The utility of the solvothermal dehydration strategy whereby superheated acetonitrile reacts with water of hydration to form ammonium acetate is demonstrated in the synthesis of [NH4]MnCl2(OAc), I, and [NH4](2)MnCl4(H2O)(2), II, from MnCl2.4H(2)O. The structure of I is shown to crystallize in the monoclinic space group C2/c (No. 15) with a = 15.191(6) Angstrom, b = 7.044(2) Angstrom, c = 13.603(6) Angstrom, beta = 107.31degrees, V = 1389.7(9) cm(-1), and Z = 8. The structure of II crystallizes in the space group /4/mmm (No. 139) with a = 7.5250(5) Angstrom, b = 8.276(2) Angstrom, V = 468.6(1) cm(-1), and Z = 2. Both structures exhibit extensive hydrogen bonding that controls both local Mn-Cl bonding and the interchain organization. I is shown to be a one-dimensional Heisenberg antiferromagnet with an intrachain exchange constant J/k = -2.39 K. This structure exhibits exchange coupling intermediate between the well-studied triply and doubly chloride-bridged one-dimensional manganese Heisenberg antiferromagnets. The structure/property correlation demonstrates a linear dependence of the exchange constant on the Mn-Cl-Mn bond angle, alpha, for alpha < 94degrees.