The Assembly of Unique Hexanuclear Copper(I) Complexes with

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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The Assembly of Unique Hexanuclear Copper(I) Complexes with Effective White Luminescence Igor D. Strelnik,*,† Irina R. Dayanova,† Ilya E. Kolesnikov,‡ Robert R. Fayzullin,† Igor A. Litvinov,† Aida I. Samigullina,† Tatiana P. Gerasimova,† Sergey A. Katsyuba,† Elvira I. Musina,† and Andrey A. Karasik†

Inorg. Chem. Downloaded from pubs.acs.org by EAST CAROLINA UNIV on 01/02/19. For personal use only.

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Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy of Sciences, Arbuzov-str, 8, 420088 Kazan, Russia ‡ Center for Optical and Laser Materials Research, Saint-Petersburg State University, Peterhof, Ulianovskaya-str, 5, 198504 Saint-Petersburg, Russia S Supporting Information *

ABSTRACT: The unique L2Cu6I6 complexes containing two Cu3I3 units have been obtained via reaction of 1,5-diaza-3,7-diphosphacyclooctanes bearing ethylpyridyl substituents at phosphorus atoms with an excess of copper iodide. The structure of one of the complexes was confirmed by X-ray diffraction. It was shown that the complexes can exist in two crystalline phases with different parameters of the unit cell, which were detected by the PXRD data analyses. The solvent-free crystalline phases of the complexes display rare solid-state white emission at room temperature, which is observed due to the presence of two broad bands in the emission spectra with maxima at 464 and 610 nm. Quantum chemical computations show that the high-energy band has 3(M+X)LCT origin, whereas the low-energy band is interpreted as 3CC. The quantum yields of white luminescence of complexes reach 15−20%.

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INTRODUCTION The development of new OLED systems based on copper(I) is strongly motivated by the low toxicity, low cost, and availability of copper compared to the noble metals and rare earths.1−3 Commonly, the copper(I) halides with any mono- or polydentate ligands form polynuclear complexes containing the Cu2X2 or Cu4X4 cores with a limited set of topologies4−10 (Figure 1). These structural motifs are extensively studied by various physical methods, including X-ray diffraction (XRD) analysis. The diversity of structures of copper(I) complexes is reflected in a rich set of photophysical properties including dual emission, thermally activated delayed fluorescence (TADF), and “stimuli-responsive” luminescence.11−16 The design and stabilization of copper(I) complexes with the various structural motifs can be performed on the basis of various N-heteroaryl substituted phosphine ligands such as pyridylphosphines.17,18 During the past decade, the large amount of works devoted to the mono-, di-, or tetranuclear copper(I) complexes based on the pyridylphosphines appeared.4−6,8,18−20 Due to the presence of a pyridyl fragment, complexes with the above-mentioned ligands demonstrate rich luminescent properties, e.g., “stimuli-responsive” luminescence or intensive emission in broad spectral ranges. It has been shown that the structure of pyridylphosphine ligands influences not only the types of formed copper clusters but also © XXXX American Chemical Society

Figure 1. Dimer and tetramer forms of CuX complexes.

luminescent characteristics within one type of complexes. The reported types of copper(I) clusters rarely differ from the Received: July 11, 2018

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DOI: 10.1021/acs.inorgchem.8b01862 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry ones shown in Figure 1: a few examples of the Cu3I321−24 (except of coordination polymers) were reviewed by Peng10 and Liu,25 while the complexes with a Cu3I3 core and phosphine ligands were described only three times.22,24,26 The luminescence of these complexes is assigned to the triplet halogen-to-ligand charge-transfer (3XLCT) and metalto-ligand charge-transfer (3MLCT) transitions involving the highest occupied molecular orbital (HOMO) localized on a metal-halide core and the lowest unoccupied molecular orbital (LUMO) spread over an organic chromophore moiety.27−34 Despite the well-studied area of the luminescent copper(I) complexes,1,10,25 the white-emissive copper(I) complexes are rather rare.35−37 In most cases, white-light emitting materials are made from combinations of the individual red, blue, and green emitters (or complementary color pairs) in multilayered, stacking, and tandem devices.38 Herein, we report the synthesis of new heterocyclic bisphosphine ligands containing pyridylethyl groups at phosphorus atoms and aryl substituents at nitrogen atoms and unusual hexanuclear copper(I) complexes based on these ligands. Two Cu3I3 metal-halide units were assembled between two bridge μ4-heterocyclic diphosphines. As far as we know, the described type of Cu3I3 core is a unique representative of the CuI clusters. It was found that obtained hexanuclear complexes display white emission in the solid state, which is based on the low- and high-energy bands. Quantum chemical computations show that the high-energy band has 3(M +X)LCT origin, whereas the low-energy band has been interpreted as 3CC.

each other. The dihedral angle between phosphorus lone pairs is ca. 16.8° and −2.6° for 1 and 2, respectively. As we have recently shown, diazadiphosphacyclooctane ligands with such geometry are preorganized to form copper(I) complexes with a P,P-bridged coordination mode,40 while the presence of the labile ethylene spacer between the phosphorus atoms and pyridyl groups allows the latter to coordinate copper(I).41 In our recent works, we demonstrated predominant P,Pchelate42−45 and rather rare P,P-bridge and P,N-chelate41,46,47 coordination modes of 1,5-diaza-3,7-diphosphacyclooctanes containing pyridyl and pyridylethyl substituents on phosphorus atoms in the mono- and dinuclear gold(I)46,47 and copper(I)41 complexes. Reaction of ligands 1 and 2 with a copper(I) iodide in the 1:3 ligand-to-metal ratio in acetonitrile immediately led to the precipitation of white powders, which were washed, recrystallized from the acetonitrile, and dried over vacuum to give pure white crystalline powders of complexes 3 and 4 in nearly quantitative yield (Scheme 2). Complexes 3 and 4 demonstrate the similar behavior in solution. In the 31P NMR spectra of both complexes, the broadened signal in the range from −36 to −40 ppm (ΔδP ∼ 9 ppm comparative to free ligands) is observed. The low field shift of the signals of the protons of aminomethylphosphine moieties is observed in the 1H NMR spectra (4.28 and 4.11 for 4 vs 4.15 and 3.48 for 2; 4.32 and 4.13 for 3 vs 4.23 and 3.51 for 1). The lack of a shift of the pyridyl protons signals in the complexes comparative to the free ligands is observed. The NMR spectra correspond to a suggested structure of the complexes. However, the possibility of fast reversible processes of formation and cleavage of Cu−N bonds in the solution cannot be excluded according to the NMR spectra. The ESI mass spectra of complexes 3 and 4 are characterized by the major peaks m/z 765.0 and 793.1, respectively, corresponding to the mass ion of [L + 2Cu + I]+ composition. The minor peaks in ESI mass spectra of 3 and 4 also indicate the transformation of the complexes to the mono- and polynuclear cations of [2L + Cu]+, [2L + 2Cu + I]+, [2L + 3Cu + 2I]+, and [2L + 4Cu + 3I]+ composition. The negative area of ESI mass spectra reveals only fragments of [xCu + (x + 1)I] − composition. Thus, the 31P and 1H NMR spectra as well as the mass analysis data indicate the formation of labile complexes with polynuclear copper iodide cores. The recrystallization of 4 from acetonitrile led to the growth of single crystals of 4a which were suitable for the X-ray analysis. According to the X-ray analysis (Figure 3), 4a is a hexanuclear complex L2Cu6I6 with the Ci symmetry and previously unknown metal-halide core. The unit cell of 4a contains highly disordered solvate molecules of acetonitrile. Two Cu3I3 units are assembled on the matrix of two heterocyclic polyfunctional ligands 2. Each of the Cu3I3 metalhalide cores can be formally regarded as consisting of two parts: metal-halide core with a “butterfly-like” shape with two

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RESULTS AND DISCUSSION The initial ligands 1 and 2 were obtained in good yields according to the condensation reaction39 of 2-(pyridine-2′yl)ethylphosphine, paraformaldehyde, and primary arylamines, namely, aniline and para-toluidine (Scheme 1). Scheme 1. Synthesis of Ligands 1 and 2

The structure of ligands 1 and 2 was confirmed by the 31P and 1H NMR spectroscopy, MALDI mass-spectrometry, elemental analysis, and X-ray analysis (Figure 2). The molecules are characterized by the C2 symmetry and “chairchair” conformation of the eight-membered rings with an equatorial position of the pyridylethyl substituents and an axial position of the phosphorus lone pairs that are nearly parallel to

Figure 2. Molecular structure of ligands 1 and 2. B


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Inorganic Chemistry Scheme 2. Synthesis of the Complexes 3 and 4

copper(I) ions bound by two μ2-iodine ions and two pyridyl groups of two ligands; this core is connected via μ3-iodide with another copper(I) ion coordinated by two μ-phosphorus atoms of two ligands. The distances between Cu(2) and Cu(3) of the “butterfly-like” part are notably shorter than the sum of van der Waals radii48 (2.5 vs 2.8 Å, respectively). The ligands in this complex have a N,P,P,N-bridge or μ4-coordination mode. The conformation of heterocyclic part of the ligand is a twist-like “chair-boat”, which is rather rare for that type of ligands.39,41−47 The bis-P,P-bridged coordination of two copper(I) ions forms a 12-membered metallomacrocycle. The cavity of the macrocycle is covered from both sides by the substituents on the one of the nitrogen atoms of each ligand. We have found that large-scale crystals of 4a are not stable and convert into the white powder of 4 after a few hours in air due to loss of the solvate acetonitrile molecules, while the following recrystallization from acetonitrile returns back the crystalline phase 4a. The complex 3 demonstrates the similar behavior.

Figure 3. Molecular structure of 4a (hydrogen atoms are omitted for clarity).

Figure 4. Theoretical powder diffractogram (black curve) for complex 4a and the experimental powder diffractograms of the crystalline powder sample 4a obtained immediately after the mother liquor removal (red curve) and during solid-phase transformation after 20 min, 30 min, 1 h, and 2 h. C


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Inorganic Chemistry

Figure 5. TG-DSC curve of crystalline phases of complex 4 (green) and 4a (red).

Figure 6. Normalized solid-state excitation and emission spectra of crystal phase 3 and 4 at room temperature.

sample is caused by the loss of 4.5 molecules of solvate acetonitrile per one molecule of the complex. The exact quantity of the solvent might be more due to its loss during the sample preparation. To shed light on structural features of the forms 4a and 4, far-IR and Raman spectra were recorded for both forms (SI, Figures S8, S9). Raman spectra of both samples practically coincide in the middle range, except for the presence of weak bands of acetonitrile in the spectrum of 4a. Minor differences are observed in relative intensities of νCuI bands: in the spectrum of 4a, the weak band at 192 cm−1 is stronger than the band at 176 cm−1; the opposite is true for the spectrum of 4. The fact that neither number of bands nor their positions are changed suggests that complex 4 holds its molecular structure upon transformation to 4a, while the relative intensity variations are probably caused by changes in the symmetry of the crystal structure. Indeed, notable differences are observed for very strong bands in the spectral region of 50− 100 cm−1, which are, most probably, associated with vibrations of the crystal lattice. In the spectrum of 4a, the band at 95 cm−1 is stronger than the neighboring band at 85 cm−1; the opposite is true for the spectrum of 4 (Table S1). Thus,

The results of powder X-ray diffraction (PXRD) of crystalline phase 4a indicate the solid-state phase transition of the crystalline sample during 2 h of experiment, which leads to the formation of the crystalline phase 4 (Figure 4). Comparisons of powder diffractograms show that intensity of the diffraction peak at 2θ = 7.84°, corresponding to crystalline phase 4a, decreases and disappears (Figure 4). At the same time, a new diffraction peak at 2θ = 7.47° corresponding to the new crystalline phase 4 appears and its intensity increases as the transition from one solid form to another occurs. In 2 h, crystals 4a fully transform into 4 crystalline phase. We suppose that the process of transformation of the crystalline phase 4a into crystalline phase 4 might be initialized by the loss of the solvent molecules from the crystals and is followed by the changing of the unit cell parameters detected with PXRD. The TG-DSC data show the similar behavior of the samples of compounds 3 and 4, which are stable until 250 and 230 °C, respectively (Figure 5; Supporting Information (SI), Figure S7). In the sample of 4a, the weight loss up to 8.5% is observed from 40 to 230 °C; the following heating of the sample results in the destruction of the sample. The observed behavior of the D


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Inorganic Chemistry

Figure 7. CIE-1931 diagrams with the emission coordinates (0.38;0.34) of complex 3 and (0.31;033) of complex 4.

Table 1. Emission Lifetimes of Each Emission Band of Complexes 3 and 4 τobs, μs (fractional intensitya), λem 464 nm, complex 3

τobs, μs (fractional intensitya), λem 610 nm, complex 3



0.6 (0.51) 2.7 (0.49)

9.4 (0.32) 3.5 (0.68)

1.8 (0.19) 0.3 (0.81)

9.3 (0.71) 2.5 (0.29)

a

Fractional intensity (f i): f i = aiti/∑(aiti).

S15). The PLQY of the white-emissive complexes 3 and 4 is 15% and 20%, respectively. Dual emission usually arises from two thermally coupled levels. Thermally coupled levels are closely spaced (the energy gap generally ranges from 200 to 2000 cm−1) and assumed to be in thermodynamic quasi-equilibrium.49 In this case, temperature induced change of intensity ratio is explained by modification of energy levels population according to the Boltzmann formula. The energy gap between high- and lowenergy triplet excited states of complexes 3 and 4 was found to be more than 5000 cm−1, which suggests that the observed phenomenon is based on nonthermally coupled levels.50 To interpret the nature of the above-mentioned bands, quantum chemical computations have been employed. The computed energy of the optimized triplet state (T1) structure of 4 (Figure 8) is higher than the energy of the ground state (S0) at the same geometry by 2.68 eV. This energy difference corresponds to a wavelength of 462 nm for the T1 − S0 vertical transition,

analysis of vibrational spectra of 4 and 4a suggests that the desolvation leads to some modification of crystal packing, while only minor changes, if any, are expected in Cu3I3 moieties. Thus, TG/DSC analysis, analysis of vibrational spectra, and powder X-ray diffractograms of 4a and 4 suggest that solidstate recrystallization leads to some modification of crystal packing caused by the loss of the solvate acetonitrile, while only minor changes, if any, are expected for Cu3I3 moieties. The crystals 3a and 4a immersed in acetonitrile display a blue luminescence, which changes rapidly to white emission during exposing the samples to air. This process corresponds to the transformation of crystals 3a and 4a to crystal phase 3 and 4, respectively. The following recrystallization of crystal phase 3 and 4 from acetonitrile leads to formation of crystal 3a and 4a with blue luminescence. The fast processes of loss of the solvate molecules do not allow recording the emission and excitation spectra of 3a and 4a in a proper manner. The UV−visible absorption spectra of 3 and 4 are similar and are in good agreement with quantum chemical calculations (SI, Figure S10). The excitation spectra of both emission bands are similar (Figure S11) and display a broad band with the maxima of the excitation at 340 and 360 nm for complexes 3 and 4, respectively, as it is shown in Figure 6. The crystalline phases of 3 and 4 display a rare white emission, which has been reported only a few times for polynuclear copper(I) complexes demonstrating dual emission.8,36,37 The white emission is observed due to the presence of the two broad bands in the emission spectra with the maxima at 465/466 and 610/615 nm for complexes 3/4 (Figure 6). The coordinates on the CIE-1931 diagram for 3 and 4 are (0.38;0.34) and (0.31;0.33), respectively ((0.33;0.33) − clear white color) (Figure 7). The origin of both emission bands is phosphorescence with lifetimes in the microsecond domain (Table 1; Figures S12−

Figure 8. Cu−I distances in optimized structure of triplet state of 4 (hydrogen atoms are omitted for clarity). E


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Inorganic Chemistry

Figure 9. HOMO (left) and LUMO (right) of the ground state calculated at the optimized T1 geometry of 4 (S0 on T1).

Figure 10. (a) Emission spectra of complex 4 measured at different temperatures. (b) Luminescence intensity ratio as a function of temperature. Red line corresponds to the best fitting.

In order to assess the effect quantitatively, the luminescence intensity ratio (LIR) between blue (450−475 nm) and red (610−635 nm) bands was calculated. Figure 10b presents the evolution of experimental LIR as a function of temperature. Interestingly, LIR demonstrates nonmonotonic behavior: it decreases within 83−273 K, but then slightly increases. The obtained LIR experimental data were perfectly fitted with the cubic function. It should be noted that the obtained fitting parameters do not have clear physical meaning, because the regarded LIR is based on nonthermally coupled levels. In such case, the choice of the fitting function is dictated primarily by its simplicity and minimization of adj. R2. Fit of the obtained LIR experimental data with the cubic function satisfied both of these criteria. The good quality of the approximation and the strong LIR dependence on temperature in the range of 83−250 K suggest the possibility of using luminophores 3 and 4 as molecular thermometers.

which is very close to the high-energy band 466 nm, observed in the experiment. The computed HOMO of the optimized triplet state resides on one of the Cu3I3 units, and the LUMO is located on the closest pyridyl group of the ligand (Figure 9). Thus, the emission is assigned to 3MLCT transitions mixed with 3XLCT transitions and, therefore, belongs to the 3(X +M)LCT state. Interestingly, in the T1 state (Figure 9), one of the Cu3I3 moieties involved in the transition retains the structure found for a single crystal, whereas the other Cu3I3 unit resembles that described by Wei and co-workers26 with two μ3- and one μ2-iodine atoms. The low-energy (LE) bands in emission spectra of 3 and 4 can be presumably interpreted as belonging to cluster centered (3CC) transition state similar to the results of De Angelis et al.50 The temperature dependence of luminescence properties of compound 4 was studied. Emission spectra were measured at temperatures varying in the range of 83−373 K (Figure 10a). The temperature increase led to the decrease of total emission intensity and affected chromaticity coordinates due to the intensity redistribution between blue and red emission bands of compound 4. Very low intensity of the LE band at 80−100 K and its increase at room temperature agree with our interpretation of this band as belonging to the 3CC state. According to De Angelis,50 this state should demonstrate large geometrical variations with respect to the ground state. Such variations are expected to become very limited at low temperatures, which should lead to quenching of the corresponding band.

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CONCLUSION New 1,5-diaza-3,7-diphosphacyclooctane with ethylpyridyl substituents at phosphorus atoms and aryl substituents at nitrogen atoms and its hexanuclear copper(I) iodide complexes were obtained in excellent yield. The hexanuclear copper(I) complexes 3 and 4 are the first representatives of Cu6I6 complexes based on the phosphine ligands and the first examples of a Cu3(μ2-I)2(μ3-I) metal-halide core. It was found that the crystallization of complexes from the acetonitrile leads to the crystalline phase 3a and 4a, which transforms to another crystalline phase if they are out of mother liquor. The solvent F


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Inorganic Chemistry

of emission at 265, 340, and 390 nm) were used in pulse mode to pump luminescence in lifetime measurements (pulse width 0.9 nm, repetition rate 100 Hz to 10 kHz). The integration sphere was used to measure the solid-state emission quantum yield for the complexes 3 and 4. The X-ray diffraction data for the single crystals of 1, 2, and 4 were collected on a Bruker Smart Apex II CCD diffractometer (ω-scan mode) using graphite monochromated MoKα (0.71073 Å) radiation at 293 K (1, and 4), and 150 K (2). The performance mode of the sealed X-ray tube was 50 kV, 30 mA. In the case of sample 2, the diffractometer was equipped with an Oxford Cryostream LT device for low temperature experiments. Suitable crystals of appropriate dimensions were mounted on glass fibers in random orientations. Preliminary unit cell parameters were determined with three sets of 12 narrow frame scans. Data collection: images were indexed and integrated using the APEX2 data reduction package (v2014.11-0, Bruker AXS). Final cell constants were determined by global refinement of reflections from the complete data set. Analysis of the integrated data did not show any decay. Data were corrected for systematic errors and absorption using SADABS-2014/5. XPREP2014/2 and ASSIGN SPACEGROUP routine of the WinGX-2014.1 were used for analysis of systematic absences and space group determination. The structures were solved by the direct methods using SHELXT2014/561 and refined by the full-matrix least-squares on F2 using SHELXL-2017/1.62 Calculations were mainly performed by means of the WinGX-2014.1 suite of programs.63 Non-hydrogen atoms were refined anisotropically. The positions of the hydrogen atoms of methyl groups were found using a rotating group refinement with idealized tetrahedral angles. The other hydrogen atoms were inserted at the calculated positions and refined as riding atoms. Both N-pivot para-tolyl substituents and the Cu2-core together with picolyl arms of complex 4 were almost equally disordered into two conformations (the relative occupancy is 0.55(6), 0.54(5), and 0.60(2) for the main components, respectively). The disorder was resolved using free variables and reasonable restraints on geometry and anisotropic displacement parameters. All the compounds studied have no unusual bond lengths and angles. Interestingly, the asymmetric parts of unit cells of 1, 2, and 4a contain half of the molecule (Z′ = 0.5). The unit cell of 4a includes highly disordered solvent molecules (most probably, acetonitrile), which were treated as a diffuse contribution to the overall scattering without specific atom positions by PLATON/SQUEEZE-290617.64 Squeezed solvent info is not included in the formula and related items such as molecular weight and calculated density. The crystal data, data collection, and structure refinement details for the investigated crystals are summarized in Tables S2−S4. Molecular structures of the investigated complexes in the crystalline phase as well as accepted partial numbering are presented as ORTEP diagrams in Figures S16−S18. Selected bond lengths are appended to the captions. Single crystals suitable for X-ray analysis were grown from toluene (1, 2) and acetonitrile (4a) solutions. The crystallographic data for the investigated phases have been deposited in the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 1586931, 1573308, and 1573309 for 1, 2, and 4a, respectively. The X-ray powder diffraction studies were performed on an automated D8 Advance X-ray diffractometer (Bruker) equipped with a Vario setup and a Vantec linear coordinate detector. The CuKα1 radiation monochromated by the curved Johansson monochromator (λ = 1.5406 Å) was used, and the performance mode of the X-ray tube was 40 kV, 40 mA. Experiments were carried out at room temperature in the Bragg−Brentano geometry. The powder sample was placed in a zero diffraction holder. Patterns were recorded in the 2θ range between 5° and 42°, in 0.016° steps, with a step time of 0.2 s and rotation 15 rpm. For calculation of the theoretical diffraction pattern of 4a, we used the “squeezed” model based on data of X-ray single crystal experiment performed at room temperature.

free crystalline phase of hexanuclear complexes demonstrates a moderate white emission with coordinates on the CIE diagram (0.38;0.34) and (0.31;0.33). The PLQY of complexes, their thermochromic behavior, and possibility of design of novel hexa- or trinuclear copper based complexes on the (orthoheteroaryl)ethylphosphies make further studies of these systems in the OLED applications rather promising. The formation of Cu3I3 units is expected to be a general phenomenon that could be reproduced with any hybrid ligands containing P-CH2-CH2-hetaryl donor sites, where hetaryl is an aromatic group containing a “hard” donor center in the ortho-position.

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EXPERIMENTAL SECTION

All reactions and manipulations were carried out under dry argon with standard vacuum line techniques. Solvents were purified, dried, deoxygenated, and distilled before use. ESI measurements were performed using an AmaZon X ion trap mass spectrometer in positive and negative modes. The mass spectral data were processed using the program XCalibur. The mass spectra are given as m/z values and relative intensities (Irel, %). MALDI mass spectra were obtained on a Bruker ULTRAFLEX III mass spectrometer (laser Nd:YAG, λ 355 nm) in a linear mode without accumulation of mass spectra. 1H NMR (400 MHz) and 31P NMR (162 MHz) spectra were recorded on a Bruker Avance-DRX 400 spectrometer. Chemical shifts are given in parts per million relative to SiMe4 (1H, internal solvent), and 85% H3PO4 (31P, external). J values are given in Hz. For the TG/DSC analysis, the device STA449-F3 (“NETZSCH”, Germany) was used. The wet samples (ca. 15 mg) were extracted from the mother liquor and plotted on an aluminum crucible; an empty aluminum crucible was used as a standard. The crucibles were heated up to 400 °C in the stream of argon (50 mL/min) with the speed of heating 10 K/min. UV/vis spectra were registered at room temperature on a PerkinElmer Lambda 35 spectrometer with a scan speed of 480 nm/min, using a spectral width of 1 nm. All samples were prepared as solutions: ligands 1, 2 in dichloromethane, complexes 3, 4 in dimethylformamide with the concentrations of ca. 10−5 mol/L and placed in 10 mm quartz cells. Raman spectra of solid samples were registered at room temperature using a BRUKER RAM II module attached to a BRUKER VERTEX 70 FTIR spectrometer (excitation 1064 nm, Ge detector at liquid nitrogen temperature, backscattering configuration; range 10−4000 cm−1, optical resolution 4 cm−1, scan number 1024). The samples were inserted in a standard aluminum crucible. IR spectra of the compounds were recorded on an FTIR spectrometer IFS 113v (Bruker) in the 100−600 cm−1 range at a resolution of 1 cm−1. Solid samples were prepared as polyethylene pellets. All calculations were performed with the Gaussian 16 suite of programs.51 The hybrid PBE0 functional52 and the Ahlrichs’ triple-ζ def-TZVP AO basis set53 were used for optimization of all structures. In all geometry optimizations, the D3 approach54 to describe the London dispersion interactions together with the Becke−Johnson (BJ) damping function55−57 were employed as implemented in the Gaussian 16 program. Time-dependent density functional theory (TD-DFT) has been employed to compute the vertical excitation energies (i.e., absorption wavelengths) and oscillator strengths for the ground-state optimized geometry of complex 4. The 10 lowest singlet excited states were taken into account. The procedure was analogous to the one described elsewhere,58 except that the range-separated CAM-B3LYP functional59 was used instead of PBE0. The calculated spectrum was shifted by −0.24 eV. The vertical T1 − S0 transition energy was computed within the Δ-SCF approach60 at the triplet-state geometry of 4 optimized by UPBE0-D3(BJ)/def-TZVP. Excitation and emission spectra in the solid state were measured on Fluoromax 4 and Fluorolog 3 spectrofluorimeters. LED (maximums G


Article

Inorganic Chemistry 1,5-Diphenyl-3,7-bis(2-(pyridine-2′-yl)ethyl)-1,5-diaza-3,7diphosphacyclooctane (1). To 2-(pyridine-2′-yl)phosphine (1 g, 7.2 mmol) was added paraformaldehyde (0.43 g, 14.4 mmol). The mixture was stirred at 120 °C until the homogenization. To the obtained mixture were added 5 mL of dry ethanol and a solution of aniline (0.67 g, 7.2 mmol) in 5 mL of ethanol. The reaction mixture was stirred for 48 h at 70 °C, giving a white precipitate. The precipitate was filltered, washed with the ethanol 3 times, and dried over low pressure. Yield: 1.3 g (73%) mp: 202 °C. Elemental analysis, calculated for C30H34N4P2 [512]: C 70.31, H6.64, N 10.94, P 12.11. Found: C 70.55, H 6.87, N 10.68, P 11.90. MS (ESIpos, m/z (Irel, %), ion): 513 (100) [M]+. 1H NMR (CD2Cl2): δH 8.61 (d, 3JHH = 5.1, 2H, H-Py) 7.66 (ddd, 3JHH = 7.9 Hz, 3JHH = 7.3 Hz, 4JHH = 1.9 Hz, 2H, H-Py), 7.26 (d, 3JHH = 7.9 Hz, 2H, H-Py), 7.18 (m., 6H, H-Ph +H-Py), 6.69 (dd, 3JHH + 3JHH = 14.6 Hz, 2H, H-Ph), 6.65 (d., 3JHH = 7.9 Hz, 4H, H-Ph), 4.23 (dd, 3JHH = 14.9 Hz, 2JPH = 14.6 Hz, 4H, H1eq), 3.51 (dd, 2JHH = 14.9, 2JPH = 4.7 Hz, 4H, H-1ax), 3.15 (dd, 2JHH = 16.2, 3JHH = 8.25 Hz, 4H, Py-CH2), 1.90 (m, 2JHH = 16.2 Hz, 3JHH = 8.25 Hz, 4H, P-CH2-CH2). 31P{1H} NMR (CD2Cl2): δP −49.6. 1,5-Bis(p-tolyl)-3,7-bis(2-(pyridine-2′-yl)ethyl)-1,5-diaza3,7-diphosphacyclooctane (2). (2) was obtained analogously as 1 from 2-(pyridine-2′-yl)ethylphosphine (1 g, 7.2 mmol), paraformaldehyde (0.43 g, 14.4 mmol) and p-toluidine (0.77 g, 7.2 mmol). Yield 1.7 g (90%) mp: 210 °C. Elemental analysis, calculated for C32H38N4P2 [540]: C 71.11, H 7.03, N 10.37, P 11.48. Found: C 71.35, H 7.26, N 10.48, P 12.10.MS (ESIpos, m/z (Irel, %), ion): 541 (100) [M]+. 1H NMR (CD2Cl2): δH 8.56 (d, 3JHH = 5.2, 2H, H-Py) 7.64 (dd, 3JHH = 7.7 Hz, 3JHH = 7.2 Hz, 2H, H-Py), 7.26 (br.d, 3JHH = 7.7 Hz, 2H, H-Py), 7.16 (ddd, 3JHH = 5.2 Hz, 3JHH = 7.2 Hz, 2H, HPy), 6.96 (d, 3JHH = 8.3 Hz, 4H, H-p-Tol), 6.51 (d, 3JHH = 8.3 Hz, 4H, H-p-Tol), 4.15 (dd, 3JHH = 14.5 Hz, 2JPH = 14.5 Hz 4H, H-1eq), 3.48 (dd, 2JHH = 14.9, 2JPH = 5.2 Hz, 4H, H-1ax), 3.10 (br.dd, 2JHH = 16.1, 3 JHH = 8.8 Hz, 4H, Py-CH2), 2.19 (s, 6H, CH3-p-Tol), 1.84 (m, 2JHH = 16.1 Hz, 3JHH = 7.9 Hz, 4H, P-CH2-CH2). 31P{1H} NMR (CD2Cl2): δP −52.7. [Tetrakis-μ-iodo-bis-μ3-iodo-bis(μ4-(P,P,N,N)-1,5-diphenyl3,7-bis(2-(pyridine-2′-yl)ethyl)-1,5-diaza-3,7-diphosphacyclooctane]hexacopper(I) (3). To a solution of CuI (0.112 g, 0.585 mmol) in acetonitrile (5 mL) was added a solution of 1 (0.100 g, 0.195 mmol) in acetonitrile (5 mL). The reaction mixture was stirred for 4 h at room temperature until the white precipitate formed. The precipitate was filtered, recrystallized from acetonitrile. The formed crystalls were filtered, washed with CH3CN, and dried over low pressure. Yield 3: 0.196 g (92%), mp: 206 °C. Elemental analysis, calculated for C60H68N8P4Cu6I6 [2170]: C 33.18, H3.13, N5.16, P5.71, Cu 17.56, I 35.12. Found: C 33.90, H 3.01, N 5.67, P 5.59, Cu 17.69, I 35.04. MS (ESIpos, m/z (Irel, %), ion): 765 (100) [L + 2Cu + I]+; 1087 (7) [2L + Cu]+; 1279 (7) [2L + 2Cu + I]+; 1467 (5) [2L + 3Cu + 2I]+; 1658 (10) [2L + 4Cu + 3I]+. 1 H NMR (DMSO-d6): δH 8.33 (m., 2H, H-Py), 8.02 (dd., 3JHH = 7.34, 3JHH = 9.70 Hz, 2H, H-Py), 7.63 (d., 3JHH = 7.34 Hz, 2H, H-Py), 7.55 (dd., 3JHH = 6.60, 3JHH = 7.34 Hz, 2H, H-Py), 6.97 (dd., 3JHH + 3 JHH = 15.40 Hz, 4H, H-Ph), 6.67 (ddd., 3JHH = 9.17, 3JHH = 6.24, 4 JHH = 1.83 Hz, 2H, H-Ph), 6.53 (d., 3JHH = 7.70, 4H, H-Ph), 4.45 (m., 8H, H-PCH2N), 3.22 (m., 4H, Py-CH2), 2.15 (m. 4H, H-P-CH2CH2). 31P{1H} NMR (DMSO-d6): δP −40.7 ppm. 1 H NMR (CD3CN): δH 8.52 (dd., 3JHH = 4.78, 2H, H-Py), 7.89 (ddd., 3JHH = 7.86, 3JHH = 7.52, 4JHH = 1.71 Hz, 2H, H-Py), 7.47 (d., 3 JHH = 7.86 Hz, 2H, H-Py), 7.40 (dd., 3JHH + 3JHH = 13.32 Hz, 2H, HPy), 7.07 (dd., 3JHH + 3JHH = 16.06 Hz, 4H, H-Ph), 6.73 (dd., 3JHH + 3 JHH = 14.69 Hz, 2H, H-Ph), 6.60 (d., 3JHH = 7.86, 4H, H-Ph), 4.32 (dd., 2JHH = 14.69, 2JPH = 5.47 Hz, 4H, Ha-PCH2N), 4.13 (dd., 2JHH = 14.69, 2JPH = 5.12 Hz, 4H, Hb-PCH2N), 3.22 (m., 4H, Py-CH2), 2.08 (m. 4H, H-P-CH2-CH2). 31P{1H} NMR (CD3CN): δP −41.1 ppm. [Tetrakis-μ-iodo-bis-μ3-iodo-bis(μ4-(P,P,N,N)-1,5-bis(p-tolyl)3,7-bis(2-(pyridine-2′-yl)ethyl)-1,5-diaza-3,7-diphosphacyclooctane]hexacopper(I) (4). The compound 4 was obtained analogously as 3 from 2 (0.100 g, 0.185 mmol) and copper iodide (0.106 g, 0.555 mmol) in acetonitrile. Yield 4: 0.18 g (90%), mp: 230 °C. Elemental analysis, calculated for C64H76N8P4Cu6I6 [2226]:

C34.50, H3.41, N5.03, P5.57, Cu 17.12, I 34.23. Found: C 34.01, H 3.52, N 5.56, P 5.43, Cu 17.69, I 33.79.MS (ESIpos, m/z (Irel, %), ion): 793 (100) [L + 2Cu + I]+; 1144 (7) [2L + Cu]+; 1333 (7) [2L + 2Cu + I]+; 1524 (3) [2L + 3Cu + 2I]+; 1713 (5) [2L + 4Cu + 3I]+. 1 H NMR (DMSO-d6): δH 8.31 (d., 2JHH= 4.28 Hz, 2H, H-Py), 8.01 (ddd., 3JHH = 7.61, 3JHH = 9.27, 4JHH = 1.43 Hz, 2H, H-Py), 7.62 (d., 2JHH = 7.84 Hz, 2H, H-Py), 7.57 (dd., 3JHH = 5.7, 3JHH = 7.61 Hz, 2H, H-Py), 6.76 (d., 3JHH = 8.08, 4H, H-p-Tol), 6.42 (d., 3JHH = 8.08, 4H, H-p-Tol), 4.41 (br.s., 8H, H-PCH2N), 3.21 (m., 4H, Py-CH2), 2.15 (s., 6H, CH3-p-Tol), 2.10 (m. 4H, H-P-CH2-CH2). 31P{1H} NMR (DMSO-d6): δP −43.9 ppm. 1 H NMR (CD3CN): δH 8.52 (br.s, 2H, H-Py), 7.90 (dd., 3JHH + 3 JHH = 16.4 Hz, 2H, H-Py), 7.37−7.51 (m., 4H, H-Py), 6.88 (d., 3JHH = 8.20 Hz, 4H, H-p-Tol), 6.50 (d., 3JHH = 8.20 Hz, 4H, H-p-Tol), 4.28 (d, 3JHH = 16.40 Hz, 4H, Ha-PCH2N), 4.11 (d, 3JHH = 16.40 Hz, 4H, H-PCH2N), 3.13−3.28 (br.d., 4H, Py-CH2), 2.19 (s., 6H, CH3-pTol), 2.06 (m. 4H, H-P-CH2-CH2). 31P{1H} NMR (CD3CN): δP −43.8 ppm.

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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.8b01862. ESI-mass spectra, NMR spectra, TG/DSC data, far-IR and Raman spectra, UV/vis and simulated spectra, excitation spectra of 4, lifetimes decay, powder XRD, crystallographic data, coordinates of the gas phase singlet and triplet optimized geometries of 4 in XYZ format (PDF) Accession Codes

CCDC 1573308, 1573309, and 1586931 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]. uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Igor D. Strelnik: 0000-0003-2166-9849 Robert R. Fayzullin: 0000-0002-3740-9833 Sergey A. Katsyuba: 0000-0001-9196-9308 Elvira I. Musina: 0000-0003-3187-8652 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The measurements of photophysical properties were carried out in the Centre for Optical and Laser Materials Research of Saint Petersburg State University Research Park. The part of work was carried out using the core facilities of St. Petersburg State University Research Park, Computer Centre. Authors are grateful to Dr. D. B. Krivolapov for the X-ray experiments mentioned in this work and to Dr. A. E. Vandyukov for registration of far-IR spectra and to Dr. A. Khamatgalimov for TG-DSC analysis. Analytical part of work was carried out in the Centre of Collective Usage of FRC KSC RAS. H


Article

Inorganic Chemistry

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