mol new solv2_center.gro
set sel [atomselect top "not water"]

# Open a file for binary writing
set fileID [open "output.dat" w]

# Loop through the elements and write them to the file
foreach line [$sel get {index radius x y z} ] {

  # Format the data for this iteration
  set out [format "%d %f %f %f %f\n" [lindex $line 0] [lindex $line 1] [lindex $line 2] [lindex $line 3] [lindex $line 4]]
    # Write the formatted string to the file
    puts -nonewline $fileID $out
}

close $fileID