096 Mn2biphen IC - Znorg. C hem. 1991, 30, 3192-3199 3192 C...

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3192 Znorg. Chem. 1991, 30, 3192-3199 Contribution from the Department of Chemistry and the Molecular Structure Center, Indiana University, Bloomington, Indiana 47405, and Department of Chemistry 0506, University of California at San Diego, La Jolla, California 92093-0506 Preparation and Properties of Mononuclear and Ferromagnetically Coupled Dinuclear Manganese Complexes with 2,2'- Bi p henoxide Ann R. Schake,Ia Edward A. Schmitt,Ib Andrew J. Conti,Ib William E. Streib,lc John C. Huffman,lc David N. Hendrickson,**lb and George Christou*,la,d Received July 20, I990 The treatment of Mn30!O2CPh),(py),(H2O) with 2,2'-biphenol (biphenH,) and NEt, in MeCN leads to formation of (NEt H)2[Mn(biphen) (biphenH)] (2). Complex 2 crystallizes in monoclinic space group F2,/c with (at -146 "C) u = 22.830 (15) A, b = 9.982 (6) A, c = 19.268 (16) A, i3 = 108.27 (3)O, Z = 4 and V = 4169.39 A'. The structure was solved by direct methods and refined to R (R,) of 6.67% (6.14%) by using 1620 unique reflections with F > 2.33a(F). The structure of the anion consists of a five-coordinate, trigonal-bipyramidal Mn"' center ligated by two chelating biphen groups and a monodentate biphenH, the second phenoxide oxygen being protonated and not ligated to the Mn. A similar reaction system using 3,3',5,5'-tetra- bromobiphenol leads to the product (NEt,H),[Mr~(Br~biphen)~(O~CPh)] (3) whose IR spectrum suggests its structure to be similar to 2 with a chelating (s2) benzoate replacing the monodentate biphenH group. Treatment of complex 2 with 2,2'-bipyridine (bpy) in CH2C12 yields a black solution: layering with hexanes and storage at -20 OC leads to crystallization of Mn,(biphen),(bi- phenH)(bpy), (4) whereas storage at room temperature leads to crystallization of (bpyH)[Mn(biphen),(bpy)] (5). Complex 4 crystallizes in monoclinic space roup P2,/c with (at -155 "C) u = 13.373 (5) A, b = 10.508 (4) A, c = 39.005 (22) A, j3 = 90.67 2607 unique reflections with F > 2.33a(F). The complex is mixed-valence (Mn", Mn"'), and the structure consists of two Mn atoms bridged by two oxygen atoms from two biphen groups, the other oxygen atoms of which are terminally ligated to the Mn"' center. Six-coordination of the latter is completed by a chelating bpy. The Mn" has a chelating bpy, and five-coordination is completed by a monodentate biphenH, the second oxygen of which is protonated as in 2. The Mn" and Mn"' coordination geometries are distorted square-pyramidal and octahedral, respectively. The structure of complex 5 is assumed to be a six-co- ordinate, distorted octahedral monomer. Variable-temperature solid-state magnetic susceptibility studies on complex 4 at 10.0 kG are reported; the effective magnetic moment, perr/Mn2, steadily increases from 7.12 pB at 302.4 K to a maximum of 8.31 pg at 8.00 K, and then decreases slightly to 8.24 at 5.00 K, consistent with an intramolecular ferromagnetic exchange interaction. Complex 4 is the first MnI1MnI1I complex to exhibit a ferromagnetic interaction. In order to characterize fully the ferromagnetic coupling in this complex, magnetic susceptibility data were collected in the low-temperature range (-2-15 K) at fields of 10.0, 24.5, 34.1, and 43.5 kG. All data, including that at high temperatures, were least-squares fit with a full-matrix (30 X 30) diagonalization approach. Isotropic Feeman interactions and magnetic exchange interactions, as well as axial zero-field splitting
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096 Mn2biphen IC - Znorg. C hem. 1991, 30, 3192-3199 3192 C...

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