Destroy Instiantated GameObject on Collision2D

hi! I am trying to destory instianitated gameobject. I can do that when I isntanitate it, and then destroy it after 2 seconds, but if I want to destroy it on collision it desnt do anything it somehow sees Clone as empty gameobject.

 using UnityEngine;
 using System.Collections;
 
 public class FireUp : MonoBehaviour {
     public GameObject hero;
     bool fired = false;
     public float currentDir;
     float energyShootSpeed;
     public GameObject energyShoot ;
     public GameObject fireball;
     public  bool bIsColliding ;
     GameObject Clone;
 
 
 
     void OnCollisionEnter2D (Collision2D col){
         Debug.Log ("Clone on Coll Enter : " + Clone);
         Destroy (Clone);    ---> Here it is empty even if I instainiatate it.    
             
         }
 
     
     void   FireLeft (){
         float timer = Time.time;
 
         if (currentDir > 0) {
             energyShootSpeed = 555f;
         }
         else if(currentDir<0){
             energyShootSpeed = -555f;
             
         }
 
         Vector3 pos = new Vector3(hero.transform.rigidbody2D.position.x,hero.transform.rigidbody2D.position.y+1, hero.transform.position.z-0.6f );
 
         fired = true;
         
          Clone = Instantiate(gameObject,pos,transform.rotation) as GameObject;
         Debug.Log ("Clone : " + Clone);   ---> Not empty , instance successfully created...
         Destroy (Clone, 2f);  
         Clone.particleSystem.enableEmission = true;
 
     }
     }
 
 }