The 40-year-old Bucchi, who had been coaching a top flight club for the first time, managed four wins in all competitions and left with his side languishing 16th in the league with 11 points. "We send our heartfelt thanks for his professionalism and passion shown in these months," Sassuolo said in a statement.
The town of Sassuolo, with a population of just over 40,000, is the smallest ever to be represented in Serie A.
Bucchi was appointed in June to replace Eusebio Di Francesco who led Sassuolo into Serie A and established them there before he was lured away to AS Roma.
Iachini, 53, has coached Venezia, Cesena, Vicenza, Piacenza, Chievo, Sampdoria, Siena and Udinese and had two stints at both Brescia and Palermo. Although he has never won a major title, he led Chievo, Brescia and Sampdoria out of Serie B to the top flight.
Sassuolo became the sixth club to change coach this season after Cagliari, Genoa, Benevento, Udinese and AC Milan, who fired Vincenzo Montella on Monday and replaced him with Gennaro Gattuso.
(Reporting by Brian Homewood, editing by Ed Osmond)
