Sprite superimpose over other sprite when drag over.

hi i'm new in Unity and i have the next problem: i'm building a game for android and Ios that is like a simulator where i have to drag sprites to other spriter to simulate action, i have sprites for tools and for objectives. the problem that i have now is when i drag a tool sprite and pass over other tool sprite they absorb each other and i can't separate them.

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class movimiento : MonoBehaviour {
 
 
     public float speed = 0.1F; 
 
     // Use this for initialization
     void Start () 
     {
         
     }
     
     // Update is called once per frame
     void Update () 
     {
         if (Input.touchCount > 0)
             print(Input.touchCount);
 
         //Gets the world position of the mouse on the screen        
         Vector2 mousePosition = Camera.main.ScreenToWorldPoint( Input.mousePosition );
 
         //Checks whether the mouse is over the sprite
         bool overSprite = this.GetComponent<SpriteRenderer>().bounds.Contains( mousePosition );
 
         //If it's over the sprite
         if (overSprite)
         {
             //If we've pressed down on the mouse (or touched on the iphone)
             if (Input.GetButton("Fire1"))
             {
                 //Set the position to the mouse position
                 this.transform.position = new Vector3(Camera.main.ScreenToWorldPoint(Input.mousePosition).x,
                     Camera.main.ScreenToWorldPoint(Input.mousePosition).y,
                     0.0f);
             }
         }
     }
 }