Electrochemical and Magnetic Exchange Interactions in Trinuclear Chain Complexes Containing Oxo-Mo(V) Fragments as a Function of the Topology of the Bridging Ligand

Abstract

The trinuclear complexes [{Mo(O)(Tp*)Cl}(μ-1, n -C 6 H 4 O 2 ){Mo(O)(Tp*)}(μ-1, n -C 6 H 4 O 2 ){Mo(O)(Tp*)Cl}] ( 1, n = 4; 2, n = 3) have been prepared [Tp* = tris(3,5-dimethylpyrazolyl)hydroborate], in which a chain of three paramagnetic oxo-Mo(V) fragments are linked by two 1,4-[OC 6 H 4 O] 2 - (for 1 ) or 1,3-[OC 6 H 4 O] 2 - (for 2 ) bridging ligands. The crystal structure of 1· (CH 2 Cl 2 ) 3.5 ·(C 6 H 14 ) 0.5 was determined: C 63.5 H 88 B 3 Cl 9 Mo 3 N 18 O 7; triclinic, P 1̄; a = 12.052(2) Å, b = 18.487(4) Å, c = 21.039(5) Å; α = 68.95(2)°, β = 86.12(2)°, γ = 78.637(13)°; V = 4289(2) Å 3; Z = 2. It shows a V-shaped Mo−L−Mo−L−Mo array of three {(Tp*)Mo(O)} fragments with two 1,4-[OC 6 H 4 O] 2 - bridging ligands. The V-shape arises from the cis arrangement of the two bridging ligands at the central metal atom. Electrochemical measurements show the expected Mo(IV)/Mo(V) and Mo(V)/Mo(VI) couples at potentials consistent with significant electrochemical interactions between the terminal and central metal fragments but not between the two terminal metal fragments. Variable-temperature magnetic susceptibility measurements (1.17−225 K) show the occurrence of intramolecular antiferromagnetic ( 1 ) and ferromagnetic ( 2 ) exchange interactions between adjacent metal atoms with J = −44.0 ( 1 ) and +4.5 cm - 1 ( 2 ) [based on H = − J ( S 1 S 2 + S 1 S 3 )] leading to S = 1 / 2 ( 1 ) and 3 / 2 ( 2 ) ground states. These results are in accord with the spin-polarization principle, which predicts that [1,4-C 6 H 4 O 2 ] 2 - should be an antiferromagnetic linker whereas [1,3-C 6 H 4 O 2 ] 2 - should be a ferromagnetic linker.