Synthesis, Structure, and Magnetic Properties of the Oxalate-Based Bimetallic Ferromagnetic Chain {[K(18-crown-6)][Mn(H<sub>2</sub>O)<sub>2</sub>Cr(ox)<sub>3</sub>]}<sub>∞</sub> (18-crown-6 = C<sub>12</sub>H<sub>24</sub>O<sub>6</sub>, ox = C<sub>2</sub>O<sub>4</sub><sup>2-</sup>)

The salt [K(18-crown-6)][Mn(H<sub>2</sub>O)<sub>2</sub>Cr(ox)<sub>3</sub>]·0.5(18-crown-6) (<b>1</b>) has been prepared and structurally and magnetically characterized. It crystallizes in the <i>P</i>2<sub>1</sub>/<i>c</i> space group [<i>a</i> = 21.011(2) Å, <i>b</i> = 11.265(2) Å, <i>c</i> = 15.748(3) Å, β = 105.952(6)°, <i>V</i> = 3584(1) Å<sup>3</sup>, and <i>Z</i> = 4] and contains [Mn(H<sub>2</sub>O)<sub>2</sub>Cr(ox)<sub>3</sub>]<sub>∞</sub> chains connected through hydrogen bonding to form 2D anionic networks. The magnetic exchange is ferromagnetic [<i>J</i> = +2.23(2) cm<sup>-1</sup>] in the chain and also in between chains, reaching bulk ferromagnetic ordering below 3.5 K.