Hydrothermal synthesis and solid-state structure of Tc 2 (l-O 2 CCH 3 ) 4 Cl 2 William M. Kerlin a , Frederic Poineau a , Kenneth R. Czerwinski a , Paul M. Forster a,⇑ , Alfred P. Sattelberger a,b,⇑ a Department of Chemistry, Radiochemistry Program, University of Nevada Las Vegas, Las Vegas, NV 89154, USA b Energy Engineering and Systems Analysis Directorate, Argonne National Laboratory, Argonne, IL 60439, USA article info Article history: Available online xxxx Dedicated to the memory of Michelle Millar, an outstanding synthetic chemist, chemistry pioneer, and a good friend. Her smile, sense of humor, generosity, and enthusiasm for inorganic chemistry are sorely missed. Keywords: Technetium Potassium pertechnetate Carboxylate-bridged dimers Quadruple metal–metal bonds Hydrothermal synthesis abstract Tc 2 (l-O 2 CCH 3 ) 4 Cl 2 is a key starting material for further explorations of dinuclear technetium(III) chem- istry and is obtained in 70% yield from readily available starting materials via hydrothermal techniques. Its single crystal X-ray structure reveals the familiar paddle-wheel motif of four bridging acetate groups spanning a short Tc–Tc bond (2.1758(3) Å), augmented by axial chlorides at a Tc–Cl separation of 2.5078(4) Å. The Tc–Tc quadruple bond length is slightly shorter than the one found in the pivalate deriv- ative, Tc 2 (O 2 CCMe 3 ) 4 Cl 2 (2.192(1) Å), and slightly longer than found in [Tc 2 (O 2 CCH 3 ) 4 ](TcO 4 ) 2 (2.149(1) Å), the only other structurally characterized members of the small family of Tc 2 (O 2 CR) 4 X 2 dimers. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Technetium occupies a central position among the transition elements. Because it bears a close electronic relationship to its hea- vier congener rhenium, the occurrence of analogous compounds is expected, but the radioactive nature of technetium has served to limit the development of its chemistry relative to that of rhenium [1]. Today, the number of laboratories worldwide that are equipped to pursue synthetic chemistry with the most readily available isotope, viz., 99 Tc, is severely limited. For the past several years, we have been exploring the fundamental chemistry of tech- netium, including that associated with metal–metal bonded di- mers with bonds of order 4, 3.5 and 3 [2]. We have found many similarities between the dinuclear chemistry of Tc and Re, but also subtle and sometimes frustrating differences in the synthetic chemistry that are likely a manifestation of the redox properties of the respective elements in equivalent oxidation states. One com- pound that we have found to be a very useful starting material for investigations of both dinuclear technetium(III) chemistry and as a precursor to l-TcCl 3 (Tc 3 Cl 9 ) is the acetate bridged dimer, Tc 2 (l- O 2 CCH 3 ) 4 Cl 2 (1) [3]. Its rhenium analog, Re 2 (l-O 2 CCH 3 ) 4 Cl 2 , first prepared by Taha and Wilkinson [4], played a key role at the begin- ning of the multiple metal–metal bond field and was an early example of a d 4 –d 4 dimer with a quadruple metal–metal bond. In this paper, we describe a reliable, high-yield synthesis of 1 and its characterization by single crystal X-ray diffraction. Com- plex 1 was first reported in the Russian literature in 1980 [5]. Sub- sequently, some details on its preparation using hydrothermal techniques were provided in a 1981 Russian patent [6]. A handful of additional publications dealing with 1 and its bromide analog have appeared since the patent and alternative methods for its preparation have been described. Preetz et al. [7] modeled their synthesis of 1 after that used by Cotton et al. to prepare Re 2 (l-O 2 CCH 3 ) 4 Cl 2 (Eq. (1)) [8]. This reaction provides 1 in about 40% yield, but requires the prior preparation of [n-Bu 4 N] 2 [Tc 2 Cl 8 ] (2). Complex 2 is accessible in comparable yield (40–50%) from ammonium pertechnetate, but the synthesis involves four steps and takes a minimum of 2 days. Given the fact that both reactions are performed on a small scale, an overall yield of 1 on the order of 20% is far from satisfactory. Two other technetium(III) tetracarbox- ylate complexes are known, but both were isolated in low yield. The tetrapivalate, Tc 2 (l-O 2 CCMe 3 ) 4 Cl 2 , was prepared from the reaction of (NH 4 ) 3 Tc 2 Cl 8 with molten pivalic acid [9], and the novel pertechnetate-capped tetraacetate, [Tc 2 (l-O 2 CCH 3 ) 4 ](TcO 4 ) 2 , was 0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2012.09.064 Abbreviations: SC-XRD, single crystal X-ray diffraction; EXAFS, extended X-ray absorption fine structure; FTIR, Fourier transform infrared spectroscopy; DWF, Debye–Waller factor. ⇑ Corresponding authors. Address: Energy Engineering and Systems Analysis Directorate, Argonne National Laboratory, Argonne, IL 60439, USA. Tel.: +1 630 252 3504 (A.P. Sattelberger), tel.: +1 702 895 3753 (P.M. Forster), E-mail addresses: paul.forster@unlv.edu (P.M. Forster), asattelberger@anl.gov (A.P. Sattelberger). Polyhedron xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly Please cite this article in press as: W.M. Kerlin et al., Polyhedron (2012), http://dx.doi.org/10.1016/j.poly.2012.09.064