Trinuclear Co II and Ni II complexes have been assembled using an octadentate Mannich-Schiff-base proligand H 2 L 2 which is obtained by reacting the Mannich base HL 1 with propylenediamine (2:1 molar ratio). HL 1 is obtained from 5bromo-salicylaldehyde and N,N,N′-trimethyl-ethylenediamine. The reaction of H 2 L 2 with nickel(II) and cobalt(II) as nitrate salts affords the trinuclear complexes [Ni 3 (L 2 )(NO 3 ) 4 ]·CH 3 CN (1) and [Co 3 (L 2 )(NO 3 ) 4 ]·CH 3 CN (2) in which the metal ions are bridged by one phenoxido and a nitrato-oxygen atoms. Within each complex, two of the four nitrato groups act as chelating ligands against the terminal metal ions. The central metal ions in 1 and 3 ) 2 ]· 2CH 3 CN (5). The magnetic properties of the five compounds have been investigated, revealing the occurrence on intramolecular antiferro-(1 and 2) and ferromagnetic interactions (3, 4 and 5). The nature and size of these interactions are discussed and compared to previously reported results on related systems.Scheme 1. Macrocyclic (A) and end-off (B) compartmental proligands nation environments. Such complexes have relevance in molecular magnetism, [3] biomimetic inorganic chemistry, [4] and catalysis. [5] Using 5-substituted salicylaldehydes as a platform for Mannich and Schiff reactions, the sizes of the two compartments can be tuned by choosing amine precursors with various Scheme 2. Dissymmetric proligands Full Paper numbers of carbon atoms. Moreover, the two amines can contain additional coordinating groups. Other proligands obtained following this strategy are potentially tetradentate and contain only one compartment, Mannich or Schiff (see Scheme 2). These organic molecules can generate not only binuclear complexes, but also high nuclearity clusters. [6] In this paper we report on new trinuclear complexes which are aggregated using an octadentate Schiff-Mannich base ligand featuring a salen-like moiety. Their syntheses, crystal structures and magnetic properties are discussed.
Results and DiscussionThe new ligand has been obtained starting from 5-bromosalicylaldehyde: in the first step, the Mannich reaction leads to the intermediate HL 1 species (see Scheme 3); [7] in the second step, the octadentate ligand H 2 L 2 is obtained by reacting HL 1 with propylenediamine (2:1 molar ratio). This last reaction occurs in situ, in the presence of transition metal ions. The H 2 L 2 proligand combines the rigid salen-like coordinating moiety with the flexible Mannich arms, each one with two nitrogen atoms. We have tested its coordination behavior in the reaction with nickel(II) and cobalt(II) as nitrate salts. In both cases, trinuclear complexes of formula [Ni 3 (L 2 )(NO 3 ) 4 ]·CH 3 CN (1) and [Co 3 (L 2 )(NO 3 ) 4 ]·CH 3 CN (2) have been assembled.Two nitrato ligands are chelated to the two peripheral metal ions and the other two act as monoatomic bridges. By reacting these compounds with NaN 3 and NaNCS, the bridging nitrato groups have been replaced by Figure 1. (a) Perspective view of the trinuclear complex 2. (b) Det...
