Can Coinage Metal Atoms Be Capable of Serving as an Excess

Mar 30, 2017 - Alkalides, as a representative kind of excess electron compounds, have been ... alkalide possesses a remarkably large β0 value of 180 ...
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Can Coinage Metal Atoms Be Capable of Serving as an Excess Electron Source of Alkalides with Considerable Nonlinear Optical Responses? Wei-Ming Sun,*,† Xiang-Hui Li,‡ Juan Wu,‡ Jian-Ming Lan,† Chun-Yan Li,*,† Di Wu,§ Ying Li,§ and Zhi-Ru Li§ †

The Department of Basic Chemistry, The School of Pharmacy, Fujian Medical University, Fuzhou, Fujian 350108, People’s Republic of China ‡ Medical Technology and Engineering College, Fujian Medical University, Fuzhou, Fujian 350004, People’s Republic of China § Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People’s Republic of China S Supporting Information *

ABSTRACT: Alkalides, as a representative kind of excess electron compounds, have been demonstrated to be potential nonlinear optical (NLO) materials with large static first hyperpolarizabilities (β0). The possibility of utilizing coinage metal atoms as a novel excess electron source to design a series of alkalides, i.e., (M@36adz)M′ (M = Cu, Ag, and Au; M′ = Li, Na, and K), was examined by density functional theory calculations. The alkalide characteristics of these compounds are guaranteed by their HOMOs and VIE values as well as NBO analysis. In particular, all proposed alkalides exhibit considerable first hyperpolarizabilities (β0) up to 61 590 au, indicating that they can be considered as novel NLO molecules of high performance. Moreover, a larger cage-complexant has been considered, and the resulting (Ag+@TriPip222)K− alkalide possesses a remarkably large β0 value of 180 068 au. We hope that this work will provide a new recipe for designing excess electron compounds and, on the other hand, attract more research interest and efforts in exploring new, unconventional alkalides. molecular NLO materials of high performance.14−17 Alkalides are crystalline salts in which anionic sites are occupied by alkali metal anions (e.g., Na−, K−, Rb−, or Cs−).23 The existence of such special species has been known for several decades, since the first alkalide was successfully synthesized and characterized by Dye et al.24 in 1974. Two room-temperature-stable organic alkalides, i.e., K+(Me6Aza222)K− and K+(Me6Aza222)Na−, were successfully synthesized by Dye and his colleagues in 1999,25 which brought forth the great application prospect of alkalides. To extend the application of alkalides in the NLO field, it is still urgently desired to theoretically design and study a new type of alkalides with large NLO response. Conventionally, the alkalides were obtained by doping organic molecules or inorganic molecular sieves with alkali metal atoms. In other words, the excess electron of such compound is derived from the encapsulated alkali metal atom in complexant. Recently, Redko et al.26 successfully synthesized a sodide (H+@36adz)Na− where an encapsulated hydrogen atom serves as the source of the excess electron in 2002. Later, they reported another successful attempt to synthesize a new kind of barium-based sodide Ba2+(H5Azacryptand[2.2.2]−)Na−·

1. INTRODUCTION The past several decades have witnessed increasing scientificand technology-driven interest in developing nonlinear optical (NLO) materials due to their potential advanced technological applications in photonic and electro-optical devices.1−7 Besides the dominated donor−(π-conjugate bridge)−acceptor (D−π− A) molecules,8,9 several new kinds of molecules with interesting features have been recently proposed to be potential NLO molecules. For example, Nakano et al.10,11 reported that the diradical molecules with intermediate diradical character possess larger second hyperpolarizabilities as compared to closed-shell molecules. Champagne et al.12 proposed that doping polyacetylene chains by alkali metal atoms can bring forth enhanced hyperpolarizability. Muhammad et al.13 reviewed different random investigations of sp2-hybridized carbon nanostructures for NLO application and proposed opportunities to use the sp2-hybridized carbon nanomaterials as novel NLO materials of the future. Recently, Li and coworkers14−20 opened up a new research field of NLO molecules with excess electrons since they found that an excess electron can reduce the transition energy of crucial excited states and thus lead to large second-order NLO responses.21,22 Alkalides are representative compounds with loosely bound excess electrons and thus show great potential to serve as © XXXX American Chemical Society

Received: January 28, 2017

A

DOI: 10.1021/acs.inorgchem.7b00183 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

izability (α0), and first hyperpolarizability (β0)] of the currently studied systems. Besides, Maroulis41 reported that the basis set effect on the hyperpolarizability calculations is enormous. Thereby, the studies of the basis set effect on the calculations of static electric properties were performed and are shown in Tables S3 and S4. On the basis of these results, the LANL2DZ basis set and ECP were used for coinage metal atoms (Cu, Ag, Au) and the 6-311++G(d, p) basis set was adopted for the other atoms, because they can provide static electric properties close to those obtained by the larger basis sets. Moreover, the vertical ionization energies (VIE) and natural bond orbital (NBO) charges were calculated at the same computational level. The static mean polarizability (α0) and mean first hyperpolarizability (β0) are defined as follows

2MeNH2 with alkaline earth atoms serving as the excess electron source.27 More recently, the superalkali cluster with similar chemical characteristics to alkali metal atoms has been successfully used as the source of an excess electron in the design of alkalides with large NLO responses.28−30 Consequently, searching for novel excess electron sources for alkalides should be an effective approach to design and synthesize new NLO materials of high performance. In view of the fact that the coinage metal atoms (Cu, Ag, and Au) share similar ns1 valence-electron configuration with alkali metal atoms, it is highly expected that such atoms also have the potential to serve as a novel excess electron source for the design of alkalides. Hence, this hypothesis was verified in detail by using the 36adamanzane (36adz) as complexant to encapsulate the coinage metal atoms for the design of (M@ 36adz)M′ (M = Cu, Ag, and Au; M′ = Li, Na, and K) compounds in the present work. The calculated results show that the valence electrons on the outmost s atomic orbitals of Cu, Ag, and Au atoms can be pushed out of the 36adz cage to form diffuse excess electrons around the outer alkali metal atoms, which yields a novel series of (M+@36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K) alkalides with considerable NLO response. It is hoped that this study could not only pave a new way to design various excess electron compounds but also provide inspiration for experimental chemists to synthesize such potential NLO materials in the laboratory.

α0 =

1 (αxx + αyy + αzz) 3

(1)

β0 =

(βx2

(2)

+

βy2

+

βz2)1/2

3 (β 5 iii

+ βijj + βikk ), i, j, k = x, y, z. where βi = The mean dipole moment (μ0) is noted as μ0 = (μx2 + μy2 + μz2 )1/2

(3)

In addition, the time-dependent density functional theory (TDDFT) calculations were performed by using the BHandHLYP method in conjunction with the same basis sets for the β0 calculation to get the crucial excited states and absorption spectra of the related structures. All spectra were reflected with Gaussian curves under a full-width at half-maximum of 0.10 eV. All of the above calculations were performed by using the GAUSSIAN 09 program package.42 Dimensional plots of molecular configurations and orbitals were generated with the GaussView program.43

2. COMPUTATIONAL DETAILS Geometric structures of the studied compounds with all real frequencies are obtained by using the Coulomb-attenuating exchange-correlation density functional method (CAM-B3LYP),31,32 which was developed to handle the inaccuracies of the non-Coulomb part of exchange functionals at long distances. Limacher et al.33 reported that CAM-B3LYP can provide molecular geometries close to experimentally observed structures. Besides, the choice of suitable basis sets for molecular structure and property calculations is crucial in modern computational quantum chemistry. For predicting the geometric structures and physicochemical properties of transition metal systems, the Los Alamos set of the double-ζ-type LANL2DZ basis set34−36 for transition metals and Pople-type basis sets for the others have been proven to be competent.37 Hence, the LANL2DZ basis set and effective core potential (ECP) were used for the coinage metal atoms, while the 6-31+G(d) was used for the other atoms, which can show molecular geometries close to the one obtained by the larger basis set (see Table S1). With regard to the calculation of the first hyperpolarizabilities (β0) of these large systems in the present study, choosing a proper method is important. The B3LYP method has been reported to overestimate the (hyper)polarizabilities for some large systems.38 The MP2 method is more reliable than B3LYP in the (hyper)polarizability calculations, but it is very costly for these large systems. To choose a proper method, a computational test was performed to investigate the effects of different methods on the calculation of β0 by sampling the (Cu+@ 36adz)Li− compound (see Table S2). It can be clearly seen from Table S2 that the B3LYP excessively overestimates the β0 of (Cu+@ 36adz)Li−, while the BHandHLYP, CAM-B3LYP, and LC-BLYP values agree well with the MP2 result. In particular, all of the static electric properties obtained by BHandHLYP are close to the MP2 values. Just as proposed by Champagne et al., the BHandHLYP successfully reduces the overestimation of the (hyper)polarizability.39 Besides, Nakano and co-workers pointed out that the BHandHLYP method can also reproduce the (hyper)polarizability values from the more sophisticated CCSD(T).40 Thus, the BHandHLYP method with satisfactory performance in both quality and efficiency is chosen to explore the static electric properties [dipole moment (μ0), polar-

3. RESULTS AND DISSCUSSION 3.1. Structural Characteristics. Nine equilibrium structures of (M@36adz)M′ (M = Cu, Ag, and Au; M′ = Li, Na, and K) were obtained and are given in Figure 1. Results show that

Figure 1. Geometric structure (a) and HOMO (b) of (M@36adz)M′ (M = Cu, Ag, and Au; M′ = Li, Na, and K).

these compounds possess a similar geometric structure in which the coinage metal atom lies near the center of the adz cage, while the alkali metal atom locates outside. Selected geometrical parameters of these resulting compounds are summarized in Table 1. As shown in Table 1, the distance between the encapsulated coinage metal M and the nitrogen atoms of complexant (dM−N) hardly varies upon changing the outside alkali metal M′ in these (M+@36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K) compounds. Instead, it is found that dM−N increases along with B

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Table 1. Average Distances between the M and Nitrogen Atoms (dM−N, in Å), Distances between the M and M′ Atoms (dM−M′, in Å), Vibrational Frequencies of the Stretching Modes between the Cage and the Anion (ωcage‑M′, in cm−1), NBO Charges on M (QM) and M′ (QM′), and VIE Values (in eV) of the (M@36adz)M′ (M = Cu, Ag, and Au; M′ = Li, Na, and K) Compounds compounds

dM−N

dM−M′

ωcage−M′

QM

QM′

VIE

(Cu@36adz)Li (Cu@36adz)Na (Cu@36adz)K (Ag@36adz)Li (Ag@36adz)Na (Ag@36adz)K (Au@36adz)Li (Au@36adz)Na (Au@36adz)K

2.033 2.033 2.033 2.185 2.185 2.185 2.194 2.193 2.194

5.803 5.940 6.533 5.778 5.922 6.519 5.790 5.929 6.524

118.3 67.5 44.9 114.1 66.8 43.9 124.0 65.5 43.2

0.464 0.463 0.456 0.447 0.448 0.440 0.337 0.338 0.334

−0.811 −0.822 −0.827 −0.802 −0.813 −0.814 −0.804 −0.814 −0.817

2.760 2.734 2.480 2.761 2.734 2.480 2.756 2.733 2.480

Table 2. Calculated Mean Dipole Moments (μ0, in au), Mean Polarizabilities (α0, in au), Mean First Hyperpolarizabilities (β0, in au), Transition Energies (ΔE, in eV), Oscillator Strengths ( f 0), and Difference of Dipole Moment (Δμ, in D) between the Ground and the Excited States of Crucial Excited State, and Dominated Transitions for the (M+@36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K) and (Ag+@TriPip222)K− Alkalides complex +

6

−

(Cu @3 adz)Li (Cu+@36adz)Na− (Cu+@36adz)K− (Ag+@36adz)Li− (Ag+@36adz)Na− (Ag+@36adz)K− (Au+@36adz)Li− (Au+@36adz)Na− (Au+@36adz)K− (Ag+@TriPip222)K−

μ0

α0

β0

ΔE

f0

Δμ

7.839 8.059 8.368 7.774 8.001 8.310 7.764 7.962 8.270 8.926

616 662 984 625 671 998 634 679 1008 1193

18 413 17 529 38 600 16 445 15 881 61 590 15 503 15 362 55 691 180 068

1.755 1.729 1.449 1.756 1.729 1.450 1.751 1.727 1.449 1.395

0.332 0.310 0.343 0.331 0.310 0.341 0.333 0.310 0.340 0.347

15.241 15.981 17.145 16.032 16.689 17.962 16.179 16.787 18.055 14.187

dominated transitions HOMO HOMO HOMO HOMO HOMO HOMO HOMO HOMO HOMO HOMO

→ → → → → → → → → →

LUMO+9 LUMO+9 LUMO+8 LUMO+9 LUMO+9 LUMO+8 LUMO+9 LUMO+9 LUMO+8 LUMO+9

(100%) (97.0%) (97.7%) (100%) (96.1%) (97.8%) (100%) (97.7%) (96.9%) (94.6%)

Na, and K), NBO calculations were performed, and the related results are listed in Table 1. From the table it can be seen that all of the NBO charges on the upper M′ atoms (QM′) are negative (from −0.802 to −0.827|e|), demonstrating the alkalide characteristics of these compounds. Meanwhile, the charges on the M atoms (QM) are 0.334−0.464|e|, indicating the charge transfer from the inside M to the outside M′. Thus, the studied species can be written as (M+@36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K). The alkalide identities of (M+@36adz)M′− can also be confirmed by their highest occupied molecular orbitals (HOMOs). Since the lone pairs on nitrogen atoms in the 36adz cage are all pointed inward, the s electron of the inside coinage metal atom can be strongly polarized by the cage complexant and pushed out to form a diffuse electron cloud to enwrap the outside alkali metal atom, creating an M′− anion in each compound (see Figure 1). Consequently, it is revealed that coinage metal atoms (Cu, Ag, and Au) indeed have the potential to serve as a new source of excess electrons for the design and synthesis of alkalides. The data in Table 1 reveal that the (M+@36adz)M′− with the same M but different M′ have approximately equal QM values, such as 0.464|e| (M′ = Li) ≈ 0.463|e| (M′ = Na) ≈ 0.456 |e| (M′ = K) for (Cu+@36adz)M′−. This indicates that the charge transfer from M to M′ hardly depends on the M′ atomic number in (M+@36adz)M′−. However, the QM value strongly correlates with the atomic number of encapsulated M+. No matter which alkali metal atom (Li, Na, or K) serves as M′−, QM decreases in the order 0.456−0.464 |e| (M = Cu) > 0.440− 0.448 |e| (M = Ag) > 0.334−0.338 |e| (M = Au), which is opposite to the increasing atomic number of M. In contrast, the NBO charges on the alkali-metal anions (QM′) increase along

the increasing atomic number of coinage metal M, that is, the larger the atomic number of M, the longer the M−N distance. On the contrary, the M−M′ distance is shown to depend on the atomic number of outside M′ but does not much correlate with the atomic number of inside M. To be specific, the M−Li, M−Na, and M−K distances are ca. 5.8, 5.9, and 6.5 Å, respectively. It is noted that the dM−M′ values of potassides are much larger than those of lithides and sodides. Compared with previously reported alkalides, the M−M′ distances of these studied (M@36adz)M′ (M = Cu, Ag, and Au; M′ = Li, Na, and K) are longer than the corresponding Li+−M′− distances in Li+(calix[4]pyrrole)M′− (M′ = Li, Na, and K)15 by ca. 2.0 Å. With the same complexant (36adz), the dM−M′ values of (M@ 36adz)M′ (M = Cu, Ag, and Au; M′ = Li, Na, and K) are longer than those of (M+@36adz)M′− (M, M′ = Li, Na, and K)17 by ca. 0.2 Å. In addition, it is of interest to understand the strength of the bond between the cage part and the outside alkali-metal M′. Thus, the vibrational frequencies of the corresponding stretching modes (between the cage and M′), ωcage−M′, are also listed in Table 1. It can be observed that ωcage−M′ obviously depends on the atomic number of the outside M′ but not the inside M. With the same M, ωcage−M′ decreases in the order ωcage−Li > ωcage−Na > ωcage−K, which can be attributed to the fact that the alkalide (M@36adz)M′ with a larger M′ atomic number has a longer cage−M′ distance, leading to the weaker interaction between the cage and M′ as well as the smaller frequency of the corresponding stretching mode between the cage and M′. 3.2. Alkalide Characteristics. To explore the electronic characteristics of (M@36adz)M′ (M = Cu, Ag, and Au; M′ = Li, C

DOI: 10.1021/acs.inorgchem.7b00183 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 2. Dependences of (a) polarizability α0 and (b) the first hyperpolarizability β0 values on the atomic number of alkali-metal anion M′− and coinage metal cation M+ of (M+@36adz)M′−.

with the increasing M′− atomic number for the (M+@ 36adz)M′− compounds with the same M. Moreover, it should be mentioned that the QM′ values (from −0.802 to −0.827|e|) of these studied (M+@36adz)M′− alkalides are much larger than those (from −0.253 to −0.361|e|) of Li+(calix[4]pyrrole)M′− (M′ = Li, Na, and K),15 that (−0.371|e|) of superalkalibased Li3O+(calix[4]pyrrole)K−,28 and that (−0.45|e|) of the synthesized (H+@36adz)Na− alkalide.14 The vertical ionization energies (VIEs) of (M+@36adz)M′− are in the range of 2.480−2.761 eV (see Table 1), which are even smaller than the ionization energy (3.89 eV) of the Cs atom. Such low VIE values further confirm that the investigated systems contain diffuse electrons. From Table 1 it is observed that the VIE values hardly depend on the inside coinage metal cations but decrease with increasing M′ atomic number, implying that the smaller the electron affnity of M′ is, the more diffuse the electron cloud is. 3.4. Nonlinear Optical Properties. As pointed out above, these designed (M+@36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K) complexes exhibit typical alkalide characteristics with loosely bound excess electrons around M′−. Hence, they could be expected to exhibit considerable NLO responses. Thus, the static electric properties of these (M+@36adz)M′− species were calculated and are listed in Table 2. From Table 2 it is observed that these proposed (M+@ 6 3 adz)M′− alkalides present considerably large β0 values up to 61 590 au. In particular, the β0 value (61 590 au) of (Ag+@ 36adz)K− is larger than those of previously reported alkalides, including alkali-metal-based Li+(calix[4]pyrrole)K− (35 934 au),15 superalkali-based Li3O+(calix[4]pyrrole)K− (33 252 au),28 and proton-based (H+@36adz)Na− (57 675 au).14 Additionally, the β0 value of (Ag+@36adz)K− is also ca. 10 times as large as that (6366 au) of the state-of-the-art organic 4(N,N-dimethylamino)-4′-nitro-stilbene (DANS),44 which continues to be a useful reference. Consequently, these proposed (M+@36adz)M′− alkalides can be regarded as novel NLO molecules of high performance. To better visualize the results, the dependences of polarizability (α0) and the first hyperpolarizability (β0) values on the atomic number of alkali-metal anion M′− and coinage metal cation M+ of (M+@36adz)M′− are exhibited in Figure 2. From Figure 2a an obvious dependence of α0 on the atomic number of M′− anion is observed for (M+@36adz)M′− species. The same holds true for the dipole moment (μ0). Take the (M+@ 36adz)M′− series as examples. Their μ0 values increase in the

order 7.839 au (M′ = Li) < 8.059 au (M′ = Na) < 8.368 au (M′ = K), and α0 values show the same sequence of 616 au (M′ = Li) < 662 au (M′ = Na) < 984 au (M′ = K), which are in accordance with the increasing M′− atomic number. However, this dependence on the atomic number of M′− is not presented for the β0 values. It is observed that with the same M+ the lithide and sodide possess approximately equal β0 values while the potasside exhibits a much larger β0 (see Figure 2b). For example, the β0 value (61 590 au) of (Ag+@36adz)K− is much larger than those of (Ag+@36adz)Na− (15 881 au) and (Ag+@ 36adz)Li− (16 445 au). How does one understand the above-mentioned relationship between the β0 value and the M′− atomic number of (M+@ 36adz)M′−? We may find some clues from the two-level model2

β0 ∝

Δμ·f0 ΔE3

where ΔE, f 0, and Δμ are the transition energy, oscillator strength, and difference in the dipole moment between the ground state and the crucial excited state, respectively. From the two-level expression, β0 is proportional to f 0 and Δμ, whereas it is inversely proportional to the third power of ΔE, and thereby the low transition energy has been proved to be the decisive factor for large first hyperpolarizabilities of (super)alkali-metal-based alkalides in previous reports.15,16,28−30 Herein, the crucial excited states of (M+@ 36adz)M′− were obtained, and the corresponding ΔE, f 0, and Δμ values as well as dominate transitions are presented in Table 2 and Figure 3, respectively. From Table 2 and Figure 3 all of the crucial excitations of (M+@36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K) are originated from their HOMO orbitals, which are mainly composed of the diffused excess electrons around M′−. Due to the fact that diffuse excess electrons can be easily excited, all of the studied alkalides show very small transition energies (ΔE) from 1.450 to 1.756 eV (see Table 2). In particular, the ΔEs (from 1.449 to 1.450 eV) of (M+@36adz)K− (M = Cu, Ag, and Au) are even smaller than those of the alkali-metal-based Li+(calix[4]pyrrole)M′− (M′ = Li, Na, and K) (1.757 eV),15 superalkali-based Li3O+(calix[4]pyrrole)M′− (1.829 eV),28 and proton-based (H+@36adz)Na− (2.111 eV),14 which justifies the larger β0 values of the former species as mentioned above. Moreover, it can be seen from Table 2 and Figure 3 that the crucial transitions of the studied lithides and sodides are D

DOI: 10.1021/acs.inorgchem.7b00183 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 4. Geometric structure and HOMO of (Ag+@TriPip222)K− alkalide. NBO charges on the Ag and K atoms as well as the Ag−K distance are also shown.

shown in Figure 4, the NBO charge on the K atom is −0.821 | e|, demonstrating the alkalide identity of this (Ag+@ TriPip222)K− compound. In this compound, the Ag+−K− distance is 6.835 Å, which is even longer than that of the above-mentioned (Ag+@36adz)K− by 0.3 Å. In particular, the TD-DFT calculation reveals that this (Ag+@TriPip222)K− alkalide possesses a smaller ΔE value of 1.395 eV and larger f 0 value of 0.347 than those of (Ag+@36adz)K−, which results in its larger β0 value of 180 068 au than that of (Ag+@36adz)K−. This indicates that with the same alkali metal anion using a larger cage complexant containing more N atoms to encapsulate the coinage metal atoms is beneficial to bring forth novel alkalides with larger NLO response.

Figure 3. Crucial transitions of the (M+@36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K) alkalides.

4. CONCLUSIONS A series of coinage metal-based compounds, namely, (M+@ 36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K), has been designed and studied by density functional theory. The alkalide characteristics of these compounds are demonstrated by analyses of NBO charges as well as their VIE values and HOMOs. It is observed that the position of the upper M′− anion in these alkalides is closely related to its atomic number but does not much correlate with the atomic number of the inside M. Compared with the previous alkalides, these novel alkalides exhibit longer M−M′ distances and larger NBO charges on M′. In particular, all of the novel alkalides show large NLO responses with considerable hyperpolarizabilities (β0), especially for the potassides. Besides, it is found that embedding the coinage metal atoms into larger cage complexants with more N atoms may be beneficial for obtaining novel alkalides with larger NLO response. Hence, this study demonstrates that the coinage metal atoms indeed can be used as a new source of excess electrons for the design of nontraditional alkalides with remarkable and tunable NLO responses.

HOMO → LUMO+9, whereas the crucial transitions of potassides are HOMO → LUMO+8. Consequently, due to the lower orbital energy of LUMO+8 than that of LUMO+9, the potassides possess smaller ΔE values of 1.449−1.450 eV than those of 1.727−1.756 eV for lithides and sodides. In addition, as shown in Table 2, the f 0 and Δμ values of crucial excited states for the potassides are also, respectively, larger than those of lithides and sodides. Hence, the combination of reduced transition energy as well as increased f 0 and Δμ values is the decisive factor for the larger β0 values of these proposed potassides compared with corresponding lithides and sodides. It is well known that the main applications of NLO materials are in second-harmonic generation (SHG), doubling frequency. In addition to a large NLO response, excellent NLO materials should be transparent under the used laser, which is of great importance in practice. Hence, the ultraviolet−visible−infrared absorption spectra of (M+@36adz)M′− (M = Cu, Ag, and Au; M′ = Li, Na, and K) are obtained and shown in Figure S1. It can be clearly seen that the absorption spectra of (M+@ 36adz)M′− with the same M+ are slightly red shifted along with the increasing atomic number of M′−. Differently, the (M+@ 36adz)M′− with identical M′− show nearly the same spectra, indicating that their absorption spectra hardly depend on the involved M+. Noticeably, the absorption of these proposed alkalides in the deep-ultraviolet and ultraviolet light region (≤300 nm) is weak, indicating that they may present a good transparency that is suitable to ultraviolet lasers. In addition, the larger TriPip222 cage complexant45 synthesized by Dye and co-workers46 has been also chosen to design an (Ag+@TriPip222)K− compound (see Figure 4). As

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00183. Computational test on the basis set used for geometry optimization and static electric property calculation, the effect of methods on the computed static electric properties; absorption spectra of the studied (M+@ E

DOI: 10.1021/acs.inorgchem.7b00183 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

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36adz)M′− alkalides; crucial transition of the (Ag+@ TriPip222)K− alkalide; Cartesian coordinates for these designed alkalides (PDF)

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AUTHOR INFORMATION

Corresponding Authors

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

Wei-Ming Sun: 0000-0002-9882-0511 Di Wu: 0000-0002-7000-0597 Zhi-Ru Li: 0000-0002-1384-0725 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 (Grant Nos. 21173095, 21303066, 21573089, 21603032), State Key Development Program for Basic Research of China (Grant No. 2013CB834801), Natural Science Foundation of Fujian Province (Grant Nos. 2016J05032, 2016J01771), Youth Scientific Research Project of Fujian Provincial Health and Family Planning Commission (Grant No. 2016-1-37), and Academic Foundation for Professor of Fujian Medical University (Grant No. JS14009). The authors also acknowledge the National Supercomputing Center in Shenzhen for providing computational resources.

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