Synthesis of the first heterometalic star-shaped oxido-bridged MnCu₃ complex and its conversion into trinuclear species modulated by pseudohalides (N₃⁻, NCS⁻ and NCO⁻): structural analyses and magnetic properties

Abstract

A tetra-nuclear, star-shaped hetero-metallic copper (II)–manganese (II) complex, [{CuL(H₂O)} ₂(CuL)Mn](ClO₄)₂ (1) has been synthesized by reacting the “complex as ligand” [CuL] with Mn(ClO₄)₂ where H₂L is the tetradentate di-Schiff base derived from 1,3-propanediamine and 2-hydroxyacetophenone. Upon treatment with the polyatomic anions azide, cyanate, or thiocyanate in methanol medium, complex 1 transforms into the corresponding trinuclear species [(CuL) ₂Mn(N₃)₂] (2), [(CuL) ₂Mn(NCO) ₂] (3) and [(CuL) ₂Mn(NCS) ₂] (4). All four complexes have been structurally and magnetically characterized. In complex 1 the central Mn (II) ion is encapsulated by three terminal [CuL] units through the formation of double phenoxido bridges between Mn (II) and each Cu (II). In complexes 2–4 one of the CuL units is replaced by a couple of terminal azide, N-bonded cyanate or N-bonded thiocyanate ions respectively and the central Mn (II) ion is connected to two terminal Cu (II) ions through a double asymmetric phenoxido bridge. Variable temperature magnetic susceptibility measurements show the presence of moderate ferrimagnetic exchange interactions in all the cases mediated through the double phenoxido bridges with J values (H = −JS_iS_{i + 1}) of −41.2, −39.8 and −12.6 cm⁻¹ (or −40.5 and −12.7 cm⁻¹ if we use a model with two different exchange coupling constants) for the tetranuclear MnCu₃ cluster in compound 1 and −20.0, −17.3 and −32.5 cm⁻¹ for the symmetric trinuclear MnCu₂ compounds 2–4. These ferrimagnetic interactions lead to spin ground states of 1 (5/2 − 3*1/2) for compound 1 and 3/2 (5/2 − 2*1/2) for compounds 2–4.