Hydrogen Bonding in Acid Li-, Ni-, Tetrabutylammonium, and Ammonium Salts of Benzene-1,2,4,5-Tetracarboxylic Acid (Pyromellitic Acid) Sven M

Hydrogen Bonding in Acid Li-, Ni-, Tetrabutylammonium, and Ammonium Salts of Benzene-1,2,4,5-tetracarboxylic Acid (Pyromellitic Acid) Sven M. Jessen and Horst Küppers* Mineralogisches Institut der Christian-Albrechts-Universität, Olshausenstraße 40, D-W-2300 Kiel 1 Dean C. Luehrs Department of Chemistry, Michigan Technological University, Houghton, MI 49931, U.S.A. Z. Naturforsch. 47b, 1141 - 1153 (1992); received October 1, 1991 /March 27, 1992 Pyromellitates, Hydrogen Bonds, Crystal Structure, Acid Pyromellitates, IR Spectra Four acid salts of pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid) have been syn­ thesized and studied by X-ray diffraction and IR spectroscopy. (1) Dilithium dihydrogen py- romellitate pentahydrate, Li2[C6H2(COO)4H 2] • 5 HzO; monoclinic, P 21/m, a = 6.214(2), b = 19.647(7), c = 6.592(2)Ä, ß = 115.90(2)°, Z = 2, R = 0.068, Rw = 0.067. (2) Hexaaquanickel dihydrogen pyromellitate, [Ni(H20 )6][C6H2(C 00)4H2]; monoclinic, P2/m, a = 6.528(1), b = 9.927(2), c = 6.472(1)Ä, ß = 115.57(1)°, Z = 1, R = 0.044, /?w = 0.039. (3) Tetrabutylammoni­ um trihydrogen pyromellitate, [(C4H9)4N][C6H-,(COO)4H3]; monoclinic, P2,/c, a = 9.719(4), b = 18.823(8), c = 15.795(5) Ä, ß = 107.42(3)°, Z = 4, R = 0.059, Rw = 0.039. (4) Diammonium dihydrogen pyromellitate, [NH4],[C6H,(COO)4H2]; monoclinic, P2l/c\ a = 4.7665(6), b = 11.681(3), c = 10.149(2) Ä, ß = 102'. 19(2)°, Z = 2, R = 0.045, Rw = 0.039. Compounds 1, 2, and 3 show very short intramolecular hydrogen bonds between adjacent carboxylic groups (O -O distances 2.384(6), 2.386(5), 2 .3 8 7 (3 )respectively). Compound 4 forms intermolecular hy­ drogen bonds (O -O distance 2.642(2) A). The different hydrogen bonding modes are also evi­ dent in the IR spectra.

Introduction analyzed by single crystal X-ray methods and IR In the course of a systematic investigation of spectroscopy. compounds with short intramolecular hydrogen Experimental bonds, acid salts of pyromellitic acid (benzene- 1,2,4,5-tetracarboxylic acid) drew special interest. Synthesis: Whereas X-ray structural studies of 13 neutral (1) Dilithium dihydrogen benzene-1,2,4,5-tetra- salts of this acid have been performed [1-13], only carboxylate pentahydrate, three structures of acid salts, Co(C10H4O8)-6H 2O, Li2[C6H2(COO)4H2] • 5 H20, was synthesized by slow evaporation of an aqueous stoichiometric so­ UO2(C10H4O8)-2H 2O, and Li2(C10H4O8)-4H 2O, lution of LiOH • H20 and pyromellitic acid. are known [14-16]. The Co salt forms an intramo­ (2) Hexaaquanickel dihydrogen benzene-1,2,4,5- lecular hydrogen bond (O -O = 2.381 Ä). Some tetracarboxylate, [Ni(H20)6][C6H2(C 00)4H2], was other acid salts of pyromellitic acid are suspected synthesized by slow cooling of a hot, saturated, by IR spectroscopy to have such hydrogen bonds aqueous stoichiometric solution of basic [17], but they could not be prepared as single crys­ Ni-carbonate and pyromellitic acid. tals suitable for X-ray structure analysis. In order (3) Tetrabutylammonium (TBA) trihydrogen to get a deeper insight into the formation of the benzene-1,2,4,5-tetracarboxylate, different types of hydrogen bonds (intra- and in­ [(C4H9)4N][C6H2(COO)4H3], was synthesized by termolecular ones) and the relation between struc­ adding a stoichiometric amount of aqueous TBA hydroxide to a weighed amount of pyromellitic tural and spectroscopic properties, four new acid acid. The solution was concentrated by evapora­ pyromellitates (with Li, Ni, tetrabutylammonium, tion and allowed to cool for two days in a polystyr­ and NH4 as cations) have been synthesized and ene foam container. (4) Diammonium dihydrogen benzene-1,2,4,5- tetracarboxylate, [NH4]2 [C6H2(COO)4H2], was * Reprint requests to Prof. Dr. H. Küppers. synthesized by dissolving pyromellitic acid in Verlag der Zeitschrift für Naturforschung, warm 28% ammonium hydroxide. The solution D-W-7400 Tübingen was allowed to cool for two days in a polystyrene 0932 - 0776/92/0800-1141 /$ 01.00/0 foam container. 1142 S. M. Jessenet al. ■ Hydrogen Bonds in Acid Pyromellitates

Table I. Crystal data, data col­ Compound 1 3 2 4 lection and refinement parame­ ters of compounds 1- 4. Formula CioH140 13Li2 CioHl6®14Ni c 26h 4,n o 8 ^10^12^2^8 Formula weight 356.09 418.94 495.62 288.22 Space group P2\/m P2/m P2,/c P2 ,/c "[A] 6.214(2) 6.528(1) 9.719(4) 4.7665(6) b [A] 19.647(7) 9.927(2) 18.823(8) 11.681(3) c [A] 6.592(2) 6.472(1) 15.795(5) 10.149(2) 115.90(2) 115.57(1) 107.42(3) 102.19(2) V [A ] 724.0(4) 378.3(1) 2757(2) 552.3(2) Z 2 1 4 2 D , [g/'cm3] 1.633 1.838 1.194 1.733 H [mm '] 0.16 0.13 0.08 0.14 ^ a x H 30 30 25 30 Measured refl. 2358 1265 5228 1778 Observed inde­ 931 990 2304 1160 pendent refl. (I >3(7(1)) (I > 3cr(I)) (I > 3 <7(1)) (I > 2cr(I)) Extinction parameter g - 2.2(6)x IO’7 1.54(3)x 10“7 4.5(6) *10~7 Absorption correction no numeric no no 0.712/0.900 Refined parameters 143 82 482 117 R 0.068 0.044 0.059 0.045 Rn 0.067 0.039 0.039 0.039 Residual e- density [e/A3] 0 .39/-0.34 0.97/-0.67 0.25/-0.25 0.45/-0.29

X-ray studies: rameters. Anisotropic displacement parameters Intensity data were collected using a Siemens- were assigned to non-H atoms. Weights were as­ Stoe four-circle diffractometer AED2 with graph­ sumed to be proportional to 1 /cr(F0)2. For 2,3, and ite monochromatized MoKa radiation at room 4, extinction was corrected according to F' = temperature (295 K) by 6/26 scans. Crystals of 1 F(l-gF2/sin$) (SHELX-76) [19]. Absorption cor­ decomposed in the X-ray beam. Therefore, two rection was applied only for 3, since the crystal was specimens were necessary to collect a complete data platy (0.22 x 0.08 x 0.46 mm3). The other specimens set. Scaling was done in the data reduction process were approximately isometric with mean diame­ by means of the standard reflections. Unit cell pa­ ters of about 0.3 mm. The crystal structure data rameters were refined from 20-30 diffractometri- are listed in Table I. The atomic parameters of the cally centered high angle reflections. Details are non-hydrogen atoms and those hydrogen atoms listed in Table I. For 1, systematic absences [(0^0), which are important for the hydrogen bonds are k = 2 n\ lead to possible space groups P2, or P2,/ listed in Tables II, IV, VI, and VIII*. m. Compound 2 was assumed to be isostructural with the Co salt [14] due to the similarity of the IR studies: unit cells. Space group P2/m was adopted there­ All IR spectra were recorded with a Nicolet fore. The space groups of 3 and 4 were determined DX-5 Fourier transform spectrometer (Institut für as P2,/c. Anorganische Chemie der Universität Kiel) by The structure of 1 was solved by direct methods kind permission of Dr. H. Homborg. All com­ in space group P2j using program SHELXS-86 pounds were analysed as KBr pellets at room tem­ [18]. Since two molecules were clearly related by perature. symmetry, space group P2]/m was chosen. The structure of 2 was refined using the atomic param­ eters of the Co-salt [14] as initial values. Structures * Further details of the structure determination are of 3 and 4 were solved by direct methods. available on request from Fachinformationszentrum All structures were refined using the program Karlsruhe, Gesellschaft für wissenschaftlich-tech­ nische Information mbH, D-W-7514 Eggenstein-Leo- SHELX-76 [19], H atom positions were deter­ poldshafen 2, Germany, on quoting the deposition mined from difference Fourier syntheses and re­ number CSD 55582, the names of the authors and the fined with individual isotropic displacement pa­ journal citation. S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates 1143

Table II. Fractional atomic coordinates and Atom x/a y/b z/c u eq/u equivalent isotropic displacement parameters of 1. In this and the following tables, Ue„ is one C l 0.7786(9) 0.4662(3) 0.394(1) 0.019(1) third of the trace o f the orthogonalized Uy ten­ C2 0.7876(9) 0.5377(3) 0.380(1) 0.018(1) sor. U is given for H atoms. C3 0.009(1) 0.5684(2) 0.489(1) 0.022(1) C4 0.562(1) 0.4187(3) 0.294(1) 0.023(1) C5 0.582(1) 0.5878(3) 0.260(1) 0.024(2) O l 0.5885(7) 0.3575(2) 0.3253(8) 0.034(1) 0 2 0.3489(7) 0.4442(2) 0.1784(8) 0.034(1) 0 3 0.3666(7) 0.5649(2) 0.1536(8) 0.034(1) 0 4 0.6286(7) 0.6489(2) 0.2637(8) 0.032(1) OW1 0.105(1) 0.75 0.390(2) 0.040(2) OW 2 0.287(1) 0.25 0.408(1) 0.029(2) OW 3 0.618(1) 0.25 0.049(1) 0.026(2) OW 4 0.998(1) 0.1632(2) 0.006(1) 0.036(1) L il 0.410(3) 0.75 0.649(3) 0.038(5) Li 2 0.977(3) 0.25 0.143(3) 0.031(4) H 1 0.34(1) 0.495(4) 0.16(1) 0.08(2) HW11 -0.05(2) 0.279(7) -0.30(2) 0.25(7) HW21 0.67(1) 0.714(4) 0.48(1) 0.07(3) HW 31 0.55(1) 0.210(3) 0.97(1) 0.12(3) HW41 0.11(1) 0.149(3) 0.07(1) 0.05(2) HW 42 -0.11(1) 0.361(4) -0.02(1) 0.03(2)

Table III. Selected distances [Ä] and C 1 -C 2 1.412(7) C 4 - 0 2 1.306(7) C 2 -C 3 ' 1.381(8) C 2 - C 5 1.531(7) C 3-C 1" 1.382(7) C 5 - 0 3 1.289(7) C 1 -C 4 1.529(8) C 5 - 0 4 1.233(7) C 4 - 0 1 1.219(7) 0 2 - 0 3 2.384(6) C 2 - C 1 - C 3 ” 118.0(5) C l - C 4 - 0 2 119.7(5) C 2 - C 1 - C 4 129.2(4) Ol- C4-02 120.3(5) C 3“—C 1-C 4 112.8(4) C2- C 5 - 0 3 119.4(5) C 1 -C 2 - C 3 ' 117.4(4) C2- C 5 - 0 4 118.6(5) C 1 - C 2 - C 5 128.7(4) 03- -C 5 - 0 4 122.0(5) C 3 '-C 2 -C 5 114.0(4) C 4 - 0 2 —H 1 115(3) C2üi-C 3-C lü 124.6(4) C 5 - 0 3 - H 1 115(2) C 1 - C 4 - 0 1 120.1(5) Li 1 - O 1" 2.119(4) Li2--OW 2‘ 1.95(1) Li 1 - O liv 2.119(4) Li2- -O W 3 2.04(2) Li 1 - OW 1 1.92(2) Li2--O W 4 1.96(1) Li 1 - OW 2iv 2.07(2) Li2--O W 4v 1.96(1) Li 1 - OW 3iv 2.07(2) O-H O-H 0-0 O-H-O 0 2 —HI -0 3 1.01(8) 1.38(8) 2.384(6) 172(5) OW lvi-H W 11 •OW4vii 0.77(11) 2.25(12) 2.948(10) 152(13) OW 2iv-H W 21 - 0 4 0.98(8) 1.84(8) 2.811(7) 174(7) OW 3viii-H W 31 ” 0 4 ix 0.95(6) 1.87(6) 2.791(5) 165(6) OW4iii-HW41 »02 0.72(5) 2.25(6) 2.887(6) 148(6) O W 4vii - H W 42 • • O 3X 0.77(6) 2.06(6) 2.809(7) 167(8) Symmetry code: (i) 1 +x, y, z; (ii) 1 — x, 1 — y, 1 —z; (iii) - 1 +x, y, z; (iv) 1 ~x, 0.5+_y, 1 —z; (v) x, 0.5-j, z; (vi) —x, -0.5+y, —z; (vii) -1 +x, O.S-j, z; (viii) x,y, 1 +z; (ix) 1 -x , -0.5+j, 1 - z ; (x) - x , 1 -y, —z. 1144 S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates

Table IV. Fractional atomic coordinates and Atom x/a y/b z/c u eq/u equivalent isotropic displacement parameters o f 2. Ni 0 0 0 0.0232(2) OW1 0 0.2072(3) 0 0.043(1) OW 2 0.2533(7) 0 0.3220(7) 0.060(2) OW 3 0.2367(8) 0 -0.1270(9) 0.062(2) 0 4 0.1964(4) 0.3798(2) 0.3804(4) 0.0402(8) 0 5 0.3036(4) 0.2110(2) 0.6231(4) 0.047(1) C l 0.5 0.3641(4) 1 0.025(1) C2 0.3917(4) 0.4293(2) 0.7888(5) 0.0210(8) C 3 0.2905(4) 0.3323(3) 0.5861(6) 0.0277(9) HW1 0.027(7) 0.257(3) 0.111(6) 0.07(2) HW 2 0.266(6) 0.082(4) 0.424(6) 0.10(2) HW 3 0.248(5) 0.073(3) -0.187(6) 0.04(1) H4 0.196(8) 0.5 0.352(9) 0.07(2)

O W 4' Results HW 42' Description of the structures:

OW3 Selected distances and angles with their stand­ ard deviations were computed with ORFFE [20] and are listed in Tables III, V, VII, and IX. The OW2 shapes of the pyromellitate ions, the thermal ellip­ soids, the atom numbering schemes, and the pack­ ings within the unit cells are shown in Fig. 1-8 (ORTEP [21]). Interplanar angles were calculated with XANADU [22],

Fig. 1. Thermal ellipsoid plot and atom numbering scheme of the pyromellitate anion in 1, Li2[C6H2(COO)4HJ • 5H20. Thermal ellipsoids are drawn at the 90% probability level. H atoms are drawn with fixed radius. Thin lines indicate hydrogen bonds or Li-O bonds.

Fig. 2. Stereoscopic view of the crystal struc­ ture o f 1, Li2[C6H2(COO)4H 2] • 5 H20 . Thermal ellipsoids are drawn at the 90% probability level. Li atoms are represenred by filled ellip­ soids, H atoms are drawn with fixed radius. Thin lines indicate hydrogen bonds or Li-O bonds. S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates 1145

Table V. Selected distances [Ä] and an­ N i-O W l 2.057(3)(2 *) C 1 -C 2 1.398(3) gles [°] in 2. N i-O W 2 2.026(3)(2 X) C 2 -C 2 iv 1.404(5) N i-O W 3 2.040(7)(2 *) C2-C3 1.528(4) C 3 - 0 4 1.291(4) C3-05 1.224(4) OW 1 -N i-O W 1‘ 180.0 C 2-C l-C 2ili 124.8(3) OW 1 -N i-O W 2 90.0 C l - C 2 - C 2 iv 117.6(2) OW 1 -N i-O W 3 90.0 C1-C2-C3 113.4(2) OW 2 - N i—OW 2" 180.0 C 2iv- C 2 - C 3 129.0(1) OW 2 -N i—OW 3 89.5(2) C 2 - C 3 - 0 4 119.5(3) OW 3-N i-O W 3" 180.0 C 2 - C 3 - 0 5 119.0(3) 0 4 - C 3 - 0 5 121.6(3) O-H o - H 0 - 0 O - H - O OW 1 — HW 1 • 0 4 0.82(4) 2.02(3) 2.814(3) 160(5) 0 W 2 - H W 2 - 0 5 1.03(4) 1.76(4) 2.782(4) 174(3) 0W3-HW3-05V 0.84(3) 1.97(4) 2.793(5) 164(4) 04-H 4--04iv 1.206(9) 1.206(9) 2.386(5) 163(6) Symmetry code: (i)x, —y, z, (ii) —x, —y, —z; (iii) 1 - x, y, 2—z; (iv) x, 1 -y, z; (v) x, y, - 1 +z.

Table VI. Fractional atomic coordinates and Atom x/a y/b z/c u eq/u equivalent isotropic displacement parameters o f 3. Ol 0.0274(2) -0.1061(1) 0.7091(2) 0.058(1) 0 2 0.2589(2) -0.0998(1) 0.7289(2) 0.059(1) 03 0.4418(2) -0.0118(1) 0.7452(2) 0.069(1) 0 4 0.4647(2) 0.1039(1) 0.7510(2) 0.051(1) 0 5 0.1521(3) 0.2484(1) 0.8821(2) 0.064(1) 0 6 -0.0381(2) 0.2585(1) 0.7624(2) 0.047(1) 07 -0.1874(2) 0.1562(2) 0.8412(2) 0.061(1) 08 -0.2819(2) 0.0803(1) 0.7307(2) 0.049(1) Cl 0.1293(3) 0.0077(2) 0.7424(2) 0.028(1) C2 0.2404(3) 0.0589(2) 0.7578(2) 0.028(1) C3 0.2123(3) 0.1274(2) 0.7819(2) 0.031(1) C4 0.0793(3) 0.1475(2) 0.7905(2) 0.027(1) C5 -0.0318(3) 0.0979(2) 0.7724(2) 0.026(1) C6 -0.0051(3) 0.0294(2) 0.7485(2) 0.030(1) C7 0.1380(4) -0.0710(2) 0.7250(3) 0.038(1) C8 0.3931(3) 0.0495(2) 0.7498(3) 0.038(1) C9 0.0668(3) 0.2232(2) 0.8180(3) 0.036(1) CIO -0.1751(3) 0.1152(2) 0.7863(3) 0.035(1) H I 0.353(4) -0.058(2) 0.736(3) 0.13(1) H 3 0.041(4) -0.189(2) 0.724(3) 0.09(1) H4 -0.363(4) 0.087(2) 0.747(3) 0.14(2) N 0.5942(3) 0.2471(2) 0.5349(2) 0.044(1) C ll 0.5655(4) 0.2633(3) 0.6232(3) 0.047(1) C 12 0.4343(5) 0.3088(3) 0.6164(4) 0.057(2) C 13 0.3976(5) 0.3087(3) 0.7034(4) 0.063(2) C 14 0.2735(7) 0.3585(4) 0.7012(6) 0.086(3) C21 0.4755(4) 0.1989(2) 0.4762(3) 0.050(2) C22 0.4410(5) 0.1335(2) 0.5201(4) 0.054(2) C23 0.3336(5) 0.0868(3) 0.4521(4) 0.067(2) C24 0.2802(7) 0.0250(3) 0.4930(5) 0.089(2) C31 0.7395(4) 0.2080(3) 0.5580(4) 0.050(1) C32 0.7905(5) 0.1862(3) 0.4805(4) 0.061(2) C33 0.9427(5) 0.1528(3) 0.5154(4) 0.072(2) C34 0.0577(6) 0.2063(5) 0.5582(6) 0.087(3) C41 0.5963(4) 0.3143(3) 0.4829(4) 0.051(2) C42 0.7105(5) 0.3688(3) 0.5269(4) 0.067(2) C43 0.6784(6) 0.4398(3) 0.4801(5) 0.082(2) C44 0.796(1) 0.4935(6) 0.5082(8) 0.145(5) 1146 S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates

Table VII. Selected distances [Ä] and an­ C 1 -C 2 1.413(4) C 8 - 0 3 1.260(5) gles [°] in 3. C 2 -C 3 1.395(5) C8-04 1.236(4) C 3 -C 4 1.392(4) 0 3 - H 1 1.21(4) C 4 -C 5 1.391(4) C4-C9 1.505(5) C 5 -C 6 1.390(5) C 9 - 0 5 1.198(4) C6-C1 1.400(5) C 9 - 0 6 1.310(4) C1-C7 1.516(4) 0 6 - H 3 1.02(4) C7-01 1.222(4) C5-C10 1.510(5) C 7 - 0 2 1.278(4) C 1 0 - 0 7 1.194(5) 0 2 - H 1 1.18(4) C 1 0 - 0 8 1.317(4) C 2 -C 8 1.536(5) 08-H4 0.92(5) C 2 - C 1 - C6 118.1(3) C1-C7-02 120.5(3) C 2 - C 1 - ■Cl 128.1(3) 0 1 - C 7 - 0 2 121.4(3) C 6 - C 1 - C l 113.7(3) C7-02-H1 114(2) C 1 - C 2 - C 3 118.4(3) C2-C8-03 119.9(3) C 1 - C 2 - C8 127.9(3) C2-C8-04 117.2(3) C 3 - C 2 - C 8 113.7(3) 03-C8-04 122.8(3) C 2 - C 3 - C4 122.8(3) C 8 - 0 3 - H 1 114(2) C 3 - C 4 - C5 119.0(3) C4-C9-05 121.5(3) C 3 - C 4 - C9 116.3(3) C 4 - C 9 - 0 6 113.6(3) C 5 - C 4 - C9 124.7(3) 05-C9-06 124.7(3) C4-C5-C6 118.8(3) C 9 - 0 6 - H 3 115(2) C 4 - C 5 - CIO 121.3(3) C5-C10-07 122.9(3) C6-C5-CIO 119.6(3) C5-C10-08 111.9(3) C5-C6-Cl 122.9(3) 07-C10-08 125.2(3) C 1 - C 7 - O l 118.2(3) C 1 0 - 0 8 - H 4 109(3) O-H O - H 0 - 0 O -H - O 0 2 - H 1 - • 0 3 1.18(4) 1.21(4) 2.387(3) 174(4) 0 6 - H 3 - ■OV 1.02(4) 1.57(4) 2.584(3) 172(4) 0 8 - H 4 - ■04" 0.92(5) 1.71(5) 2.613(4) 165(5) Symmetry code: (i) -x , 0.5+j, 1.5—z; (ii) - 1 +x, y, z.

Table VIII. Fractional atomic coordinates and Atom x/a y/b z/c u eq/u equivalent isotropic displacement parameters of 4. C l 0.1663(4) 0.4557(1) 0.9134(2) 0.014(1) C2 0.0078(4) 0.5563(1) 0.8779(2) 0.014(1) C 3 -0.1570(4) 0.5990(2) 0.9651(2) 0.016(1) C4 0.3440(4) 0.4054(2) 0.8218(2) 0.017(1) C 5 0.0183(4) 0.6265(1) 0.7526(2) 0.016(1) N -0.2656(4) 0.3796(2) 0.5271(2) 0.022(1) Ol 0.3268(3) 0.4354(1) 0.7060(1) 0.031(1) 0 2 0.5205(3) 0.3247(1) 0.8810(1) 0.024(1) 0 3 -0.1439(3) 0.6015(1) 0.6431(1) 0.022(1) 0 4 0.1925(3) 0.7092(1) 0.7713(1) 0.027(1) H 1 0.624(5) 0.286(2) 0.820(3) 0.074(9) H 3 -0.119(5) 0.378(2) 0.472(3) 0.064(9) H 4 -0.250(5) 0.312(2) 0.587(3) 0.053(8) H 5 -0.240(5) 0.452(2) 0.582(2) 0.049(7) H 6 -0.435(5) 0.377(2) 0.472(2) 0.044(7) S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates 1147

Fig. 3. Thermal ellipsoid plot and atom numbering scheme of the pyromellitate anion in 2, [Ni(H20)6][C6H2(C 00)4H2]. Thermal ellipsoids are drawn at the 50% probability level. H atoms are drawn with fixed radius.

Fig. 4. Stereoscopic view of the crystal structure of 2, [Ni(H20 )6][C6H2(C 00)4H2]. Thermal ellipsoids are drawn at the 50% probability level. Ni atoms are represented by

OW3 filled ellipsoids, H atoms are drawn with fixed radius. Thin lines indicate hydrogen bonds.

Table IX. Selected distances [Ä] and angles C 1 -C 2 1.402(2) C4 - 0 2 1.320(2) [°] in 4. C2-C3 1.395(3) C2 -C 5 1.522(3) C 3 -C P 1.398(2) C 5 - 0 3 1.247(2) C 1 -C 4 1.503(3) C 5 -04 1.261(2) C 4 - 0 1 1.212(2) C2-C 1 -C 3‘ 119.6(2) Cl-C4-01 123.6(2) C2-C1-C4 120.8(2) Cl-C4-02 112.7(1) C 3‘- C 1—C4 119.5(2) O l -C4-02 123.6(2) C 1 - C 2 - C 3 118.8(2) C2--C5-03 119.6(2) C 1 -C 2 - C 5 123.7(2) C2 -C 5 - 0 4 115.0(1) C 3 -C 2 - C 5 117.4(1) 0 3 - C 5 - 0 4 125.3(2) C 2 - C 3 - C 1‘ 121.5(2) C4 - 0 2 —H 1 113(1) O -H O - H 0 - 0 O -H - O 02-H 1 -04" 0.98(3) 1.67(3) 2.642(2) 173(2) N-H O-H N-O N - H - O N —H 3 - 0 3 iH 0.98(3) 1.90(3) 2.876(3) 171(2) N-H4---04'v 0.99(3) 1.85(2) 2.823(2) 167(2) N - H 5 - 0 3 1.01(2) 1.88(2) 2.855(2) 163(2) N - H 6 - 0 3 v 0.88(2) 2.16(2) 2.983(2) 170(2) Symmetry code: (i) - x , 1- -y, 2—z; (ii) \ —x, -0.5+7, 1.5-z; (iii) -x, 1 -y, 1 -z ; (iv) -x, -0.5+7, 1.5-z; (v) - \ - x , 1 -■y, 1 —z. 1148 S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates

Fig. 5. Thermal ellipsoid plot and atom numbering scheme of the pyromellitate anion in 3, [(C4H9)4N][C6H2(COO)4H3]. Thermal ellipsoids are drawn at the 50% probability level. H atoms are drawn with fixed radius. Thin lines indicate hydrogen bonds.

Fig. 6. Stereoscopic view of the crystal structure of 3, [(C4H9)4N][C6H2(COO)4H3]. Thermal ellipsoids are drawn at the 50% probability level. H at­ oms o f the anions are drawn with fixed radius, H atoms of the ca­ tions are omitted for clarity.

Fig. 7. Thermal ellipsoid plot and atom numbering scheme of the pyromellitate anion in 4, [NH4]2[C6H2(COO)4H2]. Thermal ellipsoids are drawn at the 50% probability level. H atoms are drawn with fixed radius. S. M. Jessenet al. ■ Hydrogen Bonds in Acid Pyromellitates 1149

Fig. 8. Stereoscopic view of the crystal structure of 4, [NH4]2[C6H2(COO)4H2], Thermal ellipsoids are drawn at the 50% probability level. H atoms are drawn with fixed radius. Thin lines indicate hy­ drogen bonds.

In compound 1, the pyromellitate ion is in spe­ [001] direction by hydrogen bonds, thus forming cial position (symmetry I = Q). Two neighbour­ layers parallel to (010). These layers alternate in ing carboxylic groups are connected by a very [010] direction with (OlO)-layers built by the an­ short intramolecular hydrogen bond (distance ions. All H atoms of the water molecules form 0 2 -"OS 2.384(6)Ä) which is clearly asymmetric weak hydrogen bonds to O atoms of other water (distances 0 2 - H 1 1.01(8), 0 3 - H l 1.38(8)Ä). molecules or of the anions. This is in accord with the C -O bond lengths which Compound 2 is isostructural with the Co salt differ more within the group 0 1 -C 4 -0 2 than whose structure is described in [14]. All bond within the group 0 3 -C 5 -0 4 , which resembles lengths and angles are very similar to those of the more a COO“ group. The COO planes are rotated Co compound. The pyromellitate ion has symme­ against the mean plane through the benzene ring try 2/m (C2h) such that the twofold axis crosses the by +1.3° and -2.0°, respectively (the plus and benzene ring at C 1 (Fig. 3) and the mirror plane m minus signs here and in the following text indicate intersects the two hydrogen bonds 04•••04' per­ a different sense of rotation and mean that the “in­ pendicularly. H4 is assumed to lie on the mirror ner” O atoms (02, 03) are displaced to one side plane (its y coordinate is fixed to 0.5). From dif­ with respect to the plane of the benzene ring, and fraction data alone, however, it is usually impossi­ the “outer” O atoms (01,04) are displaced to the ble to determine whether a hydrogen atom lies pre­ other side). The small tilting angles indicate that cisely on a symmetry element (T, 2, or m) or wheth­ the molecule is almost planar. The Li ions are lo­ er it lies in a disordered manner around that cated on a mirror plane. The coordination number symmetry element in one hollow of a double mini­ of Li 1 is five and the coordination polyhedron is a mum potential. This difficulty was discussed by distorted trigonal bipyramid. Three water mole­ several authors [23] (KKM-effect) and it was cules (OW1, OW2, OW3) are the equatorial li­ shown by Hadzi [24] that spectroscopic investiga­ gands whereas two carbonyl O atoms (Ol, O f) tions can help resolve this problem. We shall re­ serve as apical ligands. The angle O 1 - Li 1 -O 1' is turn to this point in the discussion. If, in the refine­ 171(1)°, angles O W -L il-O W range from 113(1) ment, the position of the hydrogen atom was as­ to 130(1)°, angles O l- L il- O W from 85.5(6) to sumed to be split around the mirror plane, the 92.5(6)° with OW = OW 1, OW2, or OW3. Li2 is /?-value did not alter significantly. coordinated by a heavily distorted tetrahedron of Fig. 4 shows that the crystal has a “sandwich­ water O atoms (angles OW -Li2-OW ranging like” structure with alternating layers of hexa- from 98.3(5) to 142(1)°). All L i-O distances are aquanickel complexes and layers of hydrogen py­ within the usual range. The [LiOJ polyhedra share romellitate ions. corners and form infinite chains running parallel In compound 3, the pyromellitate anion (with to [100], These chains are mutually connected in three acid H atoms) has no symmetry and exhibits 1150 S. M. Jessenet al. ■ Hydrogen Bonds in Acid Pyromellitates both hydrogen bonding types. The carboxylic groups (C9, 0 5, 06, H 3) and (C 10, 07, 08, H 4) form intermolecular hydrogen bonds (06-- 0 1' = 2.584(3), 0 8 •••04' = 2.613(4)Ä). Between the car­ boxylic groups (Ol, C7, 02) and (0 3, C8, 04) however, a very short intramolecular hydrogen bond (distance 02-03 = 2.387(3)Ä) is formed by H 1. The C -O bond lenghts within these two groups to the “inner’" O atoms and to the “outer” O atoms are almost equal. This is in accord with the finding that the two O -H distances are com­ parable. The carboxylic groups (O 1, C7, 02) and (O 3, C 8, O 4) are tilted against the benzene ring by Wavenumbers ( cm "1 ) + 9.5 and -13.1°, respectively, whereas the abso­ Fig. 9. IR spectrum o f 1, Li2[C6H2(COO)4H2] • 5 H20. lute values of the respective angles for (05, C9, 0 6 ) and (0 7 , CIO, 0 8 ) are 54.2 and 33.5°. Dis­ tances and angles within the TBA ion are within expected ranges: C -N 1.513(6) to 1.540(5)Ä, C - N - C 106.5(3) to 111.6(3)°, C -C 1.49(1) to 1.549(6)Ä, N - C - C 115.2(4) to 116.4(4)°, C - C - C 109.4(4) to 115.3(6)°, C -H 0.75(7) to 1.2(1)Ä. The pyromellitate ions are connected by the inter­ molecular hydrogen bonds to layers parallel to (001). The TBA ions are located in between these layers. In 4, the pyromellitate ion is in special position (symmetry T = Q). Only intermolecular hydrogen bonds are formed in this compound (O - O dis­ tance 2.642 Ä). By these intermolecular hydrogen bonds, the anions are connected to chains running Wavenumbers ( cm ' 1 ) in [Tl 1] and [111] directions. Every anion is part of two such chains crossing within it. Thus, layers Fig. 10. IR spectrum of 2, [Ni(H20)6][C6H2(C 00)4H2]. parallel to (101) are built. Fig. 8 reveals that the ammonium cations lie in channels which ex­ tend in the viewing direction, [100]. The carboxylic group 01-C 4-02 and the carboxylate group 03-C 5-04 are rotated by 12.6 and 83.4°, re­ Table X. Vibrational frequencies [cm ’] o f 1. spectively, out of the mean plane of the benzene 3509 s 1503 m 1140 w 696 w ring. The ammonium ion has almost ideal tetra­ 3443 s 1429 m 874 w 608 w hedral shape with H -N -H angles ranging from 1580 s 1366 m 808 w 542 w 1557 s 1292 w 756 w 107(2) to 112(2)°. All ammonium H atoms form nonfurcated hydrogen bonds to O atoms of the py­ romellitate ion.

IR spectra: Table XI. Vibrational frequencies [cm' ’] o f 2.

IR spectra of 1-4 are shown in Fig. 9 to 12, the 3419s 1547 s 1155 m 608 m respective frequencies are listed in Tables X to 3288sh 1503 s 1096 m XIII. For discussion, the whole range shall be div­ 1673 m 1348 s 745 m 1584 s 1285 m 704 m ided into subranges (a: 4000-2800 (water-vOH, S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates 1151

vCH, vNH), b: 2800-1800 (vOH of medium strong hydrogen bonds), c: 1800-1200 (vCO bands), d: 1200-400 cm-1 (vOH of very short hy­ drogen bonds, among others)). 1: two strong bands are visible in range a, which are due to the vOH vibration of the crystal water molecules. Range b does not contain any bands. In range c, no strong bands around 1720 (vC=0) and 1250 cm-1 (vC -O ) are visible. 2: the spectrum resembles that of 1. 50 - 3: range a contains three bands, which are as­ 4000 3000 2000 1000 signed to vCH of the TBA ion. Range b contains Wavenumbers ( cm'1 ) four weak and broad bands, which are assigned to Fig. 11. IR spectrum of 3, [(C4H9)4N][C6H2(COO)4H3]. vOH of the intermolecular hydrogen bonds [24]. In range c, the vC = 0 band is very strong and at its normal position at 1736 cm“1. 4: five bands are visible in range a, which are as­ sumed to be caused by the vNH vibrations of the ammonium ion. Range b contains two broad bands, which are assigned to vOH of the intermo­ lecular hydrogen bond [24], In range c, vC = 0 is lo­ cated at 1705 cm-1. The very strong band at 1547 cm"1 is assigned to vas COO. The strong band at 1235 cm-1 is assigned to vC-O. No assignments will be given for the other bands, nor for any bands of range d, due to the complexity of the heavily crowded patterns.

Wavenumbers ( cm'1 ) Discussion Fig. 12. IR spectrum o f 4, [NH4]2[C6H2(COO)4H 2]. Conditions for the formation of strong intramo­ lecular hydrogen bonds in acid dicarboxylates are discussed in [25]. The structures of the present Table XII. Vibrational frequencies [cm '] o f 3. study follow the rules which were stated in [25]. In 1 and 2, the high water content might allow the 2967 s 1914 w 1260 s 768 w formation of the intramolecular hydrogen bond. 2934 m 1736 s 1113s 610 m 2878 m 1588 m 993 m 465 w (It should be mentioned that dilithium dihydrogen 2768 w 1489 s 947 s pyromellitate te/rahydrate [16], containing less wa­ 2583 w 1437 s 880 m ter than 1, forms intermolecular hydrogen bonds.) 2479 w 1383 s 801 w In 3, a possible reason for the formation of the in­ tramolecular hydrogen bond between the COO- group and the neighbouring COOH group is the Table XIII. Vibrational frequencies [cm 1] of 4. large size of the TBA cation. The other two COOH groups do not form an intramolecular hydrogen 3441 s 1705 m 1335 m 882 w bond, but, instead, as expected [26], two intermo­ 3221 s 1622 m 1287 m 845 w lecular ones. The acid Ni- and Co-pyromellitates 3036 s 1547 s 1235 s 789 m 2922 s 1470 s 1152m 739 w are isostructural, in contrast to the respective 2853 m 1439 s 1113s 575 m phthalates [27-29]. As also found in NH4 hydro­ 2600 w 1418s 1044 sh 438 w gen phthalate [30], acid NH4 pyromellitate exhibits 2460 w 1395 s 911 w intermolecular hydrogen bonds. This is in accord 1152 S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates with the fact that this compound contains neither found in the range between 1300 and 1700 cm-1, crystal water nor a large cation. where, additionally, a strong mixing occurs. This The formation of the extremely short hydrogen was demonstrated, for instance, in normal coordi­ bond and the resulting repulsion of the carboxylic nate analyses of potassium hydrogen maleate [32- groups leads to a considerable deformation of the 34] which contains such an intramolecular hydro­ molecule. Attention shall be focussed to the angles gen bond. Inspection of Tables X and XI shows, inside and around the benzene rings which usually indeed, that in 1 and 2 no strong bands around have values of about 120°. The angles built by the 1700 and 1250 cm '1 are present. carboxylic groups with the benzene ring show val­ (ii) O -H bands. The strength of the OH bond ues of 129°. Furthermore, the hexagon of the ben­ decreases drastically if an acceptor approaches. zene ring is considerably deformed: The internal For intermolecular hydrogen bonds with O -O angles at the C atoms, where the carboxylic groups distances of about 2.5 Ä, there appear three char­ are attached, are lowered to values below 118° and acteristic, rather broad bands in the range b which the angles at the C atoms between them are larger were termed “A”, “B” and “C” by Hadzi [24]. than 124°. The distances between the ring C atoms These bands are clearly visible in Fig. 11 and - less bearing the carboxylic groups even are significant­ pronounced - in Fig. 12, whereas, in Figures 9 ly increased (to approximately 1.41 Ä). and 10, range b is totally free of any bands. The oc­ The various types of short hydrogen bonds, i.e. currence of these bands in this region can be re­ intermolecular ones with single minimum (type garded as an indication of whether an intermole­ “B” according to Speakman [31]), those with dou­ cular or an intramolecular hydrogen bond is ble minimum around a space group symmetry ele­ formed [25]. ment (type “A” according to Speakman [31]), or For extremely short hydrogen bonds (O - O less extremely short intramolecular hydrogen bonds, than 2.45 Ä) a quite different spectroscopic behav­ express themselves in characteristic features of the iour occurs for the case that the H atom is in a infrared spectrum, primarily in the C -O stretch­ double minimum potential (type “A” according to ing bands (i) and in the O -H stretching frequen­ Speakman [31]). In this case, an extremely broad cies (ii). and strong absorption band is observed culminat­ (i) C-O bands. Intermolecular hydrogen bonds ing between approximately 700 and 1100 cm-1 (as those in 3 and 4) have longer O -O distances [24]. The broadness is assumed to be caused by the (than the intramolecular ones as those in 1, 2, and pronounced anharmonicity of the double mini­ 3). In that case, the H atom is attributed definitely mum potential [35]. The occurrence of this band is to one of the two carboxylic groups, thus building regarded as an indication of the double minimum a COOH group. The IR spectrum of a COOH potential, i.e. for the split position [24]. group shows strong bands due to the practically As mentioned in the foregoing section, in com­ double-bonded C=0 bond (1732 cmT1 in 3, and pound 2 the question arises whether the H 1705 cm-1 in 4; Tables XII and XIII) and strong atom lies on the mirror plane or whether it is split. bonds due to the weaker, practically single-bonded Fig. 10 does not show a broad absorption band C -O (-H ) bond (1260 cm“1 in 3, and 1235 cm-1 in around 900 cm-1. Therefore, the spectroscopic 4). In the extremely short intramolecular bonds (in data indicate that the H atom lies on the mirror 1 and 2), however, the H atom is shared between plane and the hydrogen bond is truly symmetric. the two carboxylic groups, and the more or less pronounced single and double bond character of the C -O bonds is partially lost. That means that We are grateful to Mrs. U. Bennewitz and Dr. these two bands shift towards each other and are Skowronek for technical assistance. S. M. Jessenet al. • Hydrogen Bonds in Acid Pyromellitates 1153

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