Single- vs Double-Decker Copper 12-MC-4 Metallacrown Using the Coordination Flexibility of a Soft Donor Ligand

2-Methylmercaptobenzohydroxamic acid (mmbHA) has been synthesized and used to form {(CuCl2)-Cl-II(MeOH)[12-MCCu(II)N(mmbHA)-4]}(2) center dot 4MeOH (1) and {Cu-II(mu(2)-ClO4)(MeOH)(2)(py)(4)[12-MCCu(II)N(mmbHA)-4]}ClO4 (2), a copper(II) based double-decker and a discrete metallacrown (MC) system, respectively. While 1 forms in the absence of a coordinating co-ligand, the presence of pyridine (Py) leads to a change in the coordination mode of mmbHA and a discrete MC 2 is formed. Both compounds have been structurally and magnetically characterized. The magnetic susceptibility measured from 2-300 K shows overall antiferromagnetic exchange coupling within both crown structures and the obtained coupling constants are J(1)=-88.0(1) cm(-1)and J(2)=-64.7(3) cm(-1) for 1 and J(1)=-90.0(5) cm(-1) and J(2)=-31.1(1) cm(-1) for 2. However, the ratio of the coupling parameters is highly affected by the structural change.