Assigning value of EXEC result to variable

Hi,

I want to turn the path to xml file into a variable.
So, this line
SET @xmlDoc = ( SELECT * FROM OPENROWSET ( BULK 'pathtoxml.xml', SINGLE_CLOB ) AS xmlData)
 must be
SET @xmlDoc = ( SELECT * FROM OPENROWSET ( BULK @xmlPath, SINGLE_CLOB ) AS xmlData)

I tried to create a dynamic query:
 
      Set @Sql = 'SELECT * FROM OPENROWSET ( BULK '''+@xmlPath+''', SINGLE_CLOB ) as T(xmlData)'
            exec sp_executesql @Sql, N'@res XML OUTPUT' , @xmlDoc OUTPUT

       -- this line should return the number of tags under DATA
       SELECT @xmlDoc.value('count(/XML/DATA/*)','INT')

But unfortunately @xmlDoc does not return the xml data that I am expecting.

Am I missing something?