Recrystallization of [Cu,l,( PPh,),] from toluene has yielded a new polymorph of that compound, (1 ), which has been shown by single-crystal X-ray diffraction analysis to have a tetrametallic 'cubane' structure rather than the expected 'step' structure. Crystals are monoclinic, space group P2,/n, with a = 19.47(1 ), b = 26.94(1),c = 13.528(5)A , p = 98.98(4)"Z, = 4 tetramers; R was 0.06 for No = 3 681. Cu-l distances range from 2.653(3) to 2.732(3) A, with Cu Cu 2.874(5)-3.164(4) and I I 4 . 2 3 4 ( 2 ) 4 . 4 9 6 ( 3 )A . Alladducts of stoicheiometry [ M,X,( PPh,),] (M = Cu or Ag; X = CI, Br, or I) have now been synthesized and structurally characterized in a cubane configuration. Recrystallization of copper( I) chloride and bromide from triethylamine also yields tetrameric cubane 1 : 1 adducts [X = CI (2) or Br (3)], as does the reaction of copper(1) chloride with the very bulky ligand 2-[bis(trimethylsilyl)methyl] pyridine, to give [Cu,Cl,(tmspy),] (4). These three complexes have also been crystallographically characterized, (2) and (4) being the first reported cubane type tetramers for the copper(i) chloride-nitrogen base system. Complexes (2) and (3) are isostructural with their triethylarsine and -phosphine counterparts, being cubic, space group lif3m, with a = 12.1 62(5) A in (2) and 12.368(3) A in (3); Z = 2 tetramers. Cu-CI,Br distances are 2.441 (4) and 2.537(3) A respectively. For (4), the crystals are tetragonal, space group 14,/a, with a = 18.620(4), c = 20.079(5) A, Z = 4 tetramers. Although the Cu,CI, cubane core of the molecule has crystallographically imposed 4 symmetry, the geometry is very unsymmetrical as a consequence of the ligand bulk, with Cu-CI 2.225(2)-2.636(2), Cu 9 . - Cu 2.960(2)-3.194(2), and CI ..* CI 3.838(3)-3.866(3) A. Residuals R for ( 2 ) r (3), (4) were 0.040,0.038, and 0.040 respectively for No = 136,136, and 1 008 'observed' reflections. The solid-state ,'P n.m.r. spectra of the triphenylphosphine cubane clusters show significant differences to those with a 'step' geometry; these differences are related to the crystallographic environment of the phosphorus nuclei.