SYNTHESIS AND CHARACTERIZATION OF MONONUCLEAR AND BINUCLEAR IRON(II) COMPLEXES OF PENTADENTATE AND BIS(PENTADENTATE) LIGANDS DERIVED FROM 1,4,7-TRIAZACYCLONONANE

Mononuclear iron(II) complexes of the pentadentate ligand 1,4-bis(2-py ridylmethyl)-1,4,7-triazacyclononane (dmptacn) of composition [Fe-II(d mptacn)Cl]PF6 (I) and [Fe-II(dmptacn)NCS]PF6 (II) have been prepared a nd characterised. II, C19N25N6F6FePS, crystallises in the monoclinic s pace group P2(1)/n (No. 14) with cell dimensions a = 13.856(6); b = 10 .980(4); c = 16.580(5) Angstrom; beta = 110.33(3)degrees; V = 2365(1) Angstrom(3) and Z = 4. The structure of II shows that the Fe atom is i n a distorted octahedral geometry defined by a N-6 donor set derived f rom dmptacn and an N-bound thiocyanate. Complex I is high spin while c omplex II is low spin. Replacement of a chloride by a thiocyanate liga nd induces sufficient change to the ligand field to cause a change in spin state. Analogous binuclear iron(LI) complexes of the bis(pentaden tate) ligand (2-pyridylmethyl)-1,4,7-triazacyclonon-1-yl)ethane (tmpdt ne) III and IV are also reported. III.2dmf crystallises in the monocli nic space group P2(1)/c (No. 14) with cell dimensions a = 11.745(2); b = 14.817(3); c = 15.725(3) Angstrom; beta = 95.35(2)degrees; V = 2724 .8(8) Angstrom(3) and Z = 2. The X-ray structure of III.2dmf shows tha t, in the centrosymmetric binuclear cation, each iron atom adopts a di storted octahedral geometry defined by an N-5 compartment of tmpdtne a nd a chloro ligand. The longest Fe-N distance corresponds to the nitro gen atom which links the two macrocyclic compartments together. Mossba uer and magnetic moment data confirmed that both [Fe-2(tmpdtne)Cl-2] ( PF6)(2) (III) and [Fe-2(tmpdtne) (NCS)(2)] (ClO4)(2) (IV) were high sp in. (C) 1998 Elsevier Science S.A. All rights reserved.