D. Irish, J. Semmler, N. Taylor
Nov 15, 1991
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Acta Crystallographica Section C-crystal Structure Communications
Abstract
Tetraaquabis(acetato-O)magnesium, [Mg(C2H302)2(H20)4] ,_ ~ Mr = 214.49, monoclinic, P2Jc, a = 4.8084 (4), b = 11.9943 (13), c = 8.5548 (8) A, fl = 95.355 (7) °, V = 491.24 (8) A 3, Z = 2 , D x = 1 " 4 5 g c m -3, M o K a , A=0.71073]k (graphite monochromator), /x = 1.86cm -1, F(000) = 228, T = 295 K, final R = 0.0423 and wR = 0.0579 for 1905 observed reflections. A new, more precise determination of the structure of magnesium acetate tetrahydrate has been performed which allows significant distinctions between the various M g O and C O bonds to be made. Details of the hydrogenbonding scheme are also more reliably determined. Introduction. The structure of magnesium acetate tetrahydrate was originally obtained by Shankar, Khubchandani & Padmanabhan (1957) using a multiple film projection technique. However, the need for a more precise determination, especially of the hydrogen positions, has been pointed out, for example by Padmanabhan & Srinivasan (1973), to facilitate spectroscopic work. To some extent the deficiencies in the original publication have been circumvented because of a more recent and more refined X-ray determination of the structure of the isomorphous nickel acetate (Downie, Harrison, Raper & Hepworth, 1971) which has aided various spectroscopic studies on solid magnesium acetate (Raghuvanshi, Khandelwal & Bist, 1982, 1985). We have recently carried out an extensive Raman investigation of aqueous solutions of magnesium acetate (Semmler, 1989; Semmler, Irish & Ozeki, 1990) during which we hoped to determine the structures of the various complexes which exist in solution. To complement this work a new X-ray determination of the structure of crystalline magnesium acetate tetrahydrate was carried out and is reported here. During the review process we have become aware of a more recent determination (Trunov & Endeladze, 1986). This is a considerable improvement on the earlier * Currently at Ontario Environment Ministry, Trace Organics Section, 125 Resources Road, Rexdale, Ontario, Canada M9W 5L1. I" To whom all correspondence should be addressed. 0108-2701/91 / 112322-03503.00 work of Shankar et al., but its precision is significantly less than that of the work presented here. In particular we are able to distinguish different Mg---O and C---O bonds. Experimental. Colorless needle-like crystals of the title compound were obtained by slow evaporation of water from a saturated aqueous solution of magnesium acetate. From one of these needles a prism (0.42 × 0.40 × 0.46 mm) was cut and used for X-ray work. Accurate unit-cell parameters were derived from the refined angles of 30 general reflections (22 < 20 < 32°), well distributed in reciprocal space, on a Siemens R3m/V diffractometer. The data were collected by 20-0 scans (3-5 < 20 < 70.0 °) using variable scan speeds, the rates (2.93-29.30 ° min1) being determined from a quick preliminary scan; scan width 1 ° below Kal to 1 ° above Ka2. Background measurements were made at the beginning and end of each scan for a total time equal to one quarter of the scan time. Crystal stability was checked by monitoring two reflections (080; 006) every 100 measurements (only __ 2% variation). Empirical absorption corrections were derived from W-scan data (transmission factors 0.82-0.90). From 2160 total reflections, 1905 were considered observed [F_> 6tr(F), h:0---,7, k:0---, 19, l: 13--, 13]. The structure was solved by Patterson and Fourier techniques and refined by full-matrix least-squares methods, the function minimized being Y.w(Fo-Fc) 2, using Nicolet-Siemens SHELXTL-Plus software (Sheldrick, 1987). Hydrogen atoms were located from a difference Fourier synthesis and included in the refinement with isotropic thermal parameters. The number of parameters refined was 90 (data-toparameter ratio 21.2:1). In the final cycle of refinement an extinction correction X=0-041 (8) {where F* = F[1 + O.O02xF2/sin(20)] -~/4} was used. The weighting scheme was w 1 = o-2(F)+ 0.0037F 2. The goodness of fit parameter, S, was 1.24 and the largest and mean A/tr values were 0" 191 and 0-008, respectively. The maximum and minimum residual electron densities were +0.32 and 0 . 3 1 e A -3. The source of atomic scattering factors was International Tables for X-ray Crystallography (1974, Vol. IV). © 1991 International Union of Crystallography D. E. IRISH, J. SEMMLER, N. J. TAYLOR A N D G. E. TOOGOOD 2323 Table 1. Atomic coordinates (x 104; for H × 103) and isotropic or equivalent isotropic displacement parameters (A 2 x 104; for H × 10 3) Equivalent isotropic U defined as one third of the trace of the orthogonalized Uu tensor. x y z U/Ueq Mg 0 0 0 230 (2) 0(1) 2302 (2) 1452.8 (7) 165 (I) 304 (2) 0(2) -660 (3) -2529.4 (9) 1623 (2) 451 (3) 0(3) 2699 (2) 839-9 (7) 1411 (I) 292 (2) 0(4) 2499 (2) 448.6 (9) 1984 (1) 320 (3) C(I) 1434 (3) -2404.8 (9) -664 (2) 283 (3) C(2) 3001 (4) 3413 (I) 34 (2) 466 (5) II(2 I) 491 (7) 327 (3) 6 (3) 75 (9) H(22) 291 (7) 331 (3) I1t (3) 87 (9) H(23) 292 (7) 396 (3) 70 (3) 73 (8) H(31) 219 (5) 121 (2) -212 (3) 51 (6) H(32) 420 (5) 114 (2) 101 (2) 39 (5) H(41) 419 (6) 40 (2) 192 (3) 45 (5) H(42) 237 (6) 105 (2) 203 (3) 56 (7) Table 2. Bond lengths, bond angles and hydrogen-bond parameters (A, °) Mg--O(I) 2.0761 (8) Mg---O(3) 2.1091 (8) Mg--O(4) 2.0577 (9) 0(1)--C(1) 1.2754 (14) 0(2)--C( 1 ) 1.2467 (17) C(I)--C(2) 1.4981 (20) O(I)--Mg---O(3) 90-09 (3) O(I)--Mg--O(4) 90-10 (3) O(3)--Mg--O(4) 90.24 (3) O(l)---Mg---O(la) 180.00 (3) O(1)--Mg--O(3a) 89.91 (3) O(3)--Mg--O(3a) 180.00 (3) O(l)--Mg--O(4a) 89.90 (3) O(3)--Mg--O(4a) 89.76 (3) O(4)--Mg--O(4a) 180-00 (3) Mg---O(1)--C(I) 127.92 (5) O(I)--C(I)--O(2) 123.11 (6) O(1)--C(1)--C(2) 117.68 (8) O(2)--C(I)--C(2) 119.20 (9) O(4)--H(42) 0-73 (3) H(42)-.-O(2a) 1.97 (3) O(4)'..O(2a) 2"6562 (15) O(3)--H(31) 0.78 (2) H(31)...O(2d) 1-96 (2) O(3)."O(2d) 2'7035 (14) O(3)--H(32) 0"85 (2) H(32).--O(lb) 1'92 (2) O(3)"-O(lb) 2'7446 (12) O(4)--H(41) 0.82 (3) H(41)-..O(3b) 2'18 (3) O(4)...O(3b) 2.8588 (13) O(3)--H(31)-.-O(2d) 162 (2) O(4)--H(42)...O(2a) 157 (2) O(4)--H(41)..-O(3b) 140 (2) O(3)--H(32)-.-O(lb) 166 (2) Symmetric code: (a) x , y , z ; (b) l x , y , z ; (d) x , ~ + y , ~ z . •01c .~03c 03d | ~ ~ ~'~04c ~ • , O4 T , H 2 3 ~ 0 2 ~ ÷~" I01a. .~ "~ ~,,'~04 H'42~ ~'~.¢~