The 26-year-old Purrington made 31 appearances, all but five of them starts, as Charlton finished 13th in League One last season.

County manager Malky Mackay said: "He is in the prime of his career and has a great track record."

Purrington began his career with Plymouth Argyle before joining Rotherham United and initially switched to Charlton on loan, with the move becoming permanent after helping them win promotion to the Championship in 2019.

He becomes the Scottish Premiership club's third signing of the week, with 19-year-old Southampton winger Kazeem Olaigbe's loan move having been announced on Monday.

Jordy Hiwula enjoyed a good 2018-19 season at Coventry, scoring 13 goals

Hiwula, 27, moves north after scoring just once in 25 appearances, all but two of them starts, as Doncaster were relegated to League Two last season.

Having failed to break into Manchester City's first team after coming through their youth ranks, he made only appearance one for next club Huddersfield Town amid loan spells with Yeovil Town, Walsall, Wigan Athletic, Bradford City and Fleetwood Town.

He switched to Coventry City in 2018 then Portsmouth two years later before joining Doncaster last summer.

Mackay said Hiwula is "an experienced player that has scored goals across the EFL over a number of years".