Syntheses and Crystal Structures of Two Classes of Aluminum-Lanthanide-Sodium Heterotrimetallic 12-Metallacrown-4 Compounds: Individual Molecules and Dimers of Metallacrowns

Two series of aluminum-lanthanide-sodium 12-metallacrown-4 compounds have been synthesized and characterized by single-crystal X-ray analysis. For the individual LnNa(ben) 4 [12-MC Al(III)N(shi) -4] molecules, where Ln III = Eu ( 1 ), Gd ( 2 ), Tb ( 3 ), Dy ( 4 ), Ho ( 5 ), Er ( 6 ), Tm ( 7 ), Yb ( 8 ), Lu ( 9 ), and Y ( 10 ), ben − is benzoate, MC is metallacrown, and shi 3− is salicylhydroximate, two independent molecules are present in each unit cell. The aluminum(III) ions and shi 3− ligands comprise the MC framework, while the Ln III and Na + ions bind opposite of each other across the central MC cavity. The benzoate anions serve to tether the Ln III ion to the MC framework. When benzoate is replaced with the dicarboxylate anion isophthalate (iph 2− ), two [12-MC Al(III)N(shi) -4] units are connected to form a dimer of MCs: {LnNa[12-MC Al(III)N(shi) -4]} 2 (iph) 4 , where Ln III = Eu ( 11 ), Gd ( 12 ), Tb ( 13 ), Dy ( 14 ), Ho ( 15 ), Ho ( 16 ), Er ( 17 ), Yb ( 18 ), and Lu ( 19 ). As in 1 – 10 , the aluminum(III) ions and shi 3− ligands produce the MC frameworks, and one Ln III ion binds to each central MC cavity. However, there are two binding modes for the sodium ions. For 12 – 15 and 18 , the sodium ions bind to the central MC cavity opposite of the Ln III ions as in 1 – 10 . For 11 , 16 , 17 , and 19 , the sodium ions bind to the side of the MC framework by bonding to the phenolate and carboxylate oxygen atoms of two shi 3− ligands and to the carboxylate oxygen atom of an iph 2− ligand. In these structures, the MC cavity is vacant opposite of the Ln III ions. The substitution of isophthalate for benzoate does not significantly alter the [12-MC Al(III)N(shi) -4] framework as the size of the central MC cavity is not significantly different between analogous lanthanide individual and dimer MCs. However, the identity of the central Ln III ion does determine how close the Ln III ion can approach the mean plane of the oxime oxygen atoms (O ox MP) of the MC cavity. As the ion radius of the central Ln III ion decreases, the Ln III ion is able to more closely approach the O ox MP. For the individual MCs 1 – 10 , the Eu III of 1 is the farthest away from the O ox MP (1.55 Å) and this value steadily decreases to 1.44 Å for the Lu III ion of 9 . This same trend is true for the dimer MCs as the Eu III ion of 11 is 1.45 Å from the O ox MP and the Lu III ion of 19 is 1.36 Å from the O ox MP. Though the location of the sodium ions in the dimer MCs does influen