Heterotrimetallic Cyanide-Bridged 3d-4d-5d Frameworks Based on a Photomagnetic Secondary Building Unit

The rational design of coordination frameworks combining more than two different metal ions using a self-assembly approach is challenging because it rarely offers sufficient control over the building blocks at the actual self-assembly stage. In this work, we present a successful two-step strategy toward heterotrimetallic coordination frameworks by employing a new bimetallic [(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ] 4- secondary building unit (SBU). This anionic moiety has been isolated and characterized as a simple salt with an organic dppipH 2 2+ cation (dppipH 2 ) 2 [(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ]·15H 2 O ( 1 ) (dppip = 1,4-di(4-pyridinyl)piperazine). The salt presents a second-order phase transition related to cation conformational change around 250 K and a photomagnetic effect after irradiation with 450 nm light at 10 K. When combined with aqueous solutions of Mn II or Cu II complexes, it forms either a one-dimensional chain [Mn II (dpop)][Mn II (dpop)(H 2 O)][(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ]·36H 2 O ( 2 ) (dpop = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) or a photomagnetic two-dimensional honeycomb network [Cu II (cyclam)] 2 [(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ]·40.89H 2 O ( 3 ) (cyclam = 1,4,8,11-tetraazacyclotetradecane), both characterized by very large cavities in their structure filled with solvent molecules. Both 2 and 3 incorporate three different transition-metal ions and constitute a new family of 3d-4d-5d coordination frameworks. Moreover, compound 3 inherits the photomagnetic properties of the MoPtMo SBU.