Syntheses, structures and magnetic properties of the tricyanoethenolate adducts of quadridentate Schiff base manganese (III) complexes

Manganese (III) complexes [Mn(L¹)(NCO)] and [Mn(L²)(NCO)] (H₂L¹ = N,N¹-ethylenebis(3-hydroxy-4-naphthylideneiminate), H₂L² = N,N ¹-(1,1,2,2-tetramethylethylene)bis(3-hydroxy-4-naphthylideneiminate)) react with tetracyanoethylene in a mixed solution of dichloromethane and acetonitrile to give the tricyanoethenolate adducts [Mn(L¹)(TCEA)(H₂O)] (1) and [Mn(L²)(TCEA)] (2) (TCEA = tricyanoethenolate, [(NC)₂C=C(CN)O^-]), respectively. Compound 1 crystallizes in the triclinic space group P1̄ with a = 10.612(5), b= 13.369(5), c = 9.981(6) Å, α = 108.89(4), β =110.70(4), γ = 77.22(4)°. The Mn(III) assumes an elongated square bipyramidal geometry, in which two apical sites are occupied by an oxygen atom of a water molecule with Mn-O(3) = 2.305(4) Å and by a nitrogen atom of TCEA with Mn-N(3) = 2.390(4) Å. The water oxygen is hydrogen bonded to a nitrogen atom of TCEA of the adjacent molecular unit with O(3)-N(3)* = 3.081(6) Å forming a one-dimensional chain structure of head-to-tail fashion. Compound 2 crystallizes in the monoclinic space group P2₁/c with a = 14.107(6), b = 12.750(6), c = 16.481(5) Å, β = 103.64(3)°. Compound 2 has a binuclear structure of out-of-plane fashion, where the dimensions of the Mn₂O₂ core are Mn-Mn* = 3.475(2) Å and Mn-O(1)* = 2.627(3) Å. The Mn(III) assumes a distorted square bipyramidal geometry, in which two apical sites are occupied by the phenoxy oxygen atom of L² and an oxygen atom of the TCEA anion with 2.163(3) Å. The magnetic susceptibility measurements in the range 4.4-300 K showed that a weak intermolecular antiferromagnetic interaction or/and zero field splitting is operating for 1, while a intradimer ferromagnetic interaction is operating for 2.