Preparation of site-differentiated mixed ligand and mixed ligand/mixed metal metallacrowns

Assembly reactions that can prepare reliably regioselective metallamacrocyc lic complexes have been a target in the development of metalracrowns. To th is end, a series of mixed ligand and mixed Ligand/mixed metal metallacrowns have been synthesized in high yield and structurally characterized. Two di stinct connectivities have been observed in these types of metallacrowns. T he monomeric, vacant metallacrown with mixed ligand composition [12-MCNi(II )Ni(Hshi)2(pko)2-4] (1a) shows the connectivity pattern [-O-Ni-O-N-Ni-N-](2 ) while the other Ni metallacrowns, [12-MCNi(II)N(shi)2(pko)2-4] (2a) and t he coupled [12-MCNi(II)N(shi)2(pko)2-4] [12-MCNi(II)N(shi)3(pko)-3] (3a) fu sed metallacrowns as well as the mixed metal Mn-Ni metallacrown [12-MCNi(II )Mn(III)N(shi)2(pko)2-4] (4a), follow the pattern [-Ni-O-N-](4). Also, thre e distinct arrangements of the chelate rings around the metal ions have bee n observed. The syntheses an completely general, allowing for the substitut ion of different ligands into the metallacrown core. Compounds 1 and 4 show the 6-5-6--5-6-5-6-5 arrangement, compounds 2 and 3(1) the 6-6-5-5-6-6-5-5 , and the 3(2) component the 6-6-5-5-6-5-6-5. The obtained structures can b e rationalized by balancing the charge at each metal site in the metallacro wn. Variable temperature magnetic susceptibility measurements show that exc hange interactions for all the compounds are weak and dominantly antiferrom agnetic (e.e., 2a gives an exchange coupling of J = -1.2 cm(-1) with g = 2. 2). In solution, the metallacrowns are shown to be stable both to decomposi tion and ligand exchange.