Precovers, covers and dually preenvelopes and envelopes were introduced in the early 80-es by Enochs and parallely under the name left and right and minimal left and right approximations by Auslander. In the last 20 years these notions seem to be important and efficient in the categorical investigation of modules. The paper investigates the orthogonality relation induced by the functor \(\text{Ext}^1(-,-)\) for the class \({\mathcal E}\) of exact complexes in the abelian category \({\mathcal C}\) of complexes of left modules over a ring. The main result lists 16 properties concerning \({\mathcal E}, {\mathcal E}^\perp\) as well as (pre-)covers and (pre-)envelopes over them, respectively.