Metal Macrocycles DOI: 10.1002/ange.200704132 Octa-, Deca-, Trideca-, and Tetradecanuclear Heterometallic Cyclic Chromium–Copper Cages** LarryP.Engelhardt,ChristopherA.Muryn,RobinG.Pritchard,GrigoreA.Timco,* FlorianaTuna,andRichardE.P.Winpenny* We have made a series of compounds featuring a divalent metal ions (Ni II , Co II , Zn II , Mn II , Fe II ) doped into an octanuclear ring of trivalent ions (Cr III ,Fe III ,V III ,Ga III ,Al III , In III ), with the M···M vectors bridged by a fluoride and two carboxylate ligands. [1] The work builds on and extends ideas fromthegroupsofSaalfrank [2] andPecoraro. [3] Thecontrolwe have achieved has allowed us to begin detailed studies of the physics of these rings [1,4] and to make the proposal that they could be used as quantum bits (or “qubits”). [5,6] This chemistry relies on the divalent metal ion adopting an octahedral coordination geometry; when Cu II was used, a different structure resulted—a {Cr 10 Cu 2 } “hourglass”. [7] We also found that in the Cr 10 Cu 2 system the size of the templatingaminedidnothavethesamecontrollinginfluence wehadfoundwithCr–Nirings.Theseobservationssuggested a different family of structures might result from control of reaction conditions. [R 2 NH 2 ] 2 [Cr 10 Cu 2 F 14 (O 2 CCMe 3 ) 22 ] cages (R = Me 1a, iPr 1b) can be made by reaction of hydrated chromium trifluor- ide, basic copper carbonate, and the secondary amine in hot pivalicacid.Originallythereactiontimewasfivehours.Ifthe heatingtimeisextendedtolongerthanoneday,thereaction produces a green precipitate and a filtrate that contains several different {Cr x Cu y } rings. The precipitate contains [iPr 2 NH 2 ] 2 [Cr 12 Cu 2 F 16 (O 2 CCMe 3 ) 26 ](2), which we can isolate in pure form in 20% yield. The structure [8] resembles an hourglass, with the five-coordinate Cu II sites linked by {Cr 6 } chains (Figure 1); in 1 the sites were linked by {Cr 5 } chains. The copper(II) centers are five-coordinate, bridged to one Cr III centerthroughonefluorideandtwopivalateligandsand to a second Cr III center through only one fluoride and one pivalate. This second Cr III center is found at the waist of the hourglasswithaterminalfluorideligandattached.TheCr···Cr vectors are all bridged by one fluoride and two pivalate ligands. Two secondary ammonium cations are found at the center of the structure. They form H-bonds to the terminal fluorides (N···F 2.65 ). The structure is disordered, and the twoCu II ionsaredisorderedoverthefourmetalsitesadjacent to the Cr centers at the waist of the hourglass. This disorder makes it possible, but less likely, that in some molecules the Cucentersarelinkedby{Cr 4 }and{Cr 8 }chains.Althoughdo- deca-, [12] hexadeca-, [13] and octadecanuclear rings [14] are known, this is, to our knowledge, the first tetradecanuclear ring to be isolated. Thefiltratefromwhich 2 precipitatedcanbemanipulated to produce green crystals of [iPr 2 NH 2 ] 2 [Cr 11 Cu 2 F 15 - (O 2 CCMe 3 ) 24 ](3), formed in 5% yield. Structure determi- nation [8] showstheformationofatridecanuclearring,withthe twoCu II siteslinkedby{Cr 5 }and{Cr 6 }chains(Figure2).The structureisdisordered,withthetwoCu II ionsdisorderedover the four sites which are adjacent to the waist of the distorted hourglass.Asin 2,thisdisordermakesitpossiblethatthetwo copper sites are linked through {Cr 3 } and {Cr 8 } chains or through{Cr 4 }and{Cr 7 }chains.Giventhestructuresof 1 and 2, the model proposed herein looks the most plausible. This compoundisaveryrareexampleofalargepolymetalliccycle with an odd number of metal centers [15,16] and the first tridecanuclear ring. The two ammonium cations H-bond to fluorides in very different ways; N1A H-bonds in a similar mannertothetemplatesin 2,whileN2AH-bondstoonlyone terminal and two bridging fluoride ions (Figure 2). Figure 1. The crystal structure of 2. Methyl groups of ligands excluded for clarity. Atom shading: F open circles, O diagonal lines, N regular dots, Cr heavy irregular shading, Cu crosshatched; C lines. [*] Dr. C. A. Muryn, Dr. R. G. Pritchard, Dr. G. A. Timco, Dr. F. Tuna, Prof. R. E. P. Winpenny School of Chemistry The University of Manchester Oxford Road, Manchester, M13 9PL (UK) Fax: (+ 44)161-275-4616 E-mail: grigore.timco@manchester.ac.uk richard.winpenny@manchester.ac.uk Dr. L. P. Engelhardt Department of Physics and Astronomy Francis Marion University Florence, SC (USA) [**] This work was supported by the EPSRC (UK), the Leverhulme Trust and the EC “Network of Excellence” MAGMANet. We are also grateful for access to the computational facilities of the Ames National Laboratory. Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Zuschriften 938 # 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2008, 120, 938 –941