CONFIGURATIONAL PREFERENCES OF 2 1,2-DIAMINE ADDUCTS OF ENYL)-4,4,4-TRIFLUORO-1,3-BUTANEDIONATO)COBALT(II)

The preparation, the IR and ligand field spectra and the structures of the mixed-ligand addition compounds [(N,N-dimethyl-1,2-diamino-ethane )bis( hienyl)-4,4,4-trifluoro-1,3-butanedionato)cobalt], [Co(thtf)(2)m e(2)en], and [(N,N,N',N'-tetramethyl-1,2-diamino-ethane)bis( l)-4,4,4- trifluoro-1,3-butanedionato)colbalt(II)], [Co(thtf)(2)me(4)en], are re ported. The structures were determined by single crystal X-ray diffrac tion analysis (monoclinic, space group P2(1)/c, Z=4 with a=10.708(6), b=19.531(6), c=13.352(6) Angstrom, beta = 111.64(10)degrees, R-1 = 0.0 642 and R-w(2) = 0.1719 for [Co(thtf)(2)(me(2)en)] and a = 12.033(6), b = 15.565(6), c = 15.339(6) Angstrom, beta = 92.57(6)degrees, R-1 = 0 .0612 and R-w(2)=0.1504 for [Co(thtf)(2)me(4)en]). The structures are distorted octahedral and the shortest cobalt-cobalt separation distanc es are 5.388(2) Angstrom in [Co(thtf)(2)me(2)en] and 8.675(3) Angstrom in [Co(thtf)(2)me(4)en]. In both compounds the diamine molecules atta in the gauche conformation. The U(Z,Z) conformation of the beta-dione leads to a semi-chair conformation of the beta-dionato chelate rings. The relative orientation of the groups attached to the beta-dionato mo iety depends on the extent of stereoelectronic effects the N-substitut ion of the diamine entails. In [Co(thtf)(2)me(2)en] the intraligand di stance separating the trifluoromethyl carbon atoms is 5.281(18) Angstr om while in [Co(thtf)(2)me(2)en] it increases to 8.338(9) Angstrom. Th e cobalt-cobalt separation distance, the orientation of the chelate ri ngs and the extent of N-substitution seem to affect hydrogen bonding. While in [Co(thtf)(2)me(2)en] inter- and intraligand hydrogen bonding is implicated, it is totally absent in [Co(thtf)(2)me(4)en].