Two Zinc Complexes Supported by in situ Formed Etheric Ligands

2019. 9 V ol. 38, No. 9 Chinese J. Struct. Chem. 1593─1599Two Zinc Complexes Supportedby in situ Formed Etheric Ligands①YANG Le a, b LIU Yong-Lu c ZHANG En-Sheng aCHEN Xiao-Li a GAO Lou-Jun a YANG Hua a②a (Laboratory of New Energy & New Function Materials, Shaanxi Key Laboratoryof Chemical Reaction Engineering, College of Chemistry and ChemicalEngineering, Yan’an University, Sha anxi 716000, China)b (College of Chemistry and Chemical Engineering,Xi’an University of Science and Technology, Xi’an 710054, China)c (College of Chemistry, Chemical Engineering and Materials Science,Soochow University, Suzhou 215123, China)ABSTRACT Two zinc complexes, [Zn(MPIP)Cl2] (1) and [Zn(EPIP)Cl2] (2), where MPIP= 1-(methoxymethyl)-3-(pyridin-2-yl)imidazo[1,5-a]pyridine and EPIP = 1-(ethoxymethyl)-3-(pyri- din-2-yl)imidazo[1,5-a]pyridine, were synthesized under solvothermal conditions. The etheric ligand MPIP was formed in situ via metal ligand reaction between (3-(pyridin-2-yl)imidazo[1,5- a]pyridin-1-yl)methanol (HPIPM) and methanol solvent. Similarly, the ligand EPIP was generated in situ from the reaction of HPIPM with ethanol solvent. The structures of 1and 2were characterized by X-ray single-crystal diffraction analysis. They are four-coordinated mononuclear complexes, and the Zn II ion of 1and 2displays distorted tetrahedral geometry. The photo- luminescent properties of 1 and 2 were investigated. Strong emissions were observed for both 1 and 2, which were ascribed as the intraligand (π-π*) fluorescent transitions. This paper provides a simple and efficient method for the synthesis of etheric compounds.Keywords:zinc complexes, in situ reactions, etheric ligands, photoluminescent propertyDOI: 10.14102/ki.0254-5861.2011-22941 INTRODUCTIONThe coordination compounds supported by imidazo[1,5-a]pyridine and its derivatives continue to receive intense attention due to the potential applications of these complexes on catalysis, lumi- nescent materials and pharmaceuticals[1-12]. Particu- larly, the research of the Zn II complexes based on imidazo[1,5-a]pyridine and its derivatives has attracted sustainable interest owing to the relevance of these complexes to luminescent materials[13-15] and antibacterial reagents[16]. Imidazo[1,5-a]pyri-dine and its derivatives possess two or more coordination donors, and exhibit aromatic nature. These properties render them as superior ligands for the synthesis of Zn II complexes.In this work, we employed (3-(pyridin-2-yl)imi- dazo[1,5-a]pyridin-1-yl)methanol(HPIPM) as ligand to synthesize Zn II complexes. Under solvo- thermal conditions, the reaction of HPIPM and ZnCl2Received 27 December 2018; accepted 28 April 2019 (CCDC 980656 for 1 and 978921 for 2)①Supported by the Natural Science Foundation of Shaanxi Province (2018JM2055, 2018JQ2079, 2018JQ2040)②Corresponding author. E-mail: yanghua_08@1594 YANG L. et al.: Two Zinc Complexes Supported by in situ Formed Etheric Ligands No. 9in methanol gave [Zn(MPIP)Cl2] (1). The etheric ligand MPIP was formed in situ via metal ligand reaction of HPIPM and the solvent MeOH. Treatment of HPIPM with ZnCl2in methanol generated [Zn(EPIP)Cl2] (2). Similarly, the etheric ligand EPIP was afforded in situ via the reaction between HPIPM and EtOH. It is well known that the Williamson method[17]is a commonly used approach for the preparation of eherate compounds. By employing Williamson method, an etherate compound can be produced via a reaction between an alcohol and an alkyl halide at higher temperature in the presence of alkali. Compared with the Williamson method, the present approach is more simple and efficient, giving ethers under a very mild condition. Herein, we report the syntheses, struc- tures and photoluminescent properties of com- pounds 1 and 2.2 EXPERIMENTAL2. 1 Materials and physical measurementsAll manipulations were performed under aerobic and solvothermal conditions using reagents and solvents as received. The C, H and N microanalyses were carried out with an Elementar Vario EL Ⅲelemental analyzer. FT-IR spectra were recorded from KBr pellets in the range of 400～4000 cm-1 ona BRUKER EQUINOX-55 spectrometer.2. 2 Syntheses of the complexes2. 2. 1 Synthesis of [Zn(MPIP)Cl2] (1)A mixture of HPIPM (0.0225 g, 0.10 mmol), ZnCl2(0.0136 g, 0.10 mmol) and MeOH (2 mL) was sealed in a Pyrex-glass tube (8mm × 10mm, 5 mL). The tube was heated at 80 °C for 2 days under autogenous pressure (Scheme 1). Cooling of the resultant solution to room temperature gave yellow crystals. The crystals were collected by filtration, washed with MeOH (2 mL) and dried in air. Yield: 45% based on HPIPM.Elemental Anal. Calcd. for C14H13Cl2N3OZn (375.56): C, 44.77; N, 11.19; H, 3.49%. Found: C, 44.42; N, 11.17; H, 3.35%. Selected IR data for 1(KBr, cm−1): 3150(w), 2922(w), 2878(m), 2818(m), 1601(s), 1488(s), 1443(m), 1376(s), 1273(m), 1113(s), 1017(m), 960(m), 776(m), 730(m), 682(m), 645(w).2. 2. 2 Synthesis of [Zn(EPIP)Cl2] (2)A mixture of HPIPM (0.0225 g, 0.10 mmol), ZnCl2 (0.0136 g, 0.10 mmol) and EtOH (2 mL) was sealed in a Pyrex-glass tube (8mm × 10mm, 5 mL). The tube was heated at 80 °C for 2 days under autogenous pressure (Scheme 1). Cooling of the resultant solution to room temperature gave yellow crystals. The crystals were collected by filtration, washed with EtOH (2 mL) and dried in air. Yield: 45% based on HPIPM. Elemental Anal. Calcd. for C15H15Cl2N3OZn(389.59): C, 46.24; N, 10.79; H, 3.88%. Found: C, 46.04; N, 10.38; H, 3.84%. Selected IR data for 2(KBr, cm−1): 3150(w), 2974(m); 2856(m), 1601(s), 1498(s), 1374(s), 1307(m), 1272(m), 1149(s), 1084(m), 1016(m), 888(m), 774(m), 730(m), 679(m), 644(w).Scheme 1. Syntheses of complexes 1 and 22. 3 Structure determinationThe data collections for 1 and 2 were carried out on a Bruker Smart ApexII diffractometer equipped with a graphite-monochromator utilizing Mo Kαradiation (λ = 0.71073)Å with an ω-2θ scan mode. The structures were solved by direct methods using SHELXS-97 and refined on F2using full-matrix least-squares with the SHELXL program[18, 19]. All2019 V ol. 38 Chinese J. Struct. Chem. 1595non-hydrogen atoms were refined anisotropically. The collected crystal data for the two structures are shown in Table 1, and their selected bond lengths and bond angles are listed in Table 2.Table 1. Crystallographic Data and Structure Refinement Information for 1 and 2 Complex 1 2Empirical formula C14H13Cl2N3OZn C15H15Cl2N3OZn Formula weight (g·mol-1) 375.56 389.59Temperature 296(2) K 296(2) KWavelength 0.71073 Å0.71073 ÅCrystal system Monoclinic MonoclinicSpace group P21/n P21/cUnit cell dimensions a = 8.4421(17) Åa = 9.1491(18) Åb = 10.838(2) Åb = 10.897(2) Åc = 17.277(4) Åc = 17.719(5) Åα = 90° α = 90°β = 100.74(3)° β = 109.57(3)° γ = 90° γ = 90°V olume (Å3) 1553.1(5) 1664.5(6)Z 4 4ρ(g∙cm-3) 1.606 1.555F(000) 760 792Crystal size (mm3) 0.4 ⨯ 0.4 ⨯ 0.1 0.4 ⨯ 0.3 ⨯ 0.2 Theta range for data collection 3.05° to 25.35° 3.01° to 25.00°Limiting indices –9≤h≤10 –10≤h≤8 –12≤k≤13 –12≤k≤9 –17≤l≤20 –20≤l≤21Reflections collected/unique 7266 / 2804 8211 / 2902 Data / restraints / parameters 2804 / 0 / 191 2902 / 1 / 146 GOOF 1.138 1.132R, wR (I > 2σ(I)) R = 0.0765 R = 0.0816 wR = 0.1718 wR= 0.2037R, wR (all data) R= 0.1213 R = 0.1213 wR = 0.2202 wR= 0.2282Largest diff. peak and hole (e·Å-3) 0.637 and –0.860 1.310 and –0.941 Table 2. Selected Bond Lengths (Å) and Bond Angles (°) for 1 and 21596 YANG L. et al.: Two Zinc Complexes Supported by in situ Formed Etheric Ligands No. 93 RESULTS AND DISCUSSION3. 1 Structural description 3. 1. 1 Structure of 1Single-crystal X-ray diffraction analysis indicates that complex 1 crystallizes in the monoclinic space group P 21/n . The molecule of 1 consists of one Zn II ion, one MPIP ligand, and two chloride ions (Fig. 1). The Zn II ion is four-coordinated by two nitrogen atoms from the MPIP ligand and two chloride ions, thus the central metal ion exhibits distorted tetra- hedron geometry. The bond lengths of Zn(1)–N(3), Zn(1)–N(1), Zn(1)–Cl(1) and Zn(1)–Cl(2) are 2.048(6), 2.086(6), 2.193(2) and 2.217(3) Å, respectively. The bond angles of Cl(1)–Zn(1)–Cl(2), Cl(1)–Zn(1)–N(1), N(1)–Zn(1)–N(3) and N(3)– Zn(1)–Cl(2) are 115.11(10), 111.38(19), 80.7(2) and 109.03(18)°, respectively.Two types of π···π stack interactions, namely, theinteraction between pyridine and imidazole of two head-to-tail imidazo[1,5-a]pyridin units, and the π···π stacking interaction between the imidazole of (pyridin-2-yl)imidazo motif and the adjacent pyridine ring, were determined. Two π···π stacking distances are both 3.515 Å. The molecules were linked by these π···π stack interactions to generate a 1-D chain structure (Fig. 2).The most intriguing feature of the complex is the presence of etherate ligand MPIP. Undoubtedly, the ligand was generated in situ by the reaction between the ligand HPIPM and methanol solvent. Solvo- thermal in situ metal ligand reactions have attracted the attention of researchers for many years due to their applications in crystal engineering and organic synthesis [20-26]. However, to the best of our knowledge, the synthesis of ethers by solvothermal in situ metal ligand reactions has never beenreported.Fig. 1.Molecular structure of 1Fig. 2. 1-D Chain structure of 1 created by π···π stacking interactions2019 V ol. 38 Chinese J. Struct. Chem. 15973. 1. 2 Structure of 2Single-crystal X-ray diffraction reveals that complex 2 crystallizes in monoclinic space group P21/c. As can be seen from Fig. 3, the structure of complex 2 is quite similar to that of 1. The Zn II ion is four-coordinated by two nitrogen atoms from the EPIP ligand and two chloride ions, and the central metal ion also displays a distorted tetrahedral geometry. The molecules were linked by π···π stack interactions to generate a 1-D chain structure (Fig. 4). It is worth to mention that the etherate ligand EPIP was also determined in complex 2, which indicated that the reaction between HPIPM and EtOH also occurred, revealing the wide substitute scope of this in situ reaction.Complexes 1and 2join a very small family of coordination complexes supported by imidazo[1,5- a]pyridine and its derivatives[1-12].Although there are three coordination atoms in MPIP and EPIP, they still adopt common two bidentate (N, N) coordination modes in 1 and 2.Fig. 3. Molecular structure of complex 2Fig. 4.1-D Chain structure of 2 created by π···π stack interactions3. 2 Luminescent properties of the ligandand complexes 1 and 2The solid-state luminescent properties of theHPIPM ligand, complexes 1and 2were investiga-ted at room temperature. As shown in Fig. 5, thestrongest emission peak for the HPIPM ligand isobserved at 490 nm upon excitation at 370 nm.When both compounds were excited at 410 nm, theemission maxima are found to be at 520 nm for 1and at 530 nm for2, respectively, which are redshifted relative to the HPIPM ligand. The red-shifted emissions of 1 and 2 may be ascribed as theintraligand (π-π*) fluorescent transitions[27]. Thepronounced fluorescence emissions of 1and 2reveal their potential applications in photolumine-scent materials.1598 YANG L. et al.: Two Zinc Complexes Supported by in situ Formed Etheric Ligands No. 94005006007008000.00.20.40.60.81.0E m i s s i o n (a .u .)Wavelength(nm)HPIPM 10 13Fig. 5. Room-temperature emission spectra for the ligand and complexes 1 and 2 in solid state4 CONCLUSIONTwo Zn II complexes of compositions [Zn- (MPIP)Cl 2] (1) and [Zn(EPIP)Cl 2] (2) (MPIP = 1- (methoxymethyl)-3-(pyridin-2-yl)imidazo[1,5-a]- pyridine, EPIP = 1-(ethoxymethyl)-3-(pyridin-2-yl) imidazo[1,5-a]pyridine) were synthesized and characterized. The etheric ligands MPIP and EPIP were formed in situ from the reactions of (3- (pyridin-2-yl)imidazo[1,5-a]pyridin-1-yl)methanol and corresponding solvents. The photoluminescent properties of 1 and 2 were investigated. The present work gives a simple method for the preparation of etheric compounds under mild conditions.REFERENCES(1)Chen, Y . M.; Li, L.; Chen, Z.; Liu, Y . L.; Hu, H. L.; Chen, W. Q.; Liu, W.; Li, Y . H. 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