Script creates empty file when run from cron in linux

I have a script as below:
nfsiostat 2 5 > /home/user1/file1; echo ” nfsdata” | mail – s ” some message” – a /home/user1/file1 xyz@xmail.com

When I run this as. /script, I get the mail with the attachment which has the nfsiostat data, but if scheduled through cron I get a mail with an empty file attached.
Scheduling via cron as below :
*/5 * * * * /location_of_script &2>&1

Any leads on why this is happening and how this may be corrected? Thanks in advance