The molecular core of 1 consists of an eight-membered Cu4P4 ring that is capped by a P t Bu3 (P5 and P6) on Cu1 and Cu3 (Figure ). Formally, 1 has 2-fold symmetry but does not crystalize with symmetry intact. Instead, 1 adopts a chair-like configuration (Figure ) in which the greatest deviations from a least-squares plane of best fit of the eight atoms in the Cu4P4 core is -1.0453 (0.0007) and 0.9814 (0.0007) Å, for P3 and P4 respectively. The greatest distance from a plane of best fit consisting of the four copper atoms is -1.2939 Eq. 1