The oxidative insertion of In'X into the Mn-Mn bond of Mn2(CO)io in the presence of xylene led to clusters of the type [(Mn(CO)s)2ln(M-X)]2 (X = Cl, Br, I). All three clusters were characterized by osmometric, thermogravimetric, mass spectroscopic, ir, and Raman spectroscopic measurements. X-ray structural analysis shows that the three clusters are isomorphous and have similar molecular structures. The central molecular fragment of each cluster contains a planar centrosymmetric four-membered In2X2 ring. Each In atom is bonded to two µatoms and to two Mn atoms in a distorted tetrahedral arrangement. The plane defined by the four Mn atoms is perpendicular to that defined by the 1^X2 atoms. The Mn-In-Mn angles of the three clusters have the following values: X = Cl, 123.59 (3)0; X = Br, 124.97 (3)°; X = I, 126.37 (4)°. The shortest intramolecular nonbonding O-O contact lengths correspond to equatorial CO ligands of the two pairs of Mn(CO)s ligands above or below the In2X2 plane (X = Cl, 2.877 (8) Á; X = Br, 2.896 (8) Á; X = I, 2.963 (9) A) and signify a dependence of the 0-0 repulsion interaction on the atomic size of the µatoms. A consequence of the repulsive effect connected with the nonbonded interaction of the equatorial CO groups of the different Mn atoms is their staggered arrangement. The In2X2 rings have obtuse -(µ-)-(X = Cl, 100.02 (5)°; X = Br, 97.42 (2)°; X = I, 94.35 (2)°) and acute (µ-)--(µ-) angles (X = Cl, 79.98 (5)°; X = Br, 82.58 (2)°; X = I, 85.65 (2)°) and the order of the nonbonded lengths In-In and X-X is In-In > X-X. These structural features of the 1^X2 rings are reversed with respect to corresponding features of the In2U ring of the compound [ 2 (µ-)]2 (acute -(µ-)angle, obtuse (µ-)--(µ-) angle, and the order of the length In-In < X-X), in which no comparable repulsion exists between the terminal ligands. The average In-X distances in the clusters examined are for X = Cl, 2.618 (2) Á, for X = Br, 2.757