An efficient strategy for synthesis of a wide range of homo- and heterometallic polynuclear complexes is proposed. The synthesis protocol consists of a two-step one-pot reaction. The first step is the in situ generation of carboxylate anions via oxidation of aromatic aldehydes by metal nitrates in air. The aldehydes act as solvents and are also involved in redox processes. Solutions containing solely transition metal cations and aromatic carboxylates are obtained following this procedure. The second step is a tunable "à la carte" formation of a series of various polynuclear carboxylato complexes from solutions obtained at the former stage upon addition of different solvents. The polarity and donor properties of the solvents play a key role in determination of the nuclearities of the complexes. Hydrolytic processes can induce the formation of oxo- or hydroxo-bridges inside the polynuclear core as well. Complexes of various nuclearities are obtained: from discrete tri-, hexa-, or octanuclear units to 1D polymers. This protocol can be adapted with disconcerting simplicity to the synthesis of heterometallic species with similar molecular structures to their homometallic analogues starting from stoichiometric mixture of metal nitrates under the same reaction conditions. Detailed description of synthesis and the molecular structure of one representative complex for each series are presented in this paper. The temperature dependence of magnetic susceptibility of the heterometallic 1-D MnCo chain reveals typical behavior of a ferrimagnetic chain. The low-temperature investigations on single crystals show significant Ising type magnetic anisotropy.
Three new homo- and heterometallic hexanuclear complexes [Mn(2)M(II)(4)O(2)(PhCOO)(10)(DMF)(4)] (with M = Mn (1), Co (2) or Ni (3) and DMF = dimethylformamide) have been synthesized by redox generation of benzoate ligands from benzaldehyde in a one-pot reaction. All of the compounds are isostructural and crystallize in the I-42d space group of the tetragonal system, data for 1: a = 27.2249(8) Angstroms, c = 25.5182(5) Angstroms, R1 = 0.0681. The crystal structure contains isolated molecules. Each molecule consists of 2 x Mn(III) surrounded by four M(II) ions to form two edge-sharing OMn(2)M(2) tetrahedra giving rise to the [Mn(2)M(4)O(2)] core. The coordination sphere of each metal is completed by the bridging benzoate ligands and DMF molecules. The magnetic susceptibilities of 1-3 have been measured in the 1.8 K < T < 300 K temperature range. The magnetic susceptibilities for 1 and 2 pass through a broad maximum at low temperature which is characteristic of the diamagnetic ground state, while for 3 no maximum is detected down to 1.8 K. The magnetic data have been interpreted quantitatively for 1 and 3 on the basis of spin exchange interactions between the metallic centers (spin Hamiltonian for a pair being H(AB) = -J(AB) S(A).S(B)). Single-crystal measurements on [Mn(6)O(2)(PhCOO)(10)(CH(3)CN)(4)] (4) show that significant magnetic anisotropy develops at low temperature.
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