[(ZnSb6)2]4-: a new structure type for coupled norbornadiene-like subunits

Yi Wang,a Peter Zavaliji a and Bryan Eichhorn*a

a Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742

E-Mail:eichhorn@umd.edu

Experimental Section General Data. All reactions were carried out in a nitrogen atmosphere dry box (Vacuum Atmosphere Co). EDX analyses were performed on Hitachi SU-70 SEM, operated at an acceleration voltage of 10 keV.Elemental analysis of the sample [K([2.2.2]crypt)]4[Zn2Sb12]•0.65tol gave theoretical (wt%): K 4.72, Zn 3.95, Sb 44.13; experimental (wt%): K 4.32(±0.05), Zn 3.96(±0.03), Sb 44.12(±0.08), which was conducted on the ICPE-9000 ICP Atomic Emission Spectrometer. Powder X-ray di�raction (PXRD) data was collected using a Bruker D8 X-ray di�ractometer with Cu Kα radiation, λ = 1.5406 Å (step size = 0.01447°). The Laser Desorption/Ionization time-of-flight (LDI–TOF, Shimadzu Axima-CFR) mass spectra were recorded in the negative ion mode with a nitrogen pulsed laser with wavelength 337nm, 10Hz, the pulse power 140 µJ. Negative ion electrospray mass spectra were got from an a reflectron time-of-flight mass spectrometer (JEOL ACCUTOF-CS ESI-TOF) operating at 200V in ethylenediamine solution. Samples were injected utilizing an air-free ionization source. Chemicals K (Aldrich, 99%), Na (Aldrich, 99.7%), Zn (Fisher Scientific,99.9%), Sb (Aldrich, 99.999%), and benzophenone (Aldrich, 99.5%) were used as received. Melts of nominal composition of “K6ZnSb5” were prepared by fusion of stoichiometric ratios of the elements at high temperature (~1100 °C). The elements were loaded into quartz tubes in a nitrogen atmosphere dry box and then sealed under vacuum. CAUTION: the fusion process can be very exothermic and the reactions should be conducted behind blast shields on small scales (<10g) using full protective gear. 4,7,13,16,21,24-Hexaoxa-1,10-diazobicyclo[8,8,8]hexacosane (2,2,2-crypt) were purchased from Fisher Scientific. Anhydrous ethylenediamine (en) were vacuum distilled from K4Sn9, and stored under dinitrogen. Toluene was distilled from sodium/benzophenone under dinitrogen and stored under dinitrogen. Synthesis of [K([2.2.2]crypt)]4[Zn2Sb12]•0.65tol 90.9mg (0.1mmol) of “K6ZnSb5” and 75.3 mg (0.2 mmol) of [2.2.2]crypt were weighed out into a 10 mL scintillation vial. Then about 2 mL of ethylenediamine was added. The reaction mixture was allowed to stir for 15 min and sonicate for 5h. The resulting dark red solution was subsequently centrifuged and filtered through glass wool and transferred

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to a test tube, and then carefully layered by toluene (3 mL). After a week, black plate crystals of [K([2.2.2]crypt)]4[Zn2Sb12]•0.65tol obtained in approximately 12% yield (based on the precursor “K6ZnSb5”.) Crystallographic Studies A suitable single crystals of C76.55H146.2K4N8O24Sb12Zn2 (UM2819) was selected and measured on a Bruker Smart Apex II CCD diffractometer. 1 The crystal was kept at 150(2) K during data collection. The integral intensity were correct for absorption using SADABS software 2 using multi-scan method. Resulting minimum and maximum transmission are 0.749 and 0.968 respectively. The structure was solved with the ShelXT program and refined with the XL program and Least Squares minimisation using ShelX software package. 3 Number of restraints used = 4609, number of constraints - unknown. Crystal structure determination: Crystal Data for C76.55H146.2K4N8O24Sb12Zn2 (M =3310.95 g/mol): monoclinic, space group P21/c (no. 14), a = 32.346(3) Å, b = 14.3599(11) Å, c = 26.819(2) Å, β = 108.3679(11)°, V = 11822.3(16) Å3, Z = 4, T = 150(2) K, µ(MoKα) = 3.291 mm-1, Dcalc = 1.860 g/cm3, 104237 reflections measured (3.702° ≤ 2Θ ≤ 50°), 20801 unique (Rint = 0.0854, Rsig = 0.0709) which were used in all calculations. The final R1 was 0.0652 (I > 2σ(I)) and wR2 was 0.1568 (all data). Refinement details: The structure contains 4 K(C18H36N2O4) ions. Two of them are disordered in two alternative orientations for which during refinement geometric and atomic displacement parameters were restrained to be similar. Two toluene solvent molecules are also disordered, one of which was possible to model as two overlapped molecules and another was as partially occupied carbon atoms. H atoms were positioned from geometric consideration and refined as riding on the attached atom with Uiso constrained to be 20% larger than Ueqv of the attached atom. References: 1. Bruker (2010). Apex2. Bruker AXS Inc., Madison, Wisconsin, USA. 2. Sheldrick, G. M. (2008), Acta Cryst. A64, 112-122. 3. Sheldrick, G. M. (2014). SHELXL-2014. University of Gottingen, Germany. DFT Calculations were performed using the GAUSSIAN03 program package (Revision D.02) 4 and crystal structure parameters. All DFT calculations were carried out using the B3LYP functional, that is, Beck’s hybrid three-parameter exchange functional 5 with the Lee-Yang-Parr correlation functional.6 In these calculations, the solvent effects were taken into account by the Polarizable Contiuum Model.7 References 4. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and J. A. Pople, Gaussian 03, revision D.02. Gaussian, Inc., Wallingford CT, 2004.

5. D. Becke, J. Chem. Phys. 1993, 98, 5648. 6. Lee, W. Yang and R. G. Parr, Phys. Rev. B 1988, 37, 785. 7. (a) M. Cossi, G. Scalmani, N. Rega and V. Barone, J. Chem. Phys. 2002, 117, 43; (b) V.Barone,M.Cossi and J. Tomasi, J. Chem. Phys. 1997, 107, 3210.

Figure S1 Typical structures of Pn cluster complexes linked by metal(a)[ As14Sn]4-,8 (b)[ P14Zn]4-,9 (c)[ P15Sn]3-,10 (d) [Au2 As14]4-,11 (e)[Cu2As14]4-,9 (f)[Hg2As14]4-.12

References 8. R. C. Haushalter, B. W. Eichhorn, A. L. Rheingold and S. J. Geib, J. Chem. Soc., Chem. Commun., 1988, 1027-1028. 9. C. Knapp, B. Zhou, M. S. Denning, N. H. Rees and J. M. Goicoechea, Dalton Transactions, 2010, 39, 426-436. 10. C. M. Knapp, J. S. Large, N. H. Rees and J. M. Goicoechea, Dalton Transactions, 2011, 40, 735-745. 11. N. K. Chaki, S. Mandal, A. C. Reber, M. Qian, H. M. Saavedra, P. S. Weiss, S. N. Khanna and A. Sen, ACS nano, 2010, 4, 5813-5818. 12. S. Mandal, A. C. Reber, M. Qian, R. Liu, H. M. Saavedra, S. Sen, P. S. Weiss, S. N. Khanna and A. Sen, Dalton Transactions, 2012, 41, 5454-5457.

(a) (b) (c)

(d) (e) (f)

Figure S2 Sb12 in the norbornadiene-like bimetallic dimer [(ZnSb6)2]4-. Table S1. Bond lengths (angstroms) and bond angles (degrees) of [Zn2Sb12]4– in [K([2.2.2]crypt)]

4[Zn2Sb12]•0.65tol, as compared with the geometry optimized by using Becke three-

parameter density functional with the Lee–Yang–Parr correlation (B3LYP) with the LanL2DZ basis set.

Bonds(Å) experimental theoretical Sb1-Sb2 2.7722 2.8844 Sb1-Sb5 2.7797 2.9038 Sb2-Sb3 2.8615 2.9772 Sb2-Zn1 2.6377 2.8414 Sb3-Sb4 2.8309 2.9368 Sb3-Sb9 2.9171 3.0446 Sb4-Sb5 2.821 2.9289 Sb4-Zn2 2.6221 2.8518 Sb5-Sb6 2.8452 2.9896

Sb6-Sb12 2.8080 2.9183 Sb6-Zn1 2.6222 2.821 Sb7-Sb8 2.7607 2.8841

Sb7-Sb11 2.7655 2.9039 Sb8-Sb9 2.8549 2.9775 Sb8-Zn2 2.6329 2.8408 Sb9-Sb10 2.8166 2.9364

Sb10-Sb11 2.8141 2.9289 Sb10-Zn1 2.6308 2.8519

Sb11-Sb 12 2.8179 2.9899 Sb12-Zn2 2.6134 2.8219 Angles(°) experimental theoretical

Sb2-Sb1-Sb5 98.5657 99.1836 Sb1-Sb2-Sb3 101.1398 101.4378 Sb1-Sb2-Zn1 98.3229 97.2347 Sb3-Sb2-Zn1 82.0935 87.1722 Sb2-Sb3-Sb4 104.5709 103.5503 Sb2-Sb3-Sb9 98.0135 99.6383 Sb4-Sb3-Sb9 112.087 110.8015 Sb3-Sb4-Sb5 103.4224 105.2483 Sb3-Sb4-Zn2 81.706 89.6424 Sb5Sb4-Zn2 97.8699 97.2973 Sb1-Sb5-Sb4 101.6191 100.3506 Sb1-Sb5-Sb6 101.8683 103.0501 Sb4-Sb5-Sb6 104.8954 106.2365

Sb5-Sb6-Sb12 103.8051 106.1458 Sb5-Sb6-Zn1 90.1724 90.6037

Sb12-Sb6-Zn1 91.0869 94.9212 Sb8-Sb7-Sb11 98.3432 99.186 Sb7-Sb8-Sb 9 102.9029 101.4461 Sb7-Sb8-Zn2 98.6747 97.2556 Sb-9-Sb8-Zn2 80.8411 87.1104 Sb3-Sb9-Sb8 97.8954 99.6576

Sb3-Sb9-Sb10 110.4218 110.7897 Sb8-Sb9-Sb10 105.0421 103.5377

Sb9-Sb10-Sb11 102.8071 105.2645 Sb9-Sb10-Zn1 84.8836 89.7108

Sb11-Sb10-Zn1 97.9109 97.2939 Sb7-Sb11-Sb10 104.7827 100.3442 Sb7-Sb11-Sb12 99.1318 103.0406

Sb10-Sb11-Sb12 103.165 106.2425 Sb6-Sb12-Sb11 105.3019 106.1179 Sb6-Sb12-Zn2 93.5878 94.8729

Sb11-Sb12-Zn2 91.9553 90.5695 Sb2-Zn1-Sb6 119.8054 119.1681

Sb2- Zn1-Sb10 118.8068 115.281 Sb6- Zn1-Sb10 121.1399 121.3189 Sb4-Zn2-Sb8 122.3853 115.3579

Sb4-Zn2-Sb12 120.6656 121.3158 Sb8-Zn2-Sb12 116.8824 119.1605

Table S2 Mulliken populations analysis of [Zn2Sb12]4–with the sum of mulliken atomic charges = -4.00000.

Atom Charge Atom Charge Sb1 -0.626221 Sb7 -0.626176 Sb2 -0.428077 Sb8 -0.427982 Sb3 -0.267929 Sb9 -0.267934 Sb4 -0.427969 Sb10 -0.427946 Sb5 -0.257911 Sb11 -0.257908 Sb6 -0.440682 Sb12 -0.440678 Zn1 +0.44872 Zn2 +0.448694

Figure S3 Frontier molecular orbitals of 1.

HOMO-2 HOMO-1 LUMO HOMO

Figure S4 Electronic structures of 1

Figure S5 SEM images and EDX analysis of [K([2.2.2]crypt)]4[Zn2Sb12]•0.65tol. It shows the presence of K, Zn and Sb, and the absence of other elements heavier than K.

Zn

K

Sb

LUMO

HOMO

2.35

Figure S6 Powder X-ray di�raction (PXRD) of the starting alloy, which shows the precursor “K6ZnSb5” is actually a mixture of polar intermetallic compounds KSb(blue line) and KZnSb (red line) along with amorphous material .

Table S3 Selected Crystallographic, Data Collection, and Refinement Data for [K([2.2.2]crypt)]4[Zn2Sb12]•0.65tola.

Empirical formula C76.55H146.2K4N8O24Sb12Zn2 Formula weight 3310.95 Temperature/K 150(2) Crystal system monoclinic Space group P21/c

a/Å 32.346(3) b/Å 14.3599(11) c/Å 26.819(2) α/° 90 β/° 108.3679(11) γ/° 90

Volume/Å3 11822.3(16) Z 4

ρcal cg/cm3 1.860 µ/mm-1 3.291 F(000) 6406.0

Crystal size/mm3 0.36 × 0.25 × 0.01 Radiation MoKα (λ = 0.71073)

2θ range for data collection/° 3.702 to 50 Index ranges -38 ≤ h ≤ 38, -17 ≤ k ≤ 17,

-31 ≤ l ≤ 31 Reflections collected 104237

Independent reflections 20801 [Rint = 0.0854, Rsigma = 0.0709]

Data/restraints/parameters 20801/4609/1611 Goodness-of-fit on F2 1.117

R1/wR2 [I>=2σ (I)] 0.0652/0.1351 R1/wR2 [all data] 0.1166/0.1568

aSee the Crystallographic Studies Section for details on the refinement .

Figure S7 Negative-ion mode electrospray mass spectra of the reaction mixture in ethylenediamine.

Figure S8 Negative-ion mode LDI–TOF mass spectrumof [K([2.2.2]crypt)]

4[Zn2Sb12]•0.65tol crystals

deposited on carbon tape.

Alternate bonding description: In light of the Zn-Sb covalent character, the Zn2Sb124- ion can be viewed as an integral cage made up of 2e-2c localized bonds. According Zintl-Klemm comcept,19 the three-coordinated antimony atoms are neutral and therefore have no contribution to the cluster charge, while the 2 two-coordinated Sb1 and Sb7 is -1 each. As a result, each Zn will carry a minus one charge, resulting in Zn1- anions in 1. In the trigonal planar geometry, the Zn atom adopts sp2 hybridization with empty p(z) orbitals. We thank a reviewer for this bonding description. Reference: 19. R. Nesper, Z. Anorg. Allg. Chem., 2014, 640, 2639-2648