Complexes and Density Functional Theory Calculations to Study Bond

DOI: 10.1021/cg901453a

Anion-Induced Assembly of Five-Coordinated Mercury(II) Complexes and Density Functional Theory Calculations to Study Bond Dissociation Energies of Long Hg-N Bonds

2010, Vol. 10 1767–1776

Hong-Ping Zhou,* Xiao-Ping Gan, Xian-Lei Li, Zhao-Di Liu, Wen-Qian Geng, Fei-Xia Zhou, Wei-Zai Ke, Peng Wang, Lin Kong, Fu-Ying Hao, Jie-Ying Wu, and Yu-Peng Tian* Department of Chemistry, Anhui University and Key Laboratory of Functional Inorganic Materials Chemistry of Anhui Province, 230039 Hefei, P. R. China Received November 20, 2009; Revised Manuscript Received February 7, 2010

ABSTRACT: A series of new five-coordinated mercury(ΙΙ) coordination complexes (Hg(TpzT)(SCN)2 3 H2O (1), Hg(TpzT)I2 3 H2O (2), Hg(TpzT)Br2 3 H2O (3), 2Hg(TpzT)Cl2 3 HgCl2 3 2H2O (4)) have been synthesized by self-assembling the flexible ligand 2,4,6-tri(pyrazole-1-yl)-1,3,5-triazine (TpzT) with HgX2 (X = SCN, I, Br, Cl). Various weak interactions including hydrogen bonds (O-H 3 3 3 X, C-H 3 3 3 X), π-π interactions, and S 3 3 3 S contacts play significant roles in the final topological structures of the four compounds. Unexpectedly, 5 and 6 were obtained accidentally by self-assembling TpzT with MX2 (Zn(NO3)2 3 6H2O or CdI2) in methanol and were assessed by X-ray crystallography, which indicated that there are nucleophilic substitution reactions. Surprisingly, all the Hg-N bonds of approximately 2.70 A˚ in length formed by the tridentate ligand and mercuric salt are rather unusual. So density functional theory (DFT) calculations (Amsterdam density functional, ADF) were employed to study the bond dissociation energies (BDE) of Hg-N bonds in 1-4 to assess the nature of the bonds. The calculation reveals the strong coordination nature of Hg-N bonds in 1-4 compared to that of the same coordination mode of compound A ((40 -(4-[4(imidazole)phenylethylene]phenyl)-2,20 :60 ,200 -terpyridine)HgBr2 3 CHCl3) with the normal range Hg-N bond lengths. And a similar trend is that the larger the anion and BDE become, the steadier the coordination complexes are.

Introduction The self-assembly of supramolecular structures using metal coordination has attracted a great deal of attention over the past decade, due to their potential applications in the fields of catalysis, molecular recognition, magnetism, nonlinear optics, and porous zeolite mimics.1-3 One of the challenges in this field is to correctly choose the crystal structure of the building units. Nitrogen containing heterocycles are frequently used as building blocks in the construction of supramolecules, such as the heterocyclic substituted 1,3,5-triazine derivatives (2,4,6tris(2-pyridyl)-1,3,5-triazine (TPT), tris(3,5-dimethylpyrazol1-yl)-1,3,5-triazine (Me2-TpzT), 2,4,6-tri[(4-pyridyl)sulfanylmethyl]-1,3,5-triazine (TPST)),4,5 mainly because the metal derivatives exhibit rich fluxional behavior, and the ligands can adopt a bidentate or tridentate coordination mode to form flexible topological structures. Typically, Fujita et al. reported many porous materials constituted of TPT with excellent properties.6 The supramolecular assembly remains elusive despite much effort to predict and control them, and much more work is required to focus on inter- and intramolecular forces such as hydrogen bonds (Y-H 3 3 3 X), π-π interactions, and X 3 3 3 X contacts which influence the patterns of molecular structure and crystal packing in the solid state. In addition, other factors such as the nature of the metal atoms and the ligands and counterion-based interactions can also determine the structures.7 The bivalent cations (M2þ) of the second subgroup have various coordination numbers and can serve to link ligands to form coordination compounds with novel coordination pat-

Scheme 1. Schematic Drawing of the Ligand (TpzT)

*To whom correspondence should be addressed. E-mail: zhpzhp@263. net (H.-P.Z.); (Y.-P.T.).

terns. Take Hg as an example: common coordination frameworks are four-coordinated in a tetrahedral geometry,8-11 and six-coordinated with a distorted octahedral geometry.12 However, to the best of our knowledge, the five-coordinated mode of Hg(ΙΙ) with trigonal bipyramidal geometry has rarely been reported. Moreover, taking into account the large polarization, the mercury(ΙΙ) ion shows a specific affinity to the rigid N-donor ligands. Many promising topological architectures have been constructed for the Hg(ΙΙ) ion with multidentate building blocks containing a nitrogen donor, which include one-, two-, and three-dimensional (1-D, 2-D, and 3-D) various types of supramolecular structures.13 As pyrazole is an electron-rich aromatic compound, we introduced pyrazole groups to the triazine ring in high yield, by nucleophilic substitution reaction according to the method in the literature.14-18 The trident triazine ligand, 2,4,6-tri(pyrazole-1-yl)1,3,5-triazine (TpzT, Scheme 1), was applied to construct a novel coordination complex with the second subgroup transition metal salts containing Zn, Cd, and Hg. In this paper, a series of new rare five-coordinated mercury(ΙΙ) complexes (1-4) with a trigonal bipyramidal geometry based on the reaction of TpzT and mercury(II) ions were obtained by selfassembling at room temperature. Unexpectedly, in the process

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of preparing coordination complexes, 5 and 6 were obtained, which testified that the TpzT could react with the alcohol solvent (such as methanol) induced by the bivalent cations of this subgroup (Zn2þ, Cd2þ). In the past report on Hg-N bond length of tridentate coordination,19 only one or two of them are approaching 2.7 A˚, and it is rather rare to see that all three are approximately 2.70 A˚. So we calculated the bond dissociation energies (BDE) of Hg-N bonds though density functional theory (DFT) calculations (Amsterdam density functional, ADF). The results show the BDE of 1-4 and compound A with the normal range bond lengths are of the same order of magnitude corresponding to the strong coordination-bond. All the data show the same trend of the coordination-bond energies vs the halogen; that is, the largest anion possesses the strongest Hg-N coordinationbond energies, and the chloride is the lowest. Experimental Section Materials and Methods. The reagents and solvents employed were commercially available and used as received without further purification. Elemental analyses were performed with a Perkin-Elmer 240C elemental analyzer. IR spectra were recorded with a Nicolet FT-IR Nexus 870 instrument (KBr discs) in the 400-4000 cm-1 region. 1H spectra were performed on Bruker 400 or 500 MHz Ultrashield spectrometer and were reported as parts per million (ppm) from TMS (δ). Preparation of TpzT. In a 250 mL round-bottom flask (RBF), pyrazole (5.45 g, 0.08 mol) and cyanuric chloride (3.0 g, 0.016 mol) were dissolved in 100 mL of tetrahydrofuran (THF) and stirred, and then N,N-diisopropylethylamine (DIPEA, 28.4 mL, 0.163 mol) was added; the reactants were stirred at room temperature for 1 h, and then the mixture was heated up gradually to 80-85 C and refluxed for about 6 h. Thin layer chromotography (TLC) confirmed the absence of the starting material cyanuric chloride for the reactions. The solvent THF was evaporated under reduced pressure after the solution was cooled to room temperature, and the residue liquid stays steadily in the RBF. A few hours later, yellow powder and crystalloid separated out, then they were filtered, and the product was washed with water twice and dried overnight to afford L (3.77 g, 0.014 mol, 83%) as a white solid. IR (KBr cm-1): 3420 m, 1576 s, 1533 s, 1453 s, 1396 s, 1038 m, 807 m, 772 m. 1H NMR (DMSO, 500 MHz) δ/ppm: 6.74 (m, 3H), 8.03 (m, 3H), 8.96 (d, 3H, J = 2.35). MS, m/z: 279.10 (Mþ). Anal. Calc. (%) for C12H9N9 (279.10): C, 51.61; H, 3.25; N, 45.14. Found: C, 51.19; H, 3.36; N, 45.45%. Preparation of Complexes 1-6. Hg(TpzT)(SCN)2 3 H2O (1). TpzT (16.8 mg, 0.06 mmol) and Hg (SCN)2 (19.0 mg, 0.06 mmol) were dissolved in 20 mL of acetonitrile and refluxed for 3 h at 82 C. The solution was cooled to room temperature and filtered and allowed to stand for several days to give colorless block single crystals. Yield: 21.84 mg, 61%. IR (KBr cm-1): 3446 w, 3109 w, 2025 vs, 1595 m, 1459 s, 1394 s, 1040 m, 802 w, 762 w. Anal. Calc. (%) for C14H11HgN11OS2 (614.03): C, 27.38; H, 1.81; N, 25.09. Found: C, 27.69; H, 1.32; N, 25.27%. Hg(TpzT)I2 3 H2O (2). TpzT (16.8 mg, 0.06 mmol) and HgI2 (27.0 mg, 0.06 mmol) were dissolved in 10 mL of acetone and 10 mL of ethyl acetate and refluxed for 3 h at 78 C. The solution was cooled to room temperature and filtered and allowed stand for several days to give pale yellow block single crystals. Yield: 29.35 mg, 67%. IR (KBr cm-1): 3414 w, 3109 w, 1582 s, 1451 s, 1389 s, 1183 s, 804 m, 782 m. Anal. Calc. (%) for C12H11HgI2N9O (751.67): C, 19.17; H, 1.48; N, 16.77. Found: C, 19.40; H, 1.31; N, 16.41%. Hg(TpzT)Br2 3 H2O (3). TpzT (16.8 mg, 0.06 mmol) and HgBr2 (21.0 mg, 0.06 mmol) were dissolved in 10 mL of acetone and 10 mL of benzene and refluxed for 3 h at 80 C. The solution was cooled to room temperature and filtered and allowed stand for several days to give colorless block single crystals. Yield: 26.84 mg, 71%. IR (KBr disk cm-1): 3412 w, 3103 w, 1587 s, 1455 s, 1384 s, 1185 s, 808 m, 786 m. Anal. Calc. (%) for C12H11Br2HgN9O (657.67): C, 21.91; H, 1.69; N, 19.17. Found: C, 21.87; H, 1.32; N, 19.58%. 2Hg(TpzT)Cl2 3 HgCl2 3 2H2O (4). TpzT (16.8 mg, 0.06 mmol) and HgCl2 (16.3 mg, 0.06 mmol) were dissolved in 10 mL of acetone and

Zhou et al. 10 mL of benzene and refluxed for 3 h at 80 C. The solution was cooled to room temperature and filtered and allowed stand for several days to give colorless block single crystals. Yield: 21.84 mg, 61%. IR (KBr cm-1): 3417 w, 3115 w, 1573 s, 1453 s, 1394 s, 1185 w, 806 m, 782 m. Anal. Calc. (%) for C24H22Cl6Hg3N18O2 (1409.04): C, 20.46; H, 1.57; N, 17.89. Found: C, 20.80; H, 1.87; N, 17.53%. Cd(C3H4N2)2I2 (5). TpzT (16.8 mg, 0.06 mmol) and CdI2 (22.0 mg, 0.06 mmol) were dissolved in 20 mL of methanol and refluxed for 3 h at 65 C. The solution was cooled to room temperature and filtered, and allowed stand for several days to give colorless block single crystals. Yield: 5.8 mg, 15%. IR (KBr cm-1): 3324 s, 3116 w, 1519 m, 1464 m, 1399 m, 1351 m, 1039 s, 858 w, 761 s. Anal. Calc. (%) for C6H8CdI2N4 (502.37): C, 14.34; H, 1.61; N, 11.15. Found: C, 14.01; H, 1.48; N, 11.62%. X-ray Crystallography. Single-crystal X-ray diffraction measurements were carried out on a Bruker Smart 1000 CCD diffractometer equipped with a graphite crystal monochromator situated in the incident beam for data collection at room temperature. The determination of unit cell parameters and data collections were performed with Mo-KR radiation (λ = 0.71069 A˚). Unit cell dimensions were obtained with least-squares refinements, and all structures were solved by direct methods using SHELXL-97.20 The other non-hydrogen atoms were located in successive difference Fourier syntheses. The final refinement was performed by fullmatrix least-squares methods with anisotropic thermal parameters for non-hydrogen atoms on F2. The hydrogen atoms were added theoretically and riding on the concerned atoms. Crystallographic crystal data and processing parameters for the complexes 1-6 are shown in Table 1. Selected bond lengths and bond angles for the complexes 1-4 are listed in Table 2. Geometrical parameters of the hydrogen bonds (A˚, ) involved in the supramolecular construction in 1-4 (D = donor, A = acceptor) are listed in Table 3. CCDC-738023, 738026, 738024, 738025, (1, 2, 3, and 4 for the mercury complexes) and CCDC-726948, 726949 (5, 6, respectively) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Computational Details. DFT calculation has attracted much attention due to its high performance and low cost. A properly chosen DFT performs even as well as MP2. In order to compare the Hg-N bond, we performed DFT calculations with a well-known software (ADF). All the calculations are performed at LDA (VWN21) and GGA (PBE22), and basis sets used for all the atoms are from TZP (triple-ξ Slater type orbital). 1s core orbital is defined for C, N, and O. For Hg, the 4f orbital is considered, respectively. 2p core orbital is defined for both Cl and S. 3d, 4d core orbitals are defined for Br and I, respectively. Geometry optimizations are performed for all the molecules to get stable structures and frequencies analysis is done for the geometry obtained to avoid imaginary frequencies. BDE values were calculated by the following reaction for I, Br, SCN. X2 Hg-L f L þ HgX2 H ¼ E þ ZPE þ ΔH298-0 þ RT E can be obtained from single point energy calculations; further ZPE is done with no scale correction. Both ZPE and ΔH298-0 are computed in the course of frequencies analysis.23 But for Cl, the interaction between the long Hg-Cl bond is analyzed by a previous method.24 Our early study points out that the interactions between the systems are not affected by weak interaction except strong interaction such as covalent bond or coordination bond. The 148.79 kJ/mol shows that the coordination nature of Hg-Cl bond and Hg bridge takes a very important role in the molecule and cannot be omitted in further calculations. In order to learn information about the coordination bond energy between Hg and ligand, we performed optimization on the whole molecule (TpzT)2(HgCl2)3 with Ci symmetry and further optimized (HgCl2)3 and TpzT, respectively. All the structures preoptimized are directly acquired from the CIF data. 3ðX2 HgÞ-2L f 2L þ 3ðHgX2 Þ

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Table 1. Crystallographic Data for 1-6 compound

1

2

3

4

5

6

empirical formula fw crystal system space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z T (K) Dcalcd (g 3 cm-3) μ(mm-1) 2θ max (deg) total no. data no. unique data no. params refined R1 wR2 GOF

C14H11HgN11OS2 614.05 P1 triclinic 7.122(5) 10.876(5) 13.443(5) 79.767(5) 74.836(5) 79.822(5) 979.7(9) 2 298(2) 2.082 8.100 49.98 3409 2876 271 0.0300 0.0585 1.020

C12H11HgI2N9O 751.69 P1 triclinic 7.876(5) 10.659(5) 11.852(5) 74.143(5) 88.576(5) 81.308(5) 946.0(8) 2 298(2) 2.639 11.420 50.00 3215 2621 235 0.0313 0.1070 1.113

C12H11Br2HgN9O 657.71 P1 triclinic 7.871(5) 10.701(5) 11.355(5) 74.000(5) 88.998(5) 78.074(5) 898.7(8) 2 293(2) 2.430 13.031 50.00 3142 2522 233 0.0318 0.0728 1.036

C24H22Cl6Hg3N18O2 1409.07 P1 triclinic 7.595(5) 7.595(5) 12.072(5) 94.625(5) 92.903(5) 100.386(5) 935.8(9) 1 298(2) 2.500 12.757 50.00 3251 2778 250 0.0257 0.0726 0.893

C6H8CdI2N4 502.37 C2/c monoclinic 18.617(4) 4.2375(8) 14.979(3) 90.00 93.800(2) 90.00 1179.1(4) 4 296(2) 2.830 7.054 53.22 1090 963 60 0.0268 0.0607 1.096

C6H9N3O3 171.16 Pnma orthorhombic 8.474(3) 6.710(3) 14.387(5) 90.00 90.00 90.00 818.1(5) 4 296(2) 1.390 0.113 50.98 876 630 76 0.0494 0.1287 1.048

Table 2. Selected Bond Lengths (A˚) and Angles () for 1-4 Complex 1 Hg1-N5 Hg1-N7 Hg1-N9 Hg1-S1 Hg1-S2 N5-Hg1-N7 N5-Hg1-N9

2.530(4) 2.628(4) 2.620(4) 2.422(2) 2.407(2) 62.68(12) 62.90(13)

S1-Hg1-S2 S1-Hg1-N5 S1-Hg1-N7 S1-Hg1-N9 S2-Hg1-N5 S2-Hg1-N7 S2-Hg1-N9

152.06(6) 99.43(9) 98.53(10) 91.66(11) 107.98(10) 98.74(11) 95.96(11)

Complex 2 Hg1-N5 Hg1-N7 Hg1-N9 Hg1-I1 Hg1-I2 N5-Hg1-N7 N5-Hg1-N9

2.629(7) 2.722(7) 2.689(7) 2.628(1) 2.631(1) 60.20(20) 60.61(19)

I1-Hg1-I2 I1-Hg1-N5 I1-Hg1-N7 I1-Hg1-N9 I2-Hg1-N5 I2-Hg1-N7 I2-Hg1-N9

152.87(3) 103.30(14) 93.99(15) 99.20(14) 103.60(14) 96.70(15) 96.55(14)

Complex 3 Hg1-N1 Hg1-N4 Hg1-N9 Hg1-Br3 Hg1-Br2 N1-Hg1-N4 N1-Hg1-N9

2.610(5) 2.637(5) 2.710(5) 2.462(1) 2.463(1) 61.79(16) 60.86(16)

Br2-Hg1-Br3 Br3-Hg1-N1 Br1-Hg1-N7 Br1-Hg1-N9 Br2-Hg1-N1 Br2-Hg1-N4 Br2-Hg1-N9

155.60(3) 102.87(11) 98.07(12) 93.37(12) 101.10(12) 97.19(12) 94.280(12)

Complex 4 Hg2-N1 Hg2-N2 Hg2-N3 Hg2-Cl3 Hg2-Cl4 Hg1-Cl5 Hg1-Cl50 N1-Hg2-N2 N1-Hg2-N3

2.610(5) 2.683(5) 2.687(5) 2.359(2) 2.334(2) 2.296(2) 2.296(2) 60.70(14) 60.56(14)

Cl5-Hg1-Cl50 Cl4-Hg2-Cl3 Cl3-Hg2-N1 Cl3-Hg2-N3 Cl3-Hg2-N2 Cl4-Hg2-N1 Cl4-Hg2-N3 Cl4-Hg2-N2

180.00 152.93(6) 93.86(11) 95.20(12) 99.55(12) 113.03(11) 95.42(11) 96.50(12)

Results and Discussion Structure of the Complexes 1-6. Structure of Hg(TpzT)(SCN)2 3 H2O (1). Complex 1 crystallizes in the triclinic with space group P1 as shown in Figure 1a; TpzT in complex 1 possesses perfect planarity with the dihedral angles between three pyrazole rings and the central triazine unit to be 1.29,

1.57, and 3.09, respectively. As shown in Figure 1a, Hg ion is five-coordinated completed via three N atoms from TpzT, two sulfur atoms from SCN-, and a free solvent water molecule. The bond lengths Hg1-N5, Hg1-N7, Hg1-N9 are 2.530(4), 2.628(4), 2.620(4) A˚, respectively, which are longer than that reported.24,25 Each bond angles around the mercury atom are in the range 62.68(12)-152.06(6), indicating quite a distorted trigonal bipyramidal geometry. Selected bond lengths and angles are listed in Table 2. It is water that plays a significant role in the topological structures as shown in Figure 1. One of the two H in water and the N from trazine and pyrazole form the O-H 3 3 3 N hydrogen bonds with two different distances [d(O1 3 3 3 N1) = 3.038(11) A˚, d((O1)H11 3 3 3 N1) = 2.23(14) A˚, — (O1-H11 3 3 3 N1) = 160(13), d(O1 3 3 3 N4) = 3.302(7) A˚, d((O1)H11 3 3 3 N4)=2.59(4) A˚, — (O1-H11 3 3 3 N4) = 137(8)]. As shown in Figure 1b, the macrocycles are linked to a 1-D chain along the a-axis by π-π stacking with a centroid-centroid distance of 3.581 A˚ and an angle of 19.57, with each 2 þ 2 pesduo macrocycle consisting of the above depicted hydrogen bonds and the O-H 3 3 3 N hydrogen bonds via the other H of water and N from one SCN- (d(O1 3 3 3 N10) = 3.067(11) A˚, d((O1)H10 3 3 3 N10)= 2.34(11) A˚, — (O1-H10 3 3 3 N10) = 160(9)). The 1-D chains further link along the b-axis direction to form a 2-D wavelike structure through C-H 3 3 3 N interactions with the H from the pyrazole and the N from the SCN(d(C9 3 3 3 N11) = 3.633(11) A˚, d((C9)H6 3 3 3 N11) = 2.72(1) A˚, — (C9-H6 3 3 3 N11) = 164(1)). Finally, the extended 3-D topological structures were formed along the c-axis via S 3 3 3 S interactions with the distance of 3.564 A˚ in view of the van der Waals radii of the S atom being 1.85 A˚ (Figure 1d).26 B. K. Ghosh27 has discussed the S 3 3 3 S interactions that play an important role in the interpenetrating architecture for anionic tetrakis SCN complex Hg(SCN)42-. Considering the anionic steric effect and electrostatic repulsion, S 3 3 3 S interactions in the neutral complex are a little stronger than those of the anionic tetrakis SCN complex. Structure of Hg(TpzT)I2 3 H2O (2). The coordination environment of complex 2 also has a quite distorted trigonal bipyramidal geometry similar to that of complex 1. The unit consists of one mercury ion connecting three N from one ligand L and two iodine atoms, and one water molecule. The X-ray

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Table 3. Geometrical Parameters of the Hydrogen Bonds (A˚, ) Involved in the Supramolecular Construction in 1-4 (D = Donor, A = Acceptor) Complex 1 d(D-H)/A˚

D-H 3 3 3 A

d(H-A)/A˚

a

0.84(14) 2.23(14) O1-H11 3 3 3 N1 0.76(10) 2.34(11) O1-H10 3 3 3 N10b c 0.89(9) 2.59(4) O1-H11 3 3 3 N4 0.93 2.72(1) C9-H6 3 3 3 N11d a = x, -1 þ y, z, b = 1 - x, 1 - y, 1 - z, c = 2 - x, 2 - y, 1 - z, d = -x, 1 - y, 1 - z.

d(D-A)/A˚ 3.038(11) 3.067(11) 3.302(7) 3.633(11)

— DHA 160(13) 160(9) 137(8) 164(1)

Complex 2 d(D-H)/A˚

D-H 3 3 3 A

d(H-A)/A˚

a

0.86(2) 2.16(8) O1-H11 3 3 3 N2 0.92(12) 2.89(13) O1-H10 3 3 3 I1b 0.93(1) 2.36(1) C7-H4 3 3 O1c a b c = -1 þ x, 1 þ y, -1 þ z, = 1 - x, 1 - y, 1 - z, = 1 þ x -1 þ y, 1 þ z.

d(D-A)/A˚ 2.917(11) 3.798(9) 3.274(13)

— DHA 147(13) 168(12) 168(1)


D-H 3 3 3 A a

C12-H1 3 3 3 O1W 0.93 0.85 O1W-H1WA 3 3 3 Br2b c 0.85 O1W-H1WB 3 3 3 N7 0.93 C11-H2 3 3 3 O1Wd a = 1 - x, -y, 1 - z, b = x, y, z, c = 1 - x, -y, 1 - z. d = 1 þ x, y, z.

d(H-A)/A˚

d(D-A)/A˚

2.36 2.68 2.08 2.56

3.278(9) 3.512(6) 2.907(8) 3.481

— DHA 168.6(5) 165.2 163.2 172.2


D-H 3 3 3 A a

d(H-A)/A˚

O1-H101 3 3 3 N10 0.89(7) 2.11(3) 0.93(1) 2.430(6) C5-H5 3 3 3 O1b 0.93(1) 2.784(3) C13-H13 3 3 Cl5c d 0.93(1) 2.735(2) C42-H3 3 3 3 Cl3 e 0.89(8) 2.571(8) O1-H100 3 3 3 Cl3 a = x, y, z, b = x, y, z, c = 2 - x, 2 - y, 1 - z, d = -x, -y þ 1, -z. e = -x, -y þ 1, -z.

single crystal reveals that the metal complex also crystallizes in the triclinic with space group P1 as shown in Figure 2a; in the same way, TpzT of complex 2 possesses perfect planarity with the dihedral angles between three pyrazole rings and the central triazine unit to be 1.29, 1.57, and 5.41, respectively. However, different from complex 1, one of the two H’s in water and the very N from pyrazole form the O-H 3 3 3 N hydrogen bonds [d(O1 3 3 3 N2) = 2.917(11) A˚, d(O1-H11 3 3 3 N2) = 2.16(8) A˚, — (O1-H11 3 3 3 N2) = 147(13)]; in addition, the O in water and H of another pyrazole form C-H 3 3 3 O hydrogen bonds [O1 3 3 3 C7 = 3.274(13) A˚, (O1)H11 3 3 3 C7 = 2.36(1) A˚, — (O1-H1-C7) = 168(1)] Similar to complex 1, the pseudo 2 þ 2 macrocycle consists of O-H 3 3 3 N, C-H 3 3 3 O, and O-H 3 3 3 I hydrogen bonds [d(O1 3 3 3 I1) = 3.798(9) A˚, d((O1)H10 3 3 3 I1) = 2.89(13) A˚, — (O1-H10 3 3 3 I1) = 168(12)]6b containing internal π-π stacking between two pyrazole rings of the neighboring complexes with a centroid-centroid distance of 3.580 A˚ and an angle of 24.13 also constituting the 1-D chain along the a-axis via strong π-π stacking between two pyrazole rings of the neighboring complexes with a centroid-centroid distance of 3.372 A˚ and an angle of 11.54 (Figure 2b). At last, it can be seen that the complex 2 forms the stabilizing 2-D architecture along the b-axis direction through π-π stacking between two pyrazole rings of the neighboring complexes with a centroid-centroid distance of 3.806 A˚ and an angle of 29.76 (Figure 2c). Structure of Hg(TpzT)Br2 3 H2O (3). Complex 3 adopts the same coordination mode as complexes 1 and 2. The mercury coordinates with two ligands and two bromine atoms. The

d(D-A)/A˚ 2.979(8) 3.343(9) 3.609(6) 3.610(6) 3.430(6)

— DHA 174.61(98) 167.37(45) 148.49(38) 157.18(37) 163.26(7)

bond angles around mercury are in the range 60.86(10)155.60(3) indicating quite a distorted trigonal bipyramidal geometry. Like 1 and 2, TpzT of complex 3 possesses perfect planarity with the dihedral angles between three pyrazole rings and the central triazine unit to be 0.34, 0.48, and 1.91, respectively. Similar to complex 2, there are O-H 3 3 3 N hydrogen bonds [d ((O1)H1WB 3 3 3 N7) = 2.08 A˚, d(O1 3 3 3 N7) = 2.907 A˚, — O1-H1WB 3 3 N7 = 163.2] and C-H 3 3 3 O interactions [d ((C12)H1WB 3 3 3 O1W) = 2.36 A˚, d(C12 3 3 3 O7) = 3.278(9) A˚, — C12-H1 3 3 O1W = 168.6(5)] between the water molecule and the ligand L. Similar to complexes 1 and 2, the pseudo 2 þ 2 macrocycle consists of O-H 3 3 3 N, C-H 3 3 3 O, and O-H 3 3 3 Br hydrogen bonds [d(O1W 3 3 3 Br2) = 3.512(6) A˚, d((O1W)H1WA 3 3 3 Br2) = 2.68 A˚, — (O1W-H1WB 3 3 3 Br2) = 165.2] containing internal π-π stacking between two pyrazole rings of the neighboring complexes with a centroid-centroid distance of 3.574 A˚ and an angle of 22.91 also constituting the 1-D chain along the a-axis via strong π-π stacking between two pyrazole rings of the neighboring complexes with a centroid-centroid distance of 3.413 A˚ and an angle of 11.54 (Figure 3b). Finally, it can be seen that the complex 3 forms a stabilizing 2-D architecture along the b-axis direction through π-π stacking between two pyrazole rings of the neighboring complexes with a centroid-centroid distance of 3.650 A˚ and an angle of 24.85 (Figure 2c). Structure of 2Hg(TpzT)Cl2 3 HgCl2 3 2H2O (4). Complex 4 also crystallizes in the triclinic with space group P1 as shown in Figure 4a; different from 1, 2 and 3, 4 consists of two H2O,

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Figure 1. (a) Coordination environments of Hg with the atom numbering scheme. (b) The 1-D framework of complex 1 showing the O-H 3 3 3 N hydrogen bond and π-π stacking along the a-axis. (c) The 2-D framework of complex 1 showing weak C-H 3 3 3 N interactions along the b-axis. (d) The 3-D architecture of complex 1 showing weak S 3 3 3 S interactions along the c-axis.

two HgLCl2, and one HgCl2 linked by Hg-Cl interactions with a distance of 3.127 A˚ which is proven to be coordination bonds according to DFT calculations. There are two different coordination environments Hg(ΙΙ) ions; namely, one chelates with three N atoms from TpzT and two chlorine atoms showing a quite distorted trigonal bipyramidal geometry, and the other is four coordination in planar square linked with chloride. The unit is further stabilized by C-H 3 3 3 O interactions [d(O1 3 3 3 C5) = 3.343(9) A˚, d((O1)H5 3 3 3 C5) = 2.430(6) A˚, — (O1-H5 3 3 3 C5) = 167.37(45)] and O-H 3 3 3 N interactions [d(O1 3 3 3 N10) = 2.979(8) A˚, d((O1)H101 3 3 3 N10) = 2.091(7) A˚, — (O1-H101 3 3 3 N10) = 174.61(98)]. O-H 3 3 3 Cl interactions [d(O1 3 3 3 Cl3) = 3.430(6) A˚, d((O1)H100 3 3 3 Cl13) = 2.571(8) A˚, — (O1H100 3 3 3 13) = 163.26(7)] gives the form of a 1-D chain along the a-axis, which further forms a 2-D framework along the b-axis through C-H 3 3 3 Cl interactions [d(C42 3 3 3 Cl3) = 3.610(6) A˚, d((C42)H3 3 3 3 Cl3) = 2.735(2) A˚, — (C42-H3 3 3 3 Cl3) = 157.18(37)]. Taking the van der Waals radii of Hg and Cl to be 1.70 and 1.80 A˚,25 respectively, any Hg 3 3 3 Cl contact less than 3.50 A˚ may therefore potentially be considered significant. Therefore, we presume the 2-D architecture given by evidence of Hg 3 3 3 Cl interactions [d(Hg1 3 3 3 Cl13 = 3.187 A˚] along c-axis leads to the 3-D architecture, as shown in Figure 4d. Structure of 5. Figure 5 shows that the structure is different from what we had expected, but is a coordination polymer complex composed of two pyrazole molecules and one CdI2 molecules by Cd-I. The Cd atom adopted distorted octahedron geometry, the bond lengths Cd1-N1, Cd1-I7, Cd10 -

I1 are 2.332(4), 3.026(5), and 2.980(5) A˚, respectively. Each angle of Cd-I bond around cadmium atom are in the range 88.52(9)-91.48(9). It also can be seen that between two complex molecules the iodine bridge exists and an infinite 1D coordination polymer chain along the b-axis further forms. At the same time, the N-H 3 3 3 I interactions28 [d((C1)I1H2A = 2.975 A˚] also contributes to form the 1-D chain. Structure of 6. Compound 6 (Figure 6) was produced by TpzT and Zn(NO3)2 3 6H2O in methanol. Single-crystal X-ray diffraction shows that the compound is 2,4,6-trimethoxy1,3,5-triazine, and all data are consistent with the reported structure of 2,4,6-trimethoxy-1,3,5-triazine by Krygowski.29 Compounds 5 and 6 indicate that Zn2þ or Cd2þ can act as a catalyst in certain nucleophilic substitution reactions, and in the following preparation of such coordination complexes, we avoided using a nucleophilic reagent (like alcohol) as the solvent. Taking complexes 1-4 discussed above into account, Hg(II) ions of coordination complexes 1-4 rarely adopt the similar five-coordination with trigonal bipyramidal geometry,30 which perhaps is caused by the specific structure of TpzT with perfect planarity and three trident coordination sites. Water molecules play an vital role in topological structures via different hydrogen bondings. On the basis of hydrogen bonding, S 3 3 3 S interactions and π-π stacking, a series of new 2-D or 3-D supramolecular complexes were formed. It has been further demonstrated that anions can play an important role in preparing coordination complexes, which can be divided into two key effects upon the structures of the final results. First, the anions can coordinate to metal

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Figure 2. (a) Coordination environments of Hg with the atom numbering scheme. (b) The 1-D framework of complex 2 showing π-π stacking along the a-axis. (c) The 2-D framework of complex 2 showing weak π-π stacking along the b-axis.

Figure 3. (a) Coordination environments of Hg with the atom numbering scheme. (b) The 1-D framework of complex 3 showing π-π stacking along the a-axis. (c) The 2-D framework of complex 3 showing π-π stacking along the b-axis.

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Figure 4. (a) Coordination environments of Hg with the atom numbering scheme. (b) The 1-D framework of complex 4 showing C-H 3 3 3 Cl and Hg-Cl coordination bond along the b-axis. (c) The 2-D framework of complex 4 showing C-H 3 3 3 Cl l interactions along the a-axis. (d) The 3-D architecture of complex 4 showing weak Hg 3 3 3 Cl interactions along the c-axis.

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Figure 5. The 1-D framework of complex 5 along the b-axis.

Figure 7. The model selected to calculate coordination-bond energies of Hg-N. Example: 7a for 2 and 7b for 4, 7c for compound A. Figure 6. The crystal structure of compound 6.

cations and obviously influence the coordination environment of the metal cations and hence the construction of framework. Taking Cl- for example, considering the difference of the inorganic component, the SCN is widely known as a pseudo-halogen which can be safely compared with the interactions of the other three complexes; the volume size of the four kinds of halogen anions are in a SCN > I > Br > Cl sequence. Comparing the angle of X-Hg-X (X for SCN, I, Br with the angle in sequence 152.06(6), 152.87(3), 155.61(3)), one can draw an apparent rule: the smaller the volume of halogen anion is, the bigger the angle of X-Hg-X becomes, and the smaller the coordination geometries distortion of trigonal bipyramid turns. The configuration of 1, 2, 3 is similar to the literature reported,31,32 but the configuration of 4 is different. On one hand, the ligand coordinated to HgCl2 hinders it from being the largest angle. On the other hand, in order to reach a stable configuration, in HgCl2, however, disobeying the above rule, the angle (152.89) approximates to NCS-Hg-SCN and I-Hg-I due to adopting the mercury bridge. Second, the anion can participate in forming different weak interactions to change the dimension, for S 3 3 3 S and H 3 3 3 N interactions in the 3D structure of 1, H 3 3 3 N and H 3 3 3 I interactions in the 2D structure of 2, and H 3 3 3 N and H 3 3 3 Br interactions in the 2D structure of 3. Additionally, all lengths of Hg-N bonds in the four complexes approach 2.70 A˚, and are larger than the sum of the Hg and N covalent radii (2.23 A˚) but are significantly shorter than the upper limit of 2.75 A˚ for the typical HgN,33,34 also perhaps caused by the specific structure of the TpzT ligand. Although the ligand provided three N to be

Table 4. Bond Length of Hg-N (A˚) and Bond Dissociation Energies (kJ/ mol) for 1-4 and Compound A complex

bond length of Hg-N(A˚)

BDE (kJ/ mol)

1 2 3 4 compound A

2.530 (4), 2.628 (4), 2.620 (4) 2.630 (6), 2.722 (7), 2.689 (7) 2.610 (5), 2.639 (5), 2.710 (5) 2.610 (4), 2.688 (5), 2.683 (5) 2.391(8), 2.402(9), 2.447(10)

177.33 104.06 101.68 100.81 144.25

coordinated, the N-atoms cannot come so close to the metal ion due to the strain of ligand, which is rare, and proved to be coordination-bond equal to the normal Hg-N bond length by DFT. DFT Calculations. In order to study the nature of the three long Hg-N bonds in each complex, we calculated bond dissociation energies (BDE) of Hg-N bonds taking compound A (the bond length of Hg-N: 2.391(8), 2.402(9), 2.447(10); see Supporting Information) with the same coordination mode as referenced through DFT calculations (ADF). SCN is widely known as a pseudohalogen which can be safely compared with BDE of the other three complexes 2-4. The models we chose are shown in Figure 7. Figure 7a,c stands for the selected fragments of coordination complexes 2 and compound A, respectively, so are complexes 1 and 3, but for complex 4, the coordination nature of the Hg-Cl bond and mercury bridge cannot be ignored in further calculations; the selected fragments of 4 are shown in Figure 7b. All were cut out directly from the CIF data to be further optimized. Further investigations are performed on the systems discussed in Computation Details. The outcomes obtained from DFT methods are listed in Table 4. The overall BDE including compound A exceed 100 kJ/mol and are of the same order of magnitude. We recognized a trend typically observed for BDE within 1-4, that is, the

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chloride: 100.81 kJ/mol, 101.68 kJ/mol (Br), and 104.06 kJ/ mol (I), 177.33 kJ/mol (SCN); that is to say, the larger the anion and BDE become, the steadier coordination complexes are. Conclusions (4)

Complexes 1-4 have been synthesized by self-assembly of the flexible ligand 2,4,6-tri (pyrazole-1-yl)-1,3,5-triazine (TpzT) with HgX2 (X = SCN I, Br, Cl) to yield a short series of new coordination complexes with a similar five-coordinated Hg(II). C-H 3 3 3 X, O-H 3 3 3 X hydrogen bonds, S 3 3 3 S bonds and π-π stacking play significant roles in the final crystal structures. 5 and 6 are obtained by self-assembly of L with CdI2 and Zn(NO3)2 3 6H2O, which testifies that TpzT and methanol can take place in nucleophilic substitution reactions in the presence of Zn2þ or Cd2þ. DFT calculations are performed to evaluate the nature of the long Hg-N bond lengths. The results show that BDE strongly depends on the anion on the basis of the same metal and ligand, viz, the larger the anion, the stronger BDE, the steadier the coordination complexes. This article provides useful information on the synthesis of the inorganic-organic hybrid materials. Acknowledgment. The work was supported by a grant for the National Natural Science Foundation of China (50703001, 20771001), the Natural Science Foundation of Anhui Province (070414188), Doctoral Program Foundation of the Ministry of Education of China, Education Committee of Anhui Province (2006KJ032A, KJ2009A52), Team for Scientific Innovation Foundation of Anhui Province (2006KJ007TD), Young Teacher Foundation of Institution of High Education of Anhui Province (2007jq1019), Ministry of Education and Person with Ability Foundation of Anhui University, Science and Technological Fund of Anhui Province for Outstanding Youth. We also wish to thank Dr. Yu-He Kan of University of Huaiyin Teachers College for his assistance with DFT computations. Supporting Information Available: Crystallographic information files. This material is available free of charge via the Internet at http://pubs.acs.org.

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Complexes and Density Functional Theory Calculations to Study Bond

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