Inorganic Chemistry Communications 13 (2010) 306–309

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Inorganic Chemistry Communications

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A lamella 2D silver(I) coordination polymer constructed from in situ generated2-mercaptobenzoic acid

Di Sun, Geng-Geng Luo, Na Zhang, Qin-Juan Xu, Yi-Chang Jin, Zhan-Hua Wei, Cheng-Feng Yang,Li-Rong Lin, Rong-Bin Huang *, Lan-Sun ZhengState Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 7 September 2009Accepted 9 December 2009Available online 16 December 2009

Keywords:Silver2,20-Dithiodibenzoic acid2-Mercaptobenzoic acidMetal–organic polymerPhotoluminescenceSemiconductivity

1387-7003/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.inoche.2009.12.011

* Corresponding author. Fax: +86 592 2183047.E-mail address: rbhuang@xmu.edu.cn (R.-B. Huang

The reaction of Ag2O and 2,20-dithiodibenzoic acid (dtba) under ultrasonic condition gave rise to a novelmetal–organic coordination polymer [Ag4(2-mba)2�(H2O)2]n (1) (2-H2mba = 2-mercaptobenzoic acid)involving in situ generated 2-mba ligand. Complex 1 shows a lamella 2D structure with a 63-hcb netwhich is comprised of fused Ag6 hexagonal rings. Moreover, 1 exhibits photoluminescence maximizedat 468 nm upon 330 nm excitation at room temperature, which may be assigned to a ligand-to-metalcharge transfer (LMCT) transition. Semiconducting behavior was also measured at room temperaturewith r value of 3.24 � 10�5 S cm�1.

� 2009 Elsevier B.V. All rights reserved.

Recently, coordination polymers have attracted great attentiondue to their potential applications in the areas of electronics, lumi-nescence, catalysis and molecular recognition [1] and their intrigu-ing structure topologies, such as honeycomb, brick wall, ladder,diamondoid, polycatenanes and polyrotaxanes [2]. In general, thechemistry of the Ag(I) ion is extremely striking because it exhibitsdifferent coordination numbers ranging from 2 to 9 and showsclosed-shell Ag� � �Ag interaction [3]. These features make it anappealing candidate for the production of interesting structuraltopologies [4], which are widely influenced by several factors suchas the counter-anions, the metal-to-ligand ratio and the nature ofthe ligands [5,6]. Although the exploitation of the structural diver-sity and potential applications of coordination polymer is dramat-ically increasing, coordination polymers with bi- ormultifunctional properties have rarely been reported until now [7].

Finally, the arylthiolate ligands are particularly attractive forthe development of new structural types because of their versatil-ity in coordination bonding fashions. In addition, they show a richredox chemistry based on both oxidative formation and reductivecleavage of the disulfide bonds, which has been explored as anattractive route to in situ synthesis of functional ligands and novelmaterials [8]. Based on the above considerations, we self-assem-bled Ag2O and 2,20-dithiodibenzoic acid under ultrasonic conditionand obtained a novel coordination polymer [Ag4(2-mba)2�(H2O)2]n

(1), which possesses a 2D sheet structure with a 63-hcb net con-

ll rights reserved.

).

taining fused Ag6 hexagonal rings. Herein, we describe the fasci-nating structure and properties of the complex 1.

Complex 1 was obtained as yellow crystals by the reaction ofAg2O, 2,20-dithiodibenzoic acid (dtba) and NaClO4 in H2O/CH3OH/NH3 media under ultrasonic treatment [9]. Ammonia here mayserve as (i) a base to deprotonate the carboxylic groups and en-hance the solubility of the silver carboxylates and (ii) a ligand toform [Ag(NH3)2]+, which may reduce the reaction rate and facilitatethe growth of single crystals. No NH3 molecules were found in theresulting products, which is consistent with the results of severalrecent reports [10a]. The compositions of 1 were further deducedfrom X-ray single crystal diffraction, elemental analysis, IR spec-trum. The solid IR spectrum of complex 1 shows (i) an intensebroad band around 3450 cm�1 attributed to the existence of watermolecules, (ii) disappearance of the S–H stretching band around2560 cm�1 due to the SH group in the ‘‘free” H2mba, suggestingthe formation of Ag–S bond in 1, and (iii) the absence of band inthe region of 1690–1730 cm�1, indicating complete deprotonationof the carboxyl groups [10b]. Phase purity of 1 is sustained by itspowder X-ray diffraction pattern, which is consistent with thatsimulated on the basis of the single-crystal X-ray diffraction data(see Fig. S1, in Supplemental material).

X-ray single-crystal diffraction analysis [11] reveals that 1 crys-tallizes in the monoclinic P21/c space group with an asymmetricunit containing four crystallographically unique Ag(I) ions, two2-mba ligands and two coordinated water molecules. The forma-tion of 1 implies the cleavage of S–S bond of dtba. To our bestknowledge, although S–S bond of dithiodipyridine can be easily

Fig. 1. Part of the molecular structure and atom labeling of 1, shows thecoordination environments of the silver centers. All hydrogen atoms are omittedfor clarity (symmetry code: (i) �x, 1 � y, 1 � z; (ii) �x, 1 � y, �z; (iii) 1 + x, y, z).

D. Sun et al. / Inorganic Chemistry Communications 13 (2010) 306–309 307

cleaved under solvothermal condition [12a], the cleavage of S–Sbond of dtba under the ultrasonic condition has not been observedyet. The detailed bond lengths and angles are listed in Table S1. Asshown in Fig. 1, Ag2 adopts a distorted S2O2 tetrahedral geometryin which bond angles around Ag2 opened up to 129.7(2)� from theideal tetrahedral angle while the remaining angles fall in the range

Fig. 2. (a) 2D structure in 1 (b) 2D 63-hcb net constructed by hexagonal subunits.

111.16(11)–118.1(2)�. The distortion of the tetrahedron can beindicated by the calculated value of the s4 factor [12b], which is0.93 in 1 (for perfect tetrahedral geometry, s4 = 1). Ag3 adopts aSO2 Y-shaped coordination geometry. Different from Ag3, Ag1and Ag4 adopt S2O Y-shaped coordination geometries. The Ag–Sand Ag–O bond distances range from 2.441(4) to 2.907(4) and2.160(11) to 2.706(10) Å, respectively. The angles around theAg(I) ions are in the range of 81.94(9)–155.1(4)�. These structureparameters are comparable to that of previously reported com-plexes [13].

It is worth noting that 2-mba ligands link Ag(I) ions to form a 2Dsheet in which 2-mba ligands show two rare l4–j4S and l6–j1O,j2O0, j3S coordination modes (Fig. 2a and Scheme S1). To our bestknowledge, simple monothiolate ligands acting as j2 or j3 bridgeare quite common in transition metal chemistry. However, thoseacting as j4 bridge and linking metal ions to form polymers are lessknown [14]. The two coordination modes shown by 2-mba in 1 arefirstly observed in all Ag(I) complexes with 2-mba. The Ag� � �Ag dis-tances range from 2.9734(17) to 3.3232(17) Å which are shorterthan twice the Van der Waals radii of Ag(I) ion (3.44 Å). It is a clearindication of ligand-supported Ag� � �Ag interactions which could befound in many other Ag(I) coordination polymers [15]. ConsideringAg(I) center as a three-connected node, it is reasonable to simplifythe 2D structure to a 63-hcb net which is constructed from fusedAg6 hexagonal rings (Fig. 2b) and similar to previously reportedhexagonal arrays of silver atoms [16]. These Ag6 hexagons can bedivided into two types: [(Ag1)2(Ag2)4] and [(Ag1)4(Ag2)2] hexa-gons. The same type of hexagons are arranged to form a homoge-neous row along the a axis through sharing edges, and the

Fig. 3. (a) Emission spectra of 2-H2mba and the complex 1 in solid-state at roomtemperature. (b) I–V curve of 1 at room temperature.

308 D. Sun et al. / Inorganic Chemistry Communications 13 (2010) 306–309

unhomogeneous rows alternate along the c axis. (Fig. 2b) The Ag6

hexagons are slightly distorted because of different Ag� � �Ag dis-tances (3.133, 3.487, 4.549 and 4.628 Å) and Ag� � �Ag� � �Ag angles(133.76, 119.94, 106.18, 98.56 and 127.61�). Ag3 and Ag4 ions donot participate in the formation of the Ag6 hexagons and only re-side in them. All the Ag(I) ions on a 63-hcb net are nearly coplanarand the interlayer distance is ca. 10.3 Å.

Silver(I) coordination polymers incorporating arylthiolate li-gands possess promising properties including conductive and pho-toluminescence properties because the orbital energies arecompatible for sulfur and there will be greater delocalization ofthe spin density toward the bridging atom [17]. The solid-stateUV–vis absorption spectrum of 1 shows a little absorption in thevisible range (Fig. S2). The photoluminescence properties of 1 aswell as free ligand were examined in the solid state at room tem-perature. As shown in Fig. 3a, upon excitation at 330 nm, a bluephotoluminescent emission at 468 nm was observed in 1. Com-pared with the emission spectrum of 2-H2mba, red shift of 85 nmin 1 was observed. The emission of complex 1 may be assignedto the ligand-to-metal charge transfer (LMCT) [18]. Consideringthe graphite-like interlayer structure of 1, the conductivity mea-surements were also performed in compacted pellets(0.18 � 0.16 � 0.03 cm) by conventional two-probe technique atroom temperature. According to the data point at 1 V (Fig. 3b),we calculated and assigned the complex 1 to a semiconductor atroom temperature (r = 3.24 � 10�5 S cm�1; calculated from equa-tion: r = l/RS, where l is the thickness of the sample, S is area ofcross section of sample and R is resistance) [19]. Although 1 pre-sents relatively strong Ag� � �Ag interactions and possibility ofcharge-transfer transitions from the sulfur-dominated filled va-lence bond to silver-dominated empty conduction bond whichcan offer effective electron-transfer pathway, it exhibits not toohigh conductivity which may be due to the lack of direct p� � �pand Ag� � �p interactions [20].

In conclusion, we have successfully constructed a novel 2D Ag(I)coordination polymer 1 with a 63-hcb net by employing in situgenerated 2-mba ligand under ultrasonic treatment in which twonew coordination modes of 2-mba were firstly observed. More-over, both photoluminescence and semiconducting behaviors of 1were also measured.

Acknowledgments

This work was financially supported by the National NaturalScience Foundation of China (No. 20721001), 973 Project (Grant2007CB815301) from MSTC and The National Science Fund of Chi-na for Fostering Talents in Basic Science (No. J0630429).

Appendix A. Supplementary material

CCDC 742812 contains the supplementary crystallographic datafor this paper. These data can be obtained free of charge from TheCambridge Crystallographic Data Centre via http://www.ccdc.ca-m.ac.uk/data_request/cif. Supplementary data associated with thisarticle can be found, in the online version, at doi:10.1016/j.inoche.2009.12.011.

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