C(8) C(1) N(1) C(2) C(4) C(3) N(3) O(1) O(2) O(4) Zn(3) O(10) C(7) O(3) Zn(2) O(5) C(9) C(10) O(8) O(6) C(12) O(7) O Zn(1) O(9) C(14) C(13) O(9) O O(7) O(6) O(8) Zn(3) C(5) C(6) O(1) N(3) N(1) O(2) O(4) O(3) O(5) Zn(2) Zn(4) Zn(4) O(10) C(11) Rare M7O2 double tetrahedral core in molecular species: preparation, structure and properties of Zn7O2(O2CMe)10(1-Meim)2 (1-Meim = 1-methylimidazole) Nikolia Lalioti,a Catherine P. Raptopoulou,b Aris Terzis,b Abil E. Aliev,c Spyros P. Perlepes,*a Ioannis P.Gerothanassis*d and Evy Manessi-Zoupa*adagger; a Department of Chemistry, University of Patras, 265 00 Patras, Greece b Institute of Materials Science, NCSR ldquo;Demokritosrdquo;, 153 10 Aghia Paraskevi Attikis, Greece c Chemistry Department, University College London, 20 Gordon Street, London, UK WC1H OAJ d Department of Chemistry, University of Ioannina, 451 10 Ioannina, Greece The 2 : 1 reaction between Zn(O2CMe)2middot;2H2O and 1-Meim in refluxing MeCN gives Zn7O2(O2CMe)10(1-Meim)2 1 which comprises two vertex-sharing tetranuclear Zn4(m4-O)(h1 : h1 :m2-O2CMe)5(1-Meim) units; solid-state 13C and 15N NMR spectra reveal structural details of the complex.We have recently become interested in the synthesis of monoand di-/tri-nuclear zinc complexes containing carboxylate and imidazole ligands which would be satisfactory models for the carboxylatendash;histidinendash;metal triad catalytic centres in hydrolytic zinc enzymes.1ndash;4 This area of Zn chemistry has been poorly explored.Two groups have reported5,6 the preparation and X-ray structures of the mononuclear, four-coordinate complexes Zn(O2CR)2L2, where R = Me, Et and L = imidazole, 2-ethylimidazole. For the better investigation of the ZnIIndash;RCO22ndash;L systems (L = various monodentate imidazoles), we have systematically varied the nature of R, L and solvent, and both the ZnII : L and ZnII :RCO22 ratios. We have found all these parameters to have an important effect on the chemical and structural identity of obtained products.We herein report that the 2 : 1 and 3.5 : 1 reactions of Zn(O2CMe)2middot;2H2O with 1-methylimidazole (1-Meim) in MeCN lead to the assembly of the remarkable high-nuclearity product Zn7O2(O2CMe)10(1-Meim)2 1. Zn(O2CMe)2middot;2H2O (4.0 mmol) and 1-Meim (2.0 mmol) were refluxed for 30 min in MeCN (30 ml) to form a colourless solution. Layering this solution with an equal volume of Et2O afforded colourless crystals of Zn7O2(O2CMe)10(1-Meim)2middot; 2MeCN, 1middot;2MeCN in typical yields of ca. 45; the dried solid analysed as 1.Dagger; Employing a ZnII : 1-Meim ratio of 3.5 : 1 in either MeCN or MeOH complex 1 again results. The same procedure in EtOH can be employed for the 1,2-dimethylimidazole (1,2-diMeim) analogue of 1 (Zn7O2(O2CMe)10(1,2- diMeim)2 2).sect; The structrure of 1para; (Fig. 1) is extremely unusual and consists of a Zn7(m4-O)210+ core. The central Zn site Zn(1) lies on a crystallographic inversion centre and is the shared vertex of two Zn4(m4-O) units; this unit is well established in Zn chemistry.7 The peripheral ligation is provided by ten h1 : h1 : m2-acetate groups and two 1-Meim ligands bonded to Zn(4) atoms; each of the five crystallographically independent acetates spans one edge of the Zn4 tetrahedron.The Zn4O tetrahedron is slightly irregular, the Znmiddot;middot;middot;Zn distances being between 3.081(1) and 3.199(1) Aring; and the Znndash;Ondash;Zn angles varying from 103.5 to 112.5(1)deg;. The shortest Znmiddot;middot;middot;Zn distance between the tetrahedral subunits is the Zn(2)middot;middot;middot;Zn(4) one 5.333(1) Aring;.The geometry at the central Zn is distorted octahedral, while that at the peripheral metal ions can be described as distorted tetrahedral with the distortion at Zn(4) being more severe. Bond distances to Zn(1) are distinctly longer 1.979(2)ndash;2.203(2) Aring; as expected for a higher coordination number. There appear to be stacking interactions between the centrosymmetrically parallel 1-Meim ligands that belong to neighbouring heptanuclear molecules closest interatomic separation, N(1)middot;middot;middot;C(3A) = C(3)middot;middot;middot;N(1A), between opposite ligands is 3.340(5) Aring;; these interactions create a form of lsquo;chainsrsquo; along the b axis and aid in stabilizing the crystal structure.Complex 1 joins a small family of discrete heptanuclear zinc(ii) clusters,8ndash;11 the first reported example being Zn7Me6(OMe)8.8 Complex 1 becomes the second member of a homometallic molecular complex containing the M7(m4-O)2 double tetrahedral unit, the only other known example10 being also a zinc(ii) cluster.The compound is practically insoluble in all organic solvents; its high-resolution solid-state 13C NMR spectrum (recorded12 at 75.5 MHz) indicates a 2 : 1 : 1 : 1 splitting of the carboxylate carbons13,14 (d 181.4ndash;179.4) and 1 : 2 : 1 : 1 splitting of the methyl carbons (d 24.2ndash;22.2). Evidently, polynuclear zinc(ii) complexes are excellent candidates for a comparative study of X-ray structure with solid-state NMR properties because of the Fig. 1 ORTEP representation of Zn7O2(O2CMe)10(1-Meim)2 1. Some symmetry equivalent atoms are not labelled. Selected interatomic distance ranges (Aring;): Znndash;O(oxo) 1.914(2)ndash;1.979(2), Znndash;O(acetate) 1.944(3)ndash; 2.203(2), Zn(4)ndash;N(3) 2.004(3), Znmiddot;middot;middot;Zn 3.081ndash;6.375(1). Selected bond angle ranges (deg;): trans at Zn(1), 180.0; cis at Zn(1), 81.3(1)ndash;98.7(1); around Zn(2), 102.4(1)ndash;120.6(1); around Zn(3), 101.5(1)ndash;120.4(1); around Zn(4), 93.0(1)ndash;146.2(1); Znndash;O(oxo)ndash;Zn 103.5(1)ndash;112.5(1).Chem. Commun., 1998 1513very high quality 13C CP MAS spectra produced and the fact that shieldings of both CO22 and acetate CH3 groups are very sensitive to the precise crystallographic environment. In the present complex, two of the five crystallographically inequivalent acetate ligands present in the unit cell have degenerate 13C chemical shifts for both methyl and carboxylate groups. The solid-state 15N CP MAS NMR spectrum of complex 1 indicates the presence of two resonances at d2163.6 N(3) and d 2212.7 N(1) for the bound 1-Meim.Both resonances are significantly shifted to those of the free ligand (d 2120.3 N(3) and d 2219.9 N(1), neat liquid at 300 K, relative to CH3NO2 as reference). From a synthetic inorganic viewpoint, the preparation of 1 and 2 shows that it is possible to generate polynuclear zinc carboxylate complexes with unusual structures and nuclearities significantly greater than those known to date by relatively minor perturbations to the ZnIIndash;RCO22ndash;L system, in this case, the use of a high ZnII to L ratio. We are currently investigating the reactivity chemistry of 1 and 2 and seeking access to additional structural types.We thank University of London Intercollegiate Research Service for the provision of solid-state NMR facilities. Notes and References dagger; E-mail: emane@upatras.gr Dagger; The vacuum-dried complex analysed satisfactorily (C, H, N) as 1. sect; Complex 2 has been characterised by single-crystal X-ray crystallography and microanalyses.para; Crystal data for 1middot;2MeCN: C32H48Zn7O22N6, Mr = 1326.36, triclinic, space group P�1, a = 11.771(1), b = 12.616(2), c = 10.384(1) Aring;, a = 107.36(1), b = 93.39(1), g = 117.03(1)deg;, U = 1276.2(3) Aring;3, Z = 1, T = 298 K, m(Cu-Ka) = 4.283 mm21, Dc = 1.726 g cm23, 2qmax = 143deg;, wR2 (on F2) = 0.1044, R1 (on F) = 0.0372 for 4289 unique reflections with I 2s(I). The number of refined parameters is 360.The structure was solved by direct methods using SHELXS- 8615 and refined by full-matrix least-squares techniques using SHELXL-93.16 All hydrogen atoms were located by difference maps and refined isotropically. All non-hydrogen atoms were refined anisotropically. CCDC 182/890. 1 H. Bertini and C. Luchinat, in Bioinorganic Chemistry, ed. I. Bertini, H. B. Gray, S. J. Lippard and J. Valentine, University Science Books, Mill Valley, CA, 1994. 2 N. Str�ater, W. N. Lipscomb, T.Klabunde and B. Krebs, Angew. Chem., Ind. Engl., 1996, 35, 2024. 3 D. E. Fenton and H. Okawa, J. Chem. Soc., Dalton Trans., 1993, 1349. 4 A. Abufarag and H. Vahrenkamp, Inorg. Chem., 1995, 34, 2207. 5 W. D. Horrocks, Jr., J. N. Ishley and R. R. Whittle, Inorg. Chem., 1982, 21, 3265, 3270. 6 X.-M. Chen, B.-H. Ye, X.-C. Huang and Z.-T. Xu, J. Chem. Soc., Dalton Trans., 1996, 3465. 7 F. A. Cotton, L. M. Daniels, L. R. Falvello, J. H. Matonic, C. A. Murillo, X. Wang and H. Zhou, Inorg. Chim. Acta, 1997, 266, 91 and references therein. 8 M. L. Ziegler and J. Weiss, Angew. Chem., Int. Ed. Engl., 1970, 9, 905. 9 M. Ishimori, T. Hagiwara, T. Tsuruta, Y. Kai, N. Yasuoka and N. Kasai, Bull. Chem. Soc. Jpn., 1976, 49, 1165. 10 D. Attanasio, G. Dessy and V. Fares, J. Chem. Soc., Dalton Trans., 1979, 28. 11 M. Tesmer, B. Muller and H. Vahrenkamp, Chem. Commun., 1997, 721. 12 Experimental details will be given in the full paper. 13 S.-J. Lin, T.-N. Hong, J.-Y. Tung and J.-H. Chen, Inorg. Chem., 1997, 36, 3886. 14 P. A. Hunt, B. P. Straughan, A. A. M. Ali, R. K. Harris and B. J. Say, J. Chem. Soc., Dalton Trans., 1990, 2131. 15 G. M. Sheldrick, SHELXS-86, Structure Solving Program, University of G�ottingen, Germany, 1986. 16 G. M. Sheldrick, SHELXL-93, Program for Refinement of Crystal Structure, University of G�ottingen, Germany, 1993. Received in Basel, Switzerland, 15th April 1998; 8/02844C 1514 Chem. Commun.,
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