A Triple‐Decker Heptadecanuclear (CuII)15(CrIII)2 Complex Assembled from Pentanuclear Metallacrowns

Abstract

AbstractReaction of the pentanuclear CuII metallacrown [Cu5(ahpha)4](ClO4)·4H2O (ahpha2– is the dianion of 3‐amino‐3‐(hydroximino)propanehydroxamic acid), with Cr(C2O4)33– led to the formation of a heptadecanuclear complex {[Cu5(ahpha)4]3[Cr(C2O4)3]2·4H2O}·8H2O·1/3(DMF) (1·8H2O·1/3(DMF)). This compound contains three stacked Cu5(ahpha)42+ building blocks, linked by axial bonds between Cu2+ ions of one Cu5 metallacrown and hydroxamate oxygen atoms of the neighboring Cu5 unit. Two Cr(C2O4)33– anions are bonded to the two lateral Cu5(ahpha)42+ cations through axial Cu–O(oxalate) bonds. The formation of 1 may be considered the first example of metallacrown trimerization caused by anion metathesis. The compound contains 10 × 13 Å voids (about 25 % of crystal volume), filled with solvate water molecules. The magnetic properties (χMT vs. T) could be fitted as the superposition of the magnetism of 3χMT(CuII5) and 2χMT(CrIII). Exchange interactions within the CuII5 units were fit in the framework of a model based on the Hamiltonian H(CuII5) = –2J1(S1.S5 + S2.S5 + S3.S5 + S4.S5) –2J2(S1.S2 + S2.S3 + S3.S4 + S4.S1), where S5 represents the central Cu2+ ions' spins and the other spin operators correspond to the peripheral Cu2+ ions. With other possible interactions taken into account using a molecular field approach, the best fit correspondedto J1 = –153(5) cm–1, J2 = –71(2) cm–1 and zJ′ = –0.058(4) cm–1.