Chemistry - Coordination Chemistry Question with Solution | TestHub

A trans-chelating ligand must have a rigid backbone and donor atoms positioned such that they can only span the "trans" positions (180° apart) in an octahedral complex. In option (B), the para-phenylene spacer between the $(C{H}_2{)}_{3}PP{h}_2$ groups provides the necessary rigidity and distance to force the phosphorus lone pairs to coordinate from opposite sides of the metal center. Other options like (A) or (C) are either too flexible or have donor atoms oriented for "cis" coordination.