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Structure and Magnetic Properties of (meso-Tetraphenylporphinato)manganese(III) Bis(dithiolato)nickelates

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posted on 17.10.2005, 00:00 by Louise N. Dawe, Jesse Miglioi, Laura Turnbow, Michelle L. Taliaferro, William W. Shum, Joshua D. Bagnato, Lev N. Zakharov, Arnold L. Rheingold, Atta M. Arif, Marc Fourmigué, Joel S. Miller
The crystal structures of [MnTPP]{Ni[S2C2H(CN)]2} [MnTPP = (meso-tetraphenylporphinato)manganese(III)] and [MnTPP]{Ni[S2C2(CN)2]2} have been determined. These salts possess trans-μ-coordination of S = 1/2 {Ni[S2C2H(CN)]2}•- and {Ni[S2C2(CN)2]2}•- to Mn(III) and form parallel 1-D coordination polymer chains exhibiting νCN at 2210 and 2200 and 2220 and 2212 cm-1, respectively. The bis(dithiolato) monoanions are planar and bridge two cations with MnN distances of 2.339(16), and 2.394(3) Å, respectively, which are comparable to related MnN distances observed for [MnTPP][TCNE]·x(solvates). In addition, [MnTP‘P]{Ni[S2C2(CN)2]2} {H2TP‘P = meso-tetrakis[3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin] and [MnTP‘P(OH2)]{Ni[S2C2(CN)2]2} were prepared. The latter forms isolated paramagnetic ions. The room-temperature values of χT for 1-D [MnTPP]{Ni[S2C2H(CN)]2}, [MnTPP]{Ni[S2C2(CN)2]2}, and [MnTP‘P]{Ni[S2C2(CN)2]2} are 2.55, 3.28, and 2.86 emu K/mol, respectively. Susceptibility (χ) measurements between 2 and 300 K reveal weak antiferromagnetic interactions with ϑ = −5.9 and −0.2 K for [MnTPP]{Ni[S2C2H(CN)]2} and [MnTPP]{Ni[S2C2(CN)2]2}, respectively, and stronger antiferromagnetic coupling of −50 K for [MnTP‘P]{Ni[S2C2(CN)2]2} from fits of χ(T) to the Curie−Weiss law. The 1-D intrachain coupling, Jintra, of [MnTPP]{Ni[S2C2H(CN)]2} and [MnTPP]{Ni[S2C2(CN)2]2} was determined from modeling χT(T) by the Seiden expression (H = −2JSi·Sj) with J/kB = −8.00 K (−5.55 cm-1; −0.65 meV) for [MnTPP]{Ni[S2C2H(CN)]2}, J/kB = −3.00 K (−2.08 cm-1; −0.25 meV) for [MnTP‘P]{Ni[S2C2(CN)2]2}, and J/kB = −122 K (−85 cm-1) for [MnTP‘P]{Ni[S2C2(CN)2]2}. These observed negative Jintra/kB values are indicative of antiferromagnetic coupling. These materials order as ferrimagnets at 5.5, 2.3, and 8.0 K, for [MnTPP]{Ni[S2C2H(CN)]2}, [MnTPP]{Ni[S2C2(CN)2]2}, and [MnTP‘P]{Ni[S2C2(CN)2]2}, respectively, based upon the temperature at which maximum in the 10 Hz χ‘(T) data occurs. [MnTP‘P]{Ni[S2C2(CN)2]2} has a coercivity of 17 700 Oe and remanent magnetizations of 7250 emu Oe/mol at 2 K and 17 Oe and 850 emu Oe/mol at 5 K; hence, upon cooling it goes from being a soft magnet to being a very hard magnet.