From a series of 2,9-dialkyl-1,10-phenanthrolines 1, complexes of several structures were made with copper(I) chloride. These were examined in detail by H-1 NMR and X-ray crystallography. Those with stoichiometry of two phenanthrolines per copper atom have the well-known structure 2 containing a cation with distorted tetrahedral geometry about the copper atom of the general form [(2,9-dialkyl-1,10-phenanthroline)(2)Cu]Cl-+(-). The alkyl groups of compounds 2 show a marked upfield change in the chemical shift with respect to the Ligands themselves. This is ascribed to an aromatic ring current effect The complexes with 1:1 stoichiometry can have either of two isomeric structures 3 and 4, depending upon the bulk of the alkyl groups in the 2- and 9-positions of the phenanthroline system, how they are prepared, and whether they are in solution or solid phase. Isomer 3, favored with bulky alkyl groups, has the copper atom in a distorted trigonal geometry with coordinated chlorine and does not exhibit the ring-current effect seen in 2. The structures of two of these compounds were determined by X-ray crystallography. Crystals of 3f, 2,9-di-tert-butyl-1,10-phenanthroline CuCl, were tetragonal with space group P4(2)/n and a = 19.700(3) Angstrom, c = 9.680(2) Angstrom, V = 3757(2) Angstrom(3), and Z = 8. This structure shows substantial distortion from trigonal planar geometry, due to the steric bulk of the tert-butyl groups. Crystals of 3g (2,9-dineopentyl-1,10-phenanthroline . CuCl) were monoclinic with space group P2(1)/c and a = 9.545(2) Angstrom, b = 18.407(3) Angstrom, c = 12.734(2) Angstrom, beta = 107.75(2)degrees V = 2130.8(11) Angstrom(3), and Z = 4. Compounds 4 were found to have NMR identical with 2, but are isomeric with 3, having the structure [(2,9-dialkyl-1,10-phenanthroline)(2)Cu](CuCl2-)-Cu-+. The structure of 4g ([(2,9-n-pentyl-1,10-phenanthroline)(2)Cu](CuCl2-)-Cu-+] was determined by X-ray crystallography. Crystals of 4g were triclinic, space group P ($) over bar 1 with a = 13.861(3) Angstrom, b = 14.108(3) Angstrom, alpha = 65.35(2)degrees, beta = 107.75 (2)degrees, gamma = 90.05(2)degrees, V = 2155.2(8) Angstrom(3), and Z = 2. This structure clearly shows the positions of the alkyl groups of each ligand directly above the face of the aromatic system of the other in a distorted tetrahedral geometry about copper.