Trinuclear coordination assemblies of low-spin dicyano manganese(II) (S = 1/2) and iron(II) (S = 0) phthalocyanines with manganese(II) acetylacetonate, tris(cyclopentadienyl)gadolinium(III) and neodymium(III)

Abstract

The reaction of Mn^IIPc, Fe^IIPc or Fe^IIPcCl₁₆ with KCN in the presence of cryptand[2.2.2] yielded dicyano-complexes {cryptand(K⁺)}₂{M^II(CN)₂(macrocycle^2-)}^2-·XC₆H₄Cl₂ (M = Mn and Fe, X = 1 and 2) that were used for the preparation of trinuclear assemblies of the general formula {cryptand(K⁺)}₂{M^II(CN)₂Pc·(ML)₂}^2-·nC₆H₄Cl₂ (M^II = Mn^II and Fe^II; n = 1, 4 and 5). These assemblies were formed via coordination of two manganese(II) acetylacetonate (ML = Mn^II(acac)₂, S = 5/2), tris(cyclopentadienyl)gadolinium (ML = Cp₃Gd^III, S = 7/2) or tris(cyclopentadienyl)neodymium (ML = Cp₃Nd^III, S = 3/2) units to the nitrogen atoms of bidentate cyano ligands. The N(CN)-Mn{Mn^II(acac)₂} bond is 2.129(3) Å long but the bonds are elongated to 2.43-2.49 Å for tris(cyclopentadienyl)lanthanides. {Cryptand(K⁺)}₂{Mn^II(CN)₂Pc·(Mn^II(acac)₂)₂}^2-·5C₆H₄Cl₂ (2) contains three Mn(II) ions in different spin states (S = 5/2 and 1/2). Strong antiferromagnetic coupling of spins observed between them with the exchange interaction (J) of -17.6 cm^-1 enables the formation of a high S = 9/2 spin state for {Mn^II(CN)₂Pc·(Mn^II(acac)₂)₂}^2- dianions at 2 K. The estimated exchange interaction between Mn^II (S = 1/2) and Gd^III (S = 7/2) spins in {Mn^II(CN)₂Pc·(Cp₃Gd^III)₂}^2- is only -1.1 cm^-1, and in contrast to 2, nearly independent Gd^III and Mn^II centers are formed. As a result, no transition to the high-spin state is observed in {Mn^II(CN)₂Pc·(Cp₃Gd^III)₂}^2-. The {Mn^II(CN)₂Pc·(Cp₃Nd^III)₂}^2- and{Fe^II(CN)₂Pc·(Cp₃Nd^III)₂}^2- dianions with Cp₃Nd^III show a decrease of χ_MT values in the whole studied temperature range (300-1.9 K). A similar behaviour was found previously for pristine Cp₃Nd^III and Cp₃Nd^III·L complexes (L = alkylisocyanide ligand).