The First Characterized Coordination Compounds ... - ACS Publications

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The First Characterized Coordination Compounds of Macrocyclic Ligands Including Incorporated Tetrazole Rings Sergei V. Voitekhovich,*,† Alexander S. Lyakhov,† Ludmila S. Ivashkevich,† Sara Schmorl,‡ Berthold Kersting,‡ and Oleg A. Ivashkevich§ †

Research Institute for Physical Chemical Problems of Belarusian State University, Leningradskaya 14, 220006 Minsk, Belarus Institute of Inorganic Chemistry, University of Leipzig, Johannisallee 29, D-04103 Leipzig, Germany § Belarusian State University, Nezalezhnastsi Avenue 4, 220050 Minsk, Belarus ‡

S Supporting Information *

ABSTRACT: The macrocyclic binuclear tetrazole, 2,2,5,5-tetramethyl-12-oxa-1,6,7,8,16,17,18,19-octaazatricyclo[13.2.1.16,9]nonadeca-7,9(19),15(18),16-tetraene (L), reacts with copper(II) chloride or copper(II) tetrafluoroborate hexahydrate to give complexes [Cu3Cl6L2] (1) or [CuL2(H2O)2](BF4)2(H2O) (2), respectively. According to single crystal X-ray analysis, both complexes were found to be coordination polymers. In the crystal structure of complex 1, there are neutral linear bibridged trinuclear units Cu3Cl6, in which the copper atoms are linked together by double chlorine bridges. Neighboring Cu3Cl6 units are bonded to each other by two bridging macrocyclic ligands L due to coordination bonds Cu−N between terminal copper atoms of Cu3Cl6 units and the tetrazole ring nitrogen atoms of ligands L to form polymeric chains. In complex 2, the copper atom is bonded to three ligands L via the tetrazole ring nitrogen atoms, and to two water molecules, with formation of a squarepyramidal coordination of the metal. In this complex, one of two independent ligands L shows monodentate coordination, whereas another ligand plays the role of a bridge between two neighboring copper atoms being responsible for formation of polymeric cationic chains [CuL2(H2O)2]n2n+. A complex system of hydrogen bonds connects the chains and the anions BF4− into a three-dimensional network. The temperature-dependent magnetic susceptibility measurements of complex 1 revealed that the copper(II) ions were ferromagnetically coupled showing a coupling constant J of 50 cm−1.

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magnetic resonance imaging agents11 and catalysts for different chemical transformations.12 Tetrazole-based compounds are promising ligands, because tetrazoles present multidentate ligands capable of various coordination modes.13−17 One, two, three, and even four tetrazole ring nitrogen atoms can participate in binding with metal ions. This determines the application of tetrazole derivatives for the design of various metal complexes with specific properties. So, their mononuclear metallocomplexes are of interest as spin-crossover materials18 and components of organic light emitting diodes,19 whereas polynuclear ones present an important class of coordination polymers and

INTRODUCTION Macrocyclic compounds occupy a unique segment of chemical and biological sciences. Because of the size, complex structural organization, and limited conformational freedom, they are of interest as ligands for investigations of binding interactions with various targets, from small simple ions to huge molecules like peptides and DNA.1−3 These investigations have achieved significant success in the area of drug discovery.4,5 Nowadays, various macrocyclic drugs are involved in clinical practice. Complexation of macrocyclic ligands toward metal cations rather differs from linear analogues. In particular, macrocycles show specific ion selectivity and generate more stable metallocomplexes even with low coordinating cations.6,7 For this reason, macrocyclic compounds are effective sensors and extractants for determination and isolation of various cations and anions.8−10 Moreover, their metallocomplexes are used as © XXXX American Chemical Society

Received: December 7, 2016 Revised: February 21, 2017 Published: March 1, 2017 A

DOI: 10.1021/acs.cgd.6b01775 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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cm−1 range between two polyethylene plates. The thermogravimetric (TG) and differential scanning calorimetry (DSC) curves were obtained using a NETZSCH STA429 thermoanalyzer in a dynamic nitrogen atmosphere (heating rate 10 °C·min−1, aluminum oxide, mass 1−3 mg, and temperature range from room temperature up to 500 °C). 2,2,5,5-Tetramethyl-12-oxa-1,6,7,8,16,17,18,19-octaaza-tricyclo[13.2.1.16,9]nonadeca-7,9(19),15(18),16-tetraene (L). 2,5-Dimethylhexane-2,5-diol (0.336 g, 2.30 mmol) was added with stirring to a solution of 1,5-bis(tetrazol-5-yl)-3-oxapentane (0.475 g, 2.26 mmol) in 65% aqueous perchloric acid (20 mL). The solution obtained was kept at room temperature for 3 days, next diluted with water (50 mL), and extracted with chloroform (3 × 50 mL). The combined extract was dried with anhydrous sodium sulfate and concentrated to give macrocyclic compound L as a white powder. Yield: 80% (0.58 g, 1.81 mmol). Physical and spectral characteristics of the sample prepared are in agreement with previously reported data.29 [Cu3Cl6L2] (1). A solution of compound L (0.320 g, 1.0 mmol) and copper(II) chloride dihydrate (0.256 g, 1.5 mmol) in ethanol/1,2dichloroethane (25 mL, 3:2) was allowed to stand at room temperature. Three days later, green crystals of 1 suitable for X-ray analysis were formed. Yield: 55% (0.283 g, 0.275 mmol). C27H46Cl6Cu3N16O2 (1030.12): C 31.30 (calc. 31.48); H 4.59 (4.50); N 21.57 (21.76) %. FT-IR (cm−1): 2986 (m), 2928 (m), 2881 (m), 1609 (m), 1510 (s), 1457 (s), 1381 (s), 1318 (s), 1228 (s), 1149 (s), 1113 (s), 1033 (s), 937 (m), 885 (s), 814 (m), 767 (m), 694 (m), 624 (m), 592 (m), 552 (m), 477 (w). [CuL2(H2O)2](BF4)2(H2O) (2). A solution of compound L (0.160 g, 0.5 mmol) and copper(II) tetrafluoroborate hexahydrate (0.086 g, 0.25 mmol) in 15 mL of ethanol was allowed to stand at room temperature. Two days later, blue crystals of 2 suitable for X-ray analysis were formed. Yield: 75% (0.175 g, 0.188 mmol). C28H54B2CuF8N16O5 (931.99): C 36.25 (calc. 36.08); H 5.69 (5.84); N 23.88 (24.05) %. FT-IR (cm−1): 3520 (s), 3554 (s), 2985 (s), 2933 (s), 2877 (s), 1646 (m), 1611 (m), 1508 (s), 1474 (s), 1455 (s), 1434 (m), 1398 (s), 1379 (s), 1357 (s), 1319 (s), 1258 (m), 1221 (s), 1181 (m), 1152 (m), 1021 (s), 878 (s), 816 (m), 764 (m), 693 (m), 590 (m), 526 (m), 475 (m). X-ray Structure Determination. Single crystal X-ray diffraction data of compounds 1 and 2 were collected on a SMART Apex II diffractometer using graphite monochromated Mo−Kα radiation (λ = 0.71073 Å) at temperatures 100 and 296 K for complex 1 and at 100 K for complex 2. The structures were solved by direct methods (SIR2014)44 and refined on F2 by the full-matrix least-squares technique (SHELXL 2014).45 The intensities were corrected for absorption. For all compounds, non-hydrogen atoms were refined anisotropically. The water hydrogen atoms of complex 2 were determined from difference Fourier map and refined in isotropic approximation. All other H atoms of the compounds were placed in calculated positions and refined in a “riding” model, with Uiso(H) = 1.5Ueq(C) for the methyl and Uiso(H) = 1.2Ueq(C) for the methylene groups. Main crystal data of the compounds are given in Tables 1 and S1. Molecular graphics was performed with the programs ORTEP-3 for Windows46 and PLATON.47 X-ray powder diffraction data of synthesized ligand L and polycrystalline complexes 1 and 2 were used to control their purity. The powder patterns were recorded with an EMPYREAN diffractometer (PANalytical, Netherlands) using Cu-Ka radiation (Ni-filter) at 296 K (Figures S2 and S3). CCDC deposition numbers: 1504399 (complex 1, 100 K), 1504398 (complex 1, 296 K), and 1504397 (complex 2, 100 K). Magnetic Susceptibility Measurements. Temperature-dependent magnetic susceptibility measurements were carried out on a SQUID magnetometer (MPMS Quantum Design) over the temperature range 2−330 K. The applied magnetic field was 1.0 T. The observed susceptibility data were corrected for the underlying diamagnetism by using Pascal’s constants.

metal−organic frameworks with a remarkable combination of physical and chemical properties (high thermal stability, permanent porosity, selective gas sorption, molecular magnetism, etc.).20−25 Moreover, coordination properties of tetrazoles condition their applications as metal corrosion inhibitors26 and capping ligands for stabilization and assembly of nanostructures.27 Inclusion of tetrazole moieties into macrocycles can provide specific coordination ability of macrocyclic ligands and thus prospectivity of tetrazole-containing macrocycles in the abovementioned applications. However, to date, they compose a small group of scantily explored compounds,28−33represented by macrocycles with incorporated tetrazole rings and by those bearing tetrazole pendant arms. It should be noted that for macrocycles with incorporated tetrazole rings existent preparative procedures are laborious and not very effective, and, as a consequence, only a few such macrocyclic compounds have been described.28−33 As to the syntheses and investigations of coordination compounds of tetrazole-containing macrocycles, the situation is much worse. Only several complexes are known to date, and they all comprise macrocycles with tetrazole pendant arms.34−38 Among them are macrocyclic complexes of di- and trivalent metals,34−36 in which metal cations are incorporated into macrocyclic cavities. Some coordination compounds show other structural organizations.37,38 In particular, the binuclear Pd(II) complex was obtained, where two metal atoms are linked together through two macrocycles at the expense of coordination bonds Pd−N with the tetrazole ring nitrogen atoms.37 There are data on coordination clusters of lanthanides (Ln19 and Ln12), stabilized by tetrazole-functionalized macrocycles.38 Additionally, one should mention also coordination compounds of Robson-type macrocycles together with tetrazoles coligands,39−41 in which specific coordination modes of the tetrazolyl moiety were explained by accommodation of tetrazole in macrocyclic cavity. Apart from the early works of Butler et al.42,43 and McGinley et al.,28 no other complexation studies of macrocycles with incorporated tetrazole rings have been undertaken. In the above works, the formation of solids precipitated from corresponding solutions after interaction of tetratetrazole macrocycles and metal(II) isothiocyanates was reported, but no characteristics were given for products. The efforts to obtain crystals, suitable for X-ray study, were unsuccessful.28 Taking into account the above circumstance and our advances in regioselective synthesis of macrocyclic tetrazoles,29 we aimed to obtain and characterize copper(II) complexes of the 15-membered macrocyclic bistetrazole 2,2,5,5-tetramethyl-12-oxa-1,6,7,8,16,17,18,19octaazatricyclo[13.2.1.16,9]nonadeca-7,9(19),15(18),16-tetraene (L), with two incorporated tetrazol-2,5-diyl moieties connected by alkyl bridges. As follows from structural data of free ligand L,29 it is hardly able to form complexes with endocoordination of macrocycle (so-called macrocyclic complexes). In this situation, more probable exo-coordination of macrocycle is expected under complexation.

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EXPERIMENTAL SECTION

Materials and Physical Techniques. All reagents and solvents were obtained from commercial sources and used without purification. Elemental analyses for C, H, and N were performed on a FlashEA 1112 element analyzer. Infrared spectra were recorded on a Nicolet Thermo Avatar 330 FT-IR system over the 400−4000 cm−1 range in SiC cavities, and on a Bruker Optik GmbH Vertex 70 over the 50−400 B



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thermal stability, starting to decompose at a temperature of about 180 °C. Complexes are less stable. The decomposition of complex 1 begins at a temperature of about 150 °C, causing the endothermic peak at 170 °C. Complex 2 begins to decompose at an even lower temperature, showing two endothermic peaks at 126 and 184 °C. The first of them is most probably attributed to the loss of crystallization water molecules. Crystal Structure of Complexes 1 and 2. Single crystal X-ray data were collected at temperatures 100 and 296 K for complex 1, and at 100 K for complex 2. Crystal data, data collection, and structure refinement details are gathered in Table 1, including the data for complexes 1 and 2 obtained at 100 K, and in Table S1 for complex 1 at 296 K. As follows from X-ray data, complexes 1 and 2 do not show phase transitions in the temperature range 100−296 K, and therefore only the structures at 100 K are described below. Complex [Cu3Cl6L2] (1). This complex crystallizes in the monoclinic space group P21/c with two formula units in the unit cell. The asymmetric unit contains two copper and three chlorine atoms, and one macrocyclic ligand L (Figure 1). In the

Table 1. Single Crystal X-ray Data and Structure Refinement Details for 1 and 2 complex

1

2

formula formula weight temperature (K) wavelength (Å) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g cm−3) μ (mm−1) crystal size/mm reflections collected independent reflections restraints parameters goodness-of-fit R1/wR2 [I > 2σ(I)] R1/wR2 [all data]

C28H48Cl6Cu3N16O2 1044.14 100(2) 0.71073 monoclinic P21/c 10.12880(10) 8.48470(10) 24.2302(3) 90 98.3843(5) 90 2060.08(4) 2 1.683 1.975 0.33 × 0.31 × 0.07 48386 9962 0 254 1.014 0.0250/0.0608 0.0338/0.0639

C28H54B2CuF8N16O5 932.03 100(2) 0.71073 triclinic P1̅ 9.68950(10) 11.62470(10) 19.8471(2) 82.0486(6) 86.6245(5) 75.1389(6) 2139.34(4) 2 1.447 0.602 0.43 × 0.28 × 0.09 42050 10844 9 567 1.022 0.0419/0.1157 0.0474/0.1203

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RESULTS AND DISCUSSION Synthesis and Characterization. Macrocyclic binuclear tetrazole L was prepared by cycloalkylation of 1,5-bis(tetrazol5-yl)-3-oxapentane by 2,5-dimethylhexane-2,5-diol in perchloric acid according to the procedure described previously29 (Scheme 1). Scheme 1. Synthesis of Macrocyclic Ligand L

Figure 1. Asymmetric unit of complex 1, with atom-numbering scheme and displacement ellipsoids drawn at the 50% probability level. The hydrogen atoms are shown as spheres of arbitrary radii.

used atom-labeling of two tetrazole rings, the first digit corresponds to a ring number (1 or 2), and the second digit follows to the systematic numbering of the terazole ring atoms. The copper atom Cu2 lies on inversion center, whereas all other atoms occupy general positions. In the crystal structure of 1, there are neutral linear trinuclear units Cu3Cl6, in which the copper atoms are linked together by double chlorine bridges (Figure 2). The unit Cu3Cl6 is centrosymmetric, with a central copper atom Cu2 and terminal atoms Cu1 and Cu1a [symmetry code: (a) 1−x, −y, −z]. Adjacent copper atoms are separated by 3.4795(4) Å. Selected geometrical features of Cu3Cl6 unit are presented in Table 2. The unit shows a distorted planar geometry. The dihedral angle between the least-squares plane of CuCl3 core of terminal copper atom and the plane of CuCl4 core of central copper atom is of 18.485(11)°, showing a rather high degree of nonplanarity of Cu3Cl6. Terminal and bridging Cu−Cl bond lengths lie in the range of 2.2259(2)−2.5814(3) Å. Both

Ligand L belongs to 2,5-disubstituted tetrazoles, which show the weakest basicity of hetero-ring among neutral tetrazoles. Moreover, the presence of substituent at the tetrazole ring C5 atom obstructs the binding of metal cations with the most donor nitrogen atom N4 by steric reason. Hence, successful complexation of 2,5-disubstituted tetrazoles needs low coordinating solvents and sometimes removal of competitive ligands like water.13 We found that ligand L reacted with copper(II) chloride dihydrate in ethanol/1,2-dichloroethane mixture to give complex [Cu3Cl6L2] (1) in 55% yield. Tetrafluoroborate complex [CuL2(H2O)2](BF4)2(H2O) (2) was isolated in 75% yield by interaction of L with copper(II) tetrafluoroborate hexahydrate in ethanol. Thermal analyses of free ligand L and complexes 1 and 2 were performed from room temperature to 500 °C to examine their thermal stability. TG and DSC curves of the compounds are presented in Figure S1. Free ligand L shows a moderate C



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Figure 2. Front (top) and side (bottom) views of centrosymmetric unit Cu3Cl6 in the crystal structure of complex 1.

Table 2. Selected Bond Lengths and Angles (Å and °) in Complex 1 Cu1−Cl1 Cu1−Cl2 Cu1−Cl3 Cu2−Cl1 Cu2−Cl2 Cu1···Cu2 Cl1−Cu2−Cl2 Cu1−Cl2−Cu2 Cu1−Cl1−Cu2 Cl1−Cu1−Cl2 Cl2−Cu1−Cl3 Cl1−Cu1−Cl3 N11−N12/N21−N22 N11−C15/N21−C25 N12−N13/N22−N23 N13−N14/N23−N24 N14−C15/N24−C25

2.5814(3) 2.3752(3) 2.2488(3) 2.2259(2) 2.2954(2) 3.4795(4) 88.922(8) 96.299(9) 92.436(8) 79.314(8) 177.006(10) 103.382(10) 1.3295(11)/1.3374(12) 1.3305(12)/1.3309(12) 1.3125(12)/1.3099(12) 1.3306(11)/1.3254(11) 1.3535(12)/1.3586(13)

Figure 3. Fragment of polymeric coordination chain, running along the a axis, in the crystal structure of complex 1. Hydrogen atoms are omitted for clarity.

bridges Cu1−Cl1−Cu2 and Cu1−Cl2−Cu2 are asymmetrical, the first bridge showing a greater asymmetry. Complex 1 presents a one-dimensional coordination polymer, formed due to the connection of trinuclear units Cu3Cl6 by bridging macrocyclic ligands L to give coordination chains running along the a axis (Figure 3). Ligand L is bonded to two neighboring Cu3Cl6 units through the tetrazole ring nitrogen atoms N14 and N24. As a result, terminal copper atoms, additionally to three Cu−Cl bonds, form two bonds Cu−N in trans position [Cu1−N14 = 2.0096(8), Cu1−N24b = 2.0031(8) Å; symmetry code: (b) x+1, y, z], with an angle of 160.34(3)° between Cu−N bonds. These bonds complete the Cu1 coordination polyhedron to a square pyramid, with τdescriptor48 of 0.28 for penta-coordination (extreme τ-values are 0 for an ideal square pyramid and 1 for an ideal trigonal bipyramid). Chlorine atom Cl1 occupies the apical position of the pyramid, being the most distant from the Cu1 atom. The central Cu2 atom shows a square planar coordination, with usual Cu−Cl lengths. The tetrazole ring geometry in maclocycle L of complex 1 (Table 2) is typical of 2- and 2,5substituted tetrazoles. As a rule, the tetrazole rings of the 2Hisomers show a more narrow distribution of bond lengths in comparison with 1H-isomers. Moreover, in 2H-isomers, formally single bonds N2−N3 are very often observed to be shorter compared to formally double bonds N3−N4. All these features take place in the tetrazole rings of complex 1 and free macrocyclic ligand L.29

In the crystal structure of 1, there are only nonclassic hydrogen bonds, formed between the methylene H and chlorine atoms. The bonds C9−H9B···Cl1c [hydrogen bond geometry: D···A = 3.3945(10) Å, D−H···A = 123°; symmetry code: (c) 1−x, 1−y, −z] link the coordination chains to polymeric layers parallel with the ab plane. The bonds C12− H12B···Cl1d [hydrogen bond geometry: D···A = 3.3906(10) Å, D−H···A = 123°; symmetry code: (d) x−1, y, z] are additional in these layers. A search of Cambridge Structural Database49 (CSD, Version 5.37 + updates through May 2016) for structures, containing neutral linear bibridged trinuclear units Cu3Cl6, gave rise to the results, which can be divided into four groups with different structural motifs (Figure 4, structures I−IV). Molecular structure I with monodentate coordination of organic ligand L is found in two complexes of the composition Cu3Cl6L6, where L = N,N-diethylnicotinamide 50 and L = 4-(3phenylpropyl)pyridine.51 Complexes of type II also have molecular structure but show bridging coordination of ligands L. This type is represented by complexes of the composition Cu3Cl6L4, where L = 1-allylbenzotriazole52 and 2-tert-butyl-6([1,2,4]triazolo[4,3-a]quinolin-1-yl)phenol.53 It should be noted that complexes of type II with bridging ligands show considerably nonplanar units Cu3Cl6 in contrast to complexes of type I. Stacking of Cu3Cl6 units at the expense of long Cu− Cl bonds leads to the coordination polymers of type III. These D



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In this compound, bridging coordination mode of organic ligand, realized through exocyclic oxygen atom, provides the formation of a polymeric chain oriented along the Cu3Cl6 unit.57 According to the present investigation, complex 1 also shows binding of Cu3Cl6 units through ligand molecules, but its coordination chain V is organized otherwise, being oriented across the Cu3Cl6 unit. Complex [CuL2(H2O)2](BF4)2(H2O) (2). This complex crystallizes in the triclinic space group P1̅, with two formula units in the unit cell. There are one copper atom, two macrocyclic ligands L, two tetrafluoroborate anions, and three water molecules in the asymmetric unit of 2 (Figure 5). In complex 2, all the atoms are in general positions. In atomnumbering of two ligands L, the first digit corresponds to a ligand number (1 or 2) for all atoms; in atom-numbering of the tetrazole rings, the second digit refers to a ring number (1 or 2) for a given ligand L, and the third digit follows the systematic numbering of the terazole ring atoms. The copper atom is surrounded by three ligands L [one of them is a ligand 1 and two others are symmetry related ligands 2], and two water molecules, which form the CuN3O2 coordination core. The copper atom shows a square-pyramidal coordination, with τdescriptor48 for penta-coordination taking on a value of 0.12. Ligands L are coordinated via the tetrazole ring N4 atoms, lying in the basal sites together with a water oxygen atom O1W. The apical position is occupied by a water oxygen atom O2W. Coordination bonds of copper atom are usual (Table 3).

Figure 4. Structural motifs of complexes with neutral bibridged Cu3Cl6 units. The copper and chlorine atoms are depicted as black and gray balls, correspondingly. L − organic ligand, L′ − water molecule. Dashed lines show long Cu−Cl bonds, connecting Cu3Cl6 units.

Table 3. Coordination Bond Lengths (Å) in the Crystal Structure of Complex 2a Cu1−O1W Cu1−N214 Cu1−N224e Cu1−N114 Cu1−O2W

are complexes of the compositions Cu3Cl6L2 with L = acetonitile54,55 (IIIa) and Cu3Cl6(H2O)2L2 with L = tetramethylene sulphone56 (IIIb). Stacked structure IIIa presents layered polymer, whereas polymeric chains take place in structure IIIb. Both compounds reveal the planar geometry of Cu3Cl6 units. Polymeric structure IV is found in complex of the composition Cu3Cl6L2(H2O)2, where L = 2-picoline N-oxide.

a

1.9817(13) 1.9969(15) 2.0018(15) 2.0162(15) 2.1555(13)

Symmetry code. (e) x+1, y, z.

Figure 5. A part of the asymmetric unit of complex 2, including one copper atom, two ligands L, and two coordinated water molecules. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Remaining part of the asymmetric unit, not shown here, contains two anions BF4− (the atoms B1, F1−F4; B2, F5−F8) and one crystallization water molecule (an oxygen atom O3W). E



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The tetrazole ring bond lengths of complex 2 are in the following ranges: N 1 −C 5 1.326(2)−1.331(2), N 1 −N 2 1.332(2)−1.337(2), N 2 −N 3 1.307(2)−1.314(2), N 3 −N 4 1.322(2)−1.329(2), N4−C5 1.352(2)−1.355(2) Å. These values are close to those in complex 1. In complex 2, ligands 1 and 2 reveal different coordination modes. Ligand 1 is coordinated monodentately through the tetrazole ring nitrogen atom N114, whereas ligand 2 is a bridge between two neighboring metal atoms, using the tetrazole atoms N214 and N224 for the coordination, to form polymeric cationic chains [CuL2(H2O)2]n2n+ extending along the a axis (Figure 6). These chains are bonded together due to a complex hydrogen bonds system (Figure 7, Table 4).

Figure 7. Fragment of the crystal structure of 2, viewed along the b axis, showing connection of cations [CuL2(H2O)2]n2n+ via (water− tetrafluoroborate) hydrogen bonded rings. Dashed lines show corresponding hydrogen bonds. The methyl groups and non-water hydrogen atoms are omitted for clarity.

Table 4. Hydrogen Bonds Geometry (Å, °) in the Crystal Structure of Complex 2a

Figure 6. Polymeric cation [CuL2(H2O)2]n2n+ running along the a axis in the crystal structure of complex 2. Hydrogen atoms are omitted for clarity. Dashed lines show lone pair−π interaction of macrocyclic oxygen atom O11 with the π-system of the tetrazole ring N221−C225 [O11k···Cg(Tz), where Cg(Tz) is the centroid of the tetrazole ring N221−C225; symmetry code: (k) x−1, y, z].

D−H···A

D−H

D···A

D−H···A

O1W−H1WA···N124f O1W−H1WB···O3W O2W−H2WA···F5 O2W−H2WB···F7g O3W−H3WA···F1h O3W−H3WB···F3 C110−H11A···F2 C112−H11F···F1i C13−H13A···N113 C19−H19B···N223j C22−H22B···N223 C29−H29A···N113

0.833(16) 0.834(16) 0.819(16) 0.813(17) 0.857(18) 0.892(18) 0.99 0.99 0.99 0.99 0.99 0.99

2.827(2) 2.651(2) 2.717(2) 2.779(3) 2.767(3) 2.784(3) 3.208(2) 3.383(3) 3.283(2) 3.407(2) 3.199(2) 3.338(2)

178(3) 176(3) 163(3) 168(3) 155(3) 154(3) 125 157 127 140 120 148

Symmetry codes. (f) x, y−1, z. (g) 1−x, −y, 2−z. (h) 1−x, −y, 1−z. (i) 1−x, 1−y, 1−z;. (j) 1+x, y, z. a

another bridge between cationic chains takes place. All these hydrogen bonds are responsible for linking coordination chains with BF4− anions and crystallization water molecules into layers parallel with the ac plane. The hydrogen bonds O1W− H1WA···N124f [symmetry code (f) is given in Table 4] between the water H and the tetrazole ring N atoms of neighboring layers connect them to three-dimensional network. Nonclassic hydrogen bonds C−H···F and C−H···N of the methylene H atoms with the tetrafluoroborate F or the tetrazole ring N atoms are additional in this network. In the crystal structure of 2, there are also weak lone pair−π interactions (see ref 58 and references therein), realized between the tetrazole ring π-system (the ring N221−C225) and macrocyclic oxygen atom O11k [symmetry code: (k) x−1, y, z]. The distance O11k···Cg(Tz) between the oxygen atom

Both anions BF4− form with water molecules hydrogen bonded rings. So, two symmetry related tetrafluoroborate anions of B2 atom are bonded to two symmetry related coordinated water molecules of O2W atoms [symmetry code (g) in Table 4] to form hydrogen bonded ring R44 (12), which is a bridge between two neighboring cationic chains. Analogous R44(12) ring is formed by two symmetry related anions BF4− of B1 atom [symmetry code (h) in Table 4], but in this case two crystallization water molecules (oxygen atoms O3W) are included in the ring instead of coordinated water molecules. At the expense of hydrogen bonds O1W−H1WB···O3W between coordinated water and crystallization water molecules, F



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Figure 8. Macrocyclic molecules in the crystal structures of free ligand L (a), complex 1 (b), and complex 2 [on the left − ligand 1; on the right − ligand 2] (c). In all cases, the view orientation is normal to the plane O1/C1/C4 in the notation for complex 1 (see Figure 1).

and the tetrazole ring centroid takes on a value of 3.279 Å. These interactions take place inside polymeric chains [CuL2(H2O)2]n2n+ (Figure 6). It is of interest to compare some structural features of macrocyclic molecules in complexes 1, 2, and free ligand L29 (see Figure 8). For an estimation of internal dimensions of macrocycles, we found cross-macrocycle distances d1 and d2 in two directions. We determined d1 as a distance between two tetrazole ring centroids, and d2 as a distance between centers of gravity of two group atoms, namely, C10−O1−C11 and C1− C2−C3−C4 (in the notation for complex 1, see Figure 1). The observed values d1 × d2 are the following (Å): 4.785 × 5.289 (free ligand L); 5.091 × 5.148 (complex 1); 4.969 × 5.349 (complex 2, ligand 1); and 4.940 × 5.057 (complex 2, ligand 2). These characteristics show that macrocyclic cavities are rather small in the compared compounds. Moreover, because of steric reasons, two tetrazole rings should have a tendency to be parallel. Indeed, they show the dihedral angle between the tetrazole ring least-squares planes of about 19.61, 12.53, 39.97/ 7.86° for L, 1, and 2 (ligands 1/2), respectively. These circumstances hinder the formation of macrocyclic complex with CuII cation incorporated in cavity. It should be noted that the linear analogue of L, namely, 1,5bis(2-tert-butyltetrazol-5-yl)-3-oxopentane (BTOP), was found to generate complex Cu(BTOP)2Cl2 under the action of copper(II) chloride (Scheme 2).59 According to X-ray study, Cu(BTOP)2Cl2 is a mononuclear complex with a tridentate chelating coordination mode of BTOP. Realization of analogous coordination of L is hindered by the reasons mentioned above. As a result, in the formed complexes 1 and 2, macrocyclic ligand L acts via the tetrazole ring nitrogen atoms

Scheme 2. Complexation of 1,5-Bis(2-tert-butyltetrazol-5yl)-3-oxopentane

as either a monodentate or bridging ligand to form coordination polymers. Magnetic Properties of Complex 1. The presence of separated Cu3Cl6 units in complex 1 determines the interest in the magnetic investigation of the compound. Its magnetic properties were investigated by temperature-dependent magnetic susceptibility measurements in the temperature range between 2 and 330 K and an external field of B = μ0H = 1.0 T. Figure 9 shows the experimental data and the theoretical fit in the form of a μeff versus T plot. At 330 K μeff is 3.03 μB, which agrees with the value expected for three noncoupling CuII cations (S = 1/2) (μeff = 3.0 μB). The μeff value rises continuously from 3.03 μB at 330 K to 3.80 μB at 13 K and then finally decreases to 3.5 μB at 2 K. The maximum at μeff = 3.80 μB agrees with the value for three coupling CuII ions (S = 3/2) (μeff = 3.87 μB). This curve shows a ferromagnetic exchange interaction between the three copper(II) atoms. This is further G



Article

not reported until now. As to magnetic investigation of other types complexes containing bibridged Cu3Cl6 units, to our knowledge, they were carried out only for stacked structures, namely, for complex Cu3Cl6L2 with L = acetonitrile60 (type IIIa) and complex Cu3Cl6(H2O)2L2 with L = tetramethylene Sulphone61 (type IIIb). Both compounds were found to be antiferromagnets. It should be noted that similar tricopper units are available with O-bridges. Some of them also show ferromagnetic behavior.62

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CONCLUSIONS We have presented the synthesis and characterization of the first metallocomplexes of macrocyclic ligands with incorporated tetrazole rings. According to X-ray analysis, the synthesized complexes 1 and 2 are coordination polymers, formed due bridging exo-coordination of macrocyclic ligand via the tetrazole ring nitrogen atoms. Copper(II) chloride complex comprises neutral bibridged Cu3Cl6 units, which show ferromagnetic exchange interaction between the three copper(II) atoms. Obviously, further studies of complexation of the above macrocycle are of interest for target assembly of metal cations in order to design molecular-based magnetic materials.

Figure 9. Temperature dependence of μeff for complex 1 per trinuclear unit (the open circles). The solid line represents the best theoretical fit to the spin Hamiltonian (eq 1).

corroborated by the continuous increase of the μeff values from 3.03 μB at 330 K to 3.80 μB at 13 K and the following decrease to 3.5 μB at 2 K. The temperature dependence of the magnetic susceptibility was simulated using the appropriate spin-Hamiltonian (eq 1), which includes the isotropic Heisenberg−Dirac−van Vleck exchange, as well as the single-ion Zeeman interactions by using a full-matrix diagonalization approach:

■

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b01775. TG/DSC curves, additional single crystal X-ray data and structure refinement details, and PXRD patterns (PDF)

3

Ĥ = 2( −2J1S1̂ S2̂ ) + ( −2J2 S1̂ S3̂ ) + μB ∑ (gSî B)̂ i=1

ASSOCIATED CONTENT

Accession Codes

CCDC 1504397−1504399 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.

(1)

where J represents the intramolecular magnetic coupling constant, Ŝ − the Cu spin-vector operators, g − the g-factor, μB − the Bohr magneton, and B − the applied external magnetic field. Scheme 3 illustrates the exchange coupling pathways used to model the susceptibility data for complex. In this model the

■

AUTHOR INFORMATION

Corresponding Author

Scheme 3. Magnetic Exchange Pathways Used for Simulation of the Magnetic Susceptibility Data for the Trinuclear Subunits in Cu3Cl6L2

*E-mail: [email protected]. ORCID

Sergei V. Voitekhovich: 0000-0002-7015-5062 Notes

The authors declare no competing financial interest.

■

exchange interaction between the neighboring CuII ions are represented by J1, whereas J2 corresponds to the interaction between the two terminal CuII ions. The g-values were considered to be identical for the three CuII ions. A reasonable fit of the experimental susceptibility data was possible over the full range by the inclusion of a small amount of a paramagnetic impurity (CuII, S = 1/2, 6%), and led to J1 = 50.30 cm−1 and gfix = 2.0. The inclusion of the J2 parameter did not improve the fit, and so J2 was fixed (0 cm−1). As was mentioned above, no nearby structural analogues of complex 1 have been found in the literature. In terms of magnetic interactions, this complex shows a resemblance to complexes of type I (see Figure 4), because neighboring Cu3Cl6 units in 1 are considerably separated in space by macrocyclic ligands. However, magnetic properties of type I complexes were

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