228 Maichle et aI. Transition Met. Chem., 20, 228 233 (1995) Spectral studies of cobalt(III) complexes of heterocyclic 3-azacyclo- thiosemicarbazones and the structure of the acetylpyrazine 3- azabicyclo [-3.2.2]nonylthiosemicarbazone complex Cecilia Maiehle Institute of lnorfanic Chemistry, University of Tubingen, Germany Alfonso Castineiras and Rosa Carballo Departamento de Quimica lnorganica, Universidad de Santiago de Compostela, E-15706 Santiago de Compostela, Spain Haileselassie Gebremedhin, Mark A. Lockwood, Christopher E. Ooms, Timothy J. Romaek and Douglas X. West* Department of Chemistry, Illinois State University, Normal, IL 61761, USA Summary Cobalt(III) complexes of 2-acetylpyridine 3-pyrrolidinyl-, 3-piperidinyl-, 3-hexamethylcneiminyl- and 3-azabicyclo- [3.2.2]nonylthiosemicarbazone, [Co(Lpo)2]BF4, [Co- (Lpip)z]BF,~, [Co(Lhexim)2]BF 4 and [Co(Lbcn)2]BF4, respectively; 2-formylpyridine 3-piperidinyl-, 3-hexa- methyleneiminyl- and 3-azabicyclo[3.2.2]nonylthiosemi- carbazone, [Co(pip)2]BF4, [Co(hexim)2]BF 4 and I-Co(bcn)2]BF 4, respectively; and aceylpyrazine 3-aza- bicyclo[3.2.2]nonylthiosemicarbazone, [Co(Pzbcn)2]BF4, have been synthesized and their spectral properties measured. The 1H- and 13C-n.m.r. spectra show the uncomplexed thiosemicarbazones to be mixtures of as many as three isomers, and that the two ligands in the cobalt(III) complexes are nearly identical. The crystal structure of [Co(Pzbcn)z]BF 4 shows the two ligands coordinated in a mer-configuration. Bond lengths and angles in this complex are compared with data previously reported for thiosemicarbazone complexes. Introduction Although there have been numerous studies involving the isolation of thiosemicarbazone complexes and their spectral and magnetic characterization (L2), comparatively few crystal structures of these complexes have been determined, particularly those with two thiosemicarbazone ligands per coordination sphere. Results of studies on bis(thio- semicarbazone)-chromium(III) complexes show that the thione [~IN--2NH--C(=S)4NH2] and thiol [~N--N~---C(--S-)NH2] forms of pyruvic acid thio- semicarbazone are coordinated as tridentate ligands in a meridional (mer) conformationt3); for the metal-ligand bonds and the bonds within the thiosemicarbazone moiety there are differences in the bond lengths for these two different forms of the ligand, as would be expected, bis- (Salicylaldehyde thiosemicarbazonato)chromium(III) perchlorate has two equivalent tridentate ONS ligands arranged in a mer conformation t4). The same configuration has also been found for an iron(III) complex of equivalent 2-acetylpyridine 3-azabicyclo[3.2.2]nonylselenosemi- carbazonato ligands (i.e. loss of 2NH)(5). However, the structure of bis(isoquinoline-l-carboxaldehyde thioserni- carbazonato)nickel(II) monohydrate was reported to exhibit small differences in the bond lengths of the two coordinated ligands (6). Similarly, small differences were * Author to whom all correspondenceshould be directed. noted in the bond lengths for the two ligands in bis(acetyl- pyrazine 4N-dimethylthiosemicarbazone)nickel(II)(7). Crystal studies have also been reported for four- coordinate nickel(II) and copper(II) thiosemicarbazone complexes that involve thiosemicarbazones of this study (HLpo, HLpip, HLhexim, HLbcn, Hpip, Hhexim, Hbcn and H Pzbcn). The structui'es of planar [Ni(Lbcn)NCS] (s), [Cu(Lhexim)Br] w), [Ni(Lhexim)Br] (1~ and [Cu(Lpip)- Br] (1~ have recently been communicated. Also, this group has reported the structures and spectral properties of bis(2-acetylpyridine 4N-methylthiosemicarbazonato)- cobalt(III) tetrafluoroborate, [Co(L4M)a]BF4, and bis(2- formylpyridine 4N-methylthiosemicarbazonato)cobalt(III) tetrafluoroborate trihydrate, [Co(4M)2]BF 4. 3H2 O(I 1). A spectral study (~2) of a series of bis(2-acetylpyridine 4N- alkylthiosemicarbazonato)cobalt complexes prompted the latter work, as well as this present study of cobalt(III) complexes of heterocyclic 3-azacyclothiosemicarbazones. Figure 1 shows a structural formula of a heterocyclic 3-azacyclothiosemicarbazone and identifies the symbolism used throughout this study. Experimental Syntheses and materials The synthesis of the thiosemicarbazones, HLpo, HLpip, HLhexim, HLbcn, Hpip, Hhexim, Hbcn and HPzbcn was accomplished by adding solid 4N-phenyl-4N-methylthio- semicarbazide portion-wise to a warmed mixture of 2-formylpyridine, 2-acetylpyridine or acetylpyrazine and the appropriate cyclic amine and then gently refluxing for ca 2 h (13~. The solid sometimes separated on cooling and, after evaporating some of the solvent at 35 ~ the solids were filtered and washed with cold i-PrOH. All organic reagents were purchased from Aldrich Chemical Company. The cobalt(III) complexes were prepared by boiling under reflux an anhydrous EtOH 1:2 molar mixture of cobalt(II) tetrafluoroborate hydrate (Alfa) and one of the thiosemicarbazones for more than 2 h. The brown products (ca 80~o yield), which formed on refluxing, were filtered hot, washed with cold i-PrOH and dried on a warm plate (35 ~ The [Co(Pzbcn)2]BF 4 crystal was grown by slow evaporation of a dilute DMSO solution at 35 ~ Physical measurements The spectral and physical measurements of the solids and solutions were carried out as reported previcmsly(1'11). 0340-4285 9 1995 Chapman& Hall