Coordination chemistry of rhenium(V), -(IV), and -(III) with the macrocyclic ligands 1,4,7-triazacyclononane (L) and its N-methylated derivative (L'). Crystal structures of [LReCl3]Cl, [L2Re2Cl2(.mu.-Cl)(.mu.-OH)]I2.cntdot.2H2O, [L2Re2I2(.mu.-O)2]I2.cntdot.2H2O, and [L'2Re2Cl4(.mu.-O)]ZnCl4. Effect of .pi.-donors on the Re-Re bond distance