Crystal polymorphism in 2,2'-bipyrimidine-based iridium(III) complexes

Mononuclear iridium(III) complexes, NBu4[IrBr4(bpym)] (1) and [IrBr3(bpym)(MeCN)] (2a and 2b) [NBu4+ = tetra(n-butyl)ammonium cation; bpym = 2,2'-bipyrimidine], have been prepared and characterized. Their crystal structures were determined by single-crystal X-ray diffraction. 1 and 2a crystallize in the monoclinic crystal system with space groups P2(1)/c and P2(1)/n, respectively. The 2b phase crystallizes in the orthorhombic crystal system with space group P2(1)2(1)2(1). In these complexes, each iridium(III) is six-coordinate and bonded to two (1) or three (2a and 2b) nitrogen atoms from bpym and MeCN (2a and 2b) molecules and three (2a and 2b) or four (1) bromides. In all the cases, they exhibit a distorted octahedral environment. 2a and 2b display a packing polymorphism containing pi center dot center dot center dot Br, C-H center dot center dot center dot Br and Br center dot center dot center dot Br intermolecular interactions. Further analyses of their crystal structures were performed through the SHAPE and CrystalExplorer programs. The electrochemical properties of 1 and 2 were investigated through cyclic voltammetry (CV) technique, with 1 showing a reversible iridium(III)-iridium(IV) redox process.