Instantiate object only once

Int_Molecule should instantiate only once, but if it touches more than one corner (UR = UP RIGHT, UL = UP LEFT, etc.) it instantiated twice. Is there a way to instantiate the object only once?

To give you a more complete picture: External molecules have detectors that detect collision, while internal ones have holders to hold the newly instantiated molecules.

  private void UR_Attach()
         {
             
             RaycastHit2D Ext2Int = Physics2D.Raycast(UR_Detector.position, Vector2.zero, -0);
     
     
             if (Ext2Int.collider != null && Ext2Int.collider.tag == "Ext_Molecule")
             {
                 Ext2Int.collider.gameObject.tag = "Untagged";
                 Destroy(Ext2Int.collider.gameObject);
              
                 Transform Int_Molecule_Inst = Instantiate(this.Int_MoleculePrefab);
                 Int_Molecule_Inst.transform.parent = UR_Holder;
                 Int_Molecule_Inst.transform.position = UR_Holder.position;
     
             }