Syntheses and magnetic properties of hexanuclear [Cp 2 Mn 3 (L 1 ) 4 ] 2 and octanuclear [Mn 8 (L 2 ) 12 (m 4 -O) 2 ] (L 1 = 2-HNC 5 H 5 N, L 2 = 2-NH-3-Br-5-MeC 5 H 3 N, Cp = C 5 H 5 )† Carmen Soria Alvarez, a Andrew D. Bond, a Dale Cave, a Marta E. G. Mosquera, b Eilís A. Harron, a Richard A. Layfield, a Mary McPartlin, c Jeremy M. Rawson, a Paul T. Wood a and Dominic S. Wright* a a Chemistry Department, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW. E-mail: dsw1000@cus.cam.ac.uk b Departmento de Quimica Organica e Inorganica, Facultad de Quimica, Universidad de Oviedo, Julian Claveria 8, 33006 Oviedo, Spain c School of Chemistry, University of North London, Holloway Road, London, UK N7 9DB Received (in Cambridge, UK) 1st October 2002, Accepted 17th October 2002 First published as an Advance Article on the web 8th November 2002 The reactions of manganocene, Cp 2 Mn, with 2-aminopyr- idine (L 1 H) or 2-amino-3-bromo-5-methylpyridine (L 2 H) give the novel hexanuclear and octanuclear Mn( II) amido cage compounds [Cp 2 Mn 3 (L 1 ) 4 ] 2 (1) and [Mn 8 (L 2 ) 12 (m 4 -O) 2 ] (2); magnetic measurements on which provide a rare insight into the magnetic properties of amido-bridged metal clus- ters. The potential applications of manganese carboxylate cluster compounds as precursors to molecule-based magnetic materials or as molecular magnets in their own right, has attracted considerable interest in the past two decades. 1 Despite this, the chemistry and magnetic properties of related nitrogen-based manganese cluster compounds have been less explored, and so far only a handful of imido manganese compounds (containing RN 22 ligands) have been structurally characterised. The majority of these species contain Mn in the V to VII oxidation states, 2 the cationic species [Mn 6 (m 3 -NPh) 4 (THF) 4 ] 4+ being the only structurally characterised Mn II imido complex. 3d Moreo- ver, even for the more widely studied amido Mn complexes (containing R 2 N 2 ligands) only comparatively few solid-state structures of mono- and dinuclear Mn( II ) complexes have been reported. 3 In a recent communication we showed for the first time that Cp 2 Mn is capable of doubly-deprotonating the NH 2 groups of moderately acidic primary amines, providing a new route to high-nuclearity Mn( II ) imido cage compounds. 4 We report here the syntheses and structures of the polynuclear amido cages [Cp 2 Mn 3 (L 1 ) 4 ] 2 (1) (L 1 H = 2-aminopyridine) and [Mn 8 (L 2 ) 12 (m 4 -O) 2 ] (2) (L 2 H = 2-amino-3-bromo-5-methyl- pyridine). This study illustrates the general applications of transition metal metallocenes in the synthesis of high-nuclearity transition metal amido cages. The 1+1 stoichiometric reactions of Cp 2 Mn with L 1 H or L 2 H in THF (under argon) give the new Mn( II ) amido complexes [Cp 2 Mn 3 (L 1 ) 4 ] 2 (1) (93% yield) and [Mn 8 (L 2 ) 12 (m 4 -O) 2 ] (2) (32% yield), respectively, as the only crystalline products (see ESI†). Although the elaborate natures of these species (and, indeed, the exact composition in the case of 2) were only apparent once their solid-state structures had been determined, the presence of N–H stretching bands in their IR spectra suggested that only partial deprotonation of the NH 2 groups of both amines had occurred during their reactions with Cp 2 Mn. The presence of oxo-ligands in the structure of 2 is apparently due to water of crystallisation present in the amine. We have foundthat 2 is obtained reproducibly usingcommercially supplied samples of L 2 H, without further purification or drying. Molecules of 1 (Fig. 1) (see ESI†) are composed of two [Cp 2 Mn 3 (L 1 ) 4 ] units which dimerise via pyridyl-N–Mn bond- ing into a hexanuclear arrangement (possessing exact C 2 symmetry). In addition, one toluene molecule is also present in the lattice for each cage molecule of 1. The three, chemically distinct Mn( II ) centres within the [Cp 2 Mn 3 (L 1 ) 4 ] constituents form a metal triangle in which two of the Mn…Mn distances [Mn(1)…Mn(3) 3.2021(9) and Mn(2)…Mn(3) 3.2757(8)Å] are considerably shorter than the remaining Mn…Mn separation [Mn(1)…Mn(2) 3.490(1) Å]. These Mn…Mn distances can be compared to a range of 3.1594(8)–3.724(1) Å found in the structures of [{CpMn(NHpm)}{MnNpm}] 4 (pm = a substi- tuted or unsubstituted pyrimidinyl ligand). 4–6 Two coordination modes are adopted by the L 1 ligands in 1, either a bridging bidentate N,NA-coordination mode bridging [Mn(2)/Mn(3a) and Mn(1)/Mn(3)] or a bridging tridentate m 2 -N,NA-mode [i.e., for the L 1 ligands bridging Mn(3), Mn(1) and Mn(2) and Mn(3), Mn(2) and Mn(3a)]. The Mn(1) and Mn(2) centres have similar, pseudo-tetrahedral (piano-stool) coordination geometries within their h 5 -CpMnN 3 units. However, whereas Mn(1) is coordinated by the anionic NH centres of three L 1 groups [N(1) 2.215(4), N(3) 2.077(5), N(5) 2.240(4) Å], Mn(2) is bonded to two anionic NH centres [N(5) 2.166(5), N(7) 2.149(3) Å] and to a neutral pyridyl-ring N centre [N(2) 2.207(4) Å]. Both of these Mn atoms are h 5 -bonded to Cp ligands, the range of C–Mn bond lengths [Mn(1)–C 2.475(5)–2.566(5), Mn(2)–C 2.384(8)–2.627(9) Å] being similar to those found in [{CpMn(NHpm)}{MnNpm}] 4 . These bond lengths are con- sistent with high-spin (17e) electronic arrangements for these metal centres. 7 A distorted trigonal bipyramidal coordination geometry is found for Mn(3), in which two pyridyl-N centres [N(6) 2.188(4) and N(8A) 2.200(4) Å] and an anionic pyNH [N(1) 2.160(4) Å] coordinate Mn(3) at equatorial positions, with an anionic pyNH [N(4) 2.230(4) Å] and a neutral pyridyl-N centre [N(7) 2.293(3) Å] coordinating at axial positions. † Electronic supplementary information (ESI) available: synthesis and crystal data of 1 and 2·2THF, key bond lengths and angles for 1 and 2, models employed for 1 and 2, and cT vs. T plots for 1 and 2. See http:// www.rsc.org/suppdata/cc/b2/b209496g/ Fig. 1 Structure of the hexanuclear cage [Cp 2 Mn 3 (L 1 ) 4 ] 2 (1). H-atoms, except those attached to N, and the lattice-bound toluene solvent has been omitted for clarity. T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 2 2 9 8 0 CHEM. COMMUN., 2 0 0 2 , 2 9 8 0 – 2 9 8 1 DOI: 10.1039/b209496g Published on 08 November 2002. Downloaded by UNIVERSITY OF ALABAMA AT BIRMINGHAM on 27/10/2014 03:56:18.