SYNTHESIS AND STRUCTURE OF METALLOMACROCYCLES BASED ON ISOTHIOSEMICARBAZIDES

New isothiosemicarbazide-based heteronucleating ligands have been synthesised by Ba2+-templated (1:1) macrocyclisation of the poly-etherdialdehydes,3,3'-(3,6-dioxaoctane-1,8-diyldioxy)bis (2-hydroxybenzaldehyde) and 3,3'-(3,6,9-trioxaundecane-1,11-diyldioxy)bis(2-hydroxybenzaldehyde), by using S-methylisothiosemicarbazide as the diamine building block. Thus, the linear polyether dialdehydes (2-hydroxybenzaldehyde-3-yl)-O-(CH2CH2O)(n)-(3-yl-2-hydroxybenzaldehyde), with n=3 and 4, react with S-methylisothiosemicarbazide in the presence of Ba(CF3SO3)(2) and Ni(CH3COO)(2) . 4H(2)O to give two nickel/barium complexes 5 and 6, the crystal structures of which are described. 5: triclinic, <P(1)over bar>, a=9.886(3), b=12.376(4), c=13.845(6) Angstrom, alpha=73.97(3), beta=88.58(3), gamma=83.26(3)degrees, Z=1; 6: triclinic, <P(1)over bar>, a=10.767(2), b=13.221(2), c=15.986(2) Angstrom, alpha=102.57(1), beta=101.13(1), gamma=109.91 (1)degrees, Z=2. Treatment of these complexes with an aqueous solution of guanidinium sulfate yields the respective Ba free metallomacrocycles. The crystal structure of one of these (3 . H2O) has been determined. 3 . H2O: triclinic, <P(1)over bar>, a=8.106(3), b=11.836(4), c=13.174(4) Angstrom, alpha=88.22(3), beta=76.64(3), gamma=70.30(3)degrees, Z=2. Its geometry is compared with its parent compound 5. It reveals that coordination of the Ba2+ cation (0.6 Angstrom above the mean plane of the O atoms) has little influence on the conformation of the macrocycle. The polyether ring in the two Ba complexes differs in size yet the Ba ... Ni distances are remarkably similar (3.664(5) versus 3.723(3) Angstrom) suggesting that the two metal atoms although not bonding may be touching.