SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF LANTHANIDE(III) TEXAPHYRINS

The synthesis and characterizations of several lanthanide(III) texaphyrin complexes of 4,5,9,24-tetraethyl-16,17-dimethoxy-10,23-dimethyl-13,20,25,26,27-pentaazapentacyclo[20.2.1.1(3,6).1(8,11).0(14,19)]heptacosa-1,3,5,7,9,11(27),-12,14,16,18,20,22(25),23-tridecaene (2), 4,5,9,24-tetraethyl-16,17-bis((3-hydroxypropyl)oxy)-10,23-dimethyl-13,20,25,26,27-pentaazapentacyclo-[20.2.1.1(3,6).1(8,11).0(14,19)]heptacosa-1,3,5,7,9,11(27),12,14(19),15,17,20,22(25),-23-tridecaene (21), and 4,5-diethyl-10,23-dimethyl-9,24-bis(3-hydroxypropyl)-16,17-(3-hydroxypropyloxy)-13,-20,25,26,27-pentaazapentacyclo[20.2.1.1(3,6).1(8,11).0(14,19)]heptacosa-1,3,5,7,9,11(27),12,14,16,18,20,22(25),23-tri-decaene (30), respectively, are reported. Single crystals suitable for X-ray diffraction were obtained for the La(III) complex 3, the Gd(III) complexes 9 and 37, the Eu(III) complex 36, and the Lu(III) complex 22, by dissolving the respective complex in MeOH/CHCl3 and layering with diethyl ether. The five lanthanide(III) texaphyrin complexes all crystallize in the triclinic space group, P1BAR (No. 2), with Z = 2. The final R's, for data collected at reduced temperatures (less-than-or-equal-to 90-degrees-C), were 0.0412 for 3, 0.0373 for 9, 0.0293 for 22, 0.0320 for 36, and 0.0477 for 37. The complexes are characterized by five-coordination from the texaphyrin, a coordinated methanol molecule on one side and at least one symmetrically bidentate NO3- ion opposite the methanol. The 10-coordinate La(III) complex 3 has two bidentate NO3- ions on the same side of the macrocycle. The europium(III) and gadolinium(III) texaphyrins 36 and 37 are structurally isomorphous and are 9-coordinate species with a bidentate NO3- ion and a methanol molecule on the top side of the macrocycle. On the other hand, the lutetium(III) texaphyrin is 8-coordinate with only a single bidentate NO3-ion chelated to the ''top' side of complex. In an unusual case of disorder, the gadolinium-(III) texaphyrin 9 has both 9- and 1 0-coordinate species present in the solid state. The geometry of the 9-coordinate species is much like that found in 36 and 37, while the 10-coordinate Gd(III) species is similar to the La(III) species 3. Together, these structures reflect both the decrease in coordination number and the intrinsic contraction in cation size observed as the lanthanide series is transversed. For instance, an average decrease in nitrogen-to-metal bond length of 0. 1 2 angstrom is found when comparing the 10-coordinate La(III) complex 3 to the 9-coordinate gadolinium(III) texaphyrin species 37 and a decrease of 0.075 angstrom is observed when comparing this latter Gd(III) complex to the 8-coordinate Lu(III) system 22. Similarly, the 10-coordinate La(III) center in 3 is found to be 0.91 angstrom from the mean plane through the rive nitrogen donors of the macrocycle while the 8-coordinate Lu(III) center in 22 is only 0.27 angstrom from the plane. Finally, the root-mean-square deviation from planarity for the atoms of the macrocycle core is 0.15 angstrom in 3 and only 0.072 angstrom in 22, as compared to 0.097, 0.122, and 0.120 angstrom in 9, 36, and 37, respectively.