Photoswitchable Cu II4MoIV and Cu II2MoIV cyanido-bridged molecules

Abstract

The self-assembly of copper(II) complexes with two Schiff base ligands: L1_O = N₃ and L2 = N₄ and octacyanidomolybdate(IV) ions yields two discrete molecules of odd nuclearity, namely pentametallic [Cu(L1_O)(py)]₄[Mo^IV(CN)₈]·14H₂O (1), Cu₄Mo and trimetallic [Cu(L2)]₂[Mo^IV(CN)₈]·9H₂O (2), Cu₂Mo. Both molecular systems have been characterised structurally and magnetically, revealing a photomagnetic effect. In the case of (1) a metal-to-metal charge transfer (MMCT) mechanism is proposed. The analysis of magnetic interactions in the photogenerated state of (1) assumes the formation of the metastable cluster Cu^II₃Cu^IMo^V where metal centres in Mo^V–CN–Cu^II linkages are ferromagnetically coupled with J₂ = 104(3) cm⁻¹. In (2) the increase in the magnetisation is due to the singlet–triplet transition on the Mo^IV centre leading to the formation of the metastable Cu^II₂Mo^IV_HS. The presence of the paramagnetic Mo^IV_HS (S = 1) centre linking the Cu^II (S = 1/2) centres allows for effective ferromagnetic interaction of 3 paramagnetic centres with coupling constant J₂ = 20.2(7) cm⁻¹.