crystals Article
Synthesis, Crystal Structure and Luminescent Properties of 2D Zinc Coordination Polymers Based on Bis(1,2,4-triazol-1-yl)methane and 1,3-Bis(1,2,4-triazol-1-yl)propane Evgeny Semitut 1,2 , Taisiya Sukhikh 2,3 and Andrei Potapov 1, * ID 1 2
3
*
ID
, Evgeny Filatov 2,3
ID
, Alexey Ryadun 2
Department of Biotechnology and Organic Chemistry, National Research Tomsk Polytechnic University, 30 Lenin Ave., 634050 Tomsk, Russia;
[email protected] Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Lavrentieva Ave. 3, 630090 Novosibirsk, Russia;
[email protected] (T.S.);
[email protected] (E.F.);
[email protected] (A.R.) Department of Natural Sciences, Novosibirsk State University, Pirogova Str. 2, 630090 Novosibirsk, Russia Correspondence:
[email protected]; Tel.: +7-923-403-4103
Academic Editor: Matthias Weil Received: 8 November 2017; Accepted: 27 November 2017; Published: 29 November 2017
Two new two-dimensional zinc(II) coordination polymers containing 2,5Abstract: thiophenedicarboxylate and bitopic ligands bis(1,2,4-triazol-1-yl)methane (btrm) or 1,3-bis (1,2,4-triazol-1-yl)propane (btrp) were synthesized. Synthesized compounds were characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction, and thermal analysis. Crystal structures of coordination polymers were determined and their structural peculiarities are discussed. The differences in structural features, thermal behavior, and luminescent properties are discussed. Keywords: zinc; coordination polymer; bitopic ligand; crystal structure; thermal analysis; luminescence; 2,5-thiophenedicarboxylic acid; bis(1,2,4-triazol-1-yl)methane; 1,3-bis(1,2,4-triazol-1-yl)propane
1. Introduction Coordination polymers and metal-organic frameworks attract the unceasing attention of researchers due to their wide range of potential applications [1–6]. One of the universal approaches to the construction of metal-organic frameworks uses a combination of metal ions with aromatic dior polycarboxylate donors and rigid or flexible N-donor bitopic ligands [7,8]. Among dicarboxylic acids, 2,5-thiophenedicarboxylic acid (H2 tdc, Figure 1) was used to enhance the gas sorption properties of MOFs [9–11], fine-tune the topology of the constructed coordination polymers [12–14], prepare coordination polymers with luminescent properties [9,10,15] including those suitable for LED [16] applications, and sense metal ions and small molecules [17,18]. Metal-organic frameworks based on tdc2− donors demonstrating potential photocatalytic [19,20] and magnetic [21] applications were also reported. Bitopic heterocyclic ligands based on semi-rigid di(1,2,4-triazol-1-yl) derivatives [22] or flexible bis(imidazol-1-yl)alkanes [19,23–28] are usually used in combination with tdc2− and metal ions to build coordination networks. Despite a very large number of reported bis(imidazol-1-yl)alkane-linked frameworks based on H2 tdc, no examples of coordination polymers with structurally similar bis(1,2,4-triazol-1-yl)alkanes have been prepared so far. There are a number of publications reporting the study of zinc coordination polymers based on 1,3-bis(1,2,4-triazol-1-yl)propane (btrp, Figure 1) and aromatic di-, tri-, and tetracarboxylates [29–43], and several examples of 1D coordination polymers [44,45] and discrete complexes [44,46,47] have Crystals 2017, 7, 354; doi:10.3390/cryst7120354
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and several examples of 1D coordination polymers and discrete complexes [44,46,47] also been reported. Zinc coordination chemistry with[44,45] bis(1,2,4-triazol-1-yl)methane (btrm,have Figure 1) also less beenstudied, reported.and Zinconly coordination chemistry bis(1,2,4-triazol-1-yl)methane (btrm, 1) so is much two examples of with 1D coordination polymers have beenFigure reported is much less studied, and only two examples of 1D coordination polymers have been reported so far far [48,49]. [48,49].
Figure 1. Bis(1,2,4-triazol-1-yl)methane, 1,3-bis(1,2,4-triazol-1-yl)propane and Figure 1. Bis(1,2,4-triazol-1-yl)methane, 1,3-bis(1,2,4-triazol-1-yl)propane and 2,5-thiophenedicarboxylic 2,5-thiophenedicarboxylic ligands used in of this work for the preparation of coordination acid ligands used in this workacid for the preparation coordination polymers. polymers.
In order to explore of the thepreparation preparation of new coordination polymers In order to explorethe thepossibility possibility of of new coordination polymers based onbased on bis(1,2,4-triazol-1-yl) and H tdc ligands with enhanced functional properties, bis(1,2,4-triazol-1-yl) and H2tdc 2ligands with enhanced functional properties, we have studiedwe the have studied the between reactionzinc between zinc btrm btrpthelinkers. As a ofresult, reaction nitrate, H 2tdc, nitrate, and btrmHor btrp and linkers. As aor result, first examples 2 tdc, bis(1,2,4-triazol-1-yl)methane and 1,3-bis(1,2,4-triazol-1-yl)propane-linked zinc zinc the first examples of bis(1,2,4-triazol-1-yl)methane and 1,3-bis(1,2,4-triazol-1-yl)propane-linked -2,5-thiophenedicarboxylate coordination polymers were prepared, crystal structures, -2,5-thiophenedicarboxylate coordination polymers were prepared, andand theirtheir crystal structures, thermal thermal behavior, and luminescent properties were investigated. behavior, and luminescent properties were investigated. 2. Results Discussion 2. Results andand Discussion 2.1. Synthesis of Coordination Polymers 2.1. Synthesis of Coordination Polymers The coordination polymers 1 and 2 were characterized by thermal analysis, single crystal and
The coordination polymers 1 and 2 were characterized by thermal analysis, single crystal powder X-ray diffraction methods, CHNS analysis, and IR spectroscopy. In addition, their and powder X-ray diffraction methods, CHNS analysis, and IR spectroscopy. In addition, photoluminescence properties were investigated. their photoluminescence properties were investigated. Syntheses of coordination polymers by the reaction of zinc nitrate, btrp or btrm ligands, and Syntheses of coordination polymers by the reaction of zinc nitrate, btrp or btrm 2,5-thiophenedicarboxylic acid (H2tdc) were carried out under solvothermal conditions at ligands, 95 °C in and 2,5-thiophenedicarboxylic acid (H carried under constant solvothermal conditionsinatall95 ◦ C dimethylformamide (DMF). Zn-ligand-H 2tdc ratios out remained and equimolar 2 tdc) were experiments. The duration of heating was varied 12 to 36 h in order to optimize the yield andin all in dimethylformamide (DMF). Zn-ligand-H ratios remained constant and equimolar 2 tdcfrom purity of the crystalline product. experiments. The duration of heating was varied from 12 to 36 h in order to optimize the yield The of equimolar amounts of zinc nitrate, btrm, and H2tdc in the DMF solution (Zn2+ and purity of reaction the crystalline product. concentration 1.0 M) at 95 °C for 24ofh zinc gavenitrate, prismatic crystals coordination polymer The reaction of equimolar amounts btrm, and of H2 tdc in the DMF solution [Zn(btrm)(tdc)]∙nDMF 1. The powder XRD analysis has shown that carrying out the reaction for a 2+ ◦ (Zn concentration 1.0 M) at 95 C for 24 h gave prismatic crystals of coordination polymer longer period of time (e.g., for 36 h) results in the formation of the additional unidentified product as [Zn(btrm)(tdc)]·nDMF 1. The powder XRD analysis has shown that carrying out the reaction for an impurity. This impurity can be removed by washing the precipitate with warm DMF. The XRD a longer period time (e.g., for 36 results inby-product the formation of theinadditional patterns forof compound 1 and theh) additional are shown Figure S1. unidentified product as an impurity. This impurity can beofremoved by washing the precipitate with warm DMF. (Zn The2+ XRD When equimolar amounts zinc nitrate, btrp and H 2tdc were heated in DMF solution patterns for compound 1 and are shown in Figure S1. concentration 1.0 M) at 95the °Cadditional for 12 h, by-product and coordination polymer [Zn(btrp)(tdc)]∙nDMF 2 as prismatic crystals suitable for of X-ray obtained. The in powder When equimolar amounts zincstructure nitrate, determination btrp and H2was tdc were heated DMF XRD solution 2+ ◦ analyses of the polycrystalline sample in comparison with those simulated from single crystal data (Zn concentration 1.0 M) at 95 C for 12 h, and coordination polymer [Zn(btrp)(tdc)]·nDMF 2 patterns are shown in Figure The IR spectra of both compounds characteristic bands XRD as prismatic crystals suitable forS2. X-ray structure determination wascontain obtained. The powder associated vibrations ofsample bis(triazol-1-yl) ligands with and coordinated 2,5-thiophenedicarboxylate analyses of the with polycrystalline in comparison those simulated from single crystal data anions (Figure S3). patterns are shown in Figure S2. The IR spectra of both compounds contain characteristic bands associated withStructures vibrations of bis(triazol-1-yl) ligands and coordinated 2,5-thiophenedicarboxylate 2.2. Crystal anions (Figure S3). 2.2.1. Crystal Structure of Polymer [Zn(tdc)(btrm)]∙nDMF (1)
2.2. Crystal Structures
The complex [Zn(tdc)(btrm)]∙nDMF (1) is a 2D coordination polymer. The Zn atom coordinates two crystallographically independent (tdc)2– ligands (halves) 2.2.1. Crystal Structure of Polymer [Zn(tdc)(btrm)] ·nDMF (1)to form chains (Figure 2a). Analysis of
The complex [Zn(tdc)(btrm)]·nDMF (1) is a 2D coordination polymer. The Zn atom coordinates two crystallographically independent (tdc)2− ligands (halves) to form chains (Figure 2a). Analysis of
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bondCrystals lengths reveals 2017, 7, 354 the shortest distances for Zn1–O11 of 1.94 and Zn1–O21 of 1.99 Å typical 3 offor 11 this 2− anions act as (µ-O) -coordinating ligands. Zn1···O12 type of coordination compound. Both (tdc) bond lengths reveals the shortest distances for Zn1–O11 of 1.94 and 2 Zn1–O21 of 1.99 Å typical for 2−Zn1–O11 lengths reveals the compound. shortest distances for and Zn1–O21 of ligands. 1.99 be Å typical for as thisand type of coordination Bothare (tdc) anions actofas1.94 (μ-O) 2-coordinating Zn1∙∙∙O12 (2.99 bond Å) Zn1 ··· O22 (2.65 Å) distances much longer, although the latter can considered 2− anions act as (μ-O)2-coordinating ligands. Zn1∙∙∙O12 this type of coordination compound. Both (tdc) Å) and Zn1∙∙∙O22in(2.65 Å) distances arethe much longer,ofalthough the latter can be considered as a ) on a long(2.99 range interaction agreement with analysis normalized contact distances (dnorm (2.99 andinteraction Zn1∙∙∙O22 Å) distances much longer, thecontact latter be considered as aa the long Å) range in agreement the analysis of although normalized distances (dnorm) on a Hirshfeld surface [50,51](2.65 (Figure S4a).with Inare contrast to atom O22, atom O12can reveals contact with long rangesurface interaction in (Figure agreement with the analysis of O22, normalized contact distances norm)the on H a Hirshfeld [50,51] to atom atom of O12 reveals contact(d with H of the neighboring triazole unit,S4a). withIna contrast corresponding distance 2.25 Å (Figure S4b). {Zn(tdc)} Hirshfeld surface [50,51] (Figure S4a). In contrast to atom O22, atom O12 reveals contact with the H of the neighboring triazole unit, with a corresponding distance of 2.25 Å (Figure S4b). {Zn(tdc)} chains are linked by (µ-N)2 -coordinating btrm ligands to form corrugated layers arranged along the ac of the neighboring unit, with a btrm corresponding of 2.25 Å (Figure S4b). along {Zn(tdc)} chains are linked bytriazole (μ-N)2-coordinating ligands to distance form corrugated layers arranged the planechains (Figure 2b). Within the layer, Zn atoms deviate from their mean plane significantly bythe 3.54 Å are(Figure linked2b). by (μ-N) 2-coordinating ligands to from form their corrugated layerssignificantly arranged along ac plane Within the layer, Znbtrm atoms deviate mean plane by 3.54 (Figure S6). These layers are stacked one above the other (Figure 2c) leaving channel voids of ca. ac (Figure 2b). Within the stacked layer, Zn atoms deviate from(Figure their mean plane significantly byof3.54 Å plane (Figure S6). These layers are one above the other 2c) leaving channel voids ca. 35% filledÅ by highly disordered DMF solvent molecules (Figure 3). (Figure These disordered layers are stacked one above the other (Figure 35% filled S6). by highly DMF solvent molecules (Figure 3). 2c) leaving channel voids of ca. 35% filled by highly disordered DMF solvent molecules (Figure 3).
(b) (b)
(a) (a)
(c) (c) Figure 2. (a) Displacement ellipsoid plot of complex [Zn(tdc)(btrm)]∙nDMF (1) showing 50% Figure 2. (a) Displacement ellipsoid plot of complex [Zn(tdc)(btrm)]·nDMF (1) showing 50% probability Figure 2. (a) Displacement ellipsoid of for complex showingZn∙∙∙O 50% probability ellipsoids. H atoms are notplot shown clarity.[Zn(tdc)(btrm)]∙nDMF Dashed lines indicate (1) long-range ellipsoids. H atoms are not fornot clarity. Dashed linesDashed indicate long-range Znbrown. ···O interactions; probability H shown atoms are shown for clarity. lines indicate long-range Zn∙∙∙O interactions.ellipsoids. (b,c) Relative arrangement of the layers of 1 colored green, red, blue, and (b,c) Relative arrangement of arrangement the layers ofof1the colored red, blue, interactions. (b,c) Relative layersgreen, of 1 colored green,and red,brown. blue, and brown.
Figure 3. Representation of channel voids in the structure of the complex [Zn(tdc)(btrm)]∙nDMF (1). Figure 3. Representation channelvoids voidsin inthe the structure structure of [Zn(tdc)(btrm)]∙nDMF (1). (1). Figure 3. Representation of of channel ofthe thecomplex complex [Zn(tdc)(btrm)]·nDMF
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2017, 7, 354 2.2.2.Crystals Crystal Structure of Polymer [Zn(tdc)(btrp)]·nDMF (2)
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The [Zn(tdc)(btrp)] ·nDMF (2) also has (2) a 2D structure (Figure 4a). Similar to 1, 2.2.2. complex Crystal Structure of Polymer [Zn(tdc)(btrp)]∙nDMF a four-connected net of Zn atoms is observed, but (tdc)2– and btrp ligands alternate along the chains. The complex [Zn(tdc)(btrp)]∙nDMF (2) also has a 2D structure (Figure 4a). Similar to 1, a The whole layer is arranged ab planebut and(tdc) it less corrugated compared layers polymer 1. 2– and four-connected net of Zn along atoms the is observed, btrp ligands alternatetoalong theofchains. Within the layer, Zn atoms deviate from their mean plane by 0.55 Å (Figure S7). Similar to compound 1, The whole layer is arranged along the ab plane and it less corrugated compared to layers of polymer the dicarboxylate ligand in complex 2 adopts a (µ-O) -coordination mode, revealing pairs of short 1. Within the layer, Zn atoms deviate from their mean plane by 0.55 Å (Figure S7). Similar to 2 (1.93,compound 1.98 Å) and longdicarboxylate (2.61, 3.29 Å) Zn···inOcomplex distances. According to2-coordination the analysis mode, of the drevealing 1, the ligand 2 adopts a (μ-O) norm map on pairs of short (1.93,the 1.98 Å) atom and long (2.61, 3.29 interaction Å) Zn∙∙∙O distances. to as thewith analysis of the the Hirshfeld surface, O14 shows weak with theAccording Zn, as well the H, atom of onwith the Hirshfeld surface, Zn the··· O14 atomHshows weak interaction with 2.53 the Zn, as well as with dnorm map the triazole unit corresponding O and ···O distances of 2.61 and Å (Figure S5). On the the H, atom of the triazole unit with corresponding Zn∙∙∙O and H∙∙∙O distances of 2.61 and 2.53 Å contrary, the O12 atom reveals no close contacts with Zn and H atoms. Crystal packing differences (Figure S5). On the contrary, the O12 atom reveals no close contacts with Zn and H atoms. Crystal are observed for compounds 1 and 2. Coordination polymer 2 shows a double interpenetration packing differences are observed for compounds 1 and 2. Coordination polymer 2 shows a double of the layers with each Zn node of one array lying above or below the approximate center of the interpenetration of the layers with each Zn node of one array lying above or below the approximate spacecenter of another layerof(Figure Due to interpenetration, only separate voids voids filledfilled by DMF of the space another 4b,c). layer (Figure 4b,c). Due to interpenetration, only separate molecules are revealed (Figure 5), with the solvent accessible volume (of ca. 22%) being lower by DMF molecules are revealed (Figure 5), with the solvent accessible volume (of ca. 22%) being than in 1. Each molecule, which is disordered by two positions due to itsdue proximity lowervoid than contains in 1. Each one voidDMF contains one DMF molecule, which is disordered by two positions to proximity to an inversion center. to anits inversion center.
(b)
(a)
(c) Figure 4. (a) Displacement ellipsoid plot of complex [Zn(tdc)(btrp)]∙nDMF (2) showing 50%
Figure 4. (a) Displacement ellipsoid plot of complex [Zn(tdc)(btrp)]·nDMF (2) showing 50% probability probability ellipsoids. H atoms are not shown for clarity. Dashed lines indicate long-range Zn∙∙∙O ellipsoids. H atoms are not shown for clarity. Dashed lines indicate long-range Zn···O interactions; interactions. (b,c). Relative arrangement of the layers of 1 colored green, red, blue, and brown. (b,c). Relative arrangement of the layers of 1 colored green, red, blue, and brown.
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Figure 5. Representation of the voids in the structure of the complex [Zn(tdc)(btrp)]∙nDMF (2).
Figure 5. Representation of the voids in the structure of the complex [Zn(tdc)(btrp)]·nDMF (2). 2.3. Thermal Analysis
Figure 5. Representation of the voids in the structure of the complex [Zn(tdc)(btrp)]∙nDMF (2).
The analysis of the thermal properties of synthesized compounds revealed that the processes of 2.3. Thermal Analysis removing guest molecules from coordination polymers 1 and 2 have some significant differences
2.3. Thermal (Figure Analysis 6a,b).
The process of desolvation for compound 1 starts at about 120 °С, while the
The analysis of the thermal properties of synthesized compounds revealed that the processes desolvation process for 2 starts almost at room temperature. The number of guest molecules for 2 is The analysis of the thermal properties revealed the processes of of removing guest molecules from coordination polymers 1 and 2 have some significant differences variable and decreases under storage in of air synthesized revealed by the compounds results of CHNS analysis ofthat the samples removing guest 1 and 2 have some stored molecules in air for a fewfrom weeks.coordination The second step polymers for both compounds starts at about 250 significant °С and lasts updifferences ◦ (Figure 6a,b). The process of desolvation for compound 1 starts at about 120 C, while the desolvation to about °С for 1 and to 500 °С for 2.for compound 1 starts at about 120 °С, while the (Figure 6a,b). The400process of up desolvation process for 2 starts almost at room temperature. The number of guest molecules for 2 is variable and desolvation process for 2 starts almost at room temperature. The number of guest molecules for 2 is decreases under storage in air revealed by the results of CHNS analysis of the samples stored in air for variable and decreases under storage in air revealed by the results of CHNS analysis of the samples ◦ a fewstored weeks. The step for compounds starts at aboutstarts 250 ◦at C about and lasts upand to about in air forsecond a few weeks. Theboth second step for both compounds 250 °С lasts up400 C ◦ for 1toand up 400 to 500 about °С forC1for and2.up to 500 °С for 2.
(a)
(b)
Figure 6. Curves of thermal analysis for compound 1 (a) and for compound 2 (b).
2.4. Luminescent Properties The luminescence and excitation spectra of compounds 1 and 2 are shown in Figure 7. Upon excitation at 375 nm (for 1) and at 330 nm (for 2), the photoluminescence spectra demonstrate wide bands with maxima at 430 and 440 nm, respectively. The band of 1 is vibrationally resolved with two shoulders having bathochromic and hypsochromic shifts. The excitation spectrum of 1 also has a vibrational resolution. The ligands btrm and btrp (for images of btrp spectra, see ref. [43]) reveal
(a)
(b)
Figure 6. Curves of thermal analysis for compound 1 (a) and for compound 2 (b).
Figure 6. Curves of thermal analysis for compound 1 (a) and for compound 2 (b).
2.4. Luminescent Properties
2.4. Luminescent Properties
The luminescence and excitation spectra of compounds 1 and 2 are shown in Figure 7. Upon The luminescence and excitation spectra 1 andspectra 2 aredemonstrate shown in wide Figure 7. excitation at 375 nm (for 1) and at 330 nm (for 2), of the compounds photoluminescence bands with maxima 430(for and1)440 nm, of 1 is vibrationally resolved two Upon excitation at 375 at nm and atrespectively. 330 nm (forThe 2), band the photoluminescence spectrawith demonstrate shoulders having bathochromic and hypsochromic shifts. The excitation spectrum of 1 also has a with wide bands with maxima at 430 and 440 nm, respectively. The band of 1 is vibrationally resolved vibrational resolution. The ligands btrm and btrp (for images of btrp spectra, see ref. [43]) reveal two shoulders having bathochromic and hypsochromic shifts. The excitation spectrum of 1 also has a
vibrational resolution. The ligands btrm and btrp (for images of btrp spectra, see ref. [43]) reveal broad emission bands with the maxima at 410 and 440 nm, respectively. The excitation bands of coordination polymers are relatively narrow, while for the ligands, these bands are wide. It is interesting to note that the quantum yield (QY) for 1 is several times higher than the QY of the btrm ligand. On the contrary, the QY for 2 decreases by a few orders compared to the btrp ligand (Table 1).
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broad emission bands with the maxima at 410 and 440 nm, respectively. The excitation bands of coordination polymers are relatively narrow, while for the ligands, these bands are wide. It is interesting Crystals 2017, 7, 354to note that the quantum yield (QY) for 1 is several times higher than the QY of the btrm6 of 12 ligand. On the contrary, the QY for 2 decreases by a few orders compared to the btrp ligand (Table 1).
Figure 7. Normalized emission ex = 330 nm and 375 nm) and excitation spectra: 1, 3—compound 1; Figure 7. Normalized emission (λ(λ ex = 330 nm and 375 nm) and excitation spectra: 1, 3—compound 1; 2, 4—compound 2. Normalized emission (λex = 330 nm) spectrum of btrm. 2, 4—compound 2. Normalized emission (λex = 330 nm) spectrum of btrm. Table 1. Photoluminescence data for coordination polymers 1, 2 and ligands btrm, btrp.
Table 1. Photoluminescence data for coordination polymers 1, 2 and ligands btrm, btrp. Ex, nm Em, nm QY Ex,
1 330 1 410 (sh), 430, 460 (sh) 0.1 330
2 375 440
