Luminescent Vapochromism Due to a Change of the Ligand Field in a

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

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Luminescent Vapochromism Due to a Change of the Ligand Field in a One-Dimensional Manganese(II) Coordination Polymer Yue Wu,†,‡ Xu Zhang,*,† Liang-Jin Xu,† Ming Yang,† and Zhong-Ning Chen*,†,‡ †

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China ‡ College of Chemistry, Fuzhou University, Fuzhou, Fujian 350002, China

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S Supporting Information *

ABSTRACT: The reactions of MnBr 2 and ethane-1,2-diylbis(diphenylphosphine oxide) (dppeO2) in dichloromethane−methanol solutions gave colorless crystals with the general chemical formulas [MnBr2(dppeO2)]n (1), [MnBr2(dppeO2)(DMF)]n (1a), [Mn(dppeO2)3][MnBr4] (2), and Mn2Br4(dppeO2)2 (3) depending on the crystallization conditions. Compounds 1 and 1a display one-dimensional chain structures composed of Mn(II) ions linked by bridging dppeO2 to exhibit tetrahedral (1) or trigonal-bipyramidal (1a) coordination geometry, whereas 3 exhibits a cyclic dinuclear structure with two Mn(II) centers bridged by double dppeO2 to adopt tetrahedral geometry. Compound 2 consists of octahedrally coordinated cation [Mn(dppeO2)3]2+ and tetrahedrally arranged anion [MnBr4]2−. While 1 and 3 in crystalline and powder states are highly luminescent with green emission bands centered at ca. 510 nm, 2 shows intense orange luminescence peaking at 594 nm. Upon exposure of 1 to N,N-dimethylformamide vapor, the green emission centered at 510 nm is converted to red luminescence peaking at 630 nm, ascribed to the formation of DMFcoordinated compound 1a with a trigonal-bipyramidal ligand field, as demonstrated by X-ray crystallography. Red-emitting 1a could be reverted to the original green-emitting 1 with a tetrahedral ligand field upon heat at 160 °C, and such a reversible conversion could be perfectly repeated for several cycles. A new mechanism of luminescent vapochromism is thus proposed because of the reversible conversion of ligand fields in manganese(II) complexes.

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strong-field ligands with C, P, or S donors or π-conjugated ligands such as 2-phenylpyridine, 2,2′-bipydine, or 1,10phenanthroline derivatives are generally utilized to achieve highly efficient phosphorescence at ambient temperature.7 On the other hand, low-cost transition-metal complexes with manganese(II) are frequently phosphorescent at ambient temperature because the d−d transition state of Mn2+ can be deactivated through efficient radiative decay in these cases.8−20 Depending on the type and strength of ligand fields in various manganese(II) complexes, phosphorescent emission wavelengths and colors could be systematically modulated over the whole visible region. Nevertheless, in contrast to numerous investigations focused on phosphorescent noble-metal complexes and their applications in optoelectronic and biological fields, low-cost phosphorescent manganese(II) complexes have been extremely neglected to be exploited. Recently, we have launched a research project to develop highly efficient phosphorescent manganese(II) complexes8−10 and the use in OLEDs.21 In this Article, we report the preparation, structural characterization, and photophysical properties of phosphor-

INTRODUCTION Luminescent metal complexes have been exhaustively investigated owing to the extensive applications in the fields of lighting, display, biological sensing, imaging etc.1−6 The heavyatom effect of metal coordination conducts strong spin−orbit coupling that facilitates intersystem crossing from a singlet to a triplet excited state. As a result, the radiative transitions in metal complexes are generally phosphorescent in character. Compared to traditional fluorescent compounds with a singlet state, phosphorescent metal coordination compounds with a triplet state exhibit two extraordinary advantages, including (i) long-lived luminescence to benefit bioassay, biosensing, and bioimaging and (ii) harvesting of both singlet and triplet excitons in organic light-emitting diodes (OLEDs) to take advantage of 100% internal quantum efficiency in contrast to the intrinsic low internal quantum efficiency of 25% for fluorescent-emitting materials. In most cases, phosphorescent metal complexes contain noble-metal ions such as Ir(III),1 Pt(II),1,2 Re(I),3 Os(II),4 Au(I),5 Ru(II),6 etc. The phosphorescent emission of those heavy-metal complexes originates primarily from chargetransfer transitions between metal ions and ligands, whereas d−d transitions of metal ions are generally nonradiative. In order to suppress undesirable radiationless d−d transitions, © XXXX American Chemical Society

Received: May 2, 2018

A

DOI: 10.1021/acs.inorgchem.8b01205 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

1 and 3 are dynamic products. The interconversion route among the four manganese(II) complexes is shown in Scheme 1. The structures of these manganese(II) complexes were determined through single-crystal X-ray diffraction (XRD). As depicted in Figure 1a, complex 1 displays a one-dimensional chain structure composed of MnBr2 moieties linked by bridging dppeO2 through two Mn−O bonding linkages. The Mn center is bound to Br2O2 coordination donors to give an approximate tetrahedral geometry. The bond angles are in the range of 102.17(16)−117.82(6)°. The Mn···Mn separations are alternately 8.12 and 9.50 Å through bridging dppeO2. The Mn···Mn···Mn angle is ca. 150.0°. Compound 1a (Figure 1b) also exhibits a one-dimensional chain structure like that of 1, but the bonding of DMF exerts a significant influence on the coordination geometry and relevant bonding parameters. The Mn atom is five-coordinated with Br2O3 donors to provide a distorted trigonal-bipyramidal geometry, in which one O donor of dppeO2 and two Br atoms are situated at the trigonal plane, whereas the other O donor of dppeO2 and the O atom of DMF are at two axial positions. As listed in Table 1, both Mn−Br [dMn−Br = 2.5291(7) and 2.5597(7) Å] and Mn−O [dMn−O = 2.110(2) and 2.1127(19) Å] distances of 1a are obviously longer than those of 1 [dMn−Br = 2.4667(19) and 2.4767(18) Å; dMn−O = 2.028(4) and 2.067(4) Å]. The Mn···Mn separations are alternately 8.02 and 8.49 Å through bridging dppeO2. The one-dimensional coordination polymer adopts a zigzag chain structure with a Mn···Mn···Mn angle of 104.8°, which is much smaller than that of 1 (150.0°). Compound 2 (Figure 1c) consists of the coordination cation [Mn(dppeO2)3]2+ and anion [MnBr4]2−. The Mn atom in cationic [Mn(dppeO2)3]2+ displays an approximate octahedral geometry composed of six O donors, whereas the one in anionic [MnBr4]2− is coordinated by four Br donors to give a coordination tetrahedron. The shortest Mn···Mn separation is 8.39 Å between cationic and anionic manganese(II) complexes. The crystal structure of compound 3 (Figure 1d) contains two different binuclear manganese(II) moieties. Each binuclear structure is composed of two MnBr2 units linked by two bridging dppeO2 through four Mn−O bonds to produce a cyclic dinuclear structure. The Mn atom is surrounded by Br2O2 donors to afford a tetrahedral geometry. The Mn−Br [dMn−Br = 2.450(3) and 2.500(3) Å] and Mn−O [dMn−O = 2.058(7) and 2.069(7) Å] distances are comparable to those of 1 [dMn−Br = 2.4667(19) and 2.4767(18) Å; dMn−O = 2.028(4) and 2.067(4) Å]. The bond angles around the MnBr2O2 coordination tetrahedron are in the range of 101.4(3)− 117.13(10)°. The Mn···Mn separation through bridging dppeO2 is 6.90 Å, which is significantly shorter than those in one-dimensional chain compounds 1 (dMn−Mn = 8.12 and 9.50 Å) and 1a (dMn−Mn = 8.02 and 8.49 Å). The UV−vis spectra (Figure S1) of compounds 1, 1a, 2, and 3 in solid states display intense absorption bands at 270−280 nm together with broad bands at ca. 320 nm tailing to 550 nm. The low-energy bands due to d−d transitions are mainly overlapped by strong ligand-centered absorptions. Upon irradiation at λex > 260 nm (Figure 2), compounds 1, 1a, 2, and 3 in solid states show bright-green (λem = 510 nm), red (λem = 630 nm), orange (λem = 594 nm), and green (λem = 510 nm) luminescence at room temperature with photoluminescent quantum yields of 13.0%, 10.1%, 28.9%, and 19.8%,

escent manganese(II) complexes with ethane-1,2-diylbis(diphenylphosphine oxide) (dppeO2). Depending on the crystallization conditions, manganese(II) complexes [MnBr2(dppeO2)]n (1; CCDC 1833713), [MnBr2(dppeO2)(DMF)]n (1a; CCDC 1833712), [Mn(dppeO2)3][MnBr4] (2; CCDC 1833710), and Mn 2 Br 4 (dppeO 2 ) 2 (3; CCDC 1833711) were isolated and structurally characterized by Xray crystallography. Noticeably, the one-dimensional coordination polymer 1 with a tetrahedral ligand field displays a dramatic luminescent color change from green to red upon exposure to DMF vapor due to the formation of N,Ndimethylformamide (DMF)-coordinated complex 1a having a trigonal-bipyramidal ligand field. Furthermore, red-emitting 1a could be reverted to green-emitting 1 by heating at 160 °C. Such a reversible luminescent vapochromism could be operated for several cycles. To our knowledge, this is the first example that exhibits striking luminescent vapochromism for manganese(II) complexes due to a reversible ligand-field change.

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RESULTS AND DISCUSSION As shown in Scheme 1, the reactions of MnBr2 and dppeO2 (1:1 ratio) in CH2Cl2 solutions produced a colorless Scheme 1. Synthetic Routes to Compounds 1−3 together with Their Interconversion

precipitate, which could be dissolved by the addition of methanol (MeOH). Diffusion of ethyl acetate or diethyl ether (Et2O) to the dichloromethane (CH2Cl2)−MeOH solutions gave different crystalline forms. The crystals of the onedimensional coordination polymer 1 were grown by layering ethyl acetate to the above solutions, while those of the dinuclear complex 3 were isolated through diffusion of Et2O onto the same solutions. The crystals of the ionic compound 2 were accessible through diffusion of either ethyl acetate or Et2O. Furthermore, diffusion of Et2O to a CH2Cl2−DMF solution brought about isolation of the DMF-coordinated complex 1a as colorless crystals. Noticeably, 1 and 3 converted readily to ionic compound 2 when they were recrystallized in protic solvents such as MeOH and ethanol (EtOH). This phenomenon together with the fact that the crystals of 2 could be grown in different solvent conditions suggests that compound 2 is a thermodynamically stable product, whereas B

DOI: 10.1021/acs.inorgchem.8b01205 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Perspective views of compounds 1 (a), 1a (b), 2 (c), and 3 (d) with 30% thermal ellipsoids. Phenyl rings on P atoms in 2 and 3 were omitted for clarity.

respectively, although they are nonemissive in fluid solutions. The luminescent lifetimes (Table 2) are in the range of submillisecond to millisecond depending on the structures of the manganese(II) complexes. Long-lived luminescence, together with a large Stokes shift between the absorption and emission spectra, suggests their phosphorescent character because of the change of the spin state upon excitation. Experimental studies and spectral analyses have suggested that photoluminescence of manganese(II) complexes originates largely from the 4T1g (4G) → 6A1g (6S) state featuring d−d transitions, and the emission spectra are highly dependent on the ligand fields.22−24 The tetrahedral ligand field around the Mn(II) center usually results in green luminescence, whereas the octahedral coordination geometry gives rise to an orangeto-red emission.8−20 As depicted in Figure 2, compounds 1 and 3 with tetrahedral ligand fields display a bright-green emission peaking at 510 nm, while compound 1a with trigonal-bipyramidal geometry gives intense red luminescence with the spectrum band centered at 630 nm. Compound 2 strongly emits orange luminescence, with the structureless band peaking at 594 nm, although it consists of cationic complex [Mn(dppeO2)3]2+ with an octahedral ligand field and anionic complex [MnBr4]2− with tetrahedral geometry. The emission decay curve of 2 (Figure S2) at 300 K could be perfectly fitted by a single-exponential component, giving phosphorescent lifetimes of 21.17 and 21.49 ms upon excitation at 280 and 445 nm, respectively. This, together with the fact that the green emission band of tetrahedral coordination [MnBr4]2− is totally unobserved at ambient temperature, suggests that an efficient intercomponent energy transfer takes places likely from high-lying [MnBr4]2− to low-lying [Mn(dppeO2)3]2+.13b,17 Nevertheless, when the temperature is gradually lowered from 300 to 77 K, a weak emission band centered at ca. 517 nm (Figure S3) appears and

intensifies increasingly. This implies that energy transfer from [MnBr4]2− to [Mn(dppeO2)3]2+ is prohibited by lowering the temperature so that the emission bands from the d−d transitions of both tetrahedrally and octahedrally coordinated Mn(II) centers can be observed. Furthermore, the emission band due to the octahedral coordination Mn(II) center displays a progressive red shift with decreasing temperature from 300 (λem = 594 nm) to 77 K (λem = 618 nm) likely due to less distortion of the octahedral geometry and a stronger crystal field with contraction of the crystal lattices at low temperature.13b When green-emitting crystalline sample 1 (Figure 3) with a tetrahedral ligand field composed of a Br2O2 chromophore was exposed to DMF vapor at room temperature, the emission band centered at 510 nm was dramatically shifted to 630 nm due to the formation of DMF-bound complex 1a having a triangle-bipyramidal ligand field built by Br2O3 donors. The change from green to red luminescence corresponds to a complete transformation of 1 to 1a (Scheme 2) upon exposure to DMF vapor. On the other hand, when red-emitting sample 1a was allowed to heat at 160 °C for 0.5 h, the emission band centered at 630 nm vanished entirely whereas the emission peaking at 510 nm was only observed, implying a complete conversion of red-emitting 1a to green-emitting 1 through thermal removal of the coordination DMF. As a result, the transformation between 1 and 1a is totally reversible. As shown in Figure 3c, because the emission intensity of 1 at 510 and 1a at 630 nm did not show appreciable decay upon alternate exposure to DMF vapor and heating at 160 °C for four cycles, the interconversion process 1 ⇆ 1a could be perfectly repeated without undergoing distinct degradation of the sample. As depicted in Figure 4, the reversible transformation process 1 ⇆ 1a was well verified by powder XRD (PXRD) measurement (Figure S4). On the one hand, upon exposure of C

DOI: 10.1021/acs.inorgchem.8b01205 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Selected Bond Distances (Å) and Angles (deg) of Compounds 1, 1a, 2, and 3 1

Table 2. Luminescent Wavelengths, Lifetimes, and Quantum Yields of Compounds 1, 1a, 2, and 3 in Solid States at Ambient Temperature

1a

Br1−Mn1 Br2−Mn1 Mn1−O1 Mn1−O2

2.4767(18) 2.4667(19) 2.028(4) 2.067(4)

Mn1−Br1 Mn1−Br2 Mn1−O1 Mn1−O2 Mn1−O3

2.5597(7) 2.5291(7) 2.1127(19) 2.110(2) 2.212(2)

Br1−Mn1−Br2 O1−Mn1−O2 O1−Mn1−Br1 O2−Mn1−Br1 O1−Mn1−Br2 O2−Mn1−Br2

117.82(6) 102.17(16) 108.87(11) 108.22(11) 114.38(12) 103.88(12)

Br1−Mn1−Br2 O1−Mn1−O2 O2−Mn1−O3 O1−Mn1−O3 O1−Mn1−Br2 O2−Mn1−Br2 O3−Mn1−Br2 O2−Mn1−Br1 O1−Mn1−Br1 O3−Mn1−Br1

124.63(2) 89.69(8) 171.91(9) 82.22(8) 119.46(6) 93.13(6) 90.99(8) 91.06(6) 115.75(6) 92.32(7)

2 2.144(6) 2.157(5) 2.154(6) 2.158(6) 2.179(6) 2.139(6) 2.493(4) 2.5035(13)

Mn1−O1 Mn1−O2 Mn1−Br1 Br2−Mn1 Mn2−O3 Mn2−O4 Mn2−Br3 Mn2−Br4

2.051(7) 2.072(7) 2.463(3) 2.489(3) 2.069(7) 2.058(7) 2.450(3) 2.500(3)

O6−Mn1−O1 O6−Mn1−O3 O1−Mn1−O3 O6−Mn1−O2 O1−Mn1−O2 O3−Mn1−O2 O6−Mn1−O4 O1−Mn1−O4 O3−Mn1−O4 O2−Mn1−O4 O6−Mn1−O5 O1−Mn1−O5 O3−Mn1−O5 O2−Mn1−O5 O4−Mn1−O5 Br1−Mn2−Br2 Br1−Mn2−Br1a

86.7(3) 86.9(3) 92.6(3) 175.1(3) 90.6(2) 89.1(3) 92.8(3) 175.7(3) 91.7(2) 90.1(3) 89.9(2) 87.1(3) 176.9(3) 94.0(2) 88.6(3) 106.35(7) 112.40(6)

O1−Mn1−O2 O1−Mn1−Br1 O2−Mn1−Br1 O1−Mn1−Br2 O2−Mn1−Br2 Br1−Mn1−Br2 O4−Mn2−O3 O4−Mn2−Br3 O3−Mn2−Br3 O4−Mn2−Br4 O3−Mn2−Br4 Br3−Mn2−Br4

102.2(3) 107.7(2) 114.7(2) 106.8(2) 107.0(2) 117.13(10) 101.4(3) 109.3(2) 114.9(2) 106.5(2) 107.2(2) 116.31(11)

τem (ms)

Φem (%)

kra (s−1)

knrb (s−1)

1 1a 2

510 630 594

13.0 10.1 28.9

461 65 13

3085 577 33

3

510

0.28 1.56 21.17c 21.49d 0.33

19.8

600

2430

Radiative decay rate kr = Φem/τem. bNonradiative decay rate knr = (1 − Φem)/τem. cExcitation at 280 nm. dExcitation at 445 nm. a

1 to DMF vapor for 2 h, the XRD pattern of green-emitting 1 was totally converted to that of red-emitting 1a. On the other hand, when 1a was annealed at 160 °C for 30 min, the XRD pattern of red-emitting 1a was perfectly reverted to the original pattern of green-emitting 1. Thermogravimetric (TG) studies (Figure S5) indicated that red-emitting 1a lost solvate DMF (weight loss of 10.3% vs calculated 10.2%) before reaching 150 °C. The DMF-removed species displays the same XRD pattern as that of green-emitting 1. The DMF-removed species was then kept stable before 390 °C, and then the weight was lost quickly, implying that the thermal stability of 1 was up to 390 °C. When the green-emitting crystalline sample 1 was exposed to the vapors of other organic solvents with potential coordination character such as water (H2O), MeOH, EtOH, acetone, acetonitrile, tetrahydrofuran, dioxane, etc., obvious changes were unobserved except for H2O and alcohol. Upon exposure of crystalline sample 1 to H2O, MeOH, or EtOH vapor for a while, the green emitting changed to orange under UV illumination. Meanwhile, the emission band of 1 peaking at 510 nm is red-shifted to 594 nm, as depicted in Figure S6, which is the same as that of compound 2. This implies that green-emitting compound 1 converts to ionic compound 2 upon exposed to the vapors of protic solvents. To clarify this issue, XRD studies were performed. As depicted in Figure 5, the XRD pattern of the sample exposed to H2O or MeOH vapor coincides well with that of orange-emitting compound 2. This strongly supports that, upon exposure of green-emitting compound 1 to H2O or alcohol vapor, the one-dimensional chain structure of 1 is damaged so that a rearrangement reaction takes place to produce thermodynamically stable compound 2. In contrast, no appreciable changes of the XRD pattern (Figure S7) could be observed upon exposure of 1 to other vapors except for H2O, alcohol, and DMF.

3

Mn1−O1 Mn1−O2 Mn1−O3 Mn1−O4 Mn1−O5 Mn1−O6 Mn2−Br1 Mn2−Br2

λem (nm)

Figure 2. (a) Photoluminescent excitation (dotted line) and emission (solid line) spectra of 1, 1a, 2, and 3 in solid states. (b) Photographs of the crystals of 1, 1a, and 2 upon irradiation under ambient and UV light at 365 nm. D

DOI: 10.1021/acs.inorgchem.8b01205 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. (a) Images of the powder samples of 1 and 1a upon irradiation under ambient and UV light at 365 nm. (b) Photoluminescent emission spectra of 1 and 1a. (c) Photoluminescent intensity change of 1 at 510 nm and 1a at 630 nm upon alternate exposure to DMF vapor and heating at 160 °C for four cycles.

Scheme 2. Reversible Transformation between GreenEmitting 1 and Red-Emitting 1a

Figure 5. XRD patterns of 1 (a) and 2 (d) and XRD changes upon exposure of 1 to water (b) and MeOH (c) vapors.

When dinuclear manganese(II) complex 3 was exposed to DMF vapor, the change in the XRD pattern demonstrated clearly that 3 was transformed to 1a, as depicted in Figure S8. The transformation of 3 to 1a upon exposure to DMF vapor implies that complex 3 does not display reversible vapochromic luminescence because DMF-coordinated one-dimensional polymer 1a could not be reverted to the original binuclear complex 3 by heating. Upon exposure to the vapors of protonic solvents such as water and alcohols, complex 3 was also converted to thermodynamically stable compound 2 (Figure S8), similar to that observed for complex 1. A vapor-induced reversible luminescent change, i.e., the socalled luminescent vapochromism, has been observed in many metal complexes with gold(I), silver(I), copper(I), platinum(II), zinc(II), rhenium(I), iridium(III), ruthenium(II), etc.25−28 Such vapor-responsive luminescence changes arise mostly from the intramolecular generation of a metal−solvent bond or intermolecular variation such as the formation/ disruption of metal−metal, π−π, hydrogen-bonding, etc., interactions. Compound 1 represents the first manganese(II) complex that exhibits striking luminescent vapochromism due to the conversion between tetrahedral and trigonal-bipyramidal

Figure 4. Simulated and measured XRD patterns for 1 and 1a.

E

DOI: 10.1021/acs.inorgchem.8b01205 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry ligand fields through the reversible formation or breaking of metal−solvent bonds.29

using graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation. The CrystalClear software package was used for data reduction and empirical absorption correction. The structure was solved by direct methods using the SHELXL-97 program.31 All non-H atoms were located by Fourier synthesis and a differential electron density function. The H-atom coordinates were obtained by the differential electron density function combined with geometric analysis. All nonH-atom coordinate and anisotropy temperature factors and H-atom coordinate and isotropic temperature factors were corrected to convergence using full-matrix least-squares methods.

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CONCLUSIONS The reaction of MnBr2 and dppeO2 results in the isolation of two dynamically stable complexes (1 and 3) and one thermodynamically stable product (2) depending on the crystallization conditions. The dynamically stable complexes 1 and 3 could be converted to the thermodynamically stable product 2 through recrystallization in protic solvents. Upon exposure to DMF vapor, green-emitting one-dimensional chain compound 1 is transformed to red-emitting DMF-bound compound 1a. The dramatic red shift of the emission from 510 to 630 nm arises from a conversion of the ligand field around the Mn(II) atom from a tetrahedron to a trigonal bipyramid. The DMF-bound compound 1a could be reversibly reverted to DMF-free compound 1, accompanying red-to-green emission conversion. The adsorption of water or alcohol vapor brings about the chain structure of 1 to be disrupted and rearranged to form thermodynamically stable product 2.

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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.8b01205. Tables and figures giving the crystallographic data, UV− vis absorption spectra in the solid state, XRD patterns, and TG curves (PDF) Accession Codes

CCDC 1833710−1833713 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.

EXPERIMENTAL SECTION

General Procedures and Materials. All of the synthetic materials were commercially purchased and used without further purification. The experiment was conducted under a dry argon atmosphere, and the solvent was dried and distilled before use. The ligand dppeO2 was prepared by the literature procedure.30 [MnBr 2 (dppeO 2 )] n (1), [Mn(dppeO 2 ) 3 ][MnBr 4 ] (2), and Mn2Br4(dppeO2)2 (3). To a CH2Cl2 (15 mL) solution of dppeO2 (200 mg, 0.46 mmol) was added slowly MnBr2 (99 mg, 0.46 mmol), rapidly producing a precipitate. Upon stirring at ambient temperature for 1 day, MeOH (3 mL) was added to dissolve the precipitate, giving a colorless clear solution. Layering ethyl acetate onto the solution gave block crystals of 1 (yield: 40%) and prism crystals 2 (yield: 51%). In contrast, when Et2O was diffused to the solution, block crystals of 3 (yield: 42%) and prism crystals 2 (yield: 49%) were isolated. 1. Anal. Calcd for C26H24Br2MnO2P2: C, 48.40; H, 3.75. Found: C, 48.15; H, 3.56. IR (KBr, cm−1): 1153s (PO). 2. Anal. Calcd for C78H72Br4Mn2O6P6: C, 54.44; H, 4.22. Found: C, 54.38; H, 4.27. IR (KBr, cm−1): 1151s (PO). 3. Anal. Calcd for C26H24Br2MnO2P2: C, 48.40; H, 3.75. Found: C, 48.05; H, 3.91. IR (KBr, cm−1): 1151s (PO). [MnBr2(dppeO2)(DMF)]n (1a). To a dichloromethane (15 mL) solution of dppeO2 (200 mg, 0.46 mmol) was added slowly MnBr2 (99 mg, 0.46 mmol) to rapidly produce a precipitate. Upon stirring at ambient temperature for 1 day, DMF (1 mL) was added to dissolve the precipitate, giving a colorless clear solution. Diffusion of Et2O to the solution gave colorless column crystals. Yield: 80%. Anal. Calcd for C29H31Br2MnO3NP2: C, 48.49; H, 4.35; N, 1.95. Found: C, 48.77; H, 4.52; N, 1.86. IR (KBr, cm−1): 1153s (PO), 1647s (CO). Physical Measurements. The IR spectra were recorded on a Bruker VERTEX 70 FT-IR spectrophotometer with KBr pellets in the range of 4000−400 cm−1. The UV−vis absorption spectra were conducted on a PerkinElmer Lambda 950 UV−vis spectrophotometer. The PXRD patterns were recorded on a Miniflex II analyzer with Cu Kα (λ = 1.54184 Å) radiation in the range of 5−50° at a scan rate of 5°/min. The C, H, O, and N elemental analyses were conducted on a PerkinElmer model 240 C elemental analyzer. The TG curves were measured on a STA449C analyzer heated from 25 to 1000 °C at a ramp rate of 5.00 °C/min. The photoluminescence properties, including the emission and excitation spectra, emissive lifetimes, and quantum yields in solid states, were performed on a Edinburgh FLS920 fluorescence spectrometer. Crystal Structure Determination. Single-crystal XRD data were collected on Bruker APEX-II CCD (compound 1), Rigaku Saturn 724 (compound 1a), and Bruker P4 (compounds 2 and 3) diffractometers

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Zhong-Ning Chen: 0000-0003-3589-3745 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21531008, U1405252, 21601184, 21390392, and 21473201), the 973 Project from MSTC (Grant 2014CB845603), the CAS/SAFEA International Partnership Program for Creative Research Teams, and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDB20000000).

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DOI: 10.1021/acs.inorgchem.8b01205 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.inorgchem.8b01205 Inorg. Chem. XXXX, XXX, XXX−XXX