In Situ Ligand Modification Strategy for the Construction of One-, Two

Nov 1, 2017 - Synopsis. We report the synthesis, structures, and properties of three heterometallic-iodides driven by in situ N-methylation of polypyr...
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Article Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX

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In Situ Ligand Modification Strategy for the Construction of One‑, Two‑, and Three-Dimensional Heterometallic Iodides Ai-Huan Sun,† Jie Pan,† Song-De Han,† Xu-Yan Xue,§ Qi Wei,† Jin-Hua Li,† and Guo-Ming Wang*,† †

College of Chemistry and Chemical Engineering, Qingdao University, Shandong 266071, People’s Republic of China College of Physics, Qingdao University, Shandong 266071, People’s Republic of China

§

S Supporting Information *

ABSTRACT: Three heterometallic iodides featuring the novel in situ modified ligands N,N′,N″-trimethyl-2,4,6-tris(4-pyridyl)-1,3,5-triazine (Me3tpt3+), N,N′-dimethyl-2,4,6-tris(4-pyridyl)-1,3,5-triazine (Me2tpt2+), and N-monomethyl-2,4,6-tris(4-pyridyl)-1,3,5-triazine (Metpt+), [Pb3CuI10(Me3tpt)] (1), [Pb5Cu2I16(Me2tpt)2] (2), and [Pb3Cu6I14(Metpt)2] (3), were synthesized. Compound 1 exhibits a chain structure, in which the Pb4I16 units are connected by the CuI3 units. The negative charge of the resulting chain is balanced by the cationic Me3tpt3+ groups. 2 features a layer structure, in which the Pb−I chains are connected by the dimeric Cu2 units. The anionic layer is decorated by the Me2tpt2+ motifs via coordinating to the intralayer Cu(I) ions. 3 displays a 3D framework structure, in which the inorganic layer with an 18-membered ring is composed of the strictly alternating arrangements of trimeric Pb3 units and hexameric Cu6 units. The adjacent inorganic layer is further connected by a Metpt+ linker to form the final 3D hybrid framework. It is notable that the in situ N-methylation reaction for tpt has taken place and the resultant motif (Me3tpt3+ for 1, Me2tpt2+ for 2, and Metpt+ for 3) is captured within the corresponding structure. More importantly, the structural diversities from low-dimensional chain and layer to high-dimensional framework is accomplished via the (partial) N-methylation of tripyridine motifs in the heterometallic iodide systems. Our studies offer a new coordination mode of tripyridine motif (N-coordination together with N-methylation) and provide a general strategy to integrate the polypyridine motifs and heterometallic halide systems to generate intriguing hybrid structure and investigate the potential structure-related properties. The UV−vis spectra show that the band gaps for 1−3 are 1.48, 1.35, and 1.34 eV, respectively. Their thermal stabilities have also been studied.

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INTRODUCTION Metal halides have attracted great interest from researchers because of their fascinating structures and potential applications in a myriad of domains such as phase transition photoluminescence and semiconductor solids.1−5 The integration of distinct metal and halide ions, especially for I−, directed by various structure-directing agents (SDAs) (or template) have given birth to various desirable structures with captivating properties.6−15 Representative cases include metal halide with perovskite structures, 6−10 haloantimonates(III), and halobismuthates(III).11−15 Among the various homometallic halides, the copper(I) halide and lead(II) halide families feature rich structural characteristics and structure-related properties.16−20 The flexible coordination numbers of metal ions (from 2 to 4 for Cu(I); from 3 to 6 for Pb(II)) and halides (from terminal to μ2 and up to μ8 bridging), together with suitable SDAs, provides extra freedom in generating intriguing Cu(I)/Pb(II) halides.16−20 Thus, the marriage of Cu(I) halide and Pb(II) halide families may give birth to heterometallic Cu(I)−Pb(II) halides with novel structures and potentially interesting structurerelated physical properties. It has been corroborated that the introduction of organoamines to metal halide systems has a © XXXX American Chemical Society

significant role in the structural diversity. An overview of the literature indicated that the organic amines usually crystallize in the hybrid metal halide in three kinds of forms. The first is the protonated form, serving as a counterion and interacting with the metal halide host by electrostatic/supramolecular interactions.21,22 The second is coordinated to metal ions to form a hybrid framework,23,24 which is well reflected by extended frameworks based on the Cu(I) iodide clusters and DABCO.25,26 In comparison with the inorganic architecture based on the pure connection of metal ions and halide, the decoration of the organic moieties significantly diversify the framework constituents. The third is coordinated to the metal ions to form metal−organic complexes as SDAs to direct the assembly.27,28 As a rigid and neutral tripyridine motif, 2,4,6-tris(4-pyridyl)1,3,5-triazine (tpt) has been well-utilized in the construction of crystalline hybrid materials.29−31 As an electron-deficient organic molecule, tpt holds great promise in the construction of molecular electronic devices.32,33 In comparison to those tptbased hybrid materials, achievements with the metal halide Received: July 19, 2017

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DOI: 10.1021/acs.inorgchem.7b01807 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Crystal Data for Compounds 1−3 formula Mr space group cryst syst a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z F(000) Dc (g cm−3) μ (mm−1) Rint no. of collected rflns no. of unique rflns GOF on F2 R1, wR2 (I > 2σ(I))a,b R1, wR2 (all data) a

1

2

3

C21H21N6CuPb3I10 2311.55 P1̅ triclinic 11.3121(11) 12.5869(15) 16.2313(19) 100.176(10) 95.361(9) 104.207(9) 2182.4(4) 2 1988 3.518 19.112 0.2047 11958 7680 0.954 0.1009, 0.2428 0.2192, 0.3399

C40H36N12Cu2Pb5I16 3878.36 P1̅ triclinic 7.878(13) 16.06(3) 16.08(3) 108.931(18) 97.139(10) 95.15(2) 1891(5) 1 1676 3.406 18.208 0.2024 16066 6643 1.019 0.0920, 0.2358 0.1276, 0.2673

C38H30N12Cu6Pb3I14 3434.26 P1̅ triclinic 8.5728(8) 13.2846(13) 15.9017(17) 112.193(10) 94.642(8) 95.440(8) 1655.8(3) 1 1504 3.444 16.046 0.0416 14053 10358 1.022 0.0647, 0.1354 0.1432, 0.1787

R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = {∑[w(Fo2 − Fc2)2]/∑w(Fo2)2}1/2.

heterometallic iodide layer featuring an 18-membered ring is composed of the strict arrangements of trimeric Pb3 units and hexameric Cu6 units.The adjacent inorganic layer is further connected by Metpt+ linkers to form the resulting 3D hybrid framework. Notably, the reactant tpt was transferred in situ to Me3tpt3+ in 1, Me2tpt2+ in 2, and Metpt+ in 3 via the direct methylation reaction between tpt and CH3OH. In comparison with the Me3tpt3+ moieties, the available N sites of Me2tpt2+ and Metpt+ were coordinated to the Cu(I) ions to participate in the decoration or construction of the hybrid framework. The structural diversities from a low-dimensional chain and layer to a high-dimensional framework is realized via the (partial) Nmethylation of tripyridine motifs in the heterometallic iodide systems. This, to the best of our knowledge, is the first case of partial N-alkylation of the tripyridine motifs.

derived from tpt still remain undeveloped. Other than a few isolated cases bearing tpt in the protonated form,34,35 there are very few tpt-based metal halides with extended structures.36 Given these considerations mentioned above and as a continuing work of our studies on the metal halide derived from tpt derivatives,36,37 we attempted to explore the copper(I)/lead(II)/halide/tpt system, taking into account the following considerations. (a) Paralleling the well-explored homometallic halide mentioned above, the heterometallic halides have also received focus because the integration of distinct metal ions in one framework may give novel molecular materials.38−40 (b) The utilization of dipyridine motifs to construct novel metal halides with optoelectronic properties has been broadly explored.41−44 In comparison to the metal/ halide/dipyridine materials, the assembly of tritopic pyridyl motifs with metal halides is still undeveloped and exciting results may be expected. (c) Considering the distinct coordination modes between Cu(I) and Pb(II) ions and the great achievements in the corresponding homometallic halide system, together with the intrinsic advantage of the tritopic pyridyl motif tpt, it is feasible to synthesize tpt-based heterometallic halides with captivating structures and potential structure-related properties. Herein, we report three heterometallic iodides driven by in situ partially N-methylated tpt derivatives (N,N′,N″-trimethyl2,4,6-tris(4-pyridyl)-1,3,5-triazine (Me3tpt3+), N,N′-dimethyl2,4,6-tris(4-pyridyl)-1,3,5-triazine (Me2tpt2+), and N-monomethyl-2,4,6-tris(4-pyridyl)-1,3,5-triazine (Metpt + )), [Pb3CuI10(Me3tpt)] (1), [Pb5Cu2I16(Me2tpt)2] (2) ,and [Pb3Cu6I14(Metpt)2] (3). Compound 1 displays a chain structure with the Pb4I16 subunits linked by the CuI3 units. The negative chain is balanced by the cationic Me3tpt3+. Compound 2 exhibits a layered structure, in which the Pb−I chains are connected by the dimeric Cu2 units. The negative layer is balanced by the cationic Me2tpt2+ motifs via coordination to the intralayer Cu(I) ions. Compound 3 shows a 3D hybrid framework structure, in which the inorganic

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EXPERIMENTAL SECTION

Materials and Physical Measurements. The tpt was synthesized according to the reported method.29 The other chemicals were analytical grade and were utilized directly. The elemental analyses (EA) were measured on a Perkin-Elmer 240C analyzer. IR spectra were measured on a TENSOR 27 (Bruker) FT-IR spectrometer with KBr pellets. Powder X-ray diffraction (PXRD) spectra were measured on a Bruker D8 FOCUS diffractometer with a Cu-target tube and a graphite monochromator. The simulated PXRD spectra were derived from the single-crystal X-ray diffraction (SCXRD) data, and the diffraction-crystal module of the Mercury program is available at http://www.iucr.org. Thermogravimetric (TG) analysis was measured on a Rigaku Thermo plus EVO2 TG-DTA8121 analyzer in an air atmosphere. Ultraviolet−visible (UV−vis) spectra were measured on a Rigaku UV-3100 spectrophotometer. Computational Description. Single-crystal structural data of the compounds were used for the theoretical calculations. The electronic structure calculations were performed by first-principles calculations employing the CASTEP code with a plane-wave cutoff energy of 351.0 eV.45 The numerical integration of the Brillouin zone was performed by a 2 × 2 × 2 Monkhorst−Pack k-point sampling. The local density approximation (LDA) was adopted with the spin−orbital coupling (SOC) effects being considered. In these atoms, H 1s1, C 2s22p2, N B

DOI: 10.1021/acs.inorgchem.7b01807 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 1. In Situ N-Methylation of tpt

2s22p3, I 5s25p5, Pb 6s26p2, Cu 3d104s1 were treated as valence electrons. Synthesis of [Pb3CuI10(Me3tpt)] (1) and [Pb5Cu2I16(Me2tpt)2] (2). Compounds 1 and 2 were obtained in the form of a mixed crystal with differences in shape. A mixture of CuI (0.380 g, 0.20 mmol), PbI2 (0.460 g, 0.10 mmol), tpt (0.022 g, 0.070 mmol), HI (0.12 mL, 45%), and MeOH (5 mL) was sealed in a Teflon-lined autoclave (25 mL). The resulting mixture was stirred for about 2 h at room temperature, heated to 160 °C for 7 days, and then cooled to room temperature in 6 h. The black rod-shaped crystal of 1 was obtained in a yield of ca. 35% based on tpt. Anal. Calcd for C21H21N6CuPb3I10 (2311.55): C, 10.91; N, 3.64; H, 0.92. Found: C, 10.65; N, 3.96; H, 1.32. IR (cm−1) for 1: 3438 (s), 2921 (m), 2861 (w), 2364 (m), 1633 (s), 1519 (s), 1376 (s), 1085 (m), 804 (w), 594 (w). The black rod-shaped crystal of 2 was obtained in a yield of ca. 40% based on tpt. Anal. Calcd for C40H36N12Cu2Pb5I16 (3878.36): C, 12.39; N, 4.33; H, 0.94. Found: C, 12.57; N, 4.02; H, 1.23. IR (cm−1) for 2: 3430 (s), 2927 (m), 2854 (w), 2360 (m), 1637 (s), 1513 (s), 1386 (s), 1093 (m), 800 (w), 590 (w). Synthesis of [Pb3Cu6I14(Metpt)2] (3). A mixture of CuI (0.380 g, 0.20 mmol), PbI2 (0.460 g, 0.10 mmol), tpt (0.022 g, 0.070 mmol), HI (0.20 mL, 45%), H2O (4 mL), and MeOH (1 mL) was sealed in a Teflon-lined autoclave (25 mL). The resulting mixture was stirred for about 2 h at room temperature, heated to 145 °C for 6 days, and then cooled to room temperature in 6 h. The black block crystal was obtained in a yield of ca. 35% based on tpt. Anal. Calcd for C38H30N12Cu6Pb3I14 (3434.26): C, 13.29; N, 4.89; H, 0.88. Found: C, 13.62; N, 4.56; H, 1.15. IR (cm−1) for 3: 3434 (s), 2921 (m), 2850 (w), 2358 (m), 1637 (s), 1508 (s), 1384 (s), 1093 (m), 800 (w), 593 (w). X-ray Data Collection and Structure Determinations. The SCXRD data of compounds 1−3 were collected on a XtaLAB-mini diffractometer at 293(2) K with Mo Kα radiation (λ = 0.71073 Å) by ω scan mode. The structures for compounds 1−3 were solved by the SHELX-2016 software.46 Table 1 contains the detailed crystallographic data. Tables S1−S3 in the Supporting Information contain the selected bond lengths and angles. Full crystallographic data have been deposited with the CCDC numbers 1558662 for 1, 1546108 for 2, and 1546109 for 3, which are available via www.ccdc.cam.ac.uk/data_ request/cif.

production of CH3I in the first step of the reaction. Although the N-alkylation of linear bipyridine has been reported in the metal/halide/alcohol systems,11,42 the partial N-alkylation reaction for polypyridine is still rare. Description of Crystal Structure. Compound 1 crystallizes in the space group P1̅. The asymmetric unit consists of 3 lead(II) atoms (for Pb2 and Pb4, site occupation factor (SOF) = 0.5), 1 copper(I) atom, and 10 iodine atoms together with 1 free guest Me3tpt3+ (Figure S1 in the Supporting Information). As shown in Figure 1a, lead(II) centers feature two types of coordination environments. Pb1, together with Pb2 and Pb4, is six-coordinated, giving rise to a distorted-octahedral geometry. Pb3 exhibits a lightly distorted square pyramidal geometry. For Cu1, it is coordinated by three I atoms (I2, I7, I8), giving a {CuI3} triangular geometry. The adjacent Pb(II) ions are connected by bridging-chelating I− ions to generate the Pb4I16 subunits (Figure 1b), which are further connected with its neighbors via the CuI3 units to lead to the heterometallic iodides with a chain structure (Figure 1c). The negative chain is compensated by the cationic Me3tpt3+ groups, which are located in the interchain voids (Figure 1d). Compound 2 crystallizes in the space group P1̅. Two and a half lead(II) atoms, one copper(I) atom, and eight iodine atoms together with one coordinated Me2tpt2+group are found in the asymmetric unit. The lead(II) metal centers are located in three types of coordination environments. Pb1 is sixcoordinated, which is ligated by six μ2-I atoms (I1, I2, I3, I1A, I2A, I3A), resulting in a distorted-octahedral geometry. Pb2 exhibits a lightly distorted square pyramidal geometry, the equatorial plane of which comprises four μ2-I atoms (I2, I3, I5, I1B), and one terminal I atom occupies the axial site (I4). The remaining Pb3 atom is three-coordinated and is best portrayed as a distorted {PbI3} triangle geometry (I5, I6, I7). For Cu1, it is coordinated by three μ2-I atoms (I7, I8, I8C) and one nitrogen atom from the Me2tpt2+ ligand, giving a {CuI3N} slightly distorted tetrahedral coordination geometry.

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RESULTS AND DISCUSSION Synthesis. Although compounds 1 and 2 were obtained in the same experimental procedure, we could distinguish them by the external shape. When the volume of HI is in the range of 0.06−0.10 mL, the yield of compound 2 is obviously larger than that of 1. When the volumes of HI are between 0.10 and 0.20 mL, the yields of compounds 1 and 2 are basically the same. Unfortunately, pure crystals of 1 or 2 could not be isolated separately, though many efforts were carried out. It is notable that the volume of water (ca. 4.00 mL) is the key to produce compound 3. When the volume of water is smaller than 4.00 mL (the volume of MeOH is 1.00 mL), only the mixed crystals of compounds 1 and 2 instead of 3 were obtained. When HI, CuI, and PbI2 were substituted with HX, CuX, and PbX2 (X = Cl, Br), no crystalline samples were obtained. Compounds 1−3 were solvothermally prepared, and the in situ N-alkylation of the tpt ligand was observed. The tentative mechanism for the N-alkylation of tpt with MeOH to generate Me3tpt3+, Me2tpt2+, and Metpt+ (see Scheme 1 and Scheme S1 in the Supporting Information) may be as follows. (i) The reaction of MeOH and HI generated iodomethane (CH3I) (CH3OH + HI → CH3I + H2O). (ii) The CH3I acted as a methylating reagent to guide the generation of methylated tpt derivatives (tpt + nCH3I → Mentptn+, n = 1−3). The secondstep reaction can occur under an acidic or neutral environment; however, a strongly acidic environment is necessary for the C

DOI: 10.1021/acs.inorgchem.7b01807 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 1. (a) Coordination mode of Pb(II) and Cu(I) ions in 1, (b) a polyhedral view of the Pb4I16 subunits in 1, (c) Pb4I16 subunits linked by the CuI3 units to generate the chain in 1, and (d) the packing diagram of 1.

Figure 2. (a) Asymmetric unit of 2, (b) the inorganic Pb−I chain in 2, (c) the inorganic Pb−I chains connected by the Cu2 dimers to form the layer in 2, (d) the layer decorated by the Me2tpt2+ motifs along the [010] direction in 2, (e) view of the π···π interactions in 2.

If the Cu−I connections are ignored initially, the Pb(1)I6, Pb(2)I5, and Pb(3)I3 polyhedrons share edge and corners, to form a [Pb3I7]− subunit. Meanwhile, each subunit is connected

to four equivalent subunits via sharing bridged iodine atoms, resulting in a infinite {Pb3I7}∞ branched chain (Figure 2b). Moreover, Cu1 and Cu1B are connected by I8 and I8B, D

DOI: 10.1021/acs.inorgchem.7b01807 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. (a) The asymmetric unit of 3, (b) the Cu6 units of 3, (c) the Pb3 units of 3, (d) a single layer of 3 with 18-MR along the [100] direction.

Figure 4. (a) Packing diagram of 3 viewed along the [001] direction and (b) view of the π···π interactions in 3.

forming a rhomboid Cu2I2 dimer decorated by two Me2tpt2+ groups as terminal ligands. The Cu···Cu distance in 2 (3.230 Å) is slightly longer than the sum of the van der Waals radii of Cu atoms (2.8 Å), implying a weak metal−metal cuprophilic interaction. The neighboring inorganic chains are linked via rhomboid Cu2I2 dimers, leading to an anionic layer as depicted in Figure 2c. In 2, the organic moieties Me2tpt2+ participate in coordination, which connect with the 2D inorganic layers by Cu−N coordination interactions (Figure 1d). Due to the coordination effect and the rigidity of Me2tpt2+, strong π···π interactions between pyridine and triazine groups of adjacent layers are observed with a centroid−centroid distance of 3.676−3.838 Å (Figure 2d). Compound 3 crystallizes in the space group P1̅. The asymmetric unit has one and a half lead(II) atoms, three copper(I) atoms, and seven iodine atoms together with one coordinated Metpt+ molecule. As shown in Figure 3a, one and a

half lead(II) metal centers (for Pb2, SOF = 0.5) feature two types of coordination environments. Pb1 is pentacoordinated by three μ3-I (I2, I4, I5) and two μ2-I (I6, I7) atoms, giving rise to a distorted-square-pyramidal geometry. Pb2 exhibits a slightly distorted octahedral geometry, accomplished by the coordination of three pairs of symmetry-related μ2-I atoms (I3, I3D, I6, I6D, I7, I7D). All of the Cu atoms display a tetrahedral geometry. For Cu1, it is coordinated by three μ3-I atoms (I1, I2, I4) and one N atom from the Metpt+ ligand, forming a {CuI3N} slightly distorted tetrahedral coordination geometry. Cu2 is coordinated by three μ3-I atoms (I1, I1A, I2) and one μ2-I atom (I3). The coordination mode of Cu3 resembles that of Cu1, featuring a {CuI3N} geometry. The four coordination sites are from three μ3-I atoms (I4, I5, I5B) and one N atom of Metpt+ ligand. Three pairs of symmetry-related Cu1, Cu2, and Cu3 are connected by chelating-bridging I atoms, giving birth to the E

DOI: 10.1021/acs.inorgchem.7b01807 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry [Cu6I12]6− motif (Cu6, for short) (Figure 3b). One pair of symmetry-related Pb(1) atoms and one Pb(2) are connected by chelating-bridging I atoms, to form the [Pb3I12]6−motif (Pb3, for short) (Figure 3c). The Pb3 motifs and Cu6 motifs are strictly connected with each other via sharing of the μ2 (I3) and μ3-I (I2, I4, I5) atoms to generate the 18-membered ring (18MR) (Figure 2d). The strict alternating arrangements of 18MR via sharing edges and corners result in the single 2D inorganic heterometallic iodide layer (Figure 3d), which are further connected by Metpt+ linkers to generate the final 3D organic−inorganic hybrid framework (Figure 4a). Further analysis of the neighboring Metpt+ linkers implies that π···π interactions between triazine and triazine groups are present with a centroid−centroid distance of 3.510−3.562 Å (Figure 4b). It is notable that the starting material tpt underwent a partial in situ N-methylation reaction. The resultant motifs (Me3tpt3+ for 1, Me2tpt2+ for 2, and Metpt+ for 3) have participated in the formation of the resultant structure. There was no available Ncoordination site for the Me3tpt3+ motif. Thus, the Me3tpt3+ motif could act as a counterion in the crystallization of the heterometallic iodide subunits. Owing to the blocking effect of the Me3tpt3+ motif, the resulting products tend to be low dimensional. There was only one available N-coordination site for the Me2tpt2+ motif. Thus, the coordination mode of the Me2tpt2+ motif could be viewed as a terminal ligand, which could hinder the further connection of the inorganic heterometallic iodide subunits and give rise to the lowdimensional structure. In comparison with the Me 2tpt2+ motif, there were two available N-coordination sites for the Metpt+ motif. The coordination mode of the Metpt+ motif could be treated as a V-shaped linker, which could prompt the further connection of the inorganic heterometallic iodide subunits and result in the high-dimensional structure. Therefore, the structure diversities in compounds 1−3 are mainly ascribable to the distinct coordination mode of the in situ generated N-methylated tpt derivatives (counterion for Me3tpt3+, terminal ligand for Me2tpt2+, linking ligand for Metpt+). The partial N-alkylation reaction provides a new kind of coordination mode of the polypyridine motif (Ncoordination plus N-alkylation), which offers fresh opportunities for the generation of metal halides with novel structures and structure-related properties. PXRD and TG Analyses. As shown in Figures S2−S4 in the Supporting Information, the experimental PXRD curves agree with the fitted curves obtained from the SCXRD data, implying the pure phase of compounds 1−3. TG measurements were conducted to investigate the thermal stabilities of the title heterometallic iodide (Figure 5a). Compounds 1−3 could be stable until about 250, 240, and 300 °C, respectively. Upon heating treatment, the TG plots of 1−3 display similar multistep weight loss due to the combustion of the organic compositions. Optical Studies. The structural difference between Nmethylated tpt derivatives (Me3tpt3+, Me2tpt2+and Metpt+) and tpt is the existence of the −CH3 moiety (see Scheme 1). The N-alkylation reaction between tpt and CH3OH could also be confirmed by the characteristic IR peaks of the −CH3 moiety. For the −CH3 moiety, the stretching vibration peak of C−H (νC−H) is observable in the range of 2930−2845 cm−1, and the in-plane bending vibration peak of C−H (βC−H) is present at around 1380 cm−1.47 In the IR plots of 1−3 (Figure S5 in the Supporting Information), these characteristic peaks are present,

Figure 5. (a) TG curves of 1−3 and (b) solid-state UV−vis spectra of 1−3.

indicating the existence of N-methylated tpt derivatives in the corresponding products: νC−H(−CH3) 2921, 2861 cm−1 (1), 2927, 2854 cm−1 (2), 2921, 2850 cm−1 (3); βC−H(−CH3) 1376 cm −1 (1), 1386 cm −1 (2), 1384 cm −1 (3). Notably, νC−H(−CH3) is a weak peak, while βC−H(−CH3) is a sharp peak. Moreover, the following peaks are present: νCC/CN(ring) 1633, 1519 cm−1 (1), 1637, 1513 cm−1 (2), 1637, 1508 cm−1 (3); νC−N(ring) 1085 cm−1 (1), 1093 cm−1 (2), 1093 cm−1 (3); γC−H (ring; γ: out-of-plane bending vibration) 804 cm−1 (1), 800 cm−1 (2 and 3). The UV−vis spectra of 1−3 have been studied in the solid state (Figure 5b). Absorption (α/S) data were derived from the Kubelka−Munk equation: F(R) = α/S = (1 − R)2/2R. The band gaps for 1−3 are approximately 1.48, 1.35, and 1.34 eV, respectively. Theoretical Studies. To further explore the electron transfer mechanism, the band structures and densities of states (DOS) have been calculated by the first-principles method based on density functional theory (DFT). The calculated results show that the three compounds have similar energy bond structures (Figure S6 in the Supporting Information) and DOS (Figure 6). The calculated band gaps of 1−3 are 1.06, 1.23, and 0.91 eV, respectively, which are all smaller than the experimental band gaps due to a typical disadvantage in DFT calculations. In the total and partial DOS, the upper part of the valence band (VB) ranging from −3.5 eV to the Fermi level mainly consists of I 5p, Cu 3d, and Pb 6s states, indicating that the strong hybridization occurs in the I−Cu and I−Pb bonding states. The bottom of the conduction band (CB) is predominately derived from C 2p and N 2p states. Clearly, the hybridization among I 5p, Cu 3d, and Pb 6s raises the energy position of the VB. Therefore, the optical absorptions would be mainly attributed to the charge transitions from the Cu−I−Pb anionic moieties (heterometallic iodide chain for 1, F

DOI: 10.1021/acs.inorgchem.7b01807 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

methylation reaction for tpt has taken place and the resultant motif (Me3tpt3+ for 1, Me2tpt2+ for 2, and Metpt+ for 3) is captured within the corresponding structure. The structure diversities in 1−3 are mainly attributable to the different coordination modes of the in situ generated N-methylated tpt derivatives (counterion for Me3tpt3+, terminal ligand for Me2tpt2+, and linking ligand for Metpt+). This, to the best of our knowledge, is the first example of partial N-alkylation of the tripyridine motifs. Our works provide a new coordination mode of tripyridine motif (N-coordination together with Nmethylation or N-alkylation) and offer a general strategy to integrate the polypyridine motifs and heterometallic halide systems to generate intriguing hybrid framework structures and investigate the potential structure-related properties. Further studies on this work, including the integration of metal halide systems with other polypyridine motifs with suitable size and geometry to create new types of crystalline metal halide materials, are underway.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01807. Detailed in situ N-methylation of tpt ligand, an additional structural figure, PXRD characterizations, IR curves, band structures, and selected bond distances and angles (PDF) Accession Codes

CCDC 1546108−1546109 and 1558662 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for G.-M.W.: [email protected]. ORCID

Song-De Han: 0000-0001-6335-8083 Guo-Ming Wang: 0000-0003-0156-904X Notes

The authors declare no competing financial interest.

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Figure 6. Total and partial DOS of (a) 1, (b) 2, and (c) 3.

ACKNOWLEDGMENTS This work was supported by grants from the Natural Science Foundation of China (21571111, 21601101). We are grateful to Prof. Aiping Fu (Qingdao University) for helpful discussions on the section of theoretical studies.

heterometallic iodide layers for 2 and 3) to organic moieties (Me3tpt3+ for 1, Me2tpt2+ for 2, and Metpt+ for 3).

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CONCLUSION Three heterometallic iodides supported by in situ (partial) Nmethylation of 2,4,6-tris(4-pyridyl)-1,3,5-triazine have been successfully prepared and characterized. Compound 1 shows a chain structure with the adjacent Pb4I16 building units connected by CuI3 units. The negative chain is compensated by the Me3tpt3+ moieties. Compound 2 exhibits an inorganic heterometallic iodide layer decorated by cationic Me2tpt2+ motifs via coordination to the intralayer Cu(I) ions. Compound 3 possesses a 3D hybrid framework structure, in which the inorganic heterometallic iodide layer with 18-membered rings is further connected by Metpt+ linkers to form the final 3D organic−inorganic hybrid framework. Notably, an in situ N-

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DOI: 10.1021/acs.inorgchem.7b01807 Inorg. Chem. XXXX, XXX, XXX−XXX