Synthesis and characterisation of mononuclear and binuclear iron(II) complexes of pentadentate and bis(pentadentate) ligands derived from 1,4,7-triazacyclononane

Abstract

Mononuclear iron(II) complexes of the pentadentate ligand 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane (dmptacn) of composition [Fe 11(dmptacn)Cl]PF 6 ( I) and [Fe 11(dmptacn)NCS]PF 6 ( II) been prepared and characterised, II, C 19N 25N 6F 6FePS, crystallises in the monoclinic space group P2 1/ n (No. 14) with cell dimensions a = 13.856(6); b = 10.980(4); c = 16.580(5) A ̊ ; β = 110.33(3)° ; V = 2365(1) A ̊ 3 and Z = 4 . The structure of II shows that the Fe atom is in a distorted octahedral geometry defined by a N 6 donor set derived from dmptacn and an N-bound thiocyanate. Complex I is high spin while complex II is low spin. Replacement of a chloride by a thiocyanate ligand induces sufficient change to the ligand field to cause a change in spin state. Analogous binuclear iron(II) complexes of the bis(pentadentate) ligand 1,2-bis( N, N′-bis(2-pyridylmethyl)-1,4,7-triazacyclonon-1-yl)ethane (tmpdtne) III and IV are also reported. III·2dmf crystallines in the monoclinic space group P2 1/ c (No. 14) with cell dimensions a = 11.745(2); b = 14.817(3); c = 15.725(3) A ̊ ; β = 95.35(2)°; V = 2724.8(8) A ̊ 3 and Z = 2 . The X-ray structure of III · 2dmf shows that, in the centrosymmetric binuclear cation, each iron atom adopts a distorted octahedral geometry defined by an N 3 compartment of tmpdtne and a chloro ligand. The longest FeN distance corresponds to the nitrogen atom which links the two macrocyclic compartments together. Mössbauer and magnetic moment data confirmed that both [Fe 3(tmpdtne)Cl 2](PF 6) 2( III) and [Fe 2(tmpdtne) (NCS) 2](ClO 4) 2 ( IV) were high spin.