New Metal Chalcogenides Ba4CuGa5Q12 (Q = S, Se) Displaying

May 15, 2013 - A series of new metal chalcogenides Ba4CuGa5Q12 (Q = S, S0.75Se0.25, Se) were synthesized using KBr flux at 750 °C. The three compound...
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New Metal Chalcogenides Ba4CuGa5Q12 (Q = S, Se) Displaying Strong Infrared Nonlinear Optical Response Shu-Ming Kuo,† Yu-Ming Chang,∥ In Chung,‡,⊥ Joon-Ik Jang,§,# Bo-Hsian Her,† Siao-Han Yang,† John B. Ketterson,§ Mercouri G. Kanatzidis,‡ and Kuei-Fang Hsu†,* †

Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan Department of Chemistry and §Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, United States ∥ Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan ‡

S Supporting Information *

ABSTRACT: A series of new metal chalcogenides Ba4CuGa5Q12 (Q = S, S0.75Se0.25, Se) were synthesized using KBr flux at 750 °C. The three compounds are isostructural and adopt the noncentrosymmetric space group P4̅21c. Crystal data are as follows: Ba4CuGa5S12, 1, a = 13.040(1) Å, c = 6.304(1) Å, and Z = 2; Ba4CuGa5S9.00(1)Se2.92(1), 2, a = 13.1585(2) Å, c = 6.3520(2) Å, and Z = 2; Ba4CuGa5Se12, 3, a = 13.598(1) Å, c = 6.527(1) Å, and Z = 2. The three-dimensional framework in 1 is constructed by infinite columns 1∞[CuGa4S10]7− that surround the discrete GaS4 tetrahedra situated on a 4̅ axis. The discrete GaS4 tetrahedra on the stacking (112) planes and canted oriented edge-sharing CuS4 tetrahedra within the columns may account for the occurrence of strong second-harmonic generation (SHG) responses. Compounds 1−3 are transparent in the mid-infrared range and have the absorption edges at 2.82, 2.05, and 1.45 eV, respectively. The new nonlinear optical (NLO) materials are type-I nonphase matching at 693 nm and display strong SHG intensities that are ∼2.7, ∼2.6, and ∼1.1 times that of AgGaSe2 at 808 nm. Raman spectroscopic characterization of the compounds is reported. KEYWORDS: metal chalcogenides Ba4CuGa5Q12, SHG, infrared NLO, nonphase matching, AgGaSe2

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composed of polar chains such as [P2Se6]2− and [PSe6]1− also have impressive NLO properties.24,27 Here we represent a series of new infrared NLO materials of Ba4CuGa5Q12 (Q = S, S0.75Se0.25, Se), which are the first members discovered in the quaternary Ba/Cu/Ga/Q (Q = S, Se) systems. Their noncentrosymmetric structures belong to the point group 4̅2m, the same crystal class as the chalcopyrite structure. The Raman spectra recorded for Ba4CuGa5Q12 are then related to the modes assigned in AgGaQ2 (Q = S, Se). The optical transparencies of the three compounds can reach the mid-infrared range up to ∼20 μm. The strong SHG intensities observed by the incident laser in the optical range of 1200− 2000 nm indicate their potential applications as infrared NLO materials.

INTRODUCTION Nonlinear optical (NLO) devices for frequency transformation of high-power laser radiation require highly efficient NLO materials.1−3 The oxide-based materials LiB3O5,4 β-BaB2O4,5,6 KTiPO4,7 and LiNbO38 are well-known for their excellent NLO properties in the UV−vis range. However, the requirements of a broad transparency range, large nonlinear susceptibility, moderate birefringence, and a high laser damage threshold limits the number materials suitable for application in the IR region.2 The current commercial infrared NLO materials are the chalcopyrite semiconductors like AgGaS 2 ,9−14 AgGaSe2,15−18 ZnGeP2,19,20 and CdGeAs2.21 Recently, many chalcogenide- and pnictide-based materials with novel structures have been reported to have the promising infrared NLO properties. The polar units of building block anions,22,23 chains,24−28 or layers29−35 within these structures are believed to be critical to their high SHG responses. For example, the thick slabs in β-K2Hg3Ge2S8,29 the pucker layers in CaZnOS30 and Na2Ge2Se5,31 or the hexagonal layers in Li2CdGeS432 all have tetrahedra oriented in the same direction. Similarly, the Ba3CsGa5Se10Cll2 material has displayed the SHG intensity about 100 times that of AgGaS2 using an incident laser at 2.05 μm, whose structure contains the pseudolayers consisting of oriented supertertahedra of Ga4Se10.35 Furthermore, glassy materials with good mechanical properties and structures © XXXX American Chemical Society

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EXPERIMENTAL SECTION

Synthesis. The chemicals used in the reactions were barium (rod, 99.99%, Aldrich), copper (foil, 99.98%, Aldrich), gallium (pellet, 99.99%, Elecmat), sulfur (powder, 99.98%, Aldrich), selenium (pellet, 99.98%, Aldrich), and potassium bromide (crystals, 99.9%, J. T. Baker). All manipulations were under a dry N2 atmosphere in an OMNI-LAB glovebox. The chemicals were loaded in fused silica tubes Received: January 25, 2013 Revised: May 13, 2013

A

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(diameter: 8 mm) and sealed under vacuum ( 2σ(I)] wR2b [I > 2σ(I)]

1346.2 tetragonal P4̅21c 13.040(1) 6.304(1) 1071.9(2) 2 0.10 × 0.03 × 0.03 4.171 15.517 293 8054 1338 (0.0275)

1486.9 tetragonal P4̅21c 13.1585(2) 6.3520(2) 1099.82(4) 2 0.05 × 0.04 × 0.04 4.447 19.335 293 8382 1378 (0.0312)

1909.9 tetragonal P4̅21c 13.598(1) 6.527(1) 1206.7(3) 2 0.15 × 0.01 × 0.01 5.254 30.844 293 13773 1477 (0.0443)

1.182 0.0211 0.0577

1.119 0.0181 0.0398

1.157 0.0264 0.0665

2.92(1)

a R1 = (∑||Fo| − |Fc||)/∑|Fo|. ∑[w(Fo2)2]}1/2.

b

wR2 = {∑[w(Fo2 − Fc2)2]/

Table 2. Atomic Coordinates and Thermal Parameters (Å2) for 1, 2 and 3 x/a

y/b

Ba(1) Ga(1) Ga(2) Cu(1) S(1) S(2) S(3)

0.21665(3) 0.13519(4) 0 0 0.0052(1) 0.0799(1) 0.2813(1)

0.53251(3) 0.24754(4) 0 1/2 0.3622(1) 0.1078(1) 0.3069(1)

Ba(1) Ga(1) Ga(2) Cu(1) S/Se(1) S/Se(2) S/Se(3)

0.21472(2) 0.13758(3) 0 0 0.0051(1) 0.0818(1) 0.2842(1)

0.52942(2) 0.24525(3) 0 1/2 0.3603(1) 0.1055(1) 0.3049(1)

Ba(1) Ga(1) Ga(2) Cu(1) Se(1) Se(2) Se(3)

0.21300(4) 0.13779(6) 0 0 0.0051(1) 0.0811(1) 0.2867(1)

0.52769(4) 0.24555(6) 0 1/2 0.3617(1) 0.1056(1) 0.3075(1)

atom

z/c

Ueqa

0.45668(7) 0.44819(10) 1/2 0.7071(3) 0.4592(2) 0.2693(2) 0.2835(2)

0.0231(1) 0.0115(1) 0.0103(2) 0.0097(3) 0.0167(3) 0.0140(3) 0.0150(3)

0.45837(5) 0.44948(8) 1/2 0.7083(3) 0.4612(1) 0.2650(1) 0.2856(1)

0.0253(1) 0.0124(1) 0.0116(2) 0.0184(3) 0.0175(2) 0.0157(3) 0.0177(3)

0.45598(9) 0.44539(15) 1/2 0.7067(4) 0.4592(1) 0.2588(1) 0.2878(1)

0.0239(1) 0.0130(2) 0.0105(3) 0.0087(5) 0.0173(2) 0.0140(2) 0.0160(2)

1

2

3

a

Ueq is defined as one-third of the trace of the orthogonalized Uij tensor

reflectance data using the Kubelka−Munk function: α/S = (1 − R)2/ 2R where R is the reflectance at a given energy, α is the absorption, and S is the scattering coefficient. The scattering coefficient has been shown to be practically wavelength independent for particles larger than 5 μm, which is smaller than the particle size of samples used here. The band gap was determined as the intersection point between the B

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configurations were examined to identify all the Raman-active phonon modes in these investigated single crystals. Second−Harmonic Generation Measurements. The NLO measurements were performed in two systems, in which the pumping of laser source, the use of laser power, the size of laser spot, the record of SHG signals, and the particle sizes of sample are described in detail. Reflected second-harmonic generation (SHG) experiment was conducted with a 1064 nm, 1 W, 40 MHz, 300 fs fiber laser (Fianium, Model: FP1060-1-fs) as light source. The femtosecond laser was intensity-modulated by a mechanical chopper and focused on the glass tube sealed powder samples with an f = 30 cm plano-convex lens. The incident laser power was set to ∼1 W, and the laser beam spot size was estimated to be ∼100 μm on the sample. The backscattering SHG at 532 nm was then collected by an f = 3.5 cm plano-convex lens and measured by a 532 nm bandpass-filtered photomultiplier (Hamamatsu PMT, Model: R928) and phase-sensitive lock-in amplifier (Stanford Research System, Model: SR830). In order to verify the power law relation between the laser intensity (I) and SHG, that is, SHG ∼ I2, the laser power was regulated by rotating a 1064 nm half-wave plate located between the laser output and a Glan-Taylor polarizer. The laser intensity can be varied as a function of the half-wave plate angle (θ) and expressed as I = I0 sin2(2θ), where I0 ∼ 1.3 × 104 W/cm2. For all the investigated polycrystalline samples, four complete cycles of power-dependent SHG measurements were intentionally performed to characterize the thermal stability and SHG conversion efficiency of these materials. The particle sizes of the samples and references were prepared in the range of 106−125 μm. The frequency-tripled output of a passive-active mode-locked Nd:YAG laser with a pulse width of about 15 ps and a repletion rate of 10 Hz was applied to pump an optical parametric amplifier (OPA). The OPA generates vertically polarized pulses in the ranges 400−685 nm and 737−3156 nm. In order to check the SHG efficiency as a function of the excitation energy, we tuned the wavelengths of the incident light from 1000 to 2000 nm. In this range, the spectral bandwidth of the linearly polarized light from the OPA is rather broad, about 2 meV full width at half-maximum. However, the phase space compression phenomena ensure effective SHG where lower energy portions are exactly compensated by higher parts, thereby satisfying both energy and momentum conservation. The incident laser pulse of 300 μJ was focused onto a spot 500 μm in diameter using a 3 cm focallength lens. The corresponding incident photon flux was about 10 GW/cm2. The SHG signal was collected in a reflection geometry from the excitation surface and focused onto a fiber optic bundle. The output of the fiber optic bundle was coupled to the entrance slit of a Spex Spec-One 500 M spectrometer and detected using a nitrogencooled CCD camera. The data collection time was 20 s. The three samples were sieved into six different particle sizes falling in the ranges of 32−45, 45−63, 63−90, 90−106, 106−125, and 125−150 μm to measure the size-dependent SHG signals.

Table 3. Selected Bond Distances (Å) for 1, 2 and 3 1 Ba(1) S(3)a Ba(1) S(2)b Ba(1) S(1)c Ba(1) S(3) Ba(1) S(1)d Ba(1) S(2)e Ba(1) S(1)e Ba(1) S(1) Ga(1) S(1) Ga(1) S(2) Ga(1) S(3)e Ga(1) S(3) Ga(2) S(2)f Ga(2) S(2)g Ga(2) S(2)h Ga(2) S(2) Cu(1) S(1) Cu(1) S(1)c Cu(1) S(1)e Cu(1) S(1)i

2 3.156(1) 3.167(2) 3.202(1) 3.250(2) 3.337(2) 3.358(2) 3.367(2) 3.541(2) 2.261(1) 2.261(2) 2.276(2) 2.304(2) 2.275(1) 2.275(1) 2.275(1) 2.275(1) 2.383(2) 2.383(2) 2.400(2) 2.400(2)

Ba(1)S/ Se(3)a Ba(1)S/ Se(2)b Ba(1)S/ Se(1)c Ba(1)S/ Se(3) Ba(1)S/ Se(1)d Ba(1)S/ Se(1)e Ba(1)S/ Se(2)e Ba(1)S/ Se(1) Ga(1)S/ Se(3)e Ga(1)S/ Se(2) Ga(1)S/ Se(1) Ga(1)S/ Se(3) Ga(2)S/ Se(2)f Ga(2)S/ Se(2)g Ga(2)S/ Se(2)h Ga(2)S/ Se(2) Cu(1)S/ Se(1) Cu(1)S/ Se(1)c Cu(1)S/ Se(1)e Cu(1)S/ Se(1)i

3 3.173(1) 3.191(1) 3.236(1) 3.282(1) 3.340(1) 3.373(1) 3.396(1) 3.544(1) 2.298(1) 2.301(1) 2.310(1) 2.329(1) 2.305(1) 2.305(1) 2.305(1) 2.305(1) 2.419(1) 2.419(1) 2.442(1) 2.442(1)

Ba(1) Se(3)a Ba(1) Se(2)b Ba(1) Se(1)c Ba(1) Se(3) Ba(1) Se(1)d Ba(1) Se(1)e Ba(1) Se(2)e Ba(1) Se(1) Ga(1) Se(2) Ga(1) Se(1) Ga(1) Se(3)e Ga(1) Se(3) Ga(2) Se(2)f Ga(2) Se(2)g Ga(2) Se(2)h Ga(2) Se(2) Cu(1) Se(1) Cu(1) Se(1)c Cu(1) Se(1)e Cu(1) Se(1)i

3.289(1) 3.306(1) 3.324(1) 3.343(1) 3.427(1) 3.467(1) 3.490(1) 3.618(1) 2.387(1) 2.401(1) 2.396(1) 2.422(1) 2.340(1) 2.340(1) 2.340(1) 2.340(1) 2.479(2) 2.479(2) 2.501(2) 2.501(2)

Symmetry code: a y, x+1, −z+1. b−x+1/2, y+1/2, −z+1/2. c−x, −y+1, z. d−y+1/2, −x +1/2, z−1/2. e−y+1/2, −x+1/2, z+1/2 . f−x, −y, z. gy, −x, −z+1. h−y, x, −z+1. iy−1/2, x+1/2, z+1/2.

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energy axis and the line extrapolated from the linear portion of the absorption edge.38−40 IR Spectroscopy. The mid-infrared absorption spectra were recorded using a Perkin-Elmer Rx1 FTIR spectrophotometer. The pressed pellets were prepared by the powder samples ground with KBr and then dried at 70 °C for 1 day. The infrared spectroscopic measurements covered a wavelength range from 400 to 4000 cm−1. Raman Spectroscopy. Nonresonant micro-Raman spectroscopy in backscattering configuration was carried out by using a diode-pumped 100 mW, 532 nm neodymium-doped ytterbium aluminum garnet (Nd:YAG) laser as the light source. A 40X, NA 0.65, Olympus Plan Achromat objective was used for laser focusing and Raman signal collection. The spatial and the spectral resolution of this homemade micro-Raman system were about 1 μm and 1 cm−1, respectively. The polarization of the incident laser can be set to either P- or Spolarization with respect to the incident plane. The backscattering Raman signal was then measured in either P- or S-polarization by properly setting the half waveplate and analyzer in front of the spectrometer. The backscattering Raman signal was measured with a focal length 30 cm, f/4 spectrometer (Andor Technology, Model: Shamrock SR-303i), and a thermoelectric cooled charge coupled device (Andor Technology, Model: iDus DV-420A). Four polarization

RESULTS AND DISCUSSION Compound 1 adopts a three-dimensional framework structure, assembled by GaS4 and CuS4 tetrahedra and Ba2+ cations distributed within the framework tunnels (Figure 1a). These tetrahedra are uniform with Ga−S and Cu−S distances falling in the ranges of 2.261(2) to 2.304(2) Å and 2.383(2) to 2.400(2) Å, respectively. The linkage motif of the [CuGa5S12]8− framework consists of two distinct building units (Figure 2a). The first building unit is based on Cu(1)S4 sharing corners with four Ga(1)S4 to form [CuGa4S14]15−. Within the unit, two Ga, one Cu, and three S atoms compose a six-membered ring with a mean deviation of 0.242 Å, which plane twists in an angle of 71.9° to fuse with its counterpart. A similar linkage geometry has been observed in borate chemistry for the Siamese-twinned unit of [B5O10]5−,41 which has six-membered rings consisted of two trigonal planes (BO3) instead of two tetrahedra (GaS4) in the unit of [CuGa4S14]15−. This building unit in 1 is further extended to form an infinite column of 1∞[CuGa4S10]7− along C

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Figure 3. (a) Discrete Ga(2)S4 tetrahedra fused with four independent columns. (Two of the columns are omitted for clarity). (b) Polyhedron scheme of the framework in 1. Color scheme: CuS4 tetrahedra, cyan; Ga(1)S4 tetrahedra, blue; Ga(2)S4 tetrahedra, purple.

Ba4CuGa5Q12 compounds with the space group of P4̅21c belong to the 4̅2m crystal class, which is shared by the chalcopyrite structure. This makes it helpful to recognize the Raman peaks in crystals of 1−3 by analogy to the previously studied chalcopyrite crystals. The Raman spectrum of 1 displays an intensive peak at 294 cm−1 with respect to the position of the A1 mode found in AgGaS2 (Figure 4). The lattice vibration of the A1 mode in AgGaS2 is caused by two pairs of anions stretched symmetrically along the a and b axes, respectively.43,44 Although the spatial arrangement of tetrahedra in the framework of [CuGa5S12]8− is different from that in AgGaS2, the similar force constants of the M−S (M = Ag, Cu, Ga) bonds and the same vibrational modes may explain the mode of 294 cm−1 present in 1. The weaker active peaks at 168 cm−1, 335 cm−1, 383 cm−1, and 395 cm−1 in 1 are slightly shifted and broadened as compared with the E modes in AgGaS2. For 2, the Raman peaks occur almost in the same frequencies as in 1 except that a broadened peak arose at 246 cm−1. When the sulfide anion is substituted with selenide at x = 0.25 the positions of the Raman peaks are slightly affected in a similar fashion as that observed for AgGa(S1−xSex)2.45 For 3, the most intense Raman peak at 185 cm−1 is comparable with the A1 mode of 181 cm−1 observed in AgGaSe2.46,47 The band gap of compounds 1−3 decreases from 2.82 to 2.05 and 1.45 eV, respectively, consistent with their colors getting darker from light-yellow to dark-brown (Figure 5). The optical transparencies for the powder samples begin from their band edges at ∼450 nm for 1, ∼610 nm for 2, and ∼860 nm for 3 and end in the infrared range at ∼20 μm (500 cm−1) (Figure 6). We measured the SHG performance of the samples 1−3 using a laser with a wavelength of 1064 nm. Compound 1 showed stable SHG signals in four measured cycles detected at 532 nm with the intensity about 25% of the reference AgGaS2

Figure 1. (a) Three-dimensional framework structure of 1. Color scheme: Ba atoms, gray; Cu atoms, cyan; Ga atoms, blue; S atoms, yellow. (b) The connectivity and orientation of tetrahedra on (112) plane. Ga(1) atoms, blue; Ga(2) atoms, purple.

Figure 2. (a) ORTEP representation of the asymmetric unit in 1. Thermal ellipsoids are shown at the 95% probability level. (b) Infinite column of 1∞[CuGa4S10]7− along the c axis formed in 1.

the c axis, in which Cu(1)S4 and Ga(1)S4 tetrahedra are fused together by sharing edges and corners, respectively. The Cu(1)−Cu(1) and Ga(1)−Ga(1) distances are 3.1521(6) and 3.8226(8) Å, respectively (Figure 2b). The second building unit is the Ga(2)S4 tetrahedron, which is bonded to four infinite columns related to each other by 21 symmetry (Figure 3a). This leads to the final three-dimensional framework of [CuGa5S12]8− (Figure 3b). The Ba2+ ions within the tunnels are coordinated with eight sulfur atoms having the Ba−S distances ranged from 3.156(1) to 3.541(2) Å. In addition to the end member with x = 0, we could also prepare the compositions of Ba4CuGa5(S1−xSex)12 with x = 0.25 for 2 and x = 1 for 3. These are the copper analogues of the previously reported BaAgGa5Se12.42 The three isostructural D

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Figure 6. IR transmittance spectra for the powder samples of 1, 2, and 3. The spectra are offset along the y axis for 2 and 3.

Figure 7. (a) Observed SHG response of 1 measured as a function of the incident laser intensity, which is varied by rotating the angle of a 1064 nm half wave plate, and (b) comparison among the SHG responses of 1, 2, 3, and AgGaS2 under identical experimental configuration and parameters. Figure 4. Polarization-dependent Raman spectra for the crystals of (a) AgGaS2, (b) 1, (c) 2, and (d) 3. Here four polarization configurations were performed to identify all the Raman-active phonon modes. Color scheme: Pin−Pout, black lines; Pin−Sout, red lines; Sin−Pout, green lines; Sin−Sout, blue lines.

1−3 to be promising infrared NLO materials. The SHG intensities decreased with increasing particle size indicating compounds 1−3 have type-I nonphase-matching NLO behavior in the spectral region examined (Figure 8).48 The AgGaSe2 material with the same type of NLO behavior was then used as a reference. For 1 and 2, the SHG intensities observed in the whole range between 600 and 900 nm are stronger than the responses measured for AgGaSe2 prepared in the same form (Figure 9). For example, the SHG intensities of 1 are ∼3.5, ∼2.7, ∼1.5, and ∼1.3 times larger than the relative high intensities of AgGaSe2 measured at 768, 808, 852, and 898 nm, respectively (Figure 10). For 2, the SHG responses display similar intensities as that in 1, which are ∼3.0, ∼2.6, ∼1.4, and ∼1.1 times of AgGaSe2 measured at 768, 808, 852, and 898 nm, respectively. For 3, the SHG intensities are between ∼1.5 and ∼0.6 times of AgGaSe2 measured at the same selected wavelengths. Apparently, the SHG intensities of 1 and 2 are superior to the benchmark AgGaSe2 in the infrared range. Besides, the SHG responses of this series of compounds are also enhanced in the visible range. For example, the SHG intensities of 1−3 are ∼28.9, 16.5, and 8.1 times larger than that of AgGaSe2 measured at 659 nm. It is interesting to consider the domains of this noncentrosymmetric framework that may direct the occurrence of such high SHG intensities. The chalcopyrite framework of

Figure 5. UV−vis−NIR optical absorption spectra of 1, 2, and 3.

(Figure 7). For 2, the SHG response is slightly weaker than 1 (Supporting Information Figure S4). However, for 3, complications from thermal decomposition effects caused by two-photon absorption did not allow the SHG intensity to be measured reliably. The use of a laser with a fundamental beam varying from 1200 to 2000 nm further indicated the samples E

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Figure 8. Intensities of SHG signals depend on various particle sizes for (a) 1, (b) 2, and (c) 3. The 1386 nm fundamental beam was used to give the SHG responses at 693 nm. The errors bars are shown.

AgGaS2 have all MS4 (M = Ag, Ga) tetrahedra oriented along the same direction on the (112) planes. If this framework is dissected into the (112) and (1̅1̅2) planes and infinite chains of edge-sharing CuS4 tetrahedra along the c axis, we see that the plane consists of unique crown-like rings formed by two Ga(2)S4 tetrahedra and six Ga(1)S4 tetrahedra (Figure 1b). First, the pairs of Ga(1)S4 tetrahedra within the rings are arranged antiparallelled along the [110] direction that cancel out the majority of polarized vectors lying on the plane. Second, all the Ga(2)S4 tetrahedra point toward the [001] direction but twist slightly with respect to the ones in the neighboring rings related by a 21 symmetry. Further, the edgesharing Cu(1)S4 tetrahedra with the copper atoms lying on a twofold axis are canted to each other along the chain (Figure 3a). Therefore, the discrete Ga(2)S4 tetrahedra on the stacking (112) planes and the Cu(1)S4 infinite chains with a 21 arrangement in this framework may be responsible for the significant SHG response (Figure 3b).

Figure 9. SHG signals record at the converted wavelengths between 600 and 1000 nm for (a) 1, (b) 2, (c) 3, and (d) AgGaSe2.

Figure 10. Comparative SHG intensities for 1, 2, 3, and AgGaSe2.

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expected with their decreasing band gap.49 The calculation of band structures50 and the growth of large single crystals will be of interest in future studies to further understand the related physical properties of these new compounds.

CONCLUSION The use of Ba2+ cations as templates has successfully directed the formation of the noncentrosymmetric chalcogenide frameworks of [CuGa5Q12]8−. The good optical transparency and high SHG intensities suggest these materials to be interesting for NLO processes in the infrared region. The low vibrational frequencies of the M−Q bonds in 1 and 2 result in a spectral transparency limit similar to that of AgGaSe2 at 17 μm. A wider transmission in the infrared range may be reached for the heavier selenide analogue of 3. Interestingly, the SHG intensities of the three isotypic materials observed at various wavelengths did not show an increasing trend as might be

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ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data for 1−3 in CIF format; PXRD patterns for 1−3; and SHG response of 1−3 and reference AgGaS2 measured by rotating the angle of a 1064 nm half wave plate.This material is available free of charge via the Internet at http://pubs.acs.org. F

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AUTHOR INFORMATION

Present Addresses ⊥

(I.C.) Graduate School of Nanoscience and Technology, KAIST, Daejeon, 305-701, Korea. # (J.-I.J.) Department of Physics, Binghamton University, Binghamton, New York 13902, USA. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for the financial support of National Science Council of Taiwan (NSC100-2113-M-006-004-MY2), the NSC High Valued Instrument Centers, and NCKU Instrument Development Center. The research at Northwestern University was supported by the National Science Foundation (DMR1104965, MGK). The author Y.M.C. is grateful to acknowledge the financial support of National Science Council of Taiwan (NSC99-2112-M-002-008-MY3).

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dx.doi.org/10.1021/cm400311v | Chem. Mater. XXXX, XXX, XXX−XXX