Abstract: There are disclosed manganese compounds of the formulaMn.sup.II LX.sub.2 (Q).sub.n (I)wherein L is a monodentate ligand of the formulaPR.sup.1 R.sup.2 R.sup.3 (II)whereinR.sup.1, R.sup.2, and R.sup.3 are identical or different and are substituted or unsubstituted alkyl, cycloalkyl, alkenyl, alkynyl, or aryl or hydrogen providing that no more than two of the R.sup.1, R.sup.2, and R.sup.3 groups are substituted or unsubstituted aryl groups and that at least one of R.sup.1, R.sup.2 and R.sup.3 is a substituted or unsubstituted alkyl, cycloalkyl, alkenyl, alkynyl, or aryl group,X is a species capable of existing as an anion, e.g., Cl, Br,Q is a solvento molecule capable of forming a chemical bond to the manganese, andn is 1, 2, or 3 solvent donor atoms.The manganese compounds are useful in the separation of a gas such as oxygen, hydrogen, sulfur dioxide, an alkene, and carbon monoxide from fluids containing these gases.