Enhancement of Intermolecular Magnetic Exchange through Halogen···Halogen Interactions in Bisadeninium Rhenium(IV) Salts

Abstract

Two novel ReIV salts of general formula [H2ade]2[ReIVX6]X2·4H2O [H2ade2+ = 9H-adenine-1,7-diium; X = Cl(1) and Br(2)] have been synthesized and magnetostructurally characterized. 1 and 2 are isostructural salts that crystallize in the orthorhombic system with space group Fdd2. Both compounds are made up of discrete mononuclear [ReIVX6]2– and X– anions and doubly protonated adenine cations. The six-coordinate rhenium(IV) ion is bonded to six halide ligands [X = Cl (1) and Br (2)] in an octahedral geometry. Short intermolecular ReIV–X···X–ReIV interactions, as well as ReIV–X···H–N(H2ade) and ReIV–X···H–Ow hydrogen bonds, are present in the crystal lattice of 1 and 2. Magnetic susceptibility measurements on polycrystalline samples of 1 and 2 in the temperature range 2.0–300 K show the occurrence of significant intermolecular antiferromagnetic interactions in both compounds, resulting in the observation of maxima in χM at ca. 6.0 (1) and 12.0 K (2). The larger spin delocalization from the ReIV ion onto the pe...