1322Goodness-of-fit 1.071 1.032 1.086

a R = (Fo � Fc)/(Fo).b wR ¼ w F 2

o � F 2c

� �2=ðw F 2

o

� �2Þ1=2.

O(3)–Mn(1)–O(4) 175.10(7)

PNH to the opposite metal center. A pair of Zn(II) atomsseparated at a distance of 3.164 A are bridged by O2 andO2A from the tridentate Schiff base PPePeP–PNH into adinuclear structure. Two methanol molecules (O5, O5A)coordinate to zinc centers in each unit. The five-coordina-tion Zn(II) centers in a trigonal bipyramids, for the Zn1case, the plane being formed by two oxygen atoms (O2,O5), one nitrogen atoms (N3) of two deprotonated ligandsPPePeP–PNH with the normal bond distances of Zn(1)–O(2), Zn(1)–O(5), and Zn(1)–N(3) 2.0347(13), 2.009(2),and 2.0382(16) A. And O1, O2A are in axial positions(O(1)–Zn(1)–O(2)A = 170.09(6)�) with the drifting distancebetween the Zn1 and plane 0.2012 A. The angles of O(5)–Zn(1)–O(2), O(5)–Zn(1)–N(3) and O(2)–Zn(1)–N(3) are103.11(7)�, 124.56(9)�, 129.31(7)�, respectively, which areadded up to justly 356.98�. While the atoms (O1, C7, C8,C17, N3, and Zn1; N3, N4A, C25A, O2A, and Zn1) arecomposed of hexatomic rings and pentatomic rings(Fig. 1). The free pore volume of a unit is estimated, usingPLATON [21] program, to be 36.5 A3 (1.2% of the total).

In the structure of 2, the coordination environments ofMn(II) centers are slightly different from those of Zn(II)

Fig. 1. A centrosymmetric unit of 1 in which the Zn dimer is bridged by carbonyl oxygen atoms. Hydrogen atoms have been omitted for clarity.

Table 5Hydrogen bond data for complexes 1–3

Interaction d(D–H) (A) d(D� � �A) (A) \(DHA) (�) Symmetry operation

Compound 1

O(5)–H(5O)� � �O(6) 0.75(4) 2.620(3) 172(4) #1 �x + 1, �y + 1, �z + 1O(6)–H(6O)� � �N(2)#2 0.76(3) 2.834(3) 170(4) #2 x, �y + 1/2, z � 1/2

Compound 2

O(4)–H(4O)� � �O(7)#2 0.79(4) 2.692(4) 170(4) #2 x, �y + 3/2, z � 1/2O(7)–H(7O)� � �N(2) 0.848(19) 2.826(4) 173(6) #1 �x + 1, �y + 1, �z + 2

Compound 3

O(4)–H(4O)� � �N(2)#1 0.82(4) 2.853(3) 175(3) #1 �x + 1, �y + 1, �z

O(3)–H(3O)� � �O(5)#2 0.82(4) 2.670(3) 169(3) #2 �x + 1, �y + 1, �z + 1

Y. Yang et al. / Inorganica Chimica Acta 360 (2007) 2638–2646 2641

in complex 1. The metal centers are hexacoordinated in thedistorted octahedrons. The two manganese atoms arebridged by two methanol molecules at a distance of3.151 A. The coordination octahedron around Mn1 ion iscomposed of O1, O2, O3, O4, O3A and N3 atoms, andthe atoms O1, O3, O2 and N3 are composed of the equato-rial plane whose mean deviation is 0.1084 A and the drift-ing distance between the Mn1(II) and plane is 0.0218 A.Those indicate that the Mn1 atom is nearly in the equato-rial plain and the axis of the octahedron are held by O4 andO3A. The normal bond distances of Mn1–O1, Mn1–O2,Mn1–O3, Mn1–N3 are 1.8982(18), 1.9089(18), 1.8840(18),2.014(2) A, those of Mn1–O4, Mn1–O3A are 2.272(2)and 2.2245(18) A, respectively. For axial bond distancesare longer than the bond distances of the plane, thecoordination geometry around the manganese ion in thecomplex is elongated octahedron, which can be reasonablyexplained as being due to Jahn–Teller elongation forMn(II) ions. Bond angles also show that the coordinationgeometries are distorted octahedron, with O(3)–Mn(1)–

N(3), O(2)–Mn(1)–O(1) and O(4)–Mn(1)–O(3)A angles of172.35(8)�, 168.95(8)� and 172.91(8)�, respectively. Whilethe atoms (O1, C7, C8, C17, N3, and Mn1; N3, N4, C25,O2, and Mn1) are composed of hexatomic rings and pent-atomic rings, which are similar with 1 (Fig. 2). The freepore volume of a unit is estimated, using PLATON program,to be 66.2 A3 (2.0% of the total).

Complex 3 crystallizes in the monoclinic space group P�1with Z = 2 and the asymmetric unit consists of mononu-clear [Mn(PM4MbP–PNH)(C2H5OH)3] (Fig. 3). Hexaco-ordination of Mn(II) is completed by O1, N3, and O2 ofPM4MbP–PNH ligand and O3, O4, O5 of the ethanol mol-ecules. The coordination polyhedron is slightly distortedwith O(5)–Mn(1)–N(3), O(2)–Mn(1)–O(1), and O(3)–Mn(1)–O(4) angles of 170.56(8)�, 171.28(7)�, and 175.10(7)�, respectively. Consequently, they are not very stronglydeviated from the regular 180�. Bond distances areasymmetric with two long distances Mn(1)–O(3) andMn(1)–O(4) of 2.247(2) and 2.277(2) A, respectively,whereas the four Mn(1)–O(5), Mn(1)–O(2), Mn(1)–O(1)

Fig. 2. A centrosymmetric unit of 2 in which the Mn dimer is bridged by methanol molecules. Hydrogen atoms have been omitted for clarity.

Fig. 3. The crystal structure of 3 in which the Mn is hexacoordinated in the distorted octahedrons. Hydrogen atoms and some other groups have beenomitted for clarity.

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and Mn(1)–N(3) bond distances are shorter than 2.100 A(Table 4). The resulting four short band distances of thetetragonal plane and two long Mn–O bond lengths are alsodue to Jahn–Teller effect.

In the three complexes 1, 2, and 3, many O–H� � �O andO–H� � �N hydrogen bonding interactions were observed inthe crystal structures of these complexes. In the two net-works of 1 and 2, generally, the oxygen atoms of the coor-dinated or crystalline methanol molecules and nitrogen

atoms of the pyrazolyl heterocycles are the main part ofhydrogen bonded networks. With the different coordinatedfashions, the two networks show different lattice shape.Particularly, in 1, the oxygen atoms of the methanol mole-cules as the crystalline (O6) and the coordinated (O5) and(N2) atoms of the pyrazolyl heterocycles atoms from neigh-boring ligands contribute to form the discrete units to a 2Dnetwork (Fig. 4) with hydrogen bonds, that is O(5)–H(5O)� � �O(6) and O(6)–H(6O)� � �N(2)A. The hydrogen

Fig. 4. 2D Framework of 1 along a axis. Only hydrogen bonding atomand weak interactions are given for clarity.

Fig. 5. The hydrogen bonds linked 2D framework of 2 along a axis. Onlyhydrogen bonding atom and weak interactions are given for clarity.

Fig. 7. UV–Vis Absorption spectra of PPePeP–PNH, 1 and 2 in ethanolsolution (5.0 · 10�5 M).

Y. Yang et al. / Inorganica Chimica Acta 360 (2007) 2638–2646 2643

bonds of complex 2 are relatively much similar to complex1. The oxygen atoms of (O4) from the coordinated metha-nol molecule and (O7) from the crystallized methanol mol-ecule form hydrogen bond with N(2) atom of the pyrazolylheterocycles from neighboring ligands. That is O(4)–

Fig. 6. The 1D supramolecular chain of 3 formed by hydrogen bonds alongclarity.

H(4O)� � �O(7)A and O(7)–H(7O)� � �N(2) are responsiblefor linking repeating units [Mn(PPePeP–PNH)-(CH3-OH)2]2(CH3OH) to 2D network (Fig. 5). Over allthese strong O–H� � �O and O–H� � �N hydrogen bonds playan important role in contributing to the stability of the 2Dnetwork structure. In the packing arrangement of 3, thehydrogen bonds form an 1D supramolecular chain holdby two O(4)–H(4O)� � �N(2)#1 and O(3)–H(3O)� � �O(5)#2H-bonding interactions (Fig. 6). It is worth noting that ineach structure of them N(2) atoms of the pyrazolylheterocycles attach themselves to construct the infinitetwo-dimensional networks for 1 and 2, and one-dimen-sional supramolecular chain for 3.

3.3. UV–Vis spectra

Fig. 7 illustrates the UV–Vis spectra of the PPePeP–PNHand the complexes 1 and 2 in ethanol. In the exploited wave-length domain from 200 to 800 nm, the K band of PPePeP–PNH which is attributed to the p–p* transition is observedwith one maximum of absorption around 302 nm [22].However, this band has undergone a bathochromic shift(13 nm) and hypsochromic shift (�13 nm) resulting fromthe chelation of the ligand with the transition metal ions,and the band then appears at 315 and 289 nm in 1 and 2,respectively. The UV–Vis spectra of 1 and 2 also showabsorption bands at 415 and 414 nm attributed to the Kband of C@N and the L!M (charge transfer) transition[22f,23]. The intense bands suggest that the ligand changes

b axis. Only hydrogen bonding atom and weak interactions are given for

Fig. 8. The emission spectra of ligand and 1 at room temperature: (a) inthe solid state, (b) in 2 · 10�5 solution of acetonitrile.

2644 Y. Yang et al. / Inorganica Chimica Acta 360 (2007) 2638–2646

into a large conjugate system due to the chelation in theenolic form [22e]. These results show that the PPePeP–PNH coordination to metal ion formed complexes andincreased the molecular conjugate system and reduced theenergy system [23]. The reason for this properties is thatthe binding affinity of PPePeP–PNH toward them may con-tribute to the particularly high thermodynamic affinity ofmetal for N,O-chelate ligands and the fast metal-to-ligandbinding kinetics [24].

3.4. Fluorescent spectra of the complex

The fluorescence spectra for organic ligand and complex1 were measured at room temperature. The fluorescentspectra of PPePeP–PNH and 1 in the solid state and solu-tion are shown in Figs. 8a and 8b, respectively.

In the solid state, it can be seen that 1 exhibits weakfluorescence with maximum emission peak at 570 nm whenexcited at 450 nm. To ascertain the adscription of the emis-sion bands, the fluorescence of pure organic ligand PPe-PeP–PNH was measured, and strong emission is foundunder the same excited condition with maximum emissionpeak at 511 nm. The reason for this is that, the chemicalstructures of organic fluorescence compounds [25] gener-

ally contain an aromatic ring, fused aromatic rings, orother conjugated ring systems along with fluorophores,such as C@O, –N@O, –N@N– in PPePeP–PNH. But fluo-rescence can be quenched up on Zn(II) ions bondingthough it is not complete. On complexation with Zn(II)ions, electron transfer effect may be relieved by theincreased charge transfer. It may because upon excitationthe electron of the highest occupied molecular orbital(HOMO) of the fluorophore is promoted to the local low-est unoccupied molecular orbital (LUMO); subsequently,the electron seated on the HOMO of the donor transfersto the HOMO of the fluorophore synergistically (electrontransfer), which causes fluorescence quenching [26]. Owingto the blue–green fluorescent emission of the ligand it maybe used as an material for blue–green-light emitting diodedevices.

In acetonitrile solution, for 1, the maximum emissionpeak is at 333 nm when excited at 285 nm. For ligand,the maximum emission peak is at 325 nm under the sameexcited condition. Compared with the fluorescence spectrain solid, the fluorescence of 1 is much stronger in the ace-tonitrile solution. When 1 was dissolved in acetonitrile,with the hydrogen bond action of ground state or electro-static-steady action of the lowest singlet excitated state(p, p*), the energy of the lowest singlet state (n, p*) isincreased and the energy of the lowest singlet state (p, p*)is decreased. That may lead the (p, p*) to change into thelowest singlet excitated state. The higher polarity andhigher H-bonds acceptor capability of the solution are ben-eficial to yield fluorescence [27]. This maybe the reason for1 exhibits stronger florescence emission in acetonitrilesolution.

3.5. Thermal behavior

To investigate the stability of these complexes, thermo-gravimetric analyses (TG) on the crystalline samples werecarried out under the air atmosphere with a heating rateof 20 �C/min. The final solid products of decompositionof 2, 3 were verified by X-ray diffraction patternsregistration.

For complex 1, the first major weight loss of ca. 8.9%corresponding to the departure of both the lattice, onemethanol molecule as solvent and two bridged methanolmolecules (three methanol molecules per unit, calculated7.3%) occurred in stages starting at 85 �C and completingat 250 �C. The appreciably longer desolvated temperatureof the complex is in agreement with the structural dataand the fact one-methanol molecule in the complex is coor-dinated to the metal atom. This desolvated complex wasstable up to 300 �C and then began to decompose. Follow-ing this point, the decomposition of the proceeds was inseveral overlapping exothermic steps. These stages corre-spond to decomposition of two ligands in the temperaturerange of 300–740 �C. The observed mass loss (86.7%) coin-cides with the theoretical value (87.7%) of the ligand. Theresulting product of the decomposition is ZnO whose

Y. Yang et al. / Inorganica Chimica Acta 360 (2007) 2638–2646 2645

remaining weight of 13.3% corresponds to the percentage(12.4%) of the final product at 900 �C.

For complex 2, there are two weight loss steps. The com-plex was stable until 190 �C and the decomposition of thecomplex finished at 560 �C in two overlapping exothermicsteps. These stages correspond to decomposition of threemethanol molecules in the temperature range of 190–240 �C and the PPePeP–PNH ligand in the temperaturerange of 240–560 �C. The final residue has the observedmass 13.8%. The X-ray diffraction pattern of the complex2 heated up to 560 and 800 �C all show that 2 was trans-formed exothermically to Mn2O3 or Mn3O4 [28].

The TG curve of complex 3 is divided into two stages.The first weight loss is 1.9% in the temperature range 60–100 �C, corresponding to the loss of the adsorbent watermolecule in the air. The hydrogen-bonded 1D supramo-lecular chain is stable in the temperature rang of 100–250 �C. The second and third weight loss is 83.6% inthe temperature range 260–700 �C. It dose not lose weightat the temperatures higher than 700 �C. The final residuehas the observed mass 14.4%. No matter the X-ray dif-fraction pattern of 3 heated up to 700 �C or above800 �C, the diffraction lines were nearly the same andthe complex 3 transformed exothermically to Mn2O3 orMn3O4.

From the above results, it is possible to suggest the ther-mostability of 2 is higher than that of 1; 1, 2 are more stablethan 3, which maybe attribute to differences coordinatedfashions between 2 and 1 and differences between the 2D(1, 2) and 1D (3) structure.

4. Conclusion

In summary, we have successfully prepared three newcomplexes resulting from 4-acyl pyrazolones organicligands and transition metals. The complexes 1 and 2 exhi-bit hydrogen bonding linked 2D rhombus grid networks.The complex 3 is hydrogen bonded 1D supramolecularchain. The N(2) atoms of the pyrazolyl heterocycles playvery important role in building the hydrogen (O–H� � �Oand O–H� � �N) linked 2D networks for 1, 2 and the 1Dhydrogen bonded chain for 3. The multiple-layer 2D net-works may have potential applications in many aspects,such as molecular sorption and separation. Moreover,for 1, the fluorescent properties owing to the blue–greenfluorescent emission of the ligand may be used as anadvanced material for blue–green-light emitting diodedevices.

Acknowledgements

This work was supported by the National Natural Sci-ence Foundation of China (Nos. 20366005 and20462007), the Scientific Research Foundation in XinjiangEducational Institutions (XJEDU2005S01) and the YoungScholar Science Foundation of Xinjiang University(QN040107).

Appendix A. Supplementary material

CCDC 613450, 613451 and 615094 contain the supple-mentary crystallographic data for 1, 2 and 3. These datacan be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystal-lographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: +(44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated with thisarticle can be found, in the online version, atdoi:10.1016/j.ica.2007.01.009.

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