Two novel Re<sup>IV</sup> salts of general formula [H<sub>2</sub>ade]<sub>2</sub>[Re<sup>IV</sup>X<sub>6</sub>]X<sub>2</sub>·4H<sub>2</sub>O [H<sub>2</sub>ade<sup>2+</sup> = 9<i>H</i>-adenine-1,7-diium;
X = Cl(<b>1</b>) and Br(<b>2</b>)]
have been synthesized and magnetostructurally characterized. <b>1</b> and <b>2</b> are isostructural salts that crystallize
in the orthorhombic system with space group <i>Fdd</i>2.
Both compounds are made up of discrete mononuclear [Re<sup>IV</sup>X<sub>6</sub>]<sup>2–</sup> and X<sup>–</sup> anions
and doubly protonated adenine cations. The six-coordinate rhenium(IV)
ion is bonded to six halide ligands [X = Cl (<b>1</b>) and Br
(<b>2</b>)] in an octahedral geometry. Short intermolecular
Re<sup>IV</sup>–X···X–Re<sup>IV</sup> interactions, as well as Re<sup>IV</sup>–X···H–N(H<sub>2</sub>ade) and Re<sup>IV</sup>–X···H–O<sub>w</sub> hydrogen bonds, are present in the crystal lattice of <b>1</b> and <b>2</b>. Magnetic susceptibility measurements
on polycrystalline samples of <b>1</b> and <b>2</b> 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 χ<sub>M</sub> at ca. 6.0 (<b>1</b>) and 12.0 K (<b>2</b>). The larger spin delocalization
from the Re<sup>IV</sup> ion onto the peripheral bromide ligands when
compared to the chloride ligands accounts for the enhancement of the
magnetic exchange observed in <b>2</b>
