While the [M 4 (m 3 -X) 4 ] 4 (M transition ion, X anion or dianion) cubane structure is a common motif in transition metal chemistry and biochemistry, only a few examples of vertex-sharing double-cubane compounds are known. [1±8] We note in particular 1 (bipym 2,2'-bipyrimidine), which is the only compound with this topology whose magnetochemical properties have been fully elucidated to date. [5] We report here a new example of a heptacopper double-cubane complex, 2, whose molecular structure and magnetochemistry differ substantially from those of 1. Moreover, the unusual structure of 2 is supported by a unique pattern of supramolecular cation:anion interactions.
[{Cu 3 (bipym)
Turquoise crystals of 2 ¥ 2 CH 2 Cl 2 were grown from CH 2 Cl 2 / pentane mixtures. [9] The asymmetric unit of these crystals contains half a complex molecule with Cu(1) lying on a crystallographic inversion center, forming a [{Cu 3 (Hpz tBu ) 6 (m 3 -Cl)(m 3 -OH) 3 } 2 Cu] 6 double-cubane (Figure 1). The sharedvertex Cu(1) is ligated by six OH À ligands, with an axis of Jahn ± Teller elongation along the O(7)-Cu(1)-O(7') vector. The other Cu ions exhibit tetragonal geometries, with two OH À and two Hpz tBu ligands in the basal plane and axial contacts to two Cl À ions. Cu(3) and Cu(4) adopt almost identical geometries, with contacts of 2.7949(5) ± 2.9129(6) ä to Cl(62) and one other Cl À ligand. However, Cu(2) has a shorter distance of 2.5502(5) ä to Cl(62), and a much longer distance of 3.7433(6) ä to Cl(63) (not shown in Figure 1).
In addition to Cl(62) and its symmetry-generated equivalent, there are six Cl À ions disposed in a ring around the heptacopper core of the molecule (Figure 2). Each of these Cl À ions accepts three hydrogen bonds, from one OH À and two Hpz tBu NÀH donors. Cl(64) and Cl(65) are in near-
[*] Dr.