Trinuclear linear 3d-4f-3d complexes (3d = Mn(II), Fe(II), Co(II), Zn(II) and 4f = La(III), Gd(III), Tb(III), Dy(III)) were prepared by using a tripodal nonadentate Schiff base ligand, N,N',N''-tris(2-hydroxy-3-methoxybenzilidene)-2-(aminomethyl)-2-methyl-1,3-propanediamine. The structural determinations showed that in these complexes two distorted trigonal prismatic transition metal complexes of identical chirality are assembled through 4f cations. The Mn and Fe entities crystallize in the chiral space group P2(1)2(1)2(1) as pure enantiomers; the cobalt complexes exhibit a less straightforward behavior. All Mn, Fe, and Co complexes experience M(II)-Ln(III) ferromagnetic interactions. The Mn-Gd interaction is weak (0.08 cm(-1)) in comparison to the Fe-Gd (0.69 cm(-1)) and Co-Gd (0.52 cm(-1)) ones while the single ion zero field splitting (ZFS) term D is larger for the Fe complexes (5.7 cm(-1)) than for the cobalt ones. The cobalt complexes behave as single-molecules magnets (SMMs) with large magnetization hysteresis loops, as a consequence of the particularly slow magnetic relaxation characterizing these trinuclear molecules. Such large hysteresis loops, which are observed for the first time in Co-Ln complexes, confirm that quantum tunnelling of the magnetization does not operate in the Co-Gd-Co complex.

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The syntheses, structural determinations, and magnetic studies of two trinuclear Ni-Gd-Ni complexes are described. The structural studies demonstrate that the two complexes present a linear arrangement of the Ni and Gd ions, with Ni ions in slightly distorted square-pyramidal or octahedral environments in complexes 1 and 2, respectively. The Ni and Gd ions are linked by two or three phenoxo bridges, so that complexes 1 and 2 present edge-sharing or face-sharing bridging cores. Ferromagnetic interactions operate in these complexes. While a unique J parameter is able to fit the magnetic data of complex 2, two very different J constants are needed for 1. This result is at first sight surprising, for the structural data of the two Ni-O(2)-Gd cores in complex 1 are quite similar (similar Ni-O and Gd-O bond lengths, similar angles, and dihedral angles), the only difference coming from the angle between the planes defined by the Gd ion and the two bridging phenoxo oxygen atoms of each Ni-O(2)-Gd half core. This latter magnetic behavior can be considered as a signature for the participation of 5d Gd(III) orbitals in the exchange interaction mechanism and can explain why edge-sharing complexes have larger J parameters than face-sharing complexes.

Dinuclear [(NiL)Gd(hfac)(2)(EtOH)](H(3)L = 1,1,1-tris(N-salicylideneaminomethyl)ethane, Hhfac = hexafluoroacetylacetone), trinuclear [(NiL)(2)Gd(NO(3))], and tetranuclear [(NiL)Gd(CH(3)CO(2))(2)(MeOH)](2) complexes, were prepared by treating [Ni(HL)] with [Gd(hfac)(3)(H(2)O)(2)], Gd(NO(3))(3).6H(2)O, and Gd(CH(3)CO(2))(3).4H(2)O, respectively, in the presence of Et(3)N. All the complexes show that ferromagnetic interactions occur between the Ni(II) and Gd(III) ions.

Heterodinuclear [(Ni (II)L)Ln (III)(hfac) 2(EtOH)] (H 3L = 1,1,1-tris[(salicylideneamino)methyl]ethane; Ln = Eu, Gd, Tb, and Dy; hfac = hexafluoroacetylacetonate) complexes ( 1.Ln) were prepared by treating [Ni(H 1.5L)]Cl 0.5 ( 1) with [Ln(hfac) 3(H 2O) 2] and triethylamine in ethanol (1:1:1). All 1.Ln complexes ( 1.Eu, 1.Gd, 1.Tb, and 1.Dy) crystallized in the triclinic space group P1 (No. 2) with Z = 2 with very similar structures. Each complex is a face-sharing dinuclear molecule. The Ni (II) ion is coordinated by the L (3-) ligand in a N 3O 3 coordination sphere, and the three phenolate oxygen atoms coordinate to an Ln (III) ion as bridging atoms. The Ln (III) ion is eight-coordinate, with four oxygen atoms of two hfac (-)'s, three phenolate oxygen atoms of L (3-), and one ethanol oxygen atom coordinated. Temperature-dependent magnetic susceptibility and field-dependent magnetization measurements showed a ferromagnetic interaction between Ni (II) and Gd (III) in 1.Gd. The Ni (II)-Ln (III) magnetic interactions in 1.Eu, 1.Tb, and 1.Dy were evaluated by comparing their magnetic susceptibilities with those of the isostructural Zn (II)-Ln (III) complexes, [(ZnL)Ln(hfac) 2(EtOH)] ( 2.Ln) containing a diamagnetic Zn (II) ion. A ferromagnetic interaction was indicated in 1.Tb and 1.Dy, while the interaction between Ni (II) and Eu (III) was negligible in 1.Eu. The magnetic behaviors of 1.Dy and 2.Dy were analyzed theoretically to give insight into the sublevel structures of the Dy (III) ion and its coupling with Ni (II). Frequency dependence in the ac susceptibility signals was observed in 1.Dy.

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Two heterotrinuclear complexes, [Mn(II)(Ni(II)L)2].2CH3OH (where H3L = 1,1,1-tris(N-salicylideneaminomethyl)ethane) and [Fe(III)(Ni(II)L)2]NO3.C2H5OH, consisting of three face-sharing octahedra have been prepared; although these complexes have closely related structures and have the same 1-5/2-1 spin system, they show completely different magnetic interactions between the adjacent metal ions: ferromagnetic (Ni(II)-Mn(II)) and antiferromagnetic (Ni(II)-Fe(III)).

Alkoxycarbonyl(cyano)palladium(II) complexes trans-Pd(COOR)(CN)(PPh 3 ) 2 (1, R ) Me; 2, R ) Et; 3, R ) n Pr; 4, R ) i Pr; 5, R ) n Bu; 6, R ) t Bu; 7, R ) Bn) are prepared via oxidative addition of the corresponding cyanoformates to Pd(PPh 3 ) 4 in toluene at room temperature or 50 °C and characterized by means of NMR ( 1 H, 13 C{ 1 H}, and 31 P{ 1 H}) and IR spectroscopy as well as elemental analyses. X-ray crystallography of 3, 4, and 6 showed a square-planar coordination around the Pd center that is bonded to alkoxycarbonyl and cyano ligands in the trans configuration. The Pd-CN and Pd-COOR bonds in 1, 3, 4, and 6 are similar to those of the cyanopalladium(II) and alkoxycarbonylpalladium(II) complexes reported to date. On reaction of Pd(PPh 3 ) 4 with phenyl cyanoformate a thermally induced ligand exchange takes place to afford the dicyanopalladium(II) complex, trans-Pd(CN) 2 (PPh 3 ) 2 (8). Complex 2 is able to catalyze the reaction of norbornadiene with ethyl cyanoformate to produce (2R*,3S*)-ethyl 3-cyanobicyclo-[2.2.1]hept-5-ene-2-carboxylate (13) and is recovered after the reaction. This observation supports the identification of alkoxycarbonyl(cyano)palladium(II) complexes as intermediates in the catalytic cycle of cyanoesterification of norbornene derivatives.