Synthesis and structure of cyclic hexanuclear oxo-alkoxo–carboxylatoniobium(IV) complexes

The synthesis and crystal structure of novel oxo-alkoxo–carboxylato Nb(IV) complexes, Nb6(μ2-O)3(μ2-O2CCX3)6(μ2-OC2H5)6(OC2H5)6 (X=Cl, F) are described. The single-crystal X-ray structure determination carried out, revealed a closed ring of six Nb(IV) ions linked alternately by two carboxylato groups and an oxo group, and two ethoxo groups. The hexanuclear molecule can essentially be described as a trimer of Nb2(μ2-OC2H5)2(OC2H5)2, each linked by an μ2-oxo group and two μ2-carboxylato groups. The ethoxo-bridged Nb–Nb distances are 2.735(5) Å, which is consistent with a single metal–metal bond, while the oxo- and carboxylato-bridged non-bonding Nb–Nb distances are 3.635(2) Å.