Copper(I) complexes of the tridentate thioether ligands [PhB(CH2SCH3)(3)] (abbreviated PhTt), [PhB(CH2SPh)(3)] (phTt(Ph)), [PhB((CHSBu)-S-2-Bu-t)(3)] (PhTtBu), and [PhB(CH(2)S(p)Tol)(3)] (PhTt(pTol)) and bidentate thioether ligands [Ph2B(CH2SCH3)(2)] (Ph(2)Bt), [Et2B(CH2SCH3)(2)] (Et(2)Bt), and [Ph2B(CH2SPh)(2)] (Ph(2)Bt(Ph)) have been prepared and characterized. The solution and solid state structures are highly sensitive to the identity of the borato ligand employed. Ligands possessing the smaller (methylthio)methyl donors, [PhTt] and [Ph(2)Bt], yielded tetrameric species, [(PhTt)Cu](4) and [(Ph(2)Bt)Cu](4), containing both terminal and bridging thioether ligation. The ligands containing the larger (arylthio)methyl groups, [PhTt(Ph)] and [PhTt(pTol)], form monomeric [PhTt(Ar)]Cu(NCCH3) in solution and one-dimensional extended structures in the solid state. Each complex type reacted cleanly with acetonitrile, pyridine, or triphenylphosphine generating the corresponding four-coordinate monomer, of which [PhTt(Ph)]Cu(PPh3), [PhTt(pTol)]Cu(PPh3), and [Et(2)Bt]Cu(PPh3)(2) have been structurally characterized.