A new end-on azido bridged Mn(III) single-chain magnet and its dimeric single molecule magnet polymorph. Synthesis, structure and magnetic properties of [Mn(5-Clsalpn)N3]n and phenoxo bridged [Mn(5-Clsalpn)N3]2.

An end-on azido bridged Mn(III) coordination chain polymer [Mn(5-Clsalpn)N3]n (complex 1) and its dimeric polymorph, [Mn(5-Clsalpn)N3]2 (complex 2), where 5-Clsalpn is N,N'-bis(5-chlorosalicylidene)-1,3-diaminopropane, were prepared. Complex 1, which is obtained as two concomitant polymorphs (1a and 1b) with nearly identical molecular structures but different crystal packing, has µ-1,1(end-on) azido bridges. This single atom bridge is unsymmetrical and leads to a -1 cm(-1) antiferromagnetic interaction among Mn(III) centers of the one-dimensional coordination polymer. Mn(III) anisotropy is manifested through Jahn-Teller elongation along the N(azido)-Mn-N(azido) axis, and results in single-chain magnet behavior. The phenoxo-bridged dimer (complex 2) has terminal azido ligands and a ferromagnetic interaction is mediated by the unsymmetrical bis-phenoxo bridge. Mn(III) anisotropy is manifested through Jahn-Teller elongation along an N-Mn-O axis, and results in single molecule magnet behavior. The dimers are organized into a two-dimensional network structure via Cl···Cl and Cl···H-phenyl interactions which are also ferromagnetic.

Aperiodic spin state ordering of bistable molecules and its photoinduced erasing.

We describe a novel type of ordering phenomenon associated with the incommensurate occupational modulation of bistable molecular magnetic state in a spin-crossover material. This unusual type of aperiodicity resulting from the ordering of multistable electronic states opens new possibilities for addressing such materials by light. Here we show that light can switch the crystal from four- to three-dimensional periodic structure. Mixing aperiodicity, multistability, and photoinduced phenomenà opens new perspectives for directing complex order and function in material science.

Crystal structures and magnetic properties of new cyano-bridged two-dimensional grid-like bimetallic assemblies [Ni(tn)2]2[Cr(CN)5((NO)]OH*H2O and [NI(tn)2]2[Co(CN)6]NO3*2H2O (tn=1,3-propanediamine).

Two bimetallic assemblies, [Ni(tn)(2)](2)[Cr(CN)(5)(NO)]OH.H(2)O (1) and [Ni(tn)(2)](2)[Co(CN)(6)]NO(3).2H(2)O (2) (tn = 1,3-diaminopropane), have been prepared and structurally and magnetically characterized. Crystal data for 1 (2): space group P1 (P1), a = 8.698(3) (8.937(2)) A, b = 10.001(2) (9.863(1)) A, c = 10.158(2) (10.064(1)) A, alpha = 87.40(2) (86.064(10)) degrees, beta = 65.10(2) (65.489(10)) degrees, gamma = 81.63(2) (81.572(12)) degrees and Z = 1 (1). Both structures consist of two-dimensional grid-like polycations containing Ni-N triple bond C-M linkages (M = Cr or Co) and counteranions (OH, NO(3)). Magnetic studies of 1 showed that the complex displays a metamagnetic behavior originating from intralayer ferromagnetic and interlayer antiferromagnetic interactions. Long-range antiferromagnetic ordering was observed at T(N) = 3.3 K. Complex 2 exhibits intramolecular ferromagnetic interactions through the diamagnetic N triple bond C-Co-N triple bond C bridges, owing to superexchange involving the empty d(sigma) orbital of the diamagnetic Co(III) ion.

Toward model complexes of Co-containing nitrile hydratases: synthesis, complete characterization and reactivity toward ligands such as CN- and NO of the first square planar CoIII complex with two different carboxamido nitrogens and two thiolato sulfur donors.

A [CoIII(N2S2)]NEt4 complex, with two carboxamido nitrogens and two alkylthiolato sulfurs, was prepared from N,N'-(2-thioacetylisobutyryl)-2-aminobenzylamine, and characterized. It crystallizes with a distorted square planar structure including two short Co-N bonds (approximately 1.882 A) and two short Co-S bonds (approximately 2.134 A). The ligand defines an 11-atom chelate, which may be Co ligands in the mean plane of Co-containing nitrile hydratase. The CoIII oxidation state, reversibly reduced at -1.13 V (vs. SCE) and irreversibly oxidized at +1.29 V (vs. SCE) in DMF, is stable over a 2 V potential range. From the temperature dependence of its magnetic susceptibility, cobalt(III) was found to be in an S = 1 triplet ground state, in agreement with the broad resonances observed in its 1H-NMR spectrum. Preliminary spectral studies showed that this complex does not interact with imidazole, H2O or HO-, but binds two CN anions or two NO molecules. The IR spectrum of the dinitrosyl complex exhibits two NO stretches at 1765 and 1820 cm(-1), in the range previously observed for dinitrosylated complexes derived from cobalt(I). This result suggests that, similarly to Fe NHases, Co NHases might readily bind NO.

Synthesis, structure, and magnetic properties of the low-symmetry tetranuclear cubane-like nickel complex [Ni4(pypentO)(pym)(mu 3-OH)2(mu- Oac)2(NCS)2(OH2)].

The tetranuclear [Ni4(pypentO)(pym)(mu 3-OH)2(mu-Oac)2(NCS)2(OH2)] cubane-like complex has been prepared, and its structure and magnetic properties have been studied (pypentO and pym are the deprotonated forms of 1,5-bis[(2-pyridylmethyl)amino]pentane-3-ol and 2-pyridylmethanol, respectively). The X-ray diffraction analysis of this novel nickel complex (C61H74N14O25.5S4Ni8, monoclinic, P2(1), a = 13.9375(14) A, b = 20.6604(18) A, c = 16.6684(19) A, beta = 110.619(12) degrees, Z = 2) showed a Ni4O4 cubane arrangement of four nickel atoms, four mu 3-O bridging ligands (one pypentO, one pym, and two OH-), two syn-syn bridging acetates, and three terminal monodentate ligands (two NCS- and one OH2). In this low-symmetry elongated cubane, the four Ni-Ni long distances (3.18 A) correspond to the faces of the cube including two mu 3-OR bridges, and the two Ni-Ni short distances (2.94 A) correspond to the faces including two mu 3-OR and one acetate bridges. The temperature dependence of the magnetic susceptibility was fitted with J1 = -3.09 cm-1, J2 = 15.0 cm-1, J3 = 6.72 cm-1, and g = 2.27. The differences in sign among the J1, J2, and J3 superexchange interactions is in good agreement with the different types of faces present in this Ni4O4 cubane core. The two faces of the cube, including two mu 3-OR bridges associated with one acetate bridge, exhibit ferromagnetic interactions, while the four faces which include only mu 3-OR bridges exhibit antiferromagnetic interactions. The very small zero field splitting may be attributed to the fact that the ground state is diamagnetic. The nature of the ground state is confirmed by the good simulation of the magnetization curves at 2 and 5 K (diagonalization of the full matrix taking into account all energy levels obtained with the parameter set resulting from the fit of the susceptibility curve). The large differences in J values resulting from small differences in Ni-O-Ni angles in this Ni4O4 core of very low symmetry reflect a quite strong magnetostructural correlation.

Catalysis and kinetics of hydrogen peroxide disproportionation by dinuclear manganese(III) complexes of 1,5-bis(salicylidenamino)pentan-3-ol and the 5-bromophenyl-substituted derivative.

The dinuclear MnIII complex [Mn2(mu-OAc)(mu-OMe)(5-Br-salpentO)(MeOH)2]Br has been prepared and its structure and reactivity toward H2O2 studied in comparison with [Mn2(mu-OAc)(mu-OMe)(salpentO)(MeOH)2]Br (salpent-OH = 1,5-bis(salicylidenamino)pentan-3-ol and 5-Br-salpentOH = 1,5-bis(5-bromesalicylidenaminopentan-3-ol). The X-ray diffraction analysis of [Mn2(mu-OAc)(mu-OMe)(5-Br-salpentO)(MeOH)2]Br (monoclinic, P21/n, a = 13.081(2) A, b = 13.429(2) A, c = 17.375(2) A, beta = 102.31(1) degrees, V = 2982.0 A3, Z = 4) revealed a mu-alkoxo, mu-acetatodimanganese(III) core with a Mn...Mn separation of 2.932(1) A. The ligand lies in the meridional plane, and the sixth coordination position of each manganese atom is occupied by a methanol molecule providing two substitution-labile sites in the cis position. The two complexes showed catalytic activity toward disproportionation of H2O2 in methanol and dimethylformamide in the 0-25 degrees C temperature range. The initial rate of oxygen evolution in the presence of [Mn2(mu-OAc)(mu-OMe)(5-Br-salpentO)(MeOH)2]Br or [Mn2(mu-OAc)(mu-OMe)(salpentO)(MeOH)2]-Br is first order in catalyst concentration. The two complexes show saturation kinetics in methanol, with the higher kcat = 0.98 s-1 and kcat/KM = 70 M-1 s-1 observed for [Mn2(mu-OAc)(mu-OMe)(salpentO)(MeOH)2]Br.

Synthesis, Structure, and Magnetic Properties of Mn(salpn)N(3,) a Helical Polymer, and Fe(salpn)N(3), a Ferromagnetically Coupled Dimer (salpnH(2) = N,N'-bis(Salicylidene)-1,3-diaminopropane).

The preparation, crystal structures, and variable temperature magnetic susceptibility data are presented for two azido-bridged Schiff base complexes of Mn(III) and Fe(III). Mn(salpn)N(3) (1), where salpn is the dianion of N,N'-bis(salicylidene)-1,3-diaminopropane, crystallizes in the orthorhombic system, space group Pna2(1), with a = 11.947(2) Å, b = 11.818(2) Å, c = 11.227(5) Å, and Z = 4. Fe(salpn)N(3) (2) crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.199(7) Å, b = 14.081(6) Å, c = 12.017(3) Å, beta = 105.19(3) degrees, and Z = 4. In 1, salpn coordinates in the equatorial mode, with two azide ions coordinating in axial positions. The azide ions act as "end-to-end" (&mgr;-(1,3)) bridges, leading to an infinite helical chain propagating along the crystallographic c axis. In striking contrast, 2 has a dimeric structure in which the Schiff base adopts a cis-octahedral coordination mode. The dimer is held together by two "head-on" (&mgr;-(1,1)) bridging azide ions. The polymeric compound, 1, is weakly antiferromagnetic (J = -4.03 cm(-)(1), H(ex) = -2J summation operatorS(i)()S(i)()(+1)), while 2 is weakly ferromagnetic (J = 0.76 cm(-)(1), H(ex) = -2JS(1)S(2)).

Synthesis, Crystal Structure, Magnetic Properties, and EPR of Cu(bp3ca)Br(2).H(2)O (bp3ca = 2,2'-Bipyridine-3,3'-dicarboxylic Acid). Ferromagnetic Interactions via Unsymmetrical Bromide Bridges.

Cu(bp3ca)Br(2).H(2)O crystallizes in the triclinic space group P&onemacr; with a = 10.622(2) Å, b = 10.832(2) Å, c = 14.684(2) Å, alpha = 106.13(1) degrees, beta = 105.91(1) degrees, gamma = 102.74(1) degrees, and Z = 2. The asymmetric unit consists of a bis &mgr;-bromo unsymmetrically dibridged dimer which is further linked to its inversion-related partner to form a dimer of dimers. Weak intertetramer contacts are also observed. The magnetic data for this compound were fit to a linear tetramer model to give J(1) = J(3) = -8.69 x 10(-)(3) cm(-)(1), J(2) = 91.52 cm(-)(1), and the intertetramer interaction J' = -1.187 cm(-)(1) with g = 1.93. EPR data are consistent with the magnetic data. This system is compared to its previously reported chloro counterpart, which differs markedly in both structure and magnetic properties.