Journal of Molecular Structure 975 (2010) 17–22

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Journal of Molecular Structure

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Syntheses, structures and luminescent properties of silver(I) coordination polymersbased on aminopyrimidyl derivatives and 1,2,3,4-butanetetracarboxylic acid

Di Sun, Na Zhang, Qin-Juan Xu, 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 March 2010Received in revised form 29 March 2010Accepted 29 March 2010Available online 2 April 2010

Keywords:Silver(I)2-Amino-4-methylpyrimidine2-Amino-4,6-dimethylpyrimidine1,2,3,4-Butanetetracarboxylic acidCrystal structurePhotoluminescence

0022-2860/$ - see front matter � 2010 Elsevier B.V. Adoi:10.1016/j.molstruc.2010.03.071

* Corresponding author.E-mail address: rbhuang@xmu.edu.cn (R.-B. Huang

Two mixed-ligand silver(I) coordination polymers (CPs) of the formula {[Ag4(mapym)2(but-ca)(H2O)4]�2H2O}n (1) and [Ag4(dmapym)6(butca)�2H2O]n (2) (mapym = 2-amino-4-methylpyrimidine,dmapym = 2-amino-4,6-dimethylpyrimidine, H4butca = 1,2,3,4-butanetetracarboxylic acid) were pre-pared by reactions of Ag2O and 2-aminopyrimidyl ligands with H4butca under the ammoniacal condition.Both complexes were characterized by element analysis, IR and X-ray single-crystal diffraction. In 1, apair of l2-mapym ligands bind four Ag(I) ions to form [Ag4(mapym)2] subunits which stack into one-dimensional (1D) chains via inter-subunit p� � �p interaction. The l6-j1:j2:j1:j2-butca ligands extendthe 1D chains into a two-dimensional (2D) sheet which can be simplified into a 44-sql net. When mapymwas replaced by dmapym, we obtained 2 as a 1D chain incorporating l6-j1:j2:j1:j2-butca and l1-dma-pym ligands. The dimensions of 1–2 decrease from 2D to 1D mainly due to the steric effect of methylgroups. Additionally, the hydrogen-bonding, p� � �p and C–H� � �p interactions also direct the self-assemblyof supramolecular architectures. The photoluminescence properties of the 1 and 2 were investigated inthe solid state at room temperature.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

The construction of inorganic–organic hybrid coordinationpolymers (CPs) has been of great interest in recent years, due tonot only their intriguing architectures and topologies but also theirimpressive capabilities in optoelectronic, catalytic, and magneticmaterials [1–13]. Assembly of CPs is highly influenced by the inbe-ing of the metal ions and the predesigned organic ligands [14–18]as well as other factors such as medium [19–21], pH value of thesolution [22–25], the temperature [26–27], the counter ions withdifferent bulk or coordination ability, the templates and metal/li-gand ratio [28–30]. Including the above factors, the non-covalentforces such as hydrogen-bonding, p� � �p stacking, metal� � �metalinteractions based on d10 metal cations, metal� � �p, C–H� � �p and an-ion� � �p interactions also intensively impact the supramoleculartopology and dimensionality [31–37]. Regarding the organic li-gands, flexible or rigid multidentate tetracarboxylic acids have at-tracted much attention in the field of crystal engineering due totheir ability to chelate and to bridge metal centers in a reliablemanner [38–43]. To the best of our knowledge, CPs fabricated fromH4butca ligand and transition metals and such reactions involvingN-donor ligands have scarcely been investigated, and much work is

ll rights reserved.

).

still necessary to be done for understanding the coordinationchemistry of H4butca. In our recent studies, 2-aminopyrimidineand its derivatives mixing with different dicarboxylates have beenwidely used to construct a series of Ag(I) CPs [44–51]. As our con-tinuous work, we introduced the flexible divergent H4butca as anauxiliary ligand into our previous systems and successfully ob-tained two new CPs with the dimensions spanning from 1D to 2D.

2. Experimental section

2.1. Materials and physical measurements

All the reagents and solvents employed were commerciallyavailable and used as received without further purification. Infra-red spectra were recorded on a Nicolet AVATAT FT-IR360 spec-trometer as KBr pellets in the frequency range 4000–400 cm�1.The elemental analyses (C, H, N contents) were determined on aCE instruments EA 1110 analyzer. Photoluminescence measure-ments were performed on a Hitachi F-4500 fluorescence spectro-photometer with solid powder on a 1 cm quartz round plate.

2.2. Synthesis of complex {[Ag4(mapym)2(butca)(H2O)4]�2H2O}n (1)

A mixture of Ag2O (232 mg, 1 mmol), mapym (109 mg, 1 mmol)and H4butca (234 mg, 1 mmol) was stirred in methanol–H2O

Table 2Selected bond distances (Å) and angles (�) for 1–2.

Complex 1Ag1–O4i 2.218(4) Ag1–Ag2 3.1679(9)Ag1–N3ii 2.218(5) Ag2–O1 W 2.104(6)Ag1–O1 2.314(5) Ag2–N1 2.135(5)Ag1–O2 W 2.720(4)O4i–Ag1–N3ii 140.35(18) O4i–Ag1–O2 W 91.60(15)O4i–Ag1–O1 101.22(19) N3ii–Ag1–O2 W 102.09(16)N3ii–Ag1–O1 114.36(18) O1–Ag1–O2 W 94.43(15)

i

18 D. Sun et al. / Journal of Molecular Structure 975 (2010) 17–22

mixed solvent (16 mL, v/v: 1/1). Then aqueous NH3 solution (25%,1 mL) was dropped into the mixture to give a clear solution underultrasonic treatment. The resultant solution was allowed to evapo-rate slowly in darkness at room temperature for several days togive colorless crystals of 1 (Yield, 76% based on silver). Anal. Calc.(found) for Ag4C18H32N6O14: C, 21.88 (21.91); H, 3.26 (3.30); N,8.51 (8.46)%. IR (KBr): v (cm�1) = 3408 (s), 2965 (w), 2935 (w),1655 (s), 1585 (s), 1475 (w), 1384 (m), 1152 (w), 1049 (w), 872(w), 624 (w), 558 (w), 545 (w), 497 (w).

O4 –Ag1–Ag2 56.60(12) O1–Ag1–Ag2 119.43(12)N3ii–Ag1–Ag2 89.58(12) O1 W–Ag2–N1 172.1(2)O1 W–Ag2–Ag1 95.12(18)Symmetry codes: (i) x + 1, y, z; (ii) �x + 2, �y, �z + 1; (iii) �x, �y + 1, �z;

(iv) x � 1, y, z

Complex 2Ag1–N1 2.198(3) Ag2–N4 2.208(3)Ag1–O1 2.303(3) Ag2–N7 2.217(3)Ag1–O1i 2.338(3) Ag2–O4 2.332(3)N1–Ag1–O1 138.58(11) N7–Ag2–O4 104.66(14)N1–Ag1–O1i 143.23(12) N4–Ag2–N7 143.71(13)O1–Ag1–O1i 76.31(11) N4–Ag2–O4 111.54(14)Symmetry codes: (i) �x, �y + 1, �z + 1; (ii) �x + 1, �y + 1, �z + 1

2.3. Synthesis of complex [Ag4(dmapym)6(butca)�2H2O]n (2)

The synthesis of 2 was similar to that of 1, but with dmapym(123 mg, 1 mmol) in place of mapym. Colorless crystals of 2 wereobtained in 64% yield (based on silver). They were washed with asmall volume of cold ethanol and diethyl ether. Anal. Calc. (found)for Ag4C44H64N18O10: C, 36.79 (36.75); H, 4.49 (4.52); N, 17.55(17.59)%. IR (KBr): v (cm�1) = 3420 (s), 3314 (s), 2969 (w), 2923(w), 1674 (m), 1630 (w), 1600 (s), 1567 (s), 1265 (w), 1278 (w),1024 (w), 793 (w), 628 (w), 576 (w).

Table 3The hydrogen bond geometries for 1–2.

D–H� � �A D–H H� � �A D� � �A D–H� � �A

Complex 1N2–H2B� � �O2Wii 0.86 2.21 3.035(7) 161N2–H2A� � �O2Wv 0.86 2.11 2.910(7) 154O3 W–H3 WA� � �O3i 0.85 1.92 2.757(7) 167O3W–H3WB� � �O1vi 0.85 1.91 2.695(7) 153O2 W–H2 WA� � �O2 0.85 1.90 2.696(6) 156O2W–H2WB� � �O3i 0.85 1.90 2.681(6) 153O1 W–H1 WB� � �O3Wvii 0.85 2.12 2.916(8) 156O1 W–H1 WA� � �O2v 0.85 2.09 2.940(7) 177Symmetry codes: (i) x + 1, y, z; (ii) �x + 2, �y, �z + 1; (v) x + 1, y � 1, z;

(vi) x, y + 1, z; (vii) �x + 2, �y + 1, �z

Complex 2N2–H2A� � �N9iii 0.86 2.23 3.040(5) 156N2–H2B� � �O2 0.86 2.07 2.795(5) 142

3. X-ray crystallography

Single crystals of the complexes 1–2 with appropriate dimen-sions were mounted on a glass fiber and used for data collection.Data were collected on a Rigaku R-AXIS RAPID Imaging Plate sin-gle-crystal diffractometer equipped with a graphite-monochro-mated Mo Ka radiation source (k = 0.71073 Å) in x scan modefor 1–2. The crystal structures were solved by direct methodsand refined with the full-matrix least-squares technique on F2

using the SHELXS-97 and SHEXL-97 programs [52–53]. The posi-tions of the water H atoms were refined with the O–H bond lengthrestrained to 0.85 Å. The crystallographic details of 1–2 are sum-marized in Table 1. Selected bond lengths and angles for 1–2 arecollected in Table 2. The hydrogen bond geometries for 1–2 areshown in Table 3.

Table 1Crystallographic data for complexes 1–2.

Complexes 1 2

Formula Ag4C18H32N6O14 Ag4C44H64N18O10

Mr 987.95 1436.58Crystal system Triclinic TriclinicSpace group P1 P1a (Å) 6.9115(16) 7.528(2)b (Å) 8.251(2) 11.741(3)c (Å) 13.773(3) 15.560(4)a (deg) 75.944(4) 74.838(5)b (deg) 80.613(4) 82.293(5)c (deg) 65.600(4) 86.460(5)Z 1 1V (Å3) 692.1(3) 1314.9(6)Dc (g cm�3) 2.371 1.814l (mm�1) 2.867 1.541F (0 0 0) 482 722No. of unique reflns 2610 4520No. of obsd reflns [I > 2r(I)] 2551 3987Parameters 193 349GOF 1.069 1.031Final R indices [I > 2r(I)]a,b R1 = 0.0517,

wR2 = 0.1358R1 = 0.0411,wR2 = 0.1014

R indices (all data) R1 = 0.0526,wR2 = 0.1368

R1 = 0.0478,wR2 = 0.1059

Largest difference peak andhole (e �3)

1.547 and �2.100 0.914 and �0.426

a R1 =P

||Fo| � |Fc||/P

|Fo|.b wR2 = [

Pw(F2

o � F2c )2/

Pw(F2

o )2]0.5.

N5–H5D� � �N6iv 0.86 2.16 3.017(5) 171N5–H5E� � �O3 0.86 2.11 2.899(5) 153N8–H8A� � �O1Wv 0.86 2.21 2.961(5) 145N8–H8B� � �N3vi 0.86 2.24 3.050(5) 157O1W–H1WA� � �O4vii 0.85 2.26 2.867(5) 129O1W–H1WB� � �O3 0.85 2.00 2.816(4) 160Symmetry codes: (iii) x, y + 1, z; (iv) �x + 1, �y + 1, �z + 2; (v) x � 1, y, z;

(vi) x, y � 1, z; (vii) x + 1, y, z

4. Results and discussion

4.1. Syntheses and IR

The syntheses of complexes 1–2 are carried out in the darknessto avoid photodecomposition and summarized in Scheme 1. Theformation of the products is not significantly affected by changesof the reaction mole ratio of organic ligands to metal ions andthe resultant crystals are insoluble in water and common organicsolvents. As is well known, the reactions of Ag(I) with multicarb-oxylates in aqueous solution often result in the formation of insol-uble silver salts, presumably due to the fast coordination of thecarboxylates to Ag(I) ions to form polymers [54]. Hence, properlylowering the reaction speed, such as using ammoniacal conditions,may favor to the formation of crystalline products [55]. The infra-red spectra and elemental analyses of 1–2 are fully consistent withtheir structural characteristics as determined by X-ray single-crys-tal diffraction. Their IR spectra exhibit the absorptions in the rangeof �3400 cm�1 to �3300 cm�1, corresponding to the N–H stretch-ing vibrations of the amino group. Strong characteristic bands of

D. Sun et al. / Journal of Molecular Structure 975 (2010) 17–22 19

carboxylate groups are observed in the range of �1630 cm�1 to�1560 cm�1 for the asymmetric vibrations and �1480 cm�1 to�1350 cm�1 for symmetric vibrations, respectively. The absenceof the characteristic bands at around �1700 cm�1 attributed tothe carboxylate groups, indicating that the complete deprotonationof all carboxylate groups in 1–2 upon reaction with Ag(I) ions [56].

4.2. Crystal structures

4.2.1. Crystal structure of {[Ag4(mapym)2(butca)(H2O)4]�2H2O}n (1)Complex 1 crystallizes in the triclinic space group P1.

Scheme 1. Syntheses of

Fig. 1. (a) The coordination environments of the Ag(I) ions and the linkage modes of ligamolecules are omitted for clarity. (b) The 2D sheet structure. (c) The 44-sql net incorporat�y + 1, �z.)

It is a 2D CP constructed by [Ag4(mapym)2] subunits. Theasymmetric unit of 1 consists of two Ag(I) ions, one mapym li-gand, one half butca anion, two coordinated water moleculesand one lattice water molecule. As shown in Fig. 1a, the Ag1ion is coordinated by one nitrogen atoms from one mapym ligandand three oxygen atoms from two butca anions and one watermolecule respectively to form a distorted tetrahedral coordinationgeometry [Ag1–N3ii = 2.218(5) and average Ag–O = 2.416(4) Å].The distortion of the tetrahedron can be indicated by the calcu-lated value of the s4 parameter introduced by Houser [57] to de-scribe the geometry of a four-coordinate metal system, which are

the complexes 1–2.

nds in 1 with 30% thermal ellipsoid probability. Hydrogen atoms and lattice watering four kinds of grid. (Symmetry codes: (i) x + 1, y, z; (iii) �x,�y + 1, �z; (viii)�x + 1,

20 D. Sun et al. / Journal of Molecular Structure 975 (2010) 17–22

0.75 for Ag1 (for perfect tetrahedral geometry, s4 = 1). The secondsilver ion (Ag2) is in a T-shaped trigonal environment completedby one nitrogen atom and two oxygen atoms [Ag2–N1 = 2.135(5)and Ag2–O1 W = 2.104(6) Å, \O1 W–Ag2–N1 = 172.1(2)�]. In 1, apair of l2-mapym ligands with opposite arrangement bind fourAg(I) ions to form a [Ag4(mapym)2] subunit. The intra-subunitshortest Ag� � �Ag contact is 3.1679(9) Å, which is obviously short-er than the twice the van der Waals radius of Ag(I) [58]. The sub-units stack into 1D chains via inter-subunit p� � �p interaction(Fig. S1, Cg1� � �Cg1ix = 3.576(4) Å; slippage = 1.248 Å; Cg1 is thecentroid of N1/C1/N3/C2/C3/C4). An inversion center exists atthe center of the butca ligand (midpoint of C8–C8iii) which

Fig. 2. (a) The coordination environments of the Ag(I) ions and the linkage modes of ligmolecules are omitted for clarity. (b) The 1D chain structure incorporating Ag2O2 subhydrogen bonds (green dashed lines) (Symmetry codes: (i) �x, �y + 1, �z + 1; (ii) �x + 1,reader is referred to the web version of this article.)

extends the resulting 1D chains into a 2D sheet (Fig. 1b). Takingthe Ag(I) ions and butca ligands as four-connected nodes, this2D structure can be simplified into an undulated 44-sql netincorporating four kinds of grid with the dimensions of3.17 � 8.83, 3.17 � 6.23, 4.77 � 6.23 and 4.77 � 8.83 Å respec-tively based on the Ag� � �Ag distances (Fig. 1c). Although diversecoordination modes of butca ligand have been presented [59],l6-j1:j2:j1:j2-coordination mode of butca ligand in 1 is firstlyobserved.

Between the adjacent sheets, the O2 W as acceptor interactwith amino group of mapym to form a R2

4(8) hydrogen bond motif(Fig. S2) locating on an inversion center [60]. On the other hand,

ands in 2 with 30% thermal ellipsoid probability. Hydrogen atoms and lattice waterunits. (c) The 1D chain structure incorporating Owater� � �Ocarboxylate and N� � �Owater

�y + 1, �z + 1.) (For interpretation of the references to color in this figure legend, the

Fig. 3. Emission spectra of the ligands and complexes 1–2.

D. Sun et al. / Journal of Molecular Structure 975 (2010) 17–22 21

the uncoordinated water molecule (O3 W) was hydrogen bondedto oxygen atoms of carboxylate groups with the Owater� � �Obutca dis-tances of 2.695(7) and 2.757(7) Å. Meanwhile, the coordinatedwater molecules (O1 W and O2 W) interact with each other andcarboxylate groups to form Owater� � �Owater and Owater� � �Obutca

hydrogen bonds (Table 3) which combine with R24(8) hydrogen

bond motif to construct the resulting 3D supramolecular frame-work (Fig. S3). (Symmetry code: (ii) �x + 2, �y, �z + 1; (iii) �x,�y + 1, �z; (ix) 3 �x, �y, 1 �z.)

4.2.2. Crystal structure of [Ag4(dmapym)6(butca)�2H2O]n (2)X-ray single-crystal analysis reveals that 2 crystallizes in the

same space group to that of 1 with the asymmetric unit contain-ing two crystallographically unique Ag(I) ions, three dmapym li-gands, one half butca ligand and one lattice water molecule(Fig. 2a). In 2, Ag1 and Ag2 adopt [AgNO2] and [AgN2O] Y-shapedgeometries respectively. The largest angle around Ag1 and Ag2are opened up to 143.23(12) and 143.71(13)� respectively. TheAg–O and Ag–N distances range from 2.303(3) to 2.338(3) and2.198(3) to 2.217(3) Å, respectively, which are all within thenormal ranges observed in O-containing and N-containing Ag(I)complexes [61–68]. Different from 1, there is no evidence ofany Ag(I)� � �Ag(I) interaction, the closest Ag� � �Ag distance is3.6489(10) Å in 2. The butca ligand also lies in the inversion cen-ter and shows the same coordination mode to that of 1. Thej2-O atoms of butca ligands link Ag(I) into a 1D chain incorpo-rating rhomboid Ag2O2 subunits centered at the inversion center(Fig. 2b). The presence of one more substituents on the hetero-cycle may affect the Lewis acid–base properties and steric effectof the ligand, so the dmapym just acts as monodentate terminalligand to complete the 1D chain and doesn’t extend the 1Dstructure to the higher dimensions.

As shown in Fig. 2c, the lattice water molecules interact with theamino and carboxylate groups to form the intra-chain hydrogenbond and reinforce the 1D chain (Table 3, average Owater� � �Ocarboxylate =2.841(5); N� � �Owater = 2.847(5) Å). Furthermore, the inter-chain self-complementary N–H� � �N hydrogen bonds of two pyrimidine moie-ties (Fig. S4) extend the 1D chains into a 2D supramolecular sheet.Including the hydrogen bonds, the C–H� � �pdmapym interactions[C9–H9A� � �Cg1viii: dH� � �Cg = 2.87 Å, dC� � �Cg = 3.612(5) Å and h = 138�;C17–H17B� � �Cg2ix: dH� � �Cg = 2.98 Å, dC� � �Cg = 3.786(5) Å andh = 142�; Cg1 and Cg2 are centroids of ring N4/C13/N6/C14/C15/C16 and N7/C7/N9/C10/C9/C8; h is the angle of C� � �H� � �Cg, Fig. S5]and face-to-face p� � �p interaction (Fig. S6, Cg3� � �Cg3x = 3.407(2) Å;slippage = 0.632 Å; Cg3 is the centroid of N1/C1/N3/C2/C3/C4) actas a ‘‘glue” to reinforce the resulting 3D supramolecular framework(Fig. S7). (Symmetry code: (viii) �x + 1, �y, �z + 2; (ix) �x, �y,�z + 2; (x) �x, �y + 2, �z + 1).

4.3. Photoluminescence properties

The solid-state photoluminescence data for free ligands andcomplexes 1–2 at room temperature are shown in Fig. 3.Complexes 1 and 2 exhibit photoluminescence with emission max-ima at 487 and 360 nm respectively upon excitation at 330 nm atroom temperature. To understand the nature of the emissionbands, we analyzed the photoluminescence properties of the corre-sponding free ligands and found that free mapym, dmapym andH4butca ligands don’t emit any photoluminescence in the range400–800 nm. When compared to the photoluminescence spectrumof the free mapym, the emission band of 1 is red-shifted by137 nm, which comes from the electronic transition between porbitals (filled orbitals) of coordinated N atoms and 5s orbital(empty orbital) of Ag(I) ion, i.e., ligand-to-metal charge transfer(LMCT), mixed with metal-centered (d–s/d–p) transitions [69]. Dif-ferent from 1, the fluorescent emission of 2 is similar to that of

dmapym and should be assigned to intraligand transition of coor-dinated N-donor ligands. The shifted emission and enhancement ofluminescence of 2 were attributed to ligand coordination to themetal center, which effectively increases the rigidity of the ligandand reduces the loss of energy by radiationless decay.

5. Conclusions

In summary, we demonstrated the synthesis and characteriza-tion of two new Ag(I) CPs with the dimensions spanning from 1Dto 2D by using various 2-aminopyrimidyl derivations and versatile1,2,3,4-butanetetracarboxylic acid under the ammoniacal condi-tion. Adding one more electron-donating substituent in the pyrim-idine ring resulted in significant changes in the coordination modeof the 2-aminopyrimidyl derivations. These results also indicatethat a slight modification in the ligand structure may have a greatinfluence on the assembly process and the resulting motifs. Addi-tionally, these two CPs provide a way of understanding abundantweak interactions, such as hydrogen bond, Ag� � �Ag argentophilici-ty, p� � �p stacking and C–H� � �p interaction, and these interactionsin 1–2 further assemble the low-dimensional structures into stablesupramolecular architectures.

Acknowledgments

This work was financially supported by the National NaturalScience Foundation of China (No. 20721001), 973 Project (Grant2007CB815301) from MSTC.

Appendix A. Supplementary material

CCDC 767853 and 767854 contain the supplementary crystallo-graphic data for 1 and 2 respectively in this paper. These data canbe obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Cen-tre, 12 Union Road, Cambridge CB 21EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary dataassociated with this article can be found, in the online version.

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.molstruc.2010.03.071.

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