NEW MONONUCLEAR AND DINUCLEAR TITANIUM(III) COMPLEXES - THE CRYSTAL-STRUCTURE OF AND EXCHANGE COUPLING IN [(LTI(III)(NCO)(2))(2)(MU-O)] (L=1,4,7-TRIMETHYL-1,4, 7-TRIAZACYCLONONANE)

Ti-III(CH3CN)(3)Cl-3 in acetonitrile solution reacts with the cyclic t riamine 1,4,7-triisopropyl- 1,4,7-triazacyclononane (tiptacn) with for mation of green [(tiptacn)(TiCl3)-Cl-III] (1). The chloro ligands in 1 are readily substituted by thiocyanate generating [(tiptacn)Ti(NCS)(3 )] (2). From a mixture of tetrahydrofuran, NaOCN, water, and methanol and 1 the complex [(tiptacn)Ti-III(NCO)2(OCH3)] (3) was obtained. In t he absence of methanol and by using 1,4,7-trimethyl-1,4,7-triazacyclon onane (Me(3)tacn) as macrocyclic triamine, the neutral (mu-oxo)dititan ium(III) complex [(Me(3)tacn)(2)Ti-2 (NCO)4(mu-O)] (4) formed. The cor responding thiocyanato analogue [(Me(3)tacn)(2)Ti-2(NCS)4(mu-O)1 (5) w as obtained from an acetonitrile/water mixture of [(Me(3)tacn)Ti(NCS)( 3)]. The crystal structure of 4 has been determined by X-ray crystallo graphy: space group Pbca, a = 12.532(4) Angstrom, b = 14.379(4) Angstr om, c = 16.366(5) Angstrom, V = 2949.1(20) Angstrom(3), Z = 4. The neu tral molecules in 4 contain a linear Ti-III-O-Ti-III moiety with a Ti- O bond distance of 1.838(1) Angstrom. From temperature dependent magne tic susceptibility measurements (2.0-296 K) it is concluded that the t wo unpaired electrons in 4 and 5 are weakly intramolecularly antiferro magnetically coupled (H = -2JS(1).S-2; S1 = S-2 = 1/2; 4, J = -7.8 cm( -1); 5, J = -5.6 cm(-1)). Electronic and X-band ESR-spectra, the elect rochemistry, and the magnetic properties of complexes 1-5 have been in vestigated in detail.