Heterometallic supramolecular architectures constructed from cyanido-based [CoIII(AA)(CN)4]- building-blocks (AA = 1,10-phenantroline and 2,2’-bipyridine)

Abstract

A neutral, mixed-valence cyanido-bridged {Co2IICo2III} complex, with formula {[CoII2(L)(MeOH)2][CoIII(phen)(CN)4]2}·2H2O·0.5MeOH (1), and a cyanido-based ionic compound, with formula [MnII(MAC)(H2O)2][CoIII(bipy)(CN)4]2·3H2O (2) were obtained by reacting the heteroleptic Ph4P[CoIII(AA)(CN)4] building-block [AA = 1,10-phenanthroline, phen, (1) and 2,2’-bipyridine, bipy, (2)] with the dinuclear {Co2IIL}2+ (1) and mononuclear {MnII(MAC)}2+ (2) precursors, respectively [H2L = macrocyclic Schiff-base obtained by condensation of 2,6-diformyl-p-cresol with 1,3-diaminopropane and MAC = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-(18),2,12,14,16-pentaene]. The structures of 1 and 2 were determined by X-ray diffraction on single crystals. 1 is a neutral tetranuclear homometallic compound where two peripheral [CoIII(phen)(CN)4]- entities which act as end-cap ligands through one of its four cyanide groups towards the inner double phenoxido-bridged [Co2II(L)(MeOH)2]2+ dinuclear unit. Both cobalt(III) and cobalt(II) ions are six-coordinate with two phenanthroline-nitrogen and four cyanide-carbon atoms (at CoIII) and two phenoxido-oxygens and two imino-nitrogen atoms from the Schiff-base ligand plus a methanol molecule and a cyanide-nitrogen atom (at CoII) building somewhat distorted octahedral surroundings. The value of the cobalt(II)×××cobalt(II) separation is 3.11 Å and that of the angle at the phenoxo bridge is 99.4°. Compound 2 is a heterobimetallic ionic salt which is made up of [CoIII(bipy)(CN)4]- anions and [Mn(MAC)(H2O)2]2+ cations. Each cobalt(II) in 1 is six-coordinated, in a distorted octahedral environment built by a bidentate bipy ligand and four monodentate cyanide groups whereas the manganese(II) ion is seven-coordinated with five nitrogen atoms of the MAC ligand and two water molecules describing a distorted pentagonal bipyramid surrounding. The cryomagnetic investigation of 1 in the temperature range 1.9-300 K reveals the occurrence of strong spin-orbit coupling effects and a relatively weak antiferromagnetic interaction between the high-spin cobalt(II) ions linked by the double phenoxido bridge . The nature and magnitude of the magnetic coupling in 1 compares well with those from previous magneto-structural studies on the CoII2O2 motifs where antiferromagnetic interactions result in the examples having values at the phenoxido angle larger than 99.7º with dihedral angles smaller than 35.3°.