Journal of Molecular Structure 1118 (2016) 367e371
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Halide effects on formation and physicochemical properties of mercury(II) complexes containing Y-type tridentate N-donor Eunkyung Choi a, Nam Kwon b, Jeong Gyun Kim a, Ok-Sang Jung a, *, Young-A Lee b, ** a b
Department of Chemistry, Pusan National University, Pusan 46241, Republic of Korea Department of Chemistry, Chonbuk National University, Jeonju 54896, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 February 2016 Received in revised form 11 April 2016 Accepted 13 April 2016 Available online 16 April 2016
Self-assembly of HgX2 (X ¼ Cl, Br, and I) with Y-type 2,6-bis[(2-isonicotinoyloxy-5-methylphenyl) methyl]-1-isonicotinoyloxy-4-methylbenzene (L) yields 2D consisting of alternate prismatic P- and Mhelical-linked-layers, 1D consisting of P- and M-helices, and simple 2D sheet in a unique Y-type mode, respectively. The L/Hg(II) ratio of each product (3/3 for Cl; 2/3 for Br; 1/3 for I) is dependent on the nature of the halide anions. The coordinating environments around of Hg(II) ion approximate to a square pyramid for Cl, a square planar and a distorted tetrahedral geometry for Br, and distorted tetrahedral arrangement for I, respectively. Photoluminescence wavelengths are strongly depending on the halide anions, and coordination ability to L is in the order of X ¼ Cl > Br > I. Such physicochemical properties were explained by electronic and steric natures of halide anions. © 2016 Published by Elsevier B.V.
Keywords: Coordination polymers Halide effects Mercury complexes Prismatic helices Y-type tridentate
1. Introduction Assemblies of desirable molecular topology via suitable combination of metal cations as an angle component and organic donors as a rigid spacer have been a hot issue for the past decade, owing to their task-specific applications in the fields of gas adsorption, mixed-valence system, photo-induced electron or energy transfer, magnetic exchange, semiconductors, catalysts, luminescent chemosensors, ion-exchangers, and super-array [1e10]. In particular, various new types of organic donors have been employed for the tailor-made construction of functional skeletons. To date, tridentate donors have generated a variety of coordination skeletons including coordination cages or triangular module coordination polymers owing to flexibility in bridging ability, bite angles, and conformation of the tridentate donor ligands [11e18], but the systematic coordination polymers containing interesting Y-type tridentate ligands are relatively rare [5]. Meanwhile, (counter)anions, directly and indirectly, play significant roles in formation and function of molecular skeletons owing to their non-innocent features such as negative charge, polarizability, size, geometry, strong solvent effects, weak interactions,
* Corresponding author. ** Corresponding author. E-mail addresses:
[email protected] (O.-S. Jung),
[email protected] (Y.-A. Lee). http://dx.doi.org/10.1016/j.molstruc.2016.04.043 0022-2860/© 2016 Published by Elsevier B.V.
and pH dependence [19e23]. For instance, the ubiquitous Cl, Br, and I anions have both similarities and differences in shape, charge, size, coordinating ability, and metallophilicity [19]. In order to scrutinize the direct roles of halide anions and to confirm the proof-of-concept experiments on complexation of a Ytype tridentate N-donor ligand, self-assembly of HgX2 (X ¼ Cl, Br, and I) with 2,6-bis[(2-isonicotinoyloxy-5-methylphenyl) methyl]-1-isonicotinoyloxy-4-methylbenzene (L) was carried out. Herein we report the halides' role and driving force behind the 1D and 2D coordination polymerization along with their physicochemical properties. Their different coordination chemistry including mole ratio, coordination numbers, and related photophysical properties has been discussed. The environmently problematic mercury(II) ion utilized herein has been known to act as various directional central metal units such as linear, T-shaped, tetrahedral, and octahedral geometries [24e26]. 2. Experimental 2.1. Materials and measurements All commercialized chemicals including HgX2 (X ¼ Cl, Br, and I) were purchased from Aldrich, and used without further purification. 2,6-Bis[(2-isonicotinoyloxy-5-methylphenyl)methyl]1-isonicotinoyloxy-4-methylbenzene (L) was prepared according
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to the literature [5]. Elemental microanalyses (C, H, N) were performed on solid samples by the Pusan center, KBSI, using a Vario-EL III. Thermal analyses were undertaken under a nitrogen atmosphere at a scan rate of 10 C/min using a Labsys TGA-DSC 1600. Infrared spectra were obtained on a Nicolet 380 FT-IR spectrometer with samples prepared as KBr pellets. 1H (300 MHz) NMR spectra were recorded on a Varian Mercury Plus 300. Photoluminescence spectra were acquired on a Hitachi F-7000. 2.2. Synthesis of [HgCl2(L)],2CH2Cl2 (1) A methanol solution (2 mL) of HgCl2 (0.05 mmol, 15.6 mg) was layered onto a dichloromethane solution (2 mL) of L (0.05 mmol, 33.2 mg). After 5 days, colorless crystals suitable for single crystal X-ray diffraction were obtained in an 82% yield (40.0 mg) based on Hg(II) salt. m. p. 250 C (dec.). Anal. Calcd for C43H37N3O6Cl6Hg: C, 46.74; H, 3.37; N, 3.80%. Found: C, 45.90; H, 3.28; N, 3.85%. IR (KBr, cm1): 1744 (s, n(C]O)), 1559 (w), 1506 (w), 1415 (m), 1273 (s), 1260 (m), 1195 (m), 1129 (w), 1062 (m), 877 (w), 854 (w), 813 (w), 754 (m), 697 (m), 673 (w).
Table 1 Crystal data and structure refinement for 1e3. 1 Formula C43H37N3O6Cl6Hg Mw 1105.05 Cryst. system Triclinic Space group P1 a (Å) 8.9314(3) b (Å) 12.8564(4) c (Å) 20.9226(7) a ( ) 72.540(2) b ( ) 88.950(2) g ( ) 74.408(2) V (Å3) 2202.34(1) Z 2 3 1.666 dcalcd (g/cm ) 1 m (mm ) 3.909 Rint 0.0363 F (000) 1092 GoF on F2 1.088 R1 [I > 2s(I)]a 0.0473 b wR2 (all data) 0.1253 P P a R1 ¼ jjFojjFcjj/ jFoj. P P b wR2 ¼ ( w (F2oF2c )2/ wF2o)1/2.
2
3
C84H78N6O16Cl4Br6Hg3 2650.55 Triclinic P1 8.8491(3) 16.4620(6) 16.7092(5) 99.204(2) 101.426(2) 96.218(2) 2330.35(1) 1 1.889 7.680 0.0504 1270 1.034 0.0658 0.2170
C41H33N3O6I6Hg3 2026.87 Monoclinic P21/c 17.2464(3) 12.8289(2) 27.4204(4) 90 125.851(1) 90 4917.42(1) 4 2.738 13.155 0.1277 3624 1.013 0.0795 0.1802
2.3. Synthesis of [Hg3Br6(L)2],4H2O,2CH2Cl2 (2) 3. Results and discussion An acetonitrile solution (2 mL) of HgBr2 (0.06 mmol, 21.6 mg) was layered onto a dichloromethane solution (2 mL) of L (0.04 mmol, 26.5 mg). After 3 days, colorless crystals suitable for single crystal X-ray diffraction were obtained in an 80% yield (38.5 mg) based on Hg(II) salt. m. p. 215 C (dec.). Anal. Calcd for C84H78N6O16Cl4Br6Hg3: C, 38.06; H, 2.97; N, 3.17%. Found: C, 38.20; H, 3.01; N, 3.12%. IR (KBr, cm1): 1745 (s, n(C]O)), 1606 (w), 1564 (w), 1495 (w), 1469 (w), 1416 (m), 1325 (w), 1272 (s), 1194 (s), 1130 (m), 1087 (w), 1062 (m), 1009 (w), 876 (w), 851 (w), 809 (w), 754 (m), 698 (w), 678 (w).
3.1. Synthesis Self-assembly of HgX2 (X ¼ Cl, Br, and I) with 2,6-bis[(2isonicotinoyloxy-5-methylphenyl)methyl]-1-isonicotinoyloxy-4-
2.4. Synthesis of [Hg3(mI)3I3(L)] (3) A methanol solution (1 mL) and acetonitrile solution (0.5 mL) of HgI2 (0.06 mmol, 9.1 mg) was layered onto a chloroform solution (1 mL) of L (0.02 mmol, 13.3 mg). After 7 days, colorless crystals suitable for single crystal X-ray diffraction were obtained in an 81% yield (18.1 mg) based on Hg(II) salt. m. p. 205 C (dec.). Anal. Calcd for C41H33N3O6I6Hg3: C, 24.30; H, 1.64; N, 2.07%. Found: C, 24.20; H, 1.66; N, 2.10%. IR (KBr, cm1): 1754 (m, n(C]O)), 1736 (s, n(C]O)), 1604 (w), 1563 (w), 1498 (w), 1472 (w), 1415 (m), 1324 (w), 1282 (s), 1269 (s), 1195 (s), 1137 (w), 1114 (w), 1060 (m), 808 (w), 757 (m), 697 (w), 680 (w). 2.5. Crystal structure determinations X-ray data were collected on a Bruker SMART automatic diffractometer with a graphite-monochromated Mo Ka (l ¼ 0.71073 Å) and a CCD detector at ambient temperature. Thirtysix frames of two-dimensional diffraction images were collected and processed to obtain the cell parameters and orientation matrix. The data were corrected for Lorentz and polarization effects. Absorption effects were corrected by the multi-scan method (SADABS) [27]. The structures were solved by the direct method (SHELXS 97) and refined by full-matrix least squares techniques (SHELXL 97) [28]. The non-hydrogen atoms were refined anisotropically, and hydrogen atoms were placed in calculated positions and refined only for the isotropic displacement parameters. The crystal parameters and procedural information corresponding to the data collection and structure refinement are listed in Table 1.
Scheme 1. Synthetic procedure of 1 (X ¼ Cl), 2 (X ¼ Br), and 3 (X ¼ I).
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methylbenzene (L) yields colorless crystals suitable for X-ray single crystallographic analyses as depicted in Scheme 1. Elemental analytical results and IR spectra were consistent with formation of each skeletal structure (Fig. S1). The self-assembly reactions were originally carried out in the 1:1 mol ratio of Hg(II):L, but the mercury(II) products were obtained as a 2D consisting of 3:3 adducts (Hg(II):L) for Cle, a 1D of 3:2 adducts for Bre, and a 2D coordination polymers of 3:1 adducts for I, respectively, presumably owing to the different electronic and steric nature of halide anions. Such results show a significant relationship between the coordination ratios and the anion sizes [29]. That is, formation of each product was not significantly affected by the mole ratio, but by the nature of halide anions. Furthermore, all of the reactions afforded unique coordination polymeric species which show noteworthy differences in the coordination geometries, bond lengths, and molecular dimension in addition to the M/L ratios. In contrast, all structures with different topological skeletons preserve a rigid Y-type conformation in the crystalline state, which will be discussed in detail. In this light, the mercury(II) coordination polymers' formation might be attributable to the intrinsic properties of the rigid Ytype conformation and coordinating ability between Hg(II) and Ndonor. All of the products were dissociated in N,N-dimethylformamide and dimethyl sulfoxide, but were insoluble in acetone, acetonitrile, chloroform, dichloromethane, and n-hexane. They are stable for several days even in aqueous suspensions. Characteristic C]O vibration modes appear in the range of 1736e1754 cm1, respectively (Fig. S1). The 1H NMR spectrum of the sample was measured in Me2SO-d6 in order to confirm the solvate molecules and dissociated L even though the coordination polymers were fully dissociated (Fig. S2). 3.2. Crystal structures The crystal structures were depicted in Figs. 1 and 2, and their relevant bond lengths and angles are listed in Table 2. The skeleton of [HgCl2(L)],2CH2Cl2 (1) (Hg(II):L ¼ 3:3) is 2D consisting of alternate prismatic P-helix-linked-layer and M-helix-linked-layer (P-, right-handed; M-, left-handed). The local geometry around the Hg(II) ion approximates a square pyramidal arrangement with N(3) an apical position (HgeN ¼ 2.491(6) Å) and with two nitrogen donors (HgeN ¼ 2.621(5); 2.662(5) Å) from two L and two chloride anions (HgeCl ¼ 2.3659(2); 2.3695(2) Å). Two side arms of L connects two Hg(II) ions in a prismatic-helical fashion, and the central arm of L is linked to a neighbor prismatic helices to form a 2D, with the prismatic helical Hg,,,Hg separated-pitch of 8.9314(3) Å. For [Hg3Br6(L)2],4H2O,2CH2Cl2 (2), two L connect three Hg(II) ions in a mirror image in a twisted Y-type mode to form a 1D (Hg(II):L ¼ 3:2) consisting of two prismatic P- and M-helices (pitch ¼ 8.8491(3) Å). A central arm of L acts as a monodentate donor to give a square planar geometry of Hg(II) (N(2)eHg (2) N(2)’ ¼ 180.0(2) ; Hg(2)eN ¼ 2.680(1) Å) and two bromide (Br(1) eHg(2)Br(2)’ ¼ 180.0(2) ; Hg (2)Br ¼ 2.381(3) Å), and N-donors of two side arms act as a helical moiety to give a distorted tetrahedral Hg(II) ion. Thus, two kinds of Hg(II) geometries exist in the crystalline state. The crystal structure of [Hg3(mI)3I3(L)] (3) shows the 3:1 mol ratio of Hg(II) and L. L connects three Hg(II) ions in a Y-type fashion to form normal 2D with two bridged iodide. The local geometry around the Hg(II) ion approximates a severely distorted tetrahedral arrangement with one N-donor (Hg(II)eN ¼ 2.405(1)e2.486(1) Å) from L, two bridged iodides, and one terminal iodide. The distortion may be partly attributed to the bulky methyl group of L. There are three Hg(II) unit in an asymmetric unit. The terminal Hg(II)eI bond lengths are in the range of 3.0746(1)e3.2881(1) Å while bridged HgeI lengths are in the range of 2.6105(1)e2.6395(1) Å [30,31]. All
Fig. 1. ORTEP drawings with anisotropic displacement parameters at 20% probability and coordinating environments (inset) of 1 (a), 2 (b), and 3 (c). Hydrogen atoms and solvate molecules were omitted for clarity.
solvate molecules fill the appropriate space of the unit cell without any significant interaction with each skeleton. 3.3. Construction principle and coordination chemistry Self-assembly of HgX2 with a Y-type tridentate N-donor produces a variety of interesting coordination polymers including a unique prismatic helical motif, M/L ratios, molecular dimension, and coordination geometry (Fig. 1) depending on halide anions (Scheme 1). Their products' formation was considerably affected by halide anions attached to Hg(II) species. First of all, the reactions afford the different L/M ratio coordination polymers in the order of Cl > Br > I. The ratios are exactly coincident with the reverse order of anion size. The L/M ratios as well as the local geometries of the products appear to be delicately associated with the nature of halide anions as depicted in Fig. 3. We attributed the mole ratio to
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E. Choi et al. / Journal of Molecular Structure 1118 (2016) 367e371 Table 2 Selected bond lengths (Å) and angles ( ) for 1e3. 1 Hg(1)eCl(2) Hg(1)eCl(1) Hg(1)eN(3)a Hg(1)eN(2)b Hg(1)eN(1) 2 Hg(1)eN(3)a Hg(1)eN(1) Hg(1)eBr(1) Hg(1)eBr(2) Hg(2)Br(3) Hg(2)eN(2) 3 Hg(1)eN(2) Hg(1)eI(2) Hg(1)eI(3) Hg(1)eI(1) Hg(2)eN(1)a Hg(2)eI(5)d Hg(2)eI(4) Hg(2)eI(3) Hg(3)eN(3)a Hg(3)eI(6) Hg(3)eI(1) Hg(3)eI(5) a b c d e
2.3659(2) 2.3695(2) 2.491(6) 2.621(5) 2.662(5)
Cl(2)eHg(1)Cl(1) Cl(1)eHg(1)eN(3)a N(3)aeHg(1)N(2)b N(3)aeHg(1)N(1) N(2)bHg(1)N(1)
169.85(7) 95.18(1) 98.4(2) 103.73(2) 157.8(2)
2.427(1) 2.452(1) 2.4634(2) 2.4638(2) 2.381(3) 2.680(1)
N(3)aeHg(1)eN(1) Br(1)eHg(1)eBr(2) Br(3)eHg(2)Br(3)c Br(3)eHg(2)N(2) N(2)ceHg(2)eN(2)
97.3(3) 151.63(6) 180.0(1) 89.8(3) 180.0(2)
2.405(1) 2.6168(1) 2.6293(1) 3.2881(1) 2.486(1) 2.6259(1) 2.6395(1) 3.0746(1) 2.451(1) 2.6105(1) 2.6386(1) 3.3211(1)
N(2)eHg(1)eI(2) I(2)eHg(1)I(1) I(3)eHg(1)I(1) N(1)aHg(2)eI(4) I(5)dHg(2)eI(3) I(4)eHg(2)I(3) N(3)aHg(3)eI(6) N(3)aHg(3)eI(1) I(1)eHg(3)I(5) Hg(3)eI(1)Hg(1) Hg(1)eI(3)Hg(2) Hg(2)eI(5)eHg(3)
107.7(3) 94.06(4) 90.11(4) 101.4(3) 99.64(4) 94.84(4) 104.2(3) 97.5(3) 90.74(4) 87.83(4) 96.98(4) 95.94(4)
xþ1,y,z. xþ1,yþ1,z. xþ3,yþ2,z. x,yþ1,z. x,y1,z.
Fig. 2. Packing diagrams of 1 (a), 2 (b), and 3 (c). Red and blue arrows denote lefthanded M-helices and right-handed P-helices, respectively.
the felicitous “size influence” rather than “electronic effect”. Plenty of chemistry including topology, coordination ratios, and coordination numbers may be attributed to both the coordinating nature of unique Y-type tridentate ligand and a variety of coordination geometry of Hg(II) ion. Size and electronic effects of halide anions is another element to decide the local geometry around the Hg(II) ion as well as the mole ratio. For 1, the shorter bond of apical Hg(II)eN rather than basal Hg(II)eN bonds can be explained by the different s-orbital distribution of the hybrid orbitals. For 2, Hg(II)eBr bond length is sometimes shorter than Hg(II)eN length. For 3, terminal Hg(II)eI is much longer than bridged Hg(II)eI bond, indicating that the terminal iodide is relatively higher ionic bond character. Formation of various flexible bond lengths have been observed in many references [30,31]. The square planar geometry around Hg(II) in 2 is unusual case [30]. Although the roles of solvated molecules in construction of each topology were not clarified yet, effects on the solvent cocktail used in this assembly procedure is not so significant. According to a
Fig. 3. Correlation between the anions' ionic radii and the L/M ratio along with the dimensions of 1, 2, and 3.
preliminary coordination test, the coordination ability of the three Hg(II) halides with L is in the order of HgCl2 > HgBr2 > HgI2, owing presumably to difference in Lewis acidity and steric hindrance of mercury (II) dihalide species. 3.4. Physicochemical properties The thermogravimetric results of 1, 2, and 3 were plotted in Fig. S3. As is apparent, the skeletal structures were thermally stable up to 250, 215, and 205 C, respectively. For 1, the solvate dichloromethane molecules evaporate in the range of 25e110 C. For 2, evaporation of solvate molecules requires the wide range of 25e200 C, due to a mixture of dichloromethane and water molecules. At 700 C, the thermal residues did not exist, owing to evaporation of mercury residue. The photoluminescence (PL) properties of the present three
E. Choi et al. / Journal of Molecular Structure 1118 (2016) 367e371
Foundation of Korea 2013R1A1A3013731).
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[MEST]
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Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.molstruc.2016.04.043. References
Fig. 4. Solid-state PL spectra (lex ¼ 254 nm) of L (black), 1 (red), 2 (blue), and 3 (green).
Hg(II) coordination polymers along with L were investigated, as depicted in Fig. 4. In particular, Hg(II) coordination compounds with aromatic ligands have received much attention for the development of hybrid photoluminescent materials [32,33]. L displays solid state emission bands at 406 and 465 nm originated from the ligand-centered p*p and np transition in the solid-state (lex ¼ 254 nm), respectively, along with the shoulder band at 361 nm. 1 exhibits intense blue PL bands centered at 401 and 466 nm (lex ¼ 254 nm). 2 shows a weak emission with lmax at 413 and 467 nm. In contrast, 3 gives a single PL signal at 468 nm. The PL intensity corresponding to p*p transition is in the order of 1 > 2 > 3, revealing the significant shift relative to that (406 nm) of L, which involve charge transfer from ligand-to-metal (LMCT) [34,35]. The emission intensity and band shift strongly depends on the anions. Why does the PL intensity of the present Hg(II) compounds depend on the volume of halide anions? The exact anion-related enhancement of LMCT in this system is not yet, though most likely it is associated with the electrostatic interaction between the Hg(II) ion and the anion. 4. Conclusion Self-assembly of HgX2 with unusual Y-type tridentate L yields plenty of chemistry on mercury(II) coordination polymers, which is a systematic a proof-of-concept experiment example on Y-type ligand. This system shows significant halide effect on coordination polymerization and physicochemical properties. Furthermore, their PL wave length and intensity are sensitive to the nature of halide anions. A linear relationship between the ratio of L/Hg(II) and the bulkiness of halide anions was clearly observed. More systematic research on Hg(II) coordination chemistry, including modification of the related ligands, will provide more detailed information on the rational development of functional mercury coordination molecular materials sensitive to the external stimuli. Acknowledgments This work was supported financially by the National Research
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