Schiff base tetranuclear Zn 2 Ln 2 single-molecule magnets bridged by hydroxamic acid in association with near-infrared luminescence.

A series of Zn-Ln heteronuclear SMMs constructed by using a hexadentate compartment Schiff base Zn-precursor and lanthanoid ions were structurally and magnetically characterized, in which the two [Zn-Ln] moieties are bridged by a series of hydroxamic acids, resulting in double-decker tetranuclear complexes with the molecular formulae [ZnL 1 Ln(C 2 H 5 O)(qua)] 2 (CF 3 SO 3 ) 2 ·2C 2 H 5 OH ((1) Ln = Dy; (7) Ln = Yb), [ZnL 1 Ln(CH 3 O)(bnz)] 2 (CF 3 SO 3 ) 2 ·2CH 3 OH ((2) Ln = Dy), [ZnL 1 Ln(CH 3 O)(aca)] 2 (CF 3 SO 3 ) 2 ·2CH 3 OH ((3) Ln = Dy; (8) Ln = Yb), [ZnL 2 Dy(CH 3 O)(bnz)] 2 (CF 3 SO 3 ) 2 ·2CH 3 OH (4), [ZnL 2 Dy(CH 3 O)(aca)] 2 (CF 3 SO 3 ) 2 ·2CH 3 OH (5), and [ZnL 3 Dy(CH 3 O)(bnz)] 2 (CF 3 SO 3 ) 2 ·2CH 3 OH (6) (HL 1 = N , N '-bis(2-hydroxy-3-methoxybenzylidene)-1,2-phenylenediamine, HL 2 = N , N '-bis(2-hydroxy-3-methoxybenzylidene)-propane-1,2-diamine, HL 3 = N , N '-bis(3-methoxysalicylidene)-1,3-propanediamine, qua = 2-quinolinecarboxylic acid, bnz = benzhydroxamic acid and aca = acetohydroxamic acid). Strikingly, the slow magnetic relaxation can be tuned by modifying the steric hindrance and/or electronic effect on the backbone of the Shiff base and the terminal substituents of hydroxamic acid, as well the magneto-structural correlations are studied. Furthermore, Yb congeners 7 and 8 were synthesized to explore dual-functional materials with both magnetic and fluorescence properties, and they displayed both slow magnetic relaxation and near-infrared (NIR) properties; the low temperature NIR spectroscopic data were correlated with the corresponding slow magnetic relaxation mechanism involving thermally activated ground states to the excited state.