Partition feature is greyed out in Disk Utility

I have recently purchased a 2TB external seagate hard drive. I would like to partition this to dedicate a terabyte for time machine. I have already formatted the drive to Mac OS Extended as it was previously formatted to a windows file system. After doing that the disk utility still wouldn't let me use the partition facility. Below is a screenshot of the information of the hard drive and the current state of disk utility, partition is greyed out when the hard drive is selected. Any help would be much appreciated