get data from two different files using TCL

i have two files

file1

10   123  
9    456  
8    789  
7    111  

and file2

10  687  
8   265  
7   698  
6   222

I want the final output to be like

10  123   687  
9   456   0  
8    789   265   
7    111   698  
6    0     222    

Any help will be highly appreciated!

P.S i tried using sort, unique, awk but still couldn't figure it out