Coordination of 5-Methyl-3,7-diazanonane-1,5,9-triamine (L) to Rhodium(III). Crystal Structure of fac-[Rh(H₂L)Cl₃] Cl(ClO₄).3H₂O

Abstract

The branched, potentially quinquedentate , 5-methyl-3,7-diazanonane-1,5,9-triamine (1) reacts in hot water with rhodium(III) chloride to yield fac -[ Rh (H₂(1))Cl₃]²⁺. Only upon extended reflux for several weeks is coordination as a quinquedentate achieved. The fac complex was crystallized readily as a mixed chloride perchlorate trihydrate salt, in the triclinic space group Pī , a 8.666(2), b 10.319(2), c 12.558(3) Ǻ, α 94.34(2), β 98.86(2), γ 97.75(2)°, Z = 2; a single-crystal X-ray structure determination was refined to R_w 0.037 for 3703 'observed' reflections. The central primary amine and two adjacent secondary amines occupy an octahedral face, with the chloro ligands then necessarily fac also. The Rh -N distances vary, with the shortest distance to the primary amine [2.023(2)Ǻ] rather than to the secondary amines [2.066(2), 2.077(2) Ǻ], as do the Rh-Cl distances [range 2.345(1)-2.369(1)Ǻ]. The two primary amines on the chain terminals remain uncoordinated, the central facially capping unit preferring coordination first, possibly indicating a general intermediate for coordination of polydentate l igands containing this type of unit.