Inorganica Chimica Acta 376 (2011) 36–43

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Inorganica Chimica Acta

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Syntheses, crystal structures, and characterization of heteronuclearcomplexes based on a versatile ligand with both acetylacetonateand bis(2-pyridyl) units

Jing Xiong, Lei Sun, Ling-Chen Kang, Wei Liu, You-Xuan Zheng, Jing-Lin Zuo ⇑, Xiao-Zeng YouState Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures, NanjingUniversity, Nanjing 210093, PR ChinaAcademician Work Station of Changzhou Trina Solar Energy Co., Ltd., Changzhou 213022, PR China

a r t i c l e i n f o

Article history:Received 19 June 2010Received in revised form 6 April 2011Accepted 27 May 2011Available online 28 June 2011

Keywords:Heteronuclear complexesCrystal structuresPhotoluminescenceMultidentate ligandRhenium(I) tricarbonyl complexes

0020-1693/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.ica.2011.05.035

⇑ Corresponding author at: State Key LaboratorySchool of Chemistry and Chemical Engineering, NaMicrostructures, Nanjing University, Nanjing 210083593893; fax: +86 25 83314502.

E-mail address: zuojl@nju.edu.cn (J.-L. Zuo).

a b s t r a c t

A new type of multidentate ligand with both acetylacetonate and bis(2-pyridyl) units on the 1,3-dithiolemoiety, 3-[2-(dipyridin-2-yl-methylene)-5-methylsulfanyl-[1,3]dithiol-4-ylsulfanyl]-pentane-2, 4-dione(L), has been prepared. Through reactions of the ligand with Re(CO)5X (X = Cl, Br), new rhenium(I) tricar-bonyl complexes ClRe(CO)3(L) (2) and BrRe(CO)3(L) (3), have been obtained. With the use of 2 or 3 as theprecursors, the further reactions with (TpPh2)Co(OAc)(HpzPh2) (TpPh2 = hydrotris(3,5-diphenylpyrazol-1-yl)borate); HpzPh2 = 3,5-diphenyl-pyrazole) or M(OAc)2 (M = Mn, Zn), afford four new heteronuclearcomplexes: ClRe(CO)3(L)Co(TpPh2) (4), BrRe(CO)3(L)Co(TpPh2) (5), [ClRe(CO)3(L)]2Mn(CH3OH)2 (6) and[ClRe(CO)3(L)]2Zn(CH3OH)2 (7), respectively. Crystal structures of complexes 2 and 4–7 have beendetermined by X-ray diffraction. Their absorption spectra, photoluminescence and magnetic propertieshave been studied.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

The coordination chemistry of electro-active molecules func-tionalized by various mono or polydentate ligands has developedsteadily during the past two decades [1–5]. The design and con-struction of new molecule-based materials combining two or moreproperties such as conductive, magnetic, photophysical or photo-chemical properties is currently a challenging target for syntheticchemists [6–10].

Rhenium(I) complexes of the ClRe(CO)3L1 (L1 = 1,10-phenan-throline and related diimine ligands) type have been extensivelystudied as luminescent materials since originally reported byWrighton and Morse in 1974 [11]. With a d6 configuration, somerhenium complexes show long-lived and intense emission fromthe metal-to-ligand charge-transfer (MLCT) transition involvingpolypyridyl-based ligands [12–14]. Since the p⁄ orbital energy le-vel are related to useful photochemical and photophysical behav-iors, it is possible to select new functional groups with differentelectron-donating or -accepting properties to adjust the p⁄ orbitalenergy and optimize their properties [15–18]. As typical examples,

ll rights reserved.

of Coordination Chemistry,njing National Laboratory of93, PR China. Tel.: +86 25

rhenium diimine complexes are useful as excellent organic light-emitting devices (OLEDs) [19], emitters [20,21], photo-catalysts[22,23] and building blocks for supramolecules [24,25] and so on.

On the other hand, metal complexes with 1,2-dithiolene or 1,3-dithiole units have attracted interest for their conducting ormagnetic properties [26]. They usually have a delocalized electronsystem. Interestingly, the delocalization can be further extendedby choice of appropriate substituted groups and make them usefulbuilding blocks for the construction of extended molecular archi-tectures [27–30].

Acetylacetonate and pyridine are typical organic ligands formetal complexes. In this paper, for the first time, we incorporateboth acetylacetonate and bis(2-pyridyl) units on the same 1,3-dithiole moiety, to give a new type of multidentate ligand, 3-[2-(dipyridin-2-yl-methylene)-5-methylsulfanyl-[1,3]dithiol-4-ylsulfanyl]-pentane-2,4-dione (L). Through reactions of the li-gand with Re(CO)5X (X = Cl, Br), rhenium(I) tricarbonyl com-plexes XRe(CO)3(L) (X = Cl, 2; Br, 3), have been obtained. Thefurther reactions of 2 or 3 with (TpPh2)Co(OAc)(HpzPh2)(TpPh2 = hydrotris(3,5-diphenylpyrazol-1-yl)borate); HpzPh2 = 3,5-diphenyl-pyrazole) or M(OAc)2 (M = Mn, Zn), afford fourheteronuclear complexes: ClRe(CO)3(L)Co(TpPh2) (4), BrRe(CO)3(L)Co(TpPh2) (5), [ClRe(CO)3(L)]2Mn(CH3OH)2 (6) and [ClRe(CO)3(L)]2Zn(CH3OH)2 (7), respectively. The preparations, struc-tural analyses, spectroscopic and magnetic properties of thesecompounds are described.

J. Xiong et al. / Inorganica Chimica Acta 376 (2011) 36–43 37

2. Experimental

2.1. Materials and physical measurements

The IR spectra were taken on a Vector22 Bruker spectrophotom-eter (400–4000 cm�1) with KBr pellets. 1H NMR spectra were mea-sured on a Bruker AM 500 spectrometer. Mass spectra wererecorded on a Bruker Autoflex IITM instrument for MALDI-TOF-MS or on a Varian MAT 311A instrument for ESI-MS. ElementalAnalyses for C, H and N were performed on a Perkin–Elmer 240Canalyzer. Solutions used for spectroscopic measurements wereprepared by fresh CH2Cl2. Absorption spectra were measured ona Shimadzu UV-3600 spectrophotometer. Fluorescence spectrawere measured with a Hitachi F4600 luminescence spectropho-tometer. Photoluminescence lifetimes were measured with anEdinburgh Instruments FLS920P fluorescence spectrometer in aer-obic condition, and were also measured under the protection ofnitrogen after degassing solution by at least four freeze-pump-thaw cycles. Luminescence quantum efficiencies were calculatedby comparison of the fluorescence intensities (integrated areas)of a standard sample (air-equilibrated aqueous [Ru(bpy)3]Cl2 solu-tion, Ustd = 0.028) and the unknown sample according to Eq. (1)[31].

Uunk ¼ UstdIunk

Istd

� �Astd

Aunk

� �gunk

gstd

� �2

ð1Þ

Where Uunk is the luminescence quantum yield of the sample,Ustd is the luminescence quantum yield of air-equilibrated aque-ous [Ru(bpy)3]Cl2 solution, Iunk and Istd are the integrated fluores-cence intensities of the unknown sample and [Ru(bpy)3]Cl2

solution, respectively, and Aunk and Astd are the absorbance of theunknown sample and aqueous [Ru(bpy)3]Cl2 solution at excitationwavelengths. The gunk and gstd terms represent the refractive indi-ces of the corresponding solvents (pure solvents are assumed).

The crystal structure data for compounds 2 and 4–7 were col-lected on a Bruker Smart Apex CCD diffractometer equipped withgraphite-monochromated Mo Ka (k = 0.71073 Å) radiation usinga x-2h scan mode at 293 K. The highly redundant data sets werereduced using SAINT [32] and corrected for Lorentz and polarization

Table 1Crystallographic Data for Compounds 2 and 4–7.

2�CH3OH�H2O 4�4H2O 5�4H

Empirical formula C24H24ClN2O7ReS4 C136H110B2Cl2Co2N16O14Re2S8 C136

Mr 802.39 3031.66 312Crystal system triclinic triclinic triclSpace group P�1 P�1 P�1a (Å) 8.8924(11) 17.892(2) 17.8b (Å) 12.0301(15) 19.734(3) 19.7c (Å) 16.879(2) 25.347(3) 25.2a (�) 95.914(2) 68.827(3) 69.6b (�) 93.202(2) 74.119(4) 74.3c (�) 107.401(2) 63.542(3) 63.6V (Å3) 1706.7(4) 7403.1(16) 742Z 2 2 2qc (g cm�3) 1.561 1.360 1.39F(0 0 0) 788.0 3052 312T / K 293(2) 293(2) 293l(Mo Ka) (mm�1) 3.920 2.060 2.55Index ranges �10 6 h 6 10

�13 6 k 6 14�20 6 l 6 18

�17 6 h 6 22�16 6 k 6 24�29 6 l 6 31

�19�24�31

Goodness-of-fit (GOF) on(F2)

1.100 1.035 1.07

R1a, wR2

b (I > 2r(I)) 0.0559, 0.1468 0.0533, 0.1266 0.05R1

a, wR2b (all data) 0.0616, 0.1502 0.0691, 0.1327 0.07

a R1 =P

||C| � |Fc||/P

|Fo|.b wR2 = [

Pw(F2

o � F2c )2/

Pw(F2

o)]1/2.

effects. Absorption corrections were applied using SADABS [33] sup-plied by Bruker. The structure was solved by direct methods andrefined by full-matrix least-squares methods on F2 using SHELXTL-97 [34]. Hydrogen atoms were placed in calculated positions andrefined as riding atoms with a uniform value of Uiso. Final crystal-lographic data and values of R1 and wR2 are listed in Table 1, whileselected bond lengths and angles are listed in Tables 2–6.

The precursors 4-methylthio-5-(2-cyanoethylthio)-2-bis(2-pyr-idyl)methylene-1,3-dithiole (1) [28] and (TpPh2)Co(OAc)(HpzPh2)[35] were synthesized according to literature methods, respec-tively. All solvents and chemicals were purchased from commer-cial sources and used as received.

2.1.1. 3-[2-(Di-pyridin-2-yl-methylene)-5-methylsulfanyl-[1,3]dithiol-4-ylsulfanyl]-pentane-2,4-dione (L)

Under a nitrogen atmosphere, to a solution of 1 (1.203 g,3 mmol) in 25 mL of THF, a solution of CsOH�H2O (537 mg,3.2 mmol) in 6 mL of CH3OH was added dropwise at room temper-ature. The above mixture was allowed to stir for 30 min and3-chloro-2,4-pentanedione (0.54 mL, 3.5 mmol) was added. Thereaction mixture was stirred overnight. Then the solvent wasevaporated, and the orange residue was extracted with CH2Cl2

and washed with water. The organic extract was purified bycolumn chromatography (CH2Cl2) on silica gel. After evaporationof solvent, the light yellow oil was collected (yield: 1.11 g, 83%).IR (KBr, cm�1): 3415, 1580, 1491, 1453, 1384, 1148, 786, 771. 1HNMR (500 MHz, CDCl3, ppm): d 2.42 (s, 3H), 2.46 (s, 6H), 7.08 (m,2H, BPyH5,50), 7.16 (m, 2H, BPyH3,30), 7.66 (m, 2H, BPyH4,40), 8.76(d, 1H, BPyH6,60), 17.18 (s, 1H). MS (MALDI-TOF): m/z 447.1 ([M]+)Anal. Calc. for C20H18N2O2S4: C, 53.78; H, 4.06; N, 6.27. Found: C,53.71; H, 4.01; N, 6.31%.

2.1.2. ClRe(CO)3(L) (2)Under a nitrogen atmosphere, the reaction mixture of Re(CO)5Cl

(36 mg, 0.1 mmol) and L (45 mg, 0.1 mmol) in 10 mL of toluenewas refluxed for 1 h. After evaporation of solvents under reducedpressure, a crude product was obtained. It was purified by chroma-thography on the alumina column using CH2Cl2 as eluent to affordpure product. Yellow crystals were obtained by evaporation of the

2O 6�4CH2Cl2 7�4CH2Cl2

H110B2Br2Co2N16O14Re2S8 C52H50Cl10N4O12Re2S8Mn C52H50Cl10N4O12Re2S8Zn0.58 1961.38 1971.83inic monoclinic monoclinic

P21/c P21/c90(4) 12.5460(16) 12.8888(12)70(4) 18.360(2) 18.8906(17)22(6) 17.3034(16) 17.2725(12)89(4) 90.00 90.0042(5) 120.765(6) 121.651(5)72(4) 90.00 90.007(3) 3424.8(7) 3579.9(6)

2 25 1.906 1.8294 1922.0 1928.0(2) 293(2) 293(2)5 4.397 4.3676 h 6 226 k 6 236 l 6 25

�14 6 h 6 16�21 6 k 6 23�22 6 l 6 15

�10 6 h 6 15�23 6 k 6 23�20 6 l 6 21

3 1.052 1.061

67, 0.1106 0.0610, 0.1517 0.0580, 0.157994, 0.1142 0.1085, 0.1718 0.0798, 0.1683

Table 2Selected bond distances (Å) and angles (�) for 2.

Re(1)–N(1) 2.199(7) Re(1)–N(2) 2.183(7)Re(1)–C(1) 1.903(10) Re(1)–C(2) 1.904(10)Re(1)–C(3) 1.896(10) Re(1)–Cl(1) 2.467(3)C (22)–O(5) 1.273(15) C(21)–O(4) 1.260(14)C(14)–C(15) 1.343(11) C(16)–C(18) 1.318(12)N(2)–Re(1)–N(1) 83.2(2) C(3)–Re(1)–N(1) 175.7(3)C(2)–Re(1)–N(2) 175.7(4) C(1)–Re(1)–Cl(1) 177.0(3)

Table 3Selected bond distances (Å) and angles (�) for 4.

Re(2)–N(3) 2.195(4) Re(2)–N(4) 2.119(4)Re(2)–C(4) 1.840(5) Re(2)–C(5) 1.882(4)Re(2)–C(6) 1.898(4) Re(2)–Cl(2) 2.4658(10)Co(1)–O(9) 1.991(3) Co(1)–O(10) 1.963(3)Co(1)–N(11) 2.098(4) Co(1)–N(13) 2.137(4)Co(1)–N(15) 2.078(3) B(2)–N(12) 1.543(5)B(2)–N(14) 1.534(5) B(2)–N(16) 1.511(5)N(11)–N(12) 1.398(5)N(3)–Re(2)–N(4) 81.39(14) C(6)–Re(2)–N(4) 93.86(14)C(5)–Re(2)–N(3) 179.33(15) C(6)–Re(2)–Cl(2) 176.75(15)O(9)–Co(1)–O(10) 86.53(11) O(9)–Co(1)–N(11) 90.39(13)N(11)–Co(1)–N(13) 87.92(14) N(12)–B(1)–N(14) 106.8(3)

Table 4Selected bond distances (Å) and angles (�) for 5.

Re(1)–N(1) 2.155(4) Re(1)–N(2) 2.157(4)Re(1)–C(1) 1.868(5) Re(1)–C(2) 1.788(5)Re(1)–C(3) 1.863(5) Re(1)–Br(1) 2.6037(7)Co(1)–O(4) 1.950(3) Co(1)–O(5) 1.990(4)Co(1)–N(3) 2.159(5) Co(1)–N(5) 2.062(4)Co(1)–N(7) 2.096(4) B(1)–N(4) 1.580(6)B(1)–N(6) 1.521(6) B(1)–N(8) 1.510(6)N(3)–N(4) 1.365(6)N(1)–Re(1)–N(2) 82.73(16) C(1)–Re(1)–N(2) 93.73(15)C(3)–Re(1)–N(1) 176.3(2) C(1)–Re(1)–Br(1) 176.10(17)O(4)–Co(1)–O(5) 85.97(15) O(4)–Co(1)–N(5) 107.26(17)N(3)–Co(1)–N(5) 88.52(16) N(4)–B(1)–N(6) 107.6(4)

Table 5Selected bond distances (Å) and angles (�) for 6.

Re(1)–N(1) 2.216(7) Re(1)–N(2) 2.183(8)Re(1)–C(1) 1.903(12) Re(1)–C(2) 1.882(11)Re(1)–C(3) 1.917(10) Re(1)–Cl(1) 2.473(3)Mn(1)–O(4) 2.136(7) Mn(1)–O(5) 2.076(6)Mn(1)–O(6) 2.229(8)N(1)–Re(1)–N(2) 83.5(3) C(1)–Re(1)–N(2) 94.2(4)C(3)–Re(1)–N(1) 179.6(4) C(1)–Re(1)–Cl(1) 178.2(3)O(4)–Mn(1)–O(5) 82.9(3) O(4)–Mn(1)–O(6) 89.4(3)O(6)–Mn(1)–O(6)#1 180.0(2) O(4)–Mn(1)–O(4)#1 180.0(2)

Symmetry codes: #1 �x + 2, �y + 2, �z + 1.

Table 6Selected bond distances (Å) and angles (�) for 7.

Re(1)–N(1) 2.199(7) Re(1)–N(2) 2.197(7)Re(1)–C(1) 1.898(9) Re(1)–C(2) 1.902(10)Re(1)–C(3) 1.896(10) Re(1)–Cl(1) 2.484(3)Zn(1)–O(4) 2.007(6) Zn(1)–O(5) 1.999(5)Zn(1)–O(6) 2.243(7)N(1)–Re(1)–N(2) 82.73(16) C(1)–Re(1)–N(2) 94.7(3)C(3)–Re(1)–N(2) 173.9(3) C(1)–Re(1)–Cl(1) 178.7(3)O(4)–Zn(1)–O(5) 87.4(2) O(4)–Zn(1)–O(6) 89.2(3)O(6)–Zn(1)–O(6) #1 180.0(1) O(4)–Zn(1)–O(4)#1 180.00(19)

Symmetry codes: #1 �x + 2, �y + 2, �z + 1.

38 J. Xiong et al. / Inorganica Chimica Acta 376 (2011) 36–43

solution of CH2Cl2/CH3OH. Yield: 54 mg (72%). IR(KBr, cm�1): 2016,1893 (mC„O). 1H NMR (500 MHz, CDCl3, ppm): d 2.40 (s, 3H), 2.42 (s,6H), 7.37 (m, 2H, BPyH5,50), 7.63 (d, 1H, BPyH3), 7.71 (d, 1H, BPyH30),7.88 (m, 2H, BPyH4,40), 9.13 (d, 2H, BPyH6,60), 17.18 (s, 1H). MS(MALDI-TOF): m/z 717.1 ([M-Cl]+) Anal. Calc. for C23H18ClN2O5ReS4:C, 36.72; H, 2.41; N, 3.72. Found: C, 36.43; H, 2.52; N, 3.79%.

2.1.3. BrRe(CO)3(L) (3)Compound 3 was obtained under the similar method as de-

scribed for 2, by using Re(CO)5Br instead of Re(CO)5Cl. Yield:60 mg (75%). IR(KBr, cm�1): 2017, 1896 (mC„O). 1H NMR(500 MHz, CDCl3, ppm): d 2.40 (s, 3H), 2.42 (s, 6H), 7.35 (m, 2H,BPyH5,50), 7.63 (d, 1H, BPyH3), 7.70 (d, 1H, BPyH30), 7.88 (m, 2H,BPyH4,40), 9.26 (d, 2H, BPyH6,60), 17.18 (s, 1H). MS (MALDI-TOF):m/z 717.0 ([M-Br]+) Anal. Calc. for C23H18BrN2O5ReS4: C, 34.67; H,2.28; N, 3.52. Found: C, 34.42; H, 2.61; N, 3.65%.

2.1.4. ClRe(CO)3(L)Co(TpPh2) (4)A CH2Cl2 (5 mL) solution of (TpPh2)Co(OAc)(HpzPh2) (10.1 mg,

0.01 mmol) was added to a CH2Cl2 (5 mL) solution of 2 (7.5 mg,0.01 mmol). The resulted deep brown solution was layered withCH3OH and brown crystals were isolated after a few days. Yield:8.8 mg (60%). IR (KBr, cm�1): 2018, 1922, 1891 (mC„O). MS (ESI):m/z 1501 ([M+H2O]+) Anal. Calc. for C68H51BClCoN8O5ReS4

(4�2H2O): C, 55.19; H, 3.47; N, 7.57. Found: C, 55.11; H, 3.64; N,7.59%.

2.1.5. BrRe(CO)3(L)Co(TpPh2) (5)Complex 5 was prepared by the similar method as described for

4 by using Re(CO)5Br instead of Re(CO)5Cl. Yield: 7.7 mg (52%). IR(KBr, cm�1): 2022, 1908, 1896 (mC„O). MS (ESI): m/z 1484 ([M]+)Anal. Calc. for C68H51BBrCoN8O5ReS4 (5�2H2O): C, 53.58; H, 3.37;N, 7.35. Found: C, 53.51; H, 3.54; N, 7.49%.

2.1.6. [ClRe(CO)3(L)]2Mn(CH3OH)2 (6) and [ClRe(CO)3(L)]2Zn(CH3OH)2

(7)To a solution of M(OAc)2�xH2O (M = Mn or Zn, 0.02 mmol) in

6 mL of CH3OH was slowly added a solution of 2 (32 mg,0.04 mmol) in 8 mL of CH2Cl2. Single crystals suitable for X-raystructure determination were obtained by slow evaporation ofthe solution after several days. Yield: 31 mg (80%). Anal. Calc. for6, C48H42Cl2MnN4O12Re2S8: C, 35.55; H, 2.61; N, 3.45. Found: C,35.37; H, 3.01; N, 3.61%. IR (KBr, cm�1): 2016, 1887 (mC„O). Yield:28 mg (72%). Anal. Calc. for 7, C48H42Cl2ZnN4O12Re2S8: C, 35.32; H,2.59; N, 3.43. Found C, 35.21; H, 2.86; N, 3.54%. IR(KBr, cm�1):2016, 1885 (mC„O).

3. Results and discussions

3.1. Synthesis and characterization

As shown in Scheme 1, reactions of Re(CO)5X (X = Cl, Br) withthe ligand L and subsequent chromatographic separation of thecrude products on alumina give the precursors of rhenium(I) tri-carbonyl units (2 and 3) with high yields. In ClRe(CO)3(L) (2) andBrRe(CO)3(L) (3), the bis(2-pyridyl) group of L coordinates to therhenium(I) ion as a bidentate ligand, while the acetylacetonategroup is free and can be used as the useful coordinating site to bindother metal ions. For examples, further reactions of 2 or 3 with(TpPh2)Co(OAc)(HpzPh2) or M(OAc)2 (M = Mn and Zn), four hetero-nuclear complexes 4–7 have been prepared. As we know, in theprecursor [Co(TpPh2)(O2CMe)(HpzPh2)], the acetate (MeCO2

�) andHpzPh2 are monodentated [35] and relatively weaker coordinationligands to the cobalt center, therefore, they are easily substitutedby the bidentate acetylacetonate ligand to form new polynuclear

Ltoluene

N

N

S

S

S

SCH3

O

OReOC

OC CO

X

2 X=Cl 3 X=Br

2,3N

N

S

S

S

SCH3

O

OReOC

OC CO

X

TpPh2Co(OAc)(HpzPh2)NN

Ph Ph

N N

PhPh

N NPh

Ph

B HCo

4 X=Cl 5 X=Br

2M

CH3OH

CH3OH

CH3OH

6 M=Mn7 M=Zn

N

N

S

S

S

SCH3

O

OReOC

OC CO

Cl

N

N

S

S

S

H3CS

O

O ReCOCOCO

Cl

N

N

S

S

S

SCH3

O

ON

N

S

S

SCH2CH2CN

SCH3

i) CsOH·H2O

ii) 3-chloro-2,4-pentanedione

L1

Re(CO)3X

M(OAc)2

Scheme 1. Synthetic routes for 2–7.

Fig. 1. ORTEP view of 2 with the atom-numbering scheme. Thermal ellipsoids aredrawn at the 50% probability level. Hydrogen atoms and solvated molecules areomitted for clarity.

J. Xiong et al. / Inorganica Chimica Acta 376 (2011) 36–43 39

complexes. All new compounds are soluble in most organic sol-vents, and air stable in both solution and solid state.

Characterization of these complexes has been accomplished byIR, 1H NMR, UV–Vis and mass spectrometry. In the IR spectra for 2–7, three typical bands for rhenium(I) tricarbonyl complexes are ob-served and they are assigned to the facial arrangement of the threecarbonyl groups in the coordination sphere. In the 1H NMR spectrafor the ligand and complexes 2 and 3, the presence of the singlepeak (ca. 17.18 Hz) is attributed to the proton of mono-substitutedacetylacetone. L and 2–3 display four resonances for protons on thetwo pyridine rings at d 8.76/9.13/9.26, 7.66/7.88/7.88, 7.16/7.71/7.70 and 7.08/7.37/7.35 ppm, respectively. Compared with L, theproton signals on the pyridine rings in complexes 2 and 3 areshifted to low-field since the formation of coordination bonds thatinfluence the electronic distribution, which are in good agreementwith their structures [28,29].

3.2. Crystal structure description

Fig. 1 shows the ORTEP view with atomic numbering for com-plex 2. In the molecule, 1,3-dithiole core is nearly planar; two pyr-idine rings and the acetylacetone unit are situated on differentsides to form boat-configuration. Two pyridine planes display a‘‘butterfly-like’’ substructure with the dihedral angle of 53.8�[36]. The acetylacetone part (O4, O5, C19, C20, C21, C22, andC23) is planar. The rhenium atom is in slightly distorted octahedral

coordination geometry with three carbonyl ligands arranged in afacial fashion. The bond angles of C(2)–Re(1)–N(2), C(3)–Re(1)–N(1) and C(1)–Re(1)–Cl(1) are in the range of 175.6–177.0�,

Fig. 2. ORTEP view of 4 with the atom-numbering scheme. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms and solvated molecules are omitted forclarity.

Fig. 3. ORTEP view of 6 with the atom-numbering scheme. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms and solvated molecules are omitted forclarity.

40 J. Xiong et al. / Inorganica Chimica Acta 376 (2011) 36–43

showing only minor deviations from the ideal octahedral limit. Thebond lengths of Re–C (carbonyl) and Re–Cl are within the normalvalues for similar tricarbonyl rhenium(I) complexes [37]. The bondlengths of Re–N are 2.199(7) and 2.183(7) Å, respectively.

Compounds 4 and 5 are both dinuclear complexes and theyshow very similar structure (Fig. 2 and Fig. S1), with the exceptionthat the halide atom for complex 4 is Cl while for 5 it is Br. For com-plex 4, the rhenium atom is taking the same coordination environ-ment as 2. Compared with 2, the bond angle of N3–Re–N4(81.39(14)�) and the bond length of Re2–N4 (2.119(4) Å) are smal-ler due to the repulsive force from the TpPh2. The CoII ion is five-coordinated by three N atoms from the TpPh2 ligand and two Oatoms from the acetylacetone ligand, forming a slightly distortedsquare pyramidal coordination geometry with the Co–O bondlengths of 1.991 and 1.963 Å, respectively. The Co–Npz bondlengths are not equivalent but are within the similar range of othercobalt(II)–TpR complexes [38,39].

Trinuclear heterometallic compounds 6 and 7 are isostructuralwith the exception that the metal ion for complex 6 is Mn(II) whileit is Zn(II) for 7. In 6, the whole molecule displays a trans-configu-ration and the crystallographically independent Mn atom (Fig. 3)has a centro-symmetric environments surrounding by two CH3OHligands perpendicular to the plane of two acetylacetone units. TheMn1–O4 and Mn1–O5 distances are 2.136(4) and 2.076(5) Å,

respectively, which are similar to the values in previous reportedacetylacetone complexes [40]. 1D chain structure is formedthrough intermolecular hydrogen bonds (Fig. 4). No obvious S���Scontact is found.

3.3. Spectroscopic and magnetic properties

UV–Vis absorption spectra for compounds L, 2–7 and(TpPh2)Co(OAc)(HpzPh2) in CH2Cl2 solution are shown in Fig. 5,and the data are listed in Table 7. For the ligand L, the absorptionpeaks at 255 and 389 nm come from the spin-allowed intra-ligand(p–p⁄) transitions. Complexes 2–7 display intense absorptionbands at 240–271 nm with extinction coefficients on the order of104 M�1 cm�1, which can also be assigned to p–p⁄ transitions.Especially, the intense absorption for complexes 4 and 5 at around240 nm may result from the steric bulk TpPh2 ligand. On the basisof spectroscopic studies on similar rhenium tricarbonyl complexes[41,42], the absorptions around 410–450 nm for 2–7 are tenta-tively assigned to the dp(Re)–p⁄(L) transitions. Compared to thelow-energy MLCT transition in 6 and 7, the relative absorptionbands are red-shifted in 4 and 5. The electron-withdrawing induc-tive effect of the CoTpPh2 core may reduce the transition energy ofMLCT and thus leads to the changes in the related absorptions.

Fig. 4. The hydrogen bonds (the dotted line) between the molecules in 7 to form 1D chain (hydrogen atoms with no hydrogen bonds and solvated molecules are omitted forclarity).

300 400 500 600 70005

10152025

020406080

100

ε/ 1

03 M-1cm

-1

Wavelength/nm

L2367

45(TpPh2)Co(OAc)(Hpz Ph2)

Fig. 5. UV–Vis absorption spectra of compounds L, 2–7 and (TpPh2)Co(OAc)(HpzPh2)in CH2Cl2 solution.

J. Xiong et al. / Inorganica Chimica Acta 376 (2011) 36–43 41

Upon photoexcitation, compounds 2–7 exhibit luminescence inCH2Cl2 solution (Fig. 6). The excitation and emission data are listedin Table 7. The emission at 458 nm of the ligand can be attributedto p⁄–p relaxation. For 2–7, the emission spectra centered at ca.530–550 nm assigned to dp(Re) ? p⁄ (polypyridine) MLCT transi-tions. Compared to L, the emission maxima are observed at531 nm for 2 and the red shift results from the formation of rhe-nium(I) complex. With the further extension of the delocalizedstructure by the coordination interaction between the functionalgroup acetylacetone and TpPh2Co, complexes 4 and 5 show loweremission energy (maxima emission wavelength at 548 nm) than

Table 7Electronic absorption, luminescence quantum efficiency and lifetime data for compounds

Compounds Absorption (kabs/nm (e/M�1 cm�1)) Luminescence

Exciting wavelengt

L 255 (15650), 389 (14800) 3162 268 (24350), 427 (11200) 377, 4653 269 (25130), 427 (11800) 378, 4674 240 (93440), 442 (10480) 388, 4845 240 (97730), 443 (11170) 389, 4856 271 (25800), 427 (12110) 390, 4707 268 (19900), 426 (9500) 390, 470

2, due to the effect of the electron-accepting TpPh2Co units. Themaxima emission wavelength for complexes 6 and 7 are 538 and535 nm, respectively, showing a little red shift after coordination.

As indicated in Fig. 7 and Fig. S3, the photoluminescence life-time decay of complexes 2, 4, 6 and 7 were measured in both aer-obic and anaerobic conditions, and the results were almost thesame. Excited-state lifetimes lied on microsecond timescale. Theexcitation spectra of 2, 4, 6 and 7 are shown in Fig. S4. Excitationat either the p–p⁄ absorption band (�260 nm) or the MLCT absorp-tion band (�430 nm), leads to the same MLCT emission (�540 nm)for 2–7. This observation indicates that the potential surface cross-ing from the higher p–p⁄ state to the lower MLCT state is quite effi-cient, and the major contribution of the observed emission is fromthe MLCT state [43,44]. On the basis of the energy gap law, if thereis no potential surface crossing from the higher p–p⁄ state to thelower MLCT state, we may expect a shorter decay lifetime fromthe p–p⁄ state than the lower MLCT state [45,46]. Photolumines-cence lifetimes for 2 (1.76 ls), 4 (1.62 ls), 6 (1.78 ls) and 7(1.70 ls), are assigned to the emission from the 3MLCT state.

The luminescence quantum efficiency data of these complexeswere calculated with Eq. (1) (Table 7). For complex 2, the lumines-cence quantum efficiency is 9.2 � 10�3. However, the efficiency de-creases after the involvement of TpPh2Co for complex 4(1.8 � 10�3). Similarly tendencies were observed for heteronuclearcomplexes 6 (7.2 � 10�3) and 7 (8.1 � 10�3). The phenomenonindicates the much higher emissive energy is most likely operatingfrom the Re-based 3MLCT chromophore and is partially quenchedby the M-based (M = Co, Mn, Zn) 3MLCT state in the Re–M hetero-nuclear species [47].

L and 2–7 at 298 K.

U Lifetimes (ls)

h Maxima emission wavelength

458530 0.0092 1.76527549 0.0018 1.62548538 0.0072 1.78535 0.0081 1.70

Fig. 6. Normalized emission spectra of L and 2–7 in CH2Cl2 solution at 298 K(kex = 316, 465, 467, 484, 485, 470, 470 nm for L and 2–7, respectively).

0 20 40 60 80 100

0

1000

2000

3000

4000

5000

6000

Time(μs)

Rel

ativ

e In

tens

ity(a

.u.)

2 in CH2Cl2 solutionτ = 1.76 μs χ2 = 0.9769

Fig. 7. Photoluminescence lifetime decay measurement of complex 2 in CH2Cl2 atroom temperature (aerobic condition).

1.8

2.0

2.2

2.4

2.6

2.8

3.0

0 50 100 150 200 250 300

0.0

0.2

0.4

0.6

0.8

1.0

1.2

χM T / cm

3 mol -1 K

T / K

χ M /

cm3 m

ol-1

Fig. 8. Temperature dependence of the vM (circle) and vMT (square) products for 4at 2 kOe. Solid lines represent the best fit of the data.

42 J. Xiong et al. / Inorganica Chimica Acta 376 (2011) 36–43

Variable-temperature magnetic susceptibility measurementwas performed on polycrystalline sample of complex 4 in1.8�300 K. As shown in Fig. 8, the global feature of the vMT versusT curve is paramagnetic. At 300 K, the vMT value is2.88 cm3 K mol�1, which are significantly higher than the spin-onlyvalue of 1.875 cm3 K mol�1 (g = 2.0) expected for one isolated high-

spin CoII (S = 3/2) ions. As the temperature decreases, the vMT va-lue slowly decreases and reaches 2.74 cm3 K mol�1 at 100 K andthen rapidly drops to 1.93 cm3 K mol�1 at 1.8 K. This drasticallydecreasing of vMT mainly ascribes to the zero-field flitting (ZFS)of the octahedral high-spin CoII ions [48]. For powder magneticsusceptibility of S = 3/2 state, the following expressions are appli-cable [49]:

vk ¼Ng2b2

kBT1þ 9e�2x

4ð1þ e�2xÞ ð2Þ

v? ¼Ng2b2

kBT4þ 3

x ð1� e�2xÞ4ð1þ e�2xÞ ð3Þ

vM ¼ vCo ¼13ðvk þ 2v?Þ ð4Þ

where x = D=kBT and D is the magnitude of the ZFS. The vM versus Tplot of complex 4 is fitted with the above equations, and the bestfitting result is: g = 2.56, D = 57.9 cm�1 (R = 1.3 � 10�4). Theseparameters are comparable to the other CoII contained complexes[50].

4. Conclusions

In conclusion, a new versatile bridging ligand containing bothacetylacetonate and bis(2-pyridyl) units on the 1,3-dithiole moiety,3-[2-(di-pyridin-2-yl-methylene)-5-methylsulfanyl-[1,3]dithiol-4-ylsulfanyl]-pentane-2,4-dione (L), has been successfully prepared.Based on the ligand, two mononuclear rhenium(I) tricarbonylcomplexes and four heteronuclear complexes have been preparedand structurally characterized. Absorption spectra, photolumines-cence and magnetic properties have been studied. The resultsdemonstrate that the multidentate ligand could be useful onfurther syntheses of new multifunctional materials.

Acknowledgments

This work was supported by the Major State Basic ResearchDevelopment Program (Grant Nos. 2007CB925103 and2011CB808704), the National Science Fund for DistinguishedYoung Scholars of China (Grant No. 20725104), and AcademicianWork Station of Changzhou Trina Solar Energy Co., Ltd.

Appendix A. Supplementary material

Additional structural data for the complexes described in thiswork. Supplementary data associated with this article can befound, in the online version, at doi:10.1016/j.ica.2011.05.035.

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