Exploration of a Variety of Copper Molybdate Coordination Hybrids

Article pubs.acs.org/IC

Exploration of a Variety of Copper Molybdate Coordination Hybrids Based on a Flexible Bis(1,2,4-triazole) Ligand: A Look through the Composition-Space Diagram Ganna A. Senchyk,† Andrey B. Lysenko,*,† Konstantin V. Domasevitch,† Oliver Erhart,‡ Stefan Henfling,‡ Harald Krautscheid,‡ Eduard B. Rusanov,§ Karl W. Kram ̈ er,∥ Silvio Decurtins,∥ ,∥ and Shi-Xia Liu* †

Inorganic Chemistry Department, Taras Shevchenko National University of Kyiv, Volodimirska Str. 64, Kyiv 01033, Ukraine Institut für Anorganische Chemie, Universität Leipzig, Johannisallee 29, Leipzig D-04103, Germany § Institute of Organic Chemistry, Murmanska Str. 5, Kyiv 02660, Ukraine ∥ Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, Bern CH-3012, Switzerland ‡

S Supporting Information *

ABSTRACT: We investigated the coordination ability of the bis(1,2,4-triazolyl) module, tr2pr = 1,3-bis(1,2,4-triazol-4-yl)propane, toward the engineering of solid-state structures of copper polyoxomolybdates utilizing a composition space diagram approach. Different binding modes of the ligand including [N− N]-bridging and N-terminal coordination and the existence of favorable conformation forms (anti/anti, gauche/anti, and gauche/ gauche) resulted in varieties of mixed metal CuI/MoVI and CuII/ MoVI coordination polymers prepared under hydrothermal conditions. The composition space analysis employed was aimed at both the development of new coordination solids and their crystallization fields through systematic changes of the reagent ratios [copper(II) and molybdenum(VI) oxide precursors and the tr2pr ligand]. Nine coordination compounds were synthesized and structurally characterized. The diverse coordination architectures of the compounds are composed of cationic fragments such as [CuII3(μ2-OH)2(μ2-tr)2]4+, [CuII3(μ2-tr)6]6+, [CuII2(μ2-tr)3]4+, etc., connected to polymeric arrays by anionic species (molybdate MoO42−, isomeric α-, δ-, and β-octamolybdates {Mo8O26}4− or {Mo8O28H2}6−). The inorganic copper(I,II)/ molybdenum(VI) oxide matrix itself forms discrete or low-dimensional subtopological motifs (0D, 1D, or 2D), while the organic spacers interconnect them into higher-dimensional networks. The 3D coordination hybrids show moderate thermal stability up to 230−250 °C, while for the 2D compounds, the stability of the framework is distinctly lower (∼190 °C). The magnetic properties of the most representative samples were investigated. The magnetic interactions were rationalized in terms of analyzing the planes of the magnetic orbitals.

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INTRODUCTION Coordinative interactions between metal cations, anionic polyoxometallates, and neutral N-donor ligands are among the most fundamental paradigms in many interdisciplinary fields of chemistry dealing with extended coordination solids and their applications as catalysts, molecule-based magnets, photochromic and electrochromic materials, etc.1 The intensive research efforts in this area resulted in a tremendous number of publications accumulating new knowledge, synthetic strategies, and approaches.2 Particular attention was focused on a big library of various N-heterocyclic building blocks employed for the engineering of sophisticated materials, whose properties can be fine-tuned through molecular electronic and geometric properties of the ligand building blocks. On the other hand, the ambiguous setup of hydrothermal reactions (control over the temperature, pH, reagent ratio, and concentration as well as © XXXX American Chemical Society

knowledge about the reaction itself, which is often performed on a few milligram scale) and the lack of a clear description of synthetic subtleties led to an accumulation of multiple experimental errors and, thus, missing original synthetic protocols. In fact, this is also related to many unsuccessful attempts for some of us to reproduce the desired reaction conditions for target products. Trying to better understand the interactions in multicomponent systems that involve inorganic and organic species, Poeppelmeier et al. proposed a convenient concept of the composition space analysis toward silver(I)/vanadium(IV,V) oxide/oxyfluorides3 and pyridine-based mixed-metal oxyfluorides.4 The most promising advantage of this approach is the Received: July 7, 2017

A

DOI: 10.1021/acs.inorgchem.7b01735 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Scheme 1. (a) tr2pr Utilized in This Study Shown in Three Possible Conformations Illustrated by Newman Projections and (b) Principal Structural Archetypes of Solid-State Structures Developed in the CuI,II/MoVI/tr2pr Series

capable of simultaneously coordinating several equal or different metal centers to afford crystalline polymeric compounds (e.g., triazolyl derivatives are preferable to pyridyl derivatives; bifunctional bistriazolyl ligands are better than monofunctional derivatives as well), and (v) length and conformational features of multifunctional ligands: a long spacer is preferred over a short spacer [e.g., a (−CH2−)3 propylene spacer will supply distinguishable open channels within the resultant metal−organic architecture, which can be filled by large and/or small counteranions and/or crystallization solvent molecules]; moreover, a flexible aliphatic spacer proposes a wider choice for metal−ligand interactions [e.g., a −(CH2)3− spacer is better than p-C6H4− moieties]. These requirements are perfectly fulfilled in the copper(I,II)/ molybdenum(VI) oxide systems decorated with flexible 1,3bis(1,2,4-triazol-4-yl)propane (tr2pr). The latter adopts several favorable conformations (Scheme 1) that might offer a considerable benefit in the development of a wide series of coordination solids. In this paper, we present the conformationally flexible tr2pr ligand with the goal of preparing a rich set of copper(I,II)/ molybdenum(VI) oxide coordination polymers possessing diverse solid-state architectures. For this purpose, the composition space analysis yielded nine coordination compounds: [CuII(tr2pr){MoO4}]·H2O (1), [CuII3(OH)2(tr2pr){MoO4}2]·4H2O (2), [CuII2(tr2pr)4{δ-Mo8O26}]·4H2O (3), [CuII4(OH)4(tr2pr)2{β-Mo8O26}]·H2O (4), [CuII3(OH)2(tr2pr)3{β-Mo8O26}] (5), [CuII3(tr2pr)2{Mo8O28H2}]·9H2O (6), [CuII3(OH)2(tr2pr)2(H2O)2{Mo8O26}]·3H2O (7), [Cu I 4 (tr 2 pr) 4 {β-Mo 8 O 26 }] (8), and [Cu I 8 (tr 2 pr) 8 ]{β,αMo8O26}2·6H2O (9). The magnetic properties of the most representative samples were investigated. Recently, copper

tight interconnection between reactant ratios (“reaction input”) and product crystallization fields (“reaction output”) covering the triangle concentration diagram, as the most acceptable geometric visualization. Although several systems containing bridging organic ligands (pyrazole,5 4,4′-bipyridine,5 1,2,4triazole derivatives,5,6 1,2-di(4-pyridyl)ethane,7 isonicotinic acid,8 etc.) were examined in such a way, these investigations still remain rare, often requiring thorough analysis and larger than usual reagent sources. In a preceding publication,9 we utilized a similar methodology to study new coordination solids in the reaction system of copper(II)/molybdenum(VI) oxide and bridging 1,3-bis(1,2,4-triazol-4-yl)adamantane (tr2ad) for further application of the resultant products in catalysis and magnetism. The organic ligand, in which two tr functions are separated through a rigid adamantane core, was presumably a limiting factor responsible for only three examples of layered copper molybdate hybrids isolated, despite the presence of a structurally flexible polyoxomolybdate matrix.1,2 Thus, we hypothesized that a variety of coordination polyoxomolybdate compounds can primarily depend on the structural flexibility of all reactants and/or in situ generated components when the reaction proceeds. Obviously, the molecular tuning of the reactants should meet the following criteria: (i) high flexibility of the coordination arrangement of the central metal cation (e.g., CuII is preferable to CoII or CdII), (ii) the existence of various metal oxidation states or easy redox transformation between them (e.g., CuII → CuI), accompanied by different geometries and bonding properties for the central ions, (iii) structural diversity of the inorganic oxide matrix, which tends to provide chargecompensating, space-filling, and coordinating roles (e.g., polyoxomolybdates are particular candidates for this purpose),1,2 (iv) neutral multidentate organic ligands, which are B


Article

Inorganic Chemistry

Figure 1. Flotation method in a CHBr3/CH2Cl2 mixture employed to isolate products 4 and 5 from the reaction mixture (see experimental point 316 in Table S13). The crude crystalline powder was prepared following the hydrothermal synthesis of Cu(OAc)2·H2O, tr2pr, and (NH4)6Mo7O24· 4H2O (CuII/tr2pr/MoVI = 3:1:6). [Cu2(tr2pr)4{δ-Mo8O26}]·4H2O (3). A mixture of Cu(OAc)2·H2O (20.0 mg, 0.100 mmol), tr2pr (35.6 mg, 0.200 mmol), and (NH4)6Mo7O24·4H2O (123.2 mg, 0.100 mmol) in 5 mL of H2O (molar ratio CuII/tr2pr/MoVI = 1:2:7) was placed in a Teflon reactor. After the reaction, light-blue needles of 3 were filtered off, washed with water, and dried. Yield: 65.7 mg (63%). Anal. Calcd for C28H48Cu2Mo8N24O30: C, 16.05; H, 2.31; N, 16.04. Found: C, 16.17; H, 2.30; N, 16.12. IR (KBr disks, selected bands, cm−1): 466w, 510w, 558w, 634s, 661s, 711m, 732m, 801s, 849s, 918s, 1038w, 1084m, 1200s, 1323w, 1363w, 1399w, 1455m, 1550s, 1628m, 2950w, 3003w, 3093m, 3117m, 3448m, 3497m. [Cu4(OH)4(tr2pr)2{β-Mo8O26}]·H2O (4) and [Cu3(OH)2(tr2pr)3{βMo8O26}] (5). A mixture of Cu(OAc)2·H2O (60.0 mg, 0.300 mmol), tr2pr (17.8 mg, 0.100 mmol), and (NH4)6Mo7O24·4H2O (105.6 mg, 0.0855 mmol) in 5 mL of H2O (molar ratio CuII/tr2pr/MoVI = 3:1:6) was placed in a Teflon reactor. After the reaction, the mixture was inspected under a microscope. The polycrystalline sample consisting of compounds 4 (a major phase), 5 (∼5 mg), 3 (∼5 mg), and (an) unknown amorphous phase(s) was filtered off and placed in a test tube containing water. The mixture was treated in an ultrasonic bath, and the supernatant containing a light amorphous admixture was thoroughly decanted. The crystalline phases were filtered off, washed with methanol, and dried. The following separation of the phases was carried out based on their difference in densities, as shown in Figure 1. First, the mixture was placed in a test tube containing bromoform (CHBr3; d = 2.89 g cm−3), and then dichloromethane (CH2Cl2; d = 1.33 g cm−3) was added dropwise on top, leading to a middle mixedlayer solution having a density gradient. The heaviest fraction 4 (d = 3.07 g cm−3) was settled on the bottom, while the crystals of compound 5 (d = 2.73 g cm−3) were concentrated in the border between pure CHBr3 and its CH2Cl2 solution. The other light phases were hung around the top of the solution level. The test tube was left undisturbed for some time to achieve good separation between phases. Then the test tube was slowly immersed in liquid nitrogen to obtain phases 4 and 5 in solidified CHBr3/CH2Cl2, while the light phases were still an upper liquid solution. The top liquid layer was decanted, and the test tube containing compounds 4 and 5 was heated back to rt. A similar procedure was repeated once again to isolate fractions 4 and 5 as pure solids. They were then washed with methanol and dried in air. Yield: 53 mg (56%) for compounds 4 and 5 mg for 5. For magnetic measurements, compound 5 was prepared by repeating a dozen identical syntheses. Anal. Calcd for C14H26Cu4Mo8N12O31 (4): C, 8.94; H, 1.39; N, 8.94. Found: C, 8.90; H, 1.42; N, 8.88. IR (KBr disks, selected bands, cm−1): 451s, 522s 554m, 581m, 639s, 671s, 711s, 795m, 837s, 900s, 938s, 957s, 1005w, 1024w, 1092w, 1181w, 1224w, 1334w, 1378w, 1429m, 1456m, 1490m, 1563m, 1651w, 2946m, 3003m, 3040m, 3073m, 3134m, 3469s, 3604m.

1,2,4-triazolyl-based polyoxomolybdates have attracted special attention because of their potential applications as electrocatalysts,10 visible- and UV-light-driven photocatalysts for the degradation of organic dyes,11 and catalysts for the epoxidation of cis-cyclooctene,9 styrene, and cyclohexene12 and for the oxidation of benzyl alcohol.9

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EXPERIMENTAL SECTION

Syntheses. All chemicals were of reagent grade and were used as received without further purification. The tr2pr ligand is available in a yield of 33% through the transamination reaction under acid-catalyzed conditions from 1,3-diaminopropane and N,N-dimethylformamide azine.13 Metal−organic coordination compounds 1−9 were prepared under hydrothermal conditions using an identical thermal control regime. Reagent ratios employed were optimized in accordance with the composition space diagram at 200 mM total concentration of the CuII, MoVI, and tr2pr species. A mixture of the initial reagents, Cu(OAc)2·H2O, tr2pr, and (NH4)6Mo7O24·4H2O, in 5 mL of distilled water was placed in a 20 mL Teflon-lined stainless steel autoclave, intensively stirred (700 rpm) for 1 min, and heated at 160 °C for 24 h in an oven with further cooling to room temperature (rt) in 48 h. Reaction products were typically obtained as a complex mixture of crystalline solids that were collected, washed with water and methanol, and dried in air. Target coordination compounds were separated by employing techniques such as bath sonication, decantation of the supernatant, flotation in a CHBr3/CH2Cl2 mixture, and mechanical separation under a microscope. [Cu(tr2pr){MoO4}]·H2O (1). A mixture of Cu(OAc)2·H2O (40.0 mg, 0.200 mmol), tr2pr (106.8 mg, 0.600 mmol), and (NH4)6Mo7O24· 4H2O (35.2 mg, 0.0285 mmol) in 5 mL of H2O (molar ratio CuII/ tr2pr/MoVI = 2:6:2) was placed in a Teflon reactor. After heating to 160 °C, green hexagonal plates (a single-phase product) were filtered off, washed with water, and dried. Yield: 58.0 mg (69%). Anal. Calcd for C7H12CuMoN6O5: C, 20.03; H, 2.88; N, 20.02. Found: C, 19.98; H, 2.90; N, 20.00. IR (KBr disks, selected bands, cm−1): 493m, 634m, 675m, 813s, 834s, 854s, 906m, 993w, 1046m, 1087m, 1116m, 1205m, 1286w, 1324w, 1396w, 1408m, 1474m, 1544m, 1644m, 2988m, 3052m, 3079m, 3099m, 3341s, 3424s. [Cu3(OH)2(tr2pr){MoO4}2]·4H2O (2). A mixture of Cu(OAc)2·H2O (80.0 mg, 0.400 mmol), tr2pr (71.2 mg, 0.400 mmol), and (NH4)6Mo7O24·4H2O (35.2 mg, 0.0285 mmol) in 5 mL of H2O (molar ratio CuII/tr2pr/MoVI = 4:4:2) was placed in a Teflon reactor and heated to 160 °C. An inseparable mixture of blue plates of 2 and colorless needles of [CuI8(tr2pr)8]{β,α-Mo8O26}2·6H2O (9) was formed in an approximate ratio of 10:1. The desired product was only partially separated by hand. Anal. Calcd for C7H20Cu3Mo2N6O14: C, 10.58; H, 2.54; N, 10.57. Found: C, 10.62; H, 2.49; N, 10.63. C


Article

Inorganic Chemistry

the disorder involves the 2-(triazol-4-yl)ethylene fragment. The disorder was resolved with a set of restraints in geometry and similarity restraints in the anisotropic thermal parameters. The same approach was used for refinement of the disorder in the structure of 5, in which the organic ligand is situated across a center of inversion and the central methylene group is equally disordered by symmetry. The structure of 9 was refined as a pseudomerohedral twin (β ≈ 90°), with refined contributions of the twin components of 0.65 and 0.35. The disorder in the region of the anions was resolved smoothly and refined without geometry restraints as a superposition of two isomeric octamolybdates, namely, β-[Mo8O26]4− and α-[Mo8O26]4− anions (partial occupancy factors are 0.85 and 0.15, respectively). The oxygen atoms of the minor component were left isotropic, and their Uiso thermal values were set uniform in order to improve the refinement stability. In the cases of 2−4, 6, 7, and 9, some of the solvate water molecules are disordered over closely separated positions, and the oxygen atoms were assigned partial occupancy factors suggested by refinement of the thermal parameters. No hydrogen atoms were added to these molecules. In most other cases, OH hydrogen atoms were located and then included with fixed bond distances (0.85 Å) and Uiso values at the level of 1.5Ueq of the carrier oxygen atoms. The CH hydrogen atoms were constrained and refined as riding. In the structure of 6, it was not possible to locate the hydrogen atoms of the centrosymmetric [Mo8O28H2]6− anions. They are regarded to be equally disordered over two pairs of inversion-related positions at O1 and O14, as suggested by the hydrogen-bonding environment. Graphical visualization of the structures was made using the program Diamond 2.1e.16 Crystallographic data and experimental details for structural analyses are summarized in Table S1. The crystallographic material can also be obtained from the CCDC, through deposition numbers CCDC 1557536−1557544 for 1−9, respectively.

Anal. Calcd for C21H32Cu3Mo8N18O28 (5): C, 12.98; H, 1.66; N, 12.98. Found: C, 12.93; H, 1.68; N, 12.94. IR (KBr disks, selected bands, cm−1): 424w, 467w, 523w, 558w, 640s, 668s, 712s, 832s, 886s, 912s, 945s, 1044m, 1083m, 1200m, 1372m, 1407m, 1455m, 1541m, 1555m, 1632m, 2857w, 2947w, 3025w, 3083m, 3117m, 3496s. [Cu3(tr2pr)2{Mo8O28H2}]·9H2O (6) and [Cu3(OH)2(tr2pr)2(H2O)2{Mo8O26}]·3H2O (7). Single crystals of compounds 6 and 7 were isolated from the hydrothermal reaction of Cu(OAc)2·H2O (20.0 mg, 0.100 mmol) and tr2pr (17.8 mg, 0.100 mmol) with (NH4)6Mo7O24·4H2O (140.8 mg, 0.138 mmol) in 5 mL of H2O at the molar ratio CuII/tr2pr/MoVI = 1:1:8. Inspection of the reaction mixture under a microscope revealed that products 6 and 7 were formed as a mixture in less than 1% yield. Only several goodquality single crystals of the compounds were selected for the singlecrystal X-ray diffraction analysis. The poor quality of the samples and its close density values did not allow us to separate the compounds for magnetic measurements. [CuI4(tr2pr)4{β-Mo8O26}] (8). Orange crystals of compound 8 (minor phase ∼10%) and blue powder of complex 2 (major phase) were simultaneously formed in the hydrothermal reaction of Cu(OAc)2· H2O (100.0 mg, 0.500 mmol), tr2pr (35.6 mg, 0.300 mmol), and (NH4)6Mo7O24·4H2O (52.8 mg, 0.0427 mmol) in 5 mL of H2O (molar ratio CuII/tr2pr/MoVI = 5:2:3) that proceeded at the temperature regime described above. Anal. Calcd for C28H40Cu4Mo8N24O26 (8): C, 15.64; H, 1.87; N, 15.63. Found: C, 15.60; H, 1.90; N, 15.58. IR (KBr disks, selected bands, cm−1): 410w, 476w, 518m, 548m, 634s, 664s, 716s, 790m, 838s, 870s, 901s, 946s, 1014w, 1036w, 1078m, 1200s, 1258w, 1354w, 1396w, 1470m, 1544s, 1654w, 2866w, 2952w, 3000w, 3091m, 3112m, 3294w. [CuI8(tr2pr)8]{β,α-Mo8O26}2·6H2O (9). Analogous to compound 8, the hydrothermal reaction of Cu(OAc)2·H2O (40.0 mg, 0.200 mmol), tr2pr (124.6 mg, 0.700 mmol), and (NH4)6Mo7O24·4H2O (17.6 mg, 0.0142 mmol) in 5 mL of H2O (molar ratio CuII/tr2pr/MoVI = 2:7:1) gave colorless needles of compound 9 as a major product in a mixture with amorphous precipitate. The solid was filtered off, washed with water, and dried. Despite a relatively good yield, we were not able to isolate the product for additional studies. For analysis, a small amount of the complex was collected by a combination of flotation in CHBr3/ C H 2 C l 2 a n d m e c h a n i c a l s e pa r a t i o n . A n a l . C a l c d f o r C56H92Cu8Mo16N48O58 (9): C, 15.26; H, 2.10; N, 15.25. Found: C, 15.29; H, 2.09; N, 15.28. IR (KBr disks, selected bands, cm−1): 410w, 470w, 524m, 568m, 636s, 662s, 710s, 846s, 912s, 946s, 1086m, 1200s, 1268w, 1364w, 1402m, 1456m, 1546s, 1638w, 2860w, 2934m, 3004m, 3104s, 3478m, 3540m, 3618w. Measurements. IR spectra (400−4000 cm−1) were measured with a PerkinElmer FTIR spectrometer (KBr pellets). The rt powder X-ray diffraction (PXRD) patterns were measured using a Stoe STADIP (Cu Kα1 equipped with a Mythen detector) and a Shimadzu XRD-6000 (Cu Kα). The temperature-dependent X-ray measurements were recorded on a Stoe STADIP with a high-temperature attachment and an image-plate detector system. Elemental analysis was carried out with a Vario EL-Heraeus microanalyzer. Magnetic susceptibility data were recorded using a Quantum Design MPMS-5XL SQUID magnetometer in the temperature range 300−1.9 K and at a field of 2 kG. The magnetic data were corrected for sample holder, diamagnetic contributions, and TIP contribution for CuII. X-ray Crystallography. Crystal Structure Determination. The diffraction data were collected with graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å) using a Stoe image-plate diffraction system (Lorentz-polarization factor and face-indexed numerical absorption correction using X-RED and X-SHAPE14). Measurements for 2 were performed on a Bruker APEX II CCD area-detector diffractometer (ω scans). The data were corrected for Lorentz-polarization effects and for the effects of absorption (multiscan method). The structures were solved by direct methods and refined by full-matrix least squares on F2 using SHELXS-97 and SHELXL-2014/7.15 In 3, two molecules of the organic ligand are situated across a mirror plane and exhibit different kinds of disorder by symmetry. For μ4-bitriazole, the central CH2 group of the trimethylene linkage is equally disordered across a mirror plane, while for the ligand bearing one noncoordinated triazole core,

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RESULTS AND DISCUSSION Synthesis and Composition Space Diagram. The composition space diagram approach toward the analysis of

Figure 2. Ternary diagram of the three-component system Cu(OAc)2/tr2pr/(NH4)6Mo7O24 with seven clearly defined crystallization fields of compounds 1−5, 8, and 9 constructed based on analysis of the PXRD patterns. Crystals of compounds 6 and 7 were found as a small admixture invisible for PXRD experiments. Gray areas in the left and right bottom corners correspond to copper oxides and an unknown molybdenum-rich inorganic admixture, respectively.

mixed-metal multicomponent systems showed very promising results.3−5,7 We applied the concept to expand it for the development and systematic investigation of copper molybdate coordination solids.9,17 D


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Inorganic Chemistry

In this work, we thoroughly explored the new Cu(OAc)2/ tr2pr/(NH4)6Mo7O24 system under hydrothermal conditions (160 °C, holding for 24 h, and cooling to rt within 48 h) by varying molar ratios of reagents from 1 to 8, keeping the total concentration of the CuII, MoVI, and tr2pr species equal to 200 mM. Prior to being fractionated, the reaction mixtures were inspected under a microscope to estimate the sample crystallinity and morphology and to select the best suited single crystals for structural investigations by X-ray crystallography. The whole product was then collected by filtration, dried in air, and analyzed by PXRD measurements (see also the Supporting Information, SI), while the solution contents were neglected. As a result, the crystallization diagram (Figure 2) was constructed based on 36 reaction points (see also the SI). In the ternary diagram of Figure 2, seven overlapping regions are clearly pointed out that correspond to crystallization of compounds 1−5, 8, and 9. Phases 1−3, being complexes of divalent copper(II), dominate in the right side of the triangle, whereas the areas of copper(I) compounds 8 and 9 occupy the left side (Figure 3). The crystallization field of compound 1, strictly located in the upper corner with high tr2pr content

Figure 3. Three regions (dotted lines) of different types of compounds can be defined: areas of copper(I) species (compounds 8 and 9), copper(II) compounds with octamolybdate anions (3−7), and copper(II) compounds with OH− bridges (2, 4, 5, and 7).

Table 1. Main Structural Features of Coordination Polymers Copper(II) [or Copper(I)]/Molybdenum(VI) Decorated with the tr2pr Ligand

compound [Cu(tr2pr){MoO4}]·H2O (1) [Cu3(OH)2(tr2pr){MoO4}2]·4H2O (2) [Cu2(tr2pr)4{Mo8O26}]·4H2O (3)

[Cu4(OH)4(tr2pr)2{Mo8O26}]·H2O (4) [Cu3(OH)2(tr2pr)3{Mo8O26}] (5)

[Cu3(tr2pr)2{Mo8O28H2}]·9H2O (6) [Cu3(OH)2(tr2pr)2(H2O)2{Mo8O26}]· 3H2O (7) [CuI4(tr2pr)4{Mo8O26}] (8) [CuI8(tr2pr)8]{Mo8O26}2·6H2O (9)

type of CuII,I fragment {CuII(μ2-tr) (MoO4)} {CuII3(μ2OH)2(μ2tr)2} {CuII2(μ2tr)3}

{CuII(μ2-tr) (μ2-OH)} {CuII3(μ2OH)2(μ2tr)2}

{CuII3(μ2tr)4(μ2OMo)} {CuII3(μ2OH)2(μ2tr)2} {CuI4(μ2tr)4(tr)2} {CuI4(μ2tr)6}

VI

type of Mo fragment

geometry of tr2pr

torsion angles in tr2pr (deg)

subtopology Cu/ tr2pr → Cu/tr2pr/ Mo

subtopology Cu/ Mo → Cu/tr2pr/ Mo

[MoO4]2−

anti/gauche

74.2, 173.2

2D → 2D

1D → 2D

[MoO4]2−

anti/anti

177.6, 177.6

2D → 3D

2D → 3D

anti/gauche

70.5, 178.1

2D → 2D

0D → 2D

β-[Mo8O26]4−

anti/gauche

12.6, 167.0a 39.1, 156.3a 39.1, 138.5a 72.0, 173.0

2D → 3D

2D → 3D

β-[Mo8O26]4−

anti/gauche

61.8, 171.0

3D → 3D

1D → 3D

100.9, 105.7

[Mo8O28H2]6−

pseudogauche/ gaucheb anti/anti

174.9, 179.2

1D → 3D

2D → 3D

[Mo8O26N2]4−

anti/gauche

68.9, 174.2

1D → 3D

2D → 3D

β-[Mo8O26]4−

anti/gauche

59.6, 167.9

3D → 3D

0D → 3D

anti/anti anti/anti

170.0, 177.7 172.4, 172.4

3D → 3D

0D → 3D

δ-[Mo8O26]4−

β- and α/β[Mo8O26]4−disordered

177.9, 177.9 a

Linkage disorder. bThe −CH2− linkage is equally disordered across the center of inversion. E


Article

Inorganic Chemistry

Figure 4. (a and b) In compound 1, the copper(II) chains supported by triple bridges of two μ2-N1N2-tr and one μ2-O1O2-MoO42− interconnected by the tetradentate tr2pr ligands into layered motifs.

Figure 5. Crystal structure of compound 2 incorporating the {Cu3(μ2-OH)2(μ2-tr)2}4+ SBUs connected by μ4-MoO42− bridges into a dense inorganic sheet, in which the alternation of molybdate and copper hydroxide rows is observed along the c axis.

(ratio diapasons CuII/tr2pr/MoVI = 1−3:4−8:1−4), can be associated with a preferable stability of MoO42− at relatively higher pH. Compound 2 as a minor product of a multicomponent mixture crystallizes mostly in the central part of the

diagram within the large window diapason CuII/tr2pr/MoVI = 1−5:1−5:2−8. However, compound 3 has even a larger distribution within the ternary diagram in the ratio range CuII/tr2pr/MoVI = 1−5:1−7:2−7. In the bottom right part F


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Inorganic Chemistry

the crystallization areas of copper(II) compounds with octamolybdate/hydroxide anion bridges cover the right side. These observations agree well with the previous studies of the 1,2,4-triazolyl-based and related heterocyclic ligand system.9,17 Thus, the formation of nine coordination polymers characterized in the CuII/MoVI system with flexible tr2pr clearly supports the ternary diagram as a prospective synthetic avenue for the development of new solids. Crystal Structure Description. The chemistry of copper molybdate−organic hybrids is distinguished by the possibility of unique interactions of copper(1+) or copper(2+) cations [or polynuclear copper(I,II) units] and molybdenum oxide anions with nitrogen-donor organic ligands. In this essence, the 1,2,4triazolyl functional group exhibits a strong coordination ability not only to cationic copper(II) centers but also to neutral or anionic molybdenum(VI) oxides, even providing a rare heteronuclear link CuII-[N-N]-MoVI.17,18 This observation beneficially differentiates 1,2,4-triazole molecules from many related organic modules, making them unique as ligands. Specifically, the flexibility of tr2pr, reflected in three possible conformations (anti/anti, anti/gauche, and gauche/gauche) can be a prerequisite of a rich diversity of the coordination compounds that might be available through conformational control. However, the only five examples of compounds reported so far do not provide enough comparable statistical distribution to prove the hypothesis.13,19 An interesting situation was observed for complexes with the glutarate dianion (in this ligand, two functional groups, similarly to tr2pr, are separated by a propylene spacer). A short survey of more than 100 coordination compounds with glutarate species, deposited

Figure 6. tr2pr ligand accepting the anti/anti conformation serving as a pillar linker between the inorganic sheets to form the 3D framework of 2.

occupied by compound 2, two more crystallization fields of compounds 4 and 5 are distinguished in the ratios CuII/tr2pr/ MoVI = 2−4:1−2:4−7 and 1−3:1:6−8 for 4 and 5, respectively. The left side of the triangle at high Cu(OAc)2 and low (NH4)6Mo7O24 molar contents belongs to the area of CuI coordination solids and copper(I,II) oxides (Figure 3), while

Scheme 2. Illustration of the Polymeric Motifs Prepared in the CuII/MoVI/tr2pr Systema

The formation of large isopolymolybdate anions, isomeric β- and δ-[Mo8O26]4− forms, and related [Mo8O28H2]6− and [Mo8O26N2]4− as chargecompensating and multidentate units seems to be a favorable process under the hydrothermal reaction conditions. Except for compound 3, various polymeric chains [Cu([N-N]-tr)]n2n+ composed of trinuclear coordination fragments and coordinating μ2-hydroxo and/or octamolybdate species dominate over other possible archetypes. a

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Figure 7. (a) Dinuclear copper(II) unit and coordinating δ-Mo8O264− anions in the crystal structure of 3. (b) [CuII2(μ2-tr)3]4+ SBUs are united in a 2D 4,4′-network, whereas the square-grid cavities are occupied by charge-compensating δ-Mo8O264− groups whose size and geometry perfectly fit for encapsulation.

Figure 8. (a) Cationic [Cu(OH)(tr)]nn+ chain supported by [N-N]-tr bridges of 4. The charge-compensating {β-Mo8O26}4− anions are held between the chains joining them through the axial positions of the copper(II) centers. (b) μ4-tr2pr ligands in the anti/gauche conformation interlink the neighboring chains, resulting in the 2D layer construction. Symmetry codes: (i) 1 − x, −y, 1 − z; (ii) −1 + x, y, 1 + z; (iii) 1 − x, 1 − y, 1 − z; (iv) 2 − x, −y, −z.

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through μ4-MoO4 bridges. Two independent copper(2+) ions possess distorted {CuNO4} square-pyramidal and centrosymmetric {CuN2O4} square-bipyramidal (octahedral) arrangements (Figure 5). The organic ligands display pseudolinear conformations (anti/anti) in the tetradentate mode. This connects the neighboring sheets at a distance of 11.68 Å to a 3D framework with 3 × 3 Å open channels, running along the c axis (Figure 6). The polymerization of molybdate anions to generate polyoxomolybdates, built up from edge- or corner-sharing MoO6/MoO5/MoO4 polyhedra, is a particularly favorable process under acidic and/or hydrothermal conditions.1,20 The most ideal spherical form of the species can be realized in an octanuclear cluster. Thus, different combinations of primary MoO6 or MoO5 and MoO4 polyhedra are represented in isomeric octamolybdate [Mo8O26]4− anions, known as α, β, γ, δ, ε, ζ, η, and θ isomers.21 Despite the fact that computational analysis showed less stability of the most compact β[Mo8O26]4− isomer,22 this form still predominates over the others in a number of coordination solids. In the solid-state structure of the coordination polymers, the polyoxomolybdates basically display charge-compensating, space-filling, and coordinating roles. The crystal structures of 3−9 contain different isomeric types of [Mo8O26]4− or related [Mo8O28H2]6− (Scheme 2). In the crystal structure of 3, copper cations possess squarebipyramidal (octahedral) coordination {CuN5O} with two elongated bonds of Cu−OMo = 2.504 Å and Cu−Ntr = 2.213 Å. The cations are coupled to [CuII2(μ2-tr)3] dinuclear secondary building blocks (SBUs) supported by triple [N-N]-tr bridges, whereas the single-coordinating tr groups fill the terminal positions. Unlike the previous cases, tr2pr exploits three different coordination modes as μ4-tetradentate and two bidentate N1,N2- and N1,N1-tr2pr in a 1:1:2 ratio per each [CuII2(μ2-tr)3] coordination cluster, respectively. It is interesting to note that all of the ligand types maintain the anti/gauche conformation, connecting the SBUs into a square-grid 4,4′-network along the a and b axes (Figure 7). The octamolybdate [Mo8O26]4− anion appears in the δ form, a combination of four MoO 6 octahedra and four MoO 4 tetrahedra. Two edge-shared dioctahedra are interconnected with four tetrahedra in a corner-sharing mode to form the bicapped anion.

Figure 9. Formation of the 3D crystal structure of 4. The multidentate {β-Mo8O26}4− anions act as pillars between the [Cu4(OH)4(tr2pr)2]4+ layers.

in the CCDC database, showed that the anti/gauche form is the most frequently observed (∼49%); thus, the contribution of gauche/gauche and anti/anti is noticeably less but similar, 22 versus 29%, respectively. A summary of the solid-state structural features of compounds 1−9 is presented in Table 1. Compounds 1 and 2 both involve molybdenum(VI) oxide in the form of {MoO4}2− tetrahedral anions. In the crystal structure of 1, copper(2+) cations are organized into infinite chains along the b axis through triple bridges of two μ2-N1N2-tr and one μ2O1O2-MoO42− unit (Figure 4a). The copper(II) center possesses a {CuN4O2} square-bipyramidal (octahedral) environment with 2N + 2O in the equatorial plane and 2N in the axial positions. The organic ligand acts as a tetradentate donor and appears in an angular anti/gauche conformation connecting the neighboring copper(II) chains at a Cu···Cu distance of 10.91 Å (Figure 4b). In the crystal structure of 2, another combination of copper(II) and molybdenum(VI) centers resulted in trinuclear {Cu3(μ2-OH)2(μ2-tr)2}4+ clusters with a Cu···Cu distance of 3.377 Å. These fragments are integrated into a 2D layer

Figure 10. (a and b) In 5, the discrete {Cu3(μ2-OH)2(μ2-tr)2}4+ SBUs are joined by double [N1N2]-tr bridges, forming the cationic chain; [βMo8O26]4− isopolyanions unite them to a layered motif, while the tetradentate tr2pr is responsible for the 3D framework. Symmetry code: 1 − x, −y, 1 − z. I


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Figure 11. (a) Layered motif found in the crystal structure of compound 7 built up from interconnected {Cu3(μ2-OH)2}4+ and {Mo8O26N2}4− inorganic building blocks, which are supported by μ4-coordination of tr2pr. (b) Crystal packing of 7 (view along the b axis) illustrating a dense packing of the neighboring layers (cocrystallizing water molecules are not shown).

4.16 Å) running along the a axis (Figure 10a). Thanks to the tetradentate binding mode of tr2pr, the chains are interwoven along the b and c axes, forming a 3D framework. The squarebipyramidal (octahedral) coordination arrangements of the copper(II) centers {CuN2O2 + O2}/{CuN3O + ON} are achieved by nitrogen atoms of tr2pr and oxygen atoms of μ2OH− bridges in the equatorial planes, while the axial positions are occupied mostly by oxygen atoms of [β-Mo8O26]4− anions. The latter perfectly sit inside the framework voids, leaving no space for additional guest inclusion. Similar to compound 5, the crystal structure of 7 contains the {Cu3(μ2-OH)2(μ2-tr)2}4+ SBUs, which are integrated into the chain motifs through bridging [N-N]-tr moieties. The latter provide a rare heterolink between copper(2+) cations and molybdenum(VI) atoms of octamolybdate (Figure 11).17,23,24 In the unusual configuration of the isopolymolybdate anion, two additional nitrogen-donor atoms of triazole ligands extend the coordination to {Mo8O26N2}4− groups, a combination of edge-sharing six [MoO6] and two [MoO5N] octahedral units. Its structure can be derived from the γ-octamolybdate core by attaching two nitrogen atoms of two tr groups. These anions are additionally binding to the copper(2+) ions employing four oxygen atoms of the molybdenyl groups, thus connecting the neighboring chains into a 2D layer. In the crystal structure of closely related 6 (Figure 12), the absence of negatively charged bridging OH− species in the molecular formula is compensated by the presence of six

The crystal structure of complex 4 contains three independent copper(2+) ions, which are aligned by the double bridges of μ2-N1N2-tr and μ2-OH− in an infinite cationic chain. The coordination environments of the Cu1, Cu2, and Cu3 centers can be described as square-planar {N2O2}, squarepyramidal {N2O2 + O} and square-bipyramidal (octahedral) {N2O2 + O2}, respectively (Figure 8). Within each chain, the copper centers form the repeating sequence [Cu1−Cu2−Cu3− Cu2]n. The organic ligand in the anti/gauche conformation exhibits a tetradentate bridging mode interconnecting the adjacent copper(II) hydroxo chains at Cu···Cu distances of 9.88, 11.62, and 13.37 Å into a 2D layer. All non-hydrogen atoms occupy the general positions, whereas the crystallographic symmetry center lies in the barycenter of {βMo8O26}4−. These charge-compensating anions are located between the [Cu4(OH)4(tr2pr)2]4+ layers (Figure 9), along the cationic [Cu(OH)]nn+ chain, forming elongated coordination bonds with copper(2+) cations (distances Cu−OMo = 2.746 and 2.769 Å) and hydrogen-bonding interactions with water molecules (see Table S6). As a matter of fact, the combination of copper(2+) cations, OH− and Mo8O264− anions, and neutral triazolyl ligand can be realized in various structural archetypes.17,23 In the crystal structure of 5, the copper(2+) ions are organized in discrete centrosymmetrical trinuclear units {Cu3(μ2-OH)2(μ2-tr)2}4+ (Figure 10a). These SBUs are interlinked into infinite chains by means of double μ2-N1N2-triazole bridges (Cu···Cu distance J


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Figure 13. (a) Extended alignment of copper(I) atoms in the crystal structure of 8. (b) 3D cationic framework [CuI4(tr2pr)4]nn+, particularly suited to accommodate {β-Mo8O26}4− anions, which perform a bridging bidentate binding mode. Figure 12. (a and b) Projection of the coordination layer and 3D architecture in the crystal structure of 6, demonstrating coordination interactions between linear cations [Cu3(tr)4]6+ and bridging anions {Mo8O28H2}6− (hydrogen atoms not shown). In the centrosymmetrical {Mo8O28H2}6− unit, one hydrogen atom is attached to one O1 of a molybdenyl group, forming a strong intermolecular hydrogenbonding contact between two neighboring isopolyanions [(Mo1)− O1---H···O1(Mo1) 2.658 Å], whereas the other proton position at the μ2-O14 atom allows interaction between the octamolybdate and a water molecule [O14---H···O3w 2.864 Å; see Table S8].

of copper(I) oxide was earlier described for the Cu(OAc)2/ (NH4)6Mo7O24 inorganic reaction system itself.9 In 8, the coordination environments of copper atoms can be described as distorted tetrahedral {CuN4} and four-coordinate seesaw {CuN3O} arrangements. The copper atoms are organized in a centrosymmetric rhomboidal unit consisting of four copper atoms at the corners, four bridging [N-N]-tr, and two terminal N-tr groups (Figure 13a). The [N-N]-tr groups provide a double [N-N] connection between neighboring clusters through the two opposite corners (Cu2···Cu2i 3.747 Å), forming expanded linear motifs along the a axis. The organic ligands reveal two different coordination modes, μ4 and μ3, in a 1:1 ratio that also corresponds to anti/anti and anti/ gauche conformations, respectively. Altogether, these factors lead to the 3D cationic framework (Figure 13b), within which the encapsulated {β-Mo8O26}4− anions act in a bidentate fashion. In 9, the coordination environment of the copper atoms is distorted tetrahedral, {CuN4}. Similar to compound 8, the structural motif of the four closest copper centers can be regarded as a centrosymmetric rhomboid [Cu4(N-N)6]4+, in which copper atoms are joined by means of six bridging [N-N]tr ligands (Figure 14). The adjacent rhomboids are linked through four neighboring corners by [N-N]-tr donors. This assembly resembles similar structural motifs of silver(I) 1,2,4triazolyl derivatives.27 The organic ligands exhibit tetradentate

charged {Mo8O28H2}6− anions, which belong to a rare kind of isopolymolybdate, whose structure can be associated with γtype {Mo8O26}4−.25 The species behave as decadentate building blocks that promote the linear arrangement of trinuclear cations [Cu3(tr)4]6+ and expand the fragments into the linear [Cu3(tr)4]n chains incorporated into a 2D network subtopology. The tr2pr ligand in the anti/gauche conformation adopts a tetradentate binding mode that connects the inorganic [Cu3{Mo8O28H2}] layers in the third dimension along the b axis. Upon crystallization from the Cu(OAc) 2 /tr 2 pr/ (NH4)6Mo7O24 reaction media, two related complexes (8 and 9) of CuI were prepared. Generally, the CuII → Cu I transformation is well stabilized by the coordination of nitrogen-donor heterocyclic ligands,26 although the formation K


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Figure 14. (a) Formation of a ladder-like chain of copper(I) atoms running along the a axis of 9. (b) Combination of copper(I) atoms as the tetrahedral nodes and μ4-tr2pr as the linear spacers, which affords a 3D framework with open channels, half of which are occupied by ordered β[Mo8O26]4− anions, while the other half is populated by disordered β- and α-Mo8O264− with occupancy factors of 0.85 and 0.15, respectively.

Figure 15. IR spectra confirming isomerization of the octamolybdate anion, from the δ to β isomer for the calcined sample 3-195. (b) Temperaturedependent PXRD patterns (Guinier−Simon diagram; Cu Kα1 radiation, 2θ = 5−80°) for compound 3 indicating the thermally induced phase transition.

cooled to rt in a desiccator over CaCl2, show characteristic changes compared to the rt data of noncalcined samples. Below 195 °C, these changes are negligible, except 3, and can be associated with dehydration, whereas higher temperature experiments cause irreversible decomposition of the tr ligand, accompanied by the appearance of new absorption bands at 2198 and 2112 cm−1.9 The data show that the thermal stability of 2D 1 is lowest (up to 220 °C), whereas the other compounds possessing 3D motifs are quite stable up to 250 °C. Interestingly, in the range of ν(MoO) and ν(Mo−O−Mo) vibrations the IR spectra of compound 3 and the preheated sample 3-195 are noticeably different (e.g., the strong band at 801 cm−1 in 3 disappeared in sample 3-195, see Figures S28 and S29. On the other hand, the IR spectrum of sample 3-195 is very similar to those of 4 and 5 in the range of 1000−400 cm−1 (Figure 15a), clearly indicating thermally induced isomerization of the octamolybdate anion, from the δ isomer to the more stable β isomer. The thermal behavior of compounds 1 and 3−5 was also analyzed by temperature-dependent PXRD. Unlike the temperature-dependent PXRD of 1, 4, and 5 (Figures S39, S41, S42),

Figure 16. Thermal variation of χmT (a) for 1 and (b) for 3, respectively. The solid line is a fit.

coordination accepting anti/anti conformations. This results in adjacent ladder-like chains, which are separated in the crystal lattice at remarkably larger distances in comparison to those of complex 8. As a result, the 3D arrangement of [CuI8(tr2pr)8]8+ accommodates β and α isomers of {Mo8O26}4− and numerous crystallization water molecules. Thermal Stability. The IR spectra of the compounds, obtained after the samples were gradually heated in air (1 °C per min) from rt to 140, 195, 220, 250, and 300 °C and then L


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for which a fitting procedure seemed not to be feasible. All of these observations, however, can be rationalized while analyzing the planes of the magnetic orbitals of the copper(II) centers for complexes 1 and 3−5 (Figure 17). The mutual orientation of the adjacent planes is less favorable for exchange interactions for sample 1 and somewhat better for sample 3, which is reflected in the magnitude of their J values. These values lie in the expected range, as has been observed for similar compounds.17,30 To note, a very detailed structural correlation for the observed coupling constants can be a very effortful task, even in the case of simple and well-defined systems.31 For compound 3, one may compare the strength of the magnetic exchange interaction with that of a dimeric copper(II) complex, where similarly three bridging ligands offer a superexchange pathway and, instead of a triazole, a pyridazine acts as the bridging ligand.27 In that case, the coupling constant amounts to 2J = −35 cm−1 (g = 2.1), which lies reasonably close to the value of 3. The chain compound 1 can be compared with a similar copper(II) chain comprising also triazole-type ligands and revealing a J value of −22.3 cm−1.17 In that case, the triazole bridge is linked to the magnetic planes of both copper(II) ions, whereby for 1, one orthogonal linkage is involved; consequently, J is distinctly reduced to −7.9 cm−1. Now, samples 4 and 5 reveal an orientation of the adjacent planes of magnetic orbitals in a much more coplanar fashion, which leads to the observed strong coupling between neighboring copper(2+) ions. In a similar manner, another copper(II) chain comprising triazole-type ligands and nearly coplanar arrangements of the magnetic orbitals exhibits the analogous feature with strong antiferromagnetic coupling, so that only the decreasing tail within a χmT(T) plot is visible.17 A more quantitative structural correlation is clearly beyond the scope of this study.

Figure 17. Visualization of the planes of magnetic orbitals for complexes 1 (a), 3 (b), 4 (c), and 5(d).

the PXRD patterns of 3 have significant shifts of their diffraction peaks (Figure 15b), suggesting the formation of a new crystalline phase. This can be caused by the release of water molecules and isomerization of the octamolybdate anion. The temperature-dependent PXRD data confirmed that compounds 3−5 are thermally stable until 250 °C, although sample 1 lost its crystallinity in the range of 190−230 °C. These observations agree well with those obtained from the IR experiments for the calcined samples. Magnetic Properties. Compounds 1 and 3 were investigated by magnetic susceptibility measurements. The χmT(T) plot of a polycrystalline sample of 1 (Figure 16a) exhibits a rt value of 0.428 cm3 K mol−1 (theoretical value χmT = 0.375 cm3 K mol−1 for S = 1/2 and g = 2), which stays constant in the high-temperature region and strongly decreases for temperatures below 50 K. This behavior is characteristic for weak antiferromagnetic coupling between neighboring copper(II) centers along the chain structure. The data were modeled following the theoretical approach of Rojo et al.,28 however, by applying only one J value, reflecting the regular chain structure. On the basis of the spin Hamiltonian H = −JΣSi·Si+1, a best fit resulted in the following parameters: g = 2.16, J = −11.4 K (−7.9 cm−1). Compound 3 with dinuclear {CuII2(tr2pr)4}4+ units exhibits a rt value of 0.71 cm3 K mol−1 [for two copper(2+) ions], which is continuously decreasing toward zero with lowering temperatures (Figure 16b). A best fit of a dinuclear model according to the Bleaney−Bowers equation29 resulted in the parameters g = 2.08 and 2J = −68.2 K (−47.4 cm−1). Magnetic susceptibility measurements for compounds 4 and 5 showed a quite different picture. In stark contrast to compounds 1 and 3, the neighboring copper(II) centers in 4 and 5 are magnetically coupled more strongly. The existence of a strong antiferromagnetic exchange interaction in these compounds implicates that a plateau in a χmT(T) plot is found far above rt. In the temperature range below rt, only the decreasing tail of the χmT curve was measurable in both cases,

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CONCLUSIONS Nine coordination polymers of various architectures were developed in the Cu(OAc)2/tr2pr/(NH4)6Mo7O24 system by employing hydrothermal crystallization utilizing the composition space diagram approach. The observed structural diversity was basically caused by the coordination binding modes and conformational flexibility of the bistriazole ligand, which serves as μ4-, μ3-, and μ2-[N1N2] and μ2-[N1N1′] bridges in three conformational forms, anti/anti, anti/gauche, and gauche/ gauche. The hydrothermal conditions were the main driving force for the formation of anionic octamolybdates (α-, δ-, and β-{Mo8O26}4− and related {Mo8O28H2}6− and {Mo8O26N2}4− forms), hydroxide, and cationic copper(I) species to be generated in situ. Our study demonstrates that the composition space diagram approach can be reconsidered as the key “leitmotif” toward the development, deep analysis, and reinvestigation of many related polyoxometalate systems. For instance, the existence of large crystallization zones of copper(I)/molybdenum(VI) compounds found in the ternary diagram Cu(OAc)2/tr2pr/(NH4)6Mo7O24 can be exploited for the preprogrammed synthesis of the species in a rational manner.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01735. M


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early transition metal (Nb, Mo) oxyfluoride anions. Dalton Trans. 2009, 17, 3280−3285. (6) Cadiau, A.; Martineau, C.; Taulelle, F.; Adil, K. Investigation of the composition space diagram of the ZnF2−3,5-diamino-1,2,4triazole−HF−H2O chemical system and structural characterization of a new fluorinated guanazolate MOF [Zn3F2]·(Am2TAZ)4. J. Fluorine Chem. 2013, 150, 104−108. (7) Fernández de Luis, R.; Urtiaga, M. K.; Mesa, J. L.; Larrea, E. S.; Rojo, T.; Arriortua, M. I. Compositional space diagrams and crystallization sequences in M/Bpa/NaVO3 (M = Ni, Co) systems. Physical properties of [{Ni(H2O)(Bpa)}(VO3)2]·2H2O and {Co(Bpa)}(VO3)2 3D hybrid vanadates. CrystEngComm 2012, 14, 6921− 6933. (8) Kim, J.-Y.; Norquist, A. J.; O’Hare, D. Variable Dimensionality in the UO2(CH3CO2)2·2H2O/HF/Isonicotinic Acid System: Synthesis and Structures of Zero-, One-, and Two-Dimensional Uranium Isonicotinates. Chem. Mater. 2003, 15, 1970−1975. (9) Senchyk, G. A.; Lysenko, A. B.; Babaryk, A. A.; Rusanov, E. B.; Krautscheid, H.; Neves, P.; Valente, A. A.; Gonçalves, I. S.; Krämer, K. W.; Liu, S.-X.; Decurtins, S.; Domasevitch, K. V. Triazolyl−Based Copper−Molybdate Hybrids: From Composition Space Diagram to Magnetism and Catalytic Performance. Inorg. Chem. 2014, 53, 10112− 10121. (10) Wu, X.-Y.; Kuang, X.-F.; Zhao, Z.-G.; Chen, S.-C.; Xie, Y.-M.; Yu, R.-M.; Lu, C.-Z. A series of POM-based hybrid materials with different copper/aminotriazole motifs. Inorg. Chim. Acta 2010, 363, 1236−1242. (11) (a) Lu, X.-X.; Luo, Y.-H.; Liu, Y.-S.; Ma, W.-W.; Xu, Y.; Zhang, H. Assembly of three stable POM-based pillar-layer CuI coordination polymers with visible light driven photocatalytic properties. CrystEngComm 2016, 18, 3650−3654. (b) Tian, A.-X.; Ning, Y.-L.; Ni, H.-P.; Hou, X.; Xiao, R.; Ying, J. Two new POM-based compounds containing a linear tri-nuclear copper(II) cluster and an infinite copper(II) chain, respectively. Z. Naturforsch., B: J. Chem. Sci. 2016, 71, 1125−1134. (12) Dutta, D.; Jana, A. D.; Debnath, M.; Bhaumik, A.; Marek, J.; Ali, M. Robust 1D open rack-like architecture in coordination polymers of Anderson POMs [{Na4(H2O)14}{Cu(gly)}2][TeMo6O24] and [{Cu(en)2}3{TeW6O24}]: synthesis, characterization and heterogeneous catalytic epoxidation of olefines. Dalton Trans. 2010, 39, 11551− 11559. (13) Lysenko, A. B.; Senchyk, G. A.; Lincke, J.; Lässig, D.; Fokin, A. A.; Butova, E. D.; Schreiner, P. R.; Krautscheid, H.; Domasevitch, K. V. Metal oxide-organic frameworks (MOOFs), a new series of coordination hybrids constructed from molybdenum(VI) oxide and bitopic 1,2,4-triazole linkers. Dalton Trans. 2010, 39, 4223−4231. (14) (a) X-SHAPE, revision 1.06; Stoe & Cie GmbH: Darmstadt, Germany, 1999. (b) X-RED, version 1.22; Stoe & Cie GmbH: Darmstadt, Germany, 2001. (15) (a) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112. (b) Sheldrick, G. M. Phase annealing in SHELX-90: direct methods for larger structures. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990, 46, 467−473. (16) Brandenburg, K. Diamond 2.1e; Crystal Impact GbR: Bonn, Germany, 1999. (17) Lysenko, A. B.; Senchyk, G. A.; Lukashuk, L. V.; Domasevitch, K. V.; Handke, M.; Lincke, J.; Krautscheid, H.; Rusanov, E. B.; Krämer, K. W.; Decurtins, S.; Liu, S.-X. Composition Space Analysis in the Development of Copper Molybdate Hybrids Decorated by a Bifunctional Pyrazolyl/1,2,4-Triazole Ligand. Inorg. Chem. 2016, 55, 239−250. (18) Meng, J.-X.; Lu, Y.; Li, Y.-G.; Fu, H.; Wang, E.-B. Base-Directed Self-Assembly of Octamolybdate-Based Frameworks Decorated by Flexible N-Containing Ligands. Cryst. Growth Des. 2009, 9, 4116− 4126. (19) (a) Senchyk, G. A.; Lysenko, A. B.; Krautscheid, H.; Rusanov, E. B.; Chernega, A. N.; Krämer, K. W.; Liu, S.-X.; Decurtins, S.; Domasevitch, K. V. Functionalized Adamantane Tectons Used in the Design of Mixed-Ligand Copper(II) 1,2,4-Triazolyl/Carboxylate

Crystallographic data and experimental details of X-ray structural analyses, spectral characterization data, PXRD, thermo-PXRD diffractograms, IR spectra, and synthetic details for composition diagram (PDF) Accession Codes

CCDC 1557536−1557544 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 Authors

*E-mail: [email protected] (A.B.L.). *E-mail: [email protected] (S.-X.L.). ORCID

Andrey B. Lysenko: 0000-0002-0342-5122 Shi-Xia Liu: 0000-0001-6104-4320 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by Deutsche Forschungsgemeinschaft (Grant KR 1675/12-1) and by the Swiss National Science Foundation (Grant 200020-172659) is gratefully acknowledged.

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REFERENCES

(1) (a) Pope, M. T.; Müller, A. Polyoxometalate Chemistry From Topology via Self-Assembly to Applications; Kluwer Academic: Dordrecht, The Netherlands, 2001. (b) Dolbecq, A.; Dumas, E.; Mayer, C. R.; Mialane, P. Hybrid Organic−Inorganic Polyoxometalate Compounds: From Structural Diversity to Applications. Chem. Rev. 2010, 110, 6009−6048. (c) Clemente-Juan, J. M.; Coronado, E.; Gaita-Ariño, A. Magnetic polyoxometalates: from molecular magnetism to molecular spintronics and quantum computing. Chem. Soc. Rev. 2012, 41, 7464−7478. (d) Lv, H.; Geletii, Y. V.; Zhao, C.; Vickers, J. W.; Zhu, G.; Luo, Z.; Song, J.; Lian, T.; Musaev, D. G.; Hill, C. L. Polyoxometalate water oxidation catalysts and the production of green fuel. Chem. Soc. Rev. 2012, 41, 7572−7589. (2) (a) Miras, H. N.; Yan, J.; Long, D.-L.; Cronin, L. Engineering polyoxometalates with emergent properties. Chem. Soc. Rev. 2012, 41, 7403−7430. (b) Proust, A.; Matt, B.; Villanneau, R.; Guillemot, G.; Gouzerh, P.; Izzet, G. Functionalization and post-functionalization: a step towards polyoxometalate-based materials. Chem. Soc. Rev. 2012, 41, 7605−7622. (3) Albrecht, T. A.; Stern, C. L.; Poeppelmeier, K. R. The Ag2OV2O5-HF(aq) System and Crystal Structure of α-Ag3VO4. Inorg. Chem. 2007, 46, 1704−1708. (4) (a) Halasyamani, P.; Willis, M. J.; Stern, C. L.; Lundquist, P. M.; Wong, G. K.; Poeppelmeier, K. R. Composition Space of the (CuO, 1/ 2 Nb2O5)/(HF)x·pyridine/H2O System. Structure and Synthesis of [pyH+]2[CuNb2(py)4O2F10]−2 and CuNb(py)4OF5. Inorg. Chem. 1996, 35, 1367−1371. (b) Halasymani, P. S.; Heier, K. R.; Norquist, A. J.; Stern, C. L.; Poeppelmeier, K. R. Composition Space of the (CdO,1/2Nb2O5)/(HF)x pyridine/H2O System. Structure and Synthesis of CdNb(py) 4OF5. Inorg. Chem. 1998, 37, 369−371. (c) Norquist, A. J.; Heier, K. R.; Stern, C. L.; Poeppelmeier, K. R. Composition Space Diagrams for Mixed Transition Metal Oxide Fluorides. Inorg. Chem. 1998, 37, 6495−6501. (d) Guillory, P. C. R.; Kirsch, J. E.; Izumi, H. K.; Stern, C. L.; Poeppelmeier, K. R. Evidence for Nonpolar Alignment of [NbOF 5 ] 2 ‑ Anions in Cd(pyridine)4NbOF5 Chains. Cryst. Growth Des. 2006, 6, 382−389. (5) Mahenthirarajah, T.; Li, Y.; Lightfoot, P. Organic−inorganic hybrid chains and layers constructed from copper-amine cations and N


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Inorganic Chemistry

Studies of Dimeric CuI Complexes with Schiff-Base-Containing Triazole Ligands. Eur. J. Inorg. Chem. 2003, 8, 1548−1554. (c) Zhai, Q.; Lu, C.; Zhang, Q.; Wu, X.; Xu, X.; Chen, S.; Chen, L. Influence of substituents on the structures of hybrid complexes constructed from tetranuclear copper(I) 1,2,4-triazolate clusters and octamolybdates. Inorg. Chim. Acta 2006, 359, 3875−3887. (27) (a) Liang, N.; Cui, Y.-F.; Yuan, D.-Y.; Li, B.-L.; Li, H.-Y. Anioncontrolled four silver coordination polymers with flexible bis(1,2,4triazol-4-yl)ethane. Inorg. Chim. Acta 2011, 376, 612−618. (b) Wang, Y.; Ding, B.; Cheng, P.; Liao, D.-Z.; Yan, S.-P. Tuned Triazolate silver(I) Luminescent Complexes from Zero- to Three-Dimensionality Based on Bi- to Tetratopic Bridged Ligands. Inorg. Chem. 2007, 46, 2002−2010. (28) Cortés, R.; Drillon, M.; Solans, X.; Lezama, L.; Rojo, T. Alternating Ferromagnetic-Antiferromagnetic Interactions in a Manganese(II)-Azido One-Dimensional Compound: [Mn(bipy)(N3)2]. Inorg. Chem. 1997, 36, 677−683. (29) Bleaney, B.; Bowers, K. D. Anomalous Paramagnetism of Copper Acetate. Proc. R. Soc. London, Ser. A 1952, 214, 451−465. (30) Degtyarenko, A. S.; Handke, M.; Krämer, K. W.; Liu, S.-X.; Decurtins, S.; Rusanov, E. B.; Thompson, L. K.; Krautscheid, H.; Domasevitch, K. V. Mixed-ligand hydroxocopper(II)/pyridazine clusters embedded into 3D framework lattices. Dalton Trans. 2014, 43, 8530−8542. (31) Decurtins, S.; Güdel, H. U. Superexchange in Bis(μ-hydroxo)Bridged Chromium(III) Dimers. Optical Spectroscopic Study of Singly Excited 2Eg4A2g Pair States. Inorg. Chem. 1982, 21, 3598−3606.

Metal−Organic Frameworks. Inorg. Chem. 2013, 52, 863−872. (b) Sharga, O. V.; Lysenko, A. B.; Handke, M.; Krautscheid, H.; Rusanov, E. B.; Chernega, A. N.; Krämer, K. W.; Liu, S.-X.; Decurtins, S.; Bridgeman, A.; Domasevitch, K. V. Unprecedented Trapping of Difluorooctamolybdate Anions within an α-Polonium Type Coordination Network. Inorg. Chem. 2013, 52, 8784−8794. (20) Hagrman, P. J.; Hagrman, D.; Zubieta, J. Organic-Inorganic Hybrid Materials: From “Simple” Coordination Polymers to Organodiamine-Templated Molybdenum Oxides. Angew. Chem., Int. Ed. 1999, 38, 2638−2684. (21) (a) Allis, D. G.; Rarig, R. S.; Burkholder, E.; Zubieta, J. A threedimensional bimetallic oxide constructed from octamolybdate clusters and copper−ligand cation polymer subunits. A comment on the stability of the octamolybdate isomers. J. Mol. Struct. 2004, 688, 11− 31. (b) Rarig, R. S.; Zubieta, J. Hydrothermal synthesis and structural characterization of an organic−inorganic hybrid material: (H2tptz)2[δMo8O26]·2H2O (tptz = 2,4,6-tripyridyltriazine). Inorg. Chim. Acta 2001, 312, 188−196. (c) Shi, Y. P.; Yang, W.; Xue, G. L.; Hu, H. M.; Wang, J. W. A novel crystal coexisting with two kinds of polyoxomolybdates: [n-Bu4N]8[Mo6O19]2[α-(Mo8O26)]. J. Mol. Struct. 2006, 784, 244−248. (d) Wang, W. J.; Xu, L.; Wei, Y. G.; Li, F. Y.; Gao, G. G.; Wang, E. B. A novel hybrid crystal of chiral racemic complexes coexisting with two kinds of polyoxomolybdates: synthesis and structure of [Co(bpy)3]2[Mo6O19] [β-(H2Mo8O26)]·4H2O. J. Solid State Chem. 2005, 178, 608−612. (e) Xiao, D. R.; Hou, Y.; Wang, E. B.; Wang, S. T.; Li, Y. G.; Xu, L.; Hu, C. W. Hydrothermal synthesis and characterization of an unprecedented η-type octamolybdate: [{Ni(phen)2}2(Mo8O26)]. Inorg. Chim. Acta 2004, 357, 2525−2531. (f) Luo, L.; Lin, H.; Li, L.; Smirnova, T. I.; Maggard, P. A. CopperOrganic/Octamolybdates: Structures, Bandgap Sizes, and Photocatalytic Activities. Inorg. Chem. 2014, 53, 3464−3470. (g) Hagrman, D.; Zapf, P. J.; Zubieta, J. A two-dimensional network constructed from hexamolybdate, octamolybdate and [Cu3(4,7-phen)3]3+ clusters: [{Cu3(4,7-phen)3}2{Mo14O45}]. Chem. Commun. 1998, 1283−1284. (h) Allis, D. G.; Burkholder, E.; Zubieta, J. A new octamolybdate: observation of the θ-isomer in [Fe(tpyprz)2]2[Mo8O26]·3.7H2O (tpyprz = tetra-2-pyridylpyrazine). Polyhedron 2004, 23, 1145−1152. (i) Wang, W. J.; Xu, L.; Wei, Y. G.; Li, F. Y.; Gao, G. G.; Wang, E. B. A novel hybrid crystal of chiral racemic complexes coexisting with two kinds of polyoxomolybdates: synthesis and structure of [Co(bpy)3]2[Mo6O19] [β-(H2Mo8O26)]·4H2O. J. Solid State Chem. 2005, 178, 608−612. (22) Bridgeman, A. J. The Electronic Structure and Stability of the Isomers of Octamolybdate. J. Phys. Chem. A 2002, 106, 12151−12160. (23) Gong, Y.; Wu, T.; Jiang, P. G.; Lin, J. H.; Yang, Y. X. Octamolybdate-Based Metal−Organic Framework with Unsaturated Coordinated Metal Center As Electrocatalyst for Generating Hydrogen from Water. Inorg. Chem. 2013, 52, 777−784. (24) (a) Tian, A.-X.; Liu, X.-J.; Ying, J.; Zhu, D.-X.; Wang, X.-L.; Peng, J. A series of organopolymolybdate polymers linked by dual fuses: metal−organic moiety and organic ligand through Mo−N bonds. CrystEngComm 2011, 13, 6680−6687. (b) Zhu, M.; Su, S.-Q.; Song, X.-Z.; Hao, Z.-M.; Song, S.-Y.; Zhang, H.-L. Spin canting magnetization in a 3D Cu(II) complex based on molybdate oxide cluster and 5-triazole isophthalic acid. Dalton Trans. 2012, 41, 13267− 13270. (25) (a) Isobe, M.; Marumo, F.; Yamase, T.; Ikawa, T. The Crystal Structure of Hexakis(isopropylammonium) Dihydrogenoctamolybdate(6-) Dihydrate, (C3H10N)6[H2Mo8O28]· 2H2O. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1978, 34, 2728−2731. (b) Yamase, T.; Suga, M. Photochemical studies of alkylammonium molybdates. Part 8. Location of protons interacting with the paramagnetic electron in a single crystal of photoirradiated [NH3Pri]6[Mo8O26(OH)2]·2H2O. J. Chem. Soc., Dalton Trans. 1989, 4, 661−669. (26) (a) Drabent, K.; Bialonska, A.; Ciunik, Z. New porous crystals of Cu(I) complexes with Schiff-base-containing triazole ligands. Inorg. Chem. Commun. 2004, 7, 224−227. (b) Drabent, K.; Ciunik, Z.; Chmielewski, P. J. Synthesis, Crystallographic and Spectroscopic O


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