The structure of 1 resembles Cu4(μ-PPh2)4(PHPh2)4 (2) described by Fenske . However, in compound 2, Cu1 and Cu3 adopt tetrahedral geometry resulting from the coordination of two Ph2PH molecules per copper. The increased steric bulk of the P t Bu3 versus that of Ph2PH provides a rationale for the observed three coordinate trigonal planar geometry as only one P t Bu3 can coordinate to copper. The closest Cu-Cu distance in 2 is 3.17 Å which is larger than the corresponding distance in 1. This may be a result of 2 having a closer to linear structure than 1 with no deviations greater than 0.2 Å from the best fit plane of the Cu4P4 ring. Compound 1 also resembles Cu4(μ-PPh2)4(dppm)2 (3) (dppm = bis(diphenylphosphino)methane) that has a Cu4P4 core but is not capped at Cu1 and Cu3 but is instead supported by two dppm bridges between Cu1-Cu2 and Cu3-Cu4. Sulfide cluster (CuStBu)4(Ph3P)2 (4) is also related, consisting of a Cu4S4 core that is capped by PPh3 on Cu1 and Cu3. Similar to 1, both 3 and 4 adopt a chair-like conformation with maximum deviations of 1.52 and 1.55 Å respectively, from a plane of best fit consisting of the four copper atoms.