Reaction of the tricopper(I)-dinitrogen tris(beta-diketiminate) cyclophane, Cu-3(N-2)L, with O-atom-transfer reagents or elemental Se affords the oxido-bridged tricopper complex Cu-3(mu(3)-O)L (2) or the corresponding Cu-3(mu(3)-Se)L (4), respectively. For 2 and 4, incorporation of the bridging chalcogen donor was supported by electrospray ionization mass spectrometry and K-edge X-ray absorption spectroscopy (XAS) data. Cu L-2,L-3-edge X-ray absorption data quantify 49.5% Cu 3d character in the lowest unoccupied molecular orbital of 2, with Cu 3d participation decreasing to 33.0% in 4 and 40.8% in the related sulfide cluster Cu-3(mu(3)-S)L (3). Multiedge XAS and UV/visible/near-IR spectra are employed to benchmark density functional theory calculations, which describe the copper-chalcogen interactions as highly covalent across the series of [Cu-3(mu-E)](3+) clusters. This result highlights that the metal-ligand covalency is not reserved for more formally oxidized metal centers (i.e., Cu m + O2- vs Cu-II + O-) but rather is a significant contributor even at more typical ligand-field cases (i.e., Cu-3(II/II/I) + E2-). This bonding is reminiscent of that observed in p-block elements rather than in early-transition-metal complexes.