I know it's a 3-year gap between your posting and this note, but:
I believe we may have ancestors in common. My great-great-great-great grandfather Muzio Clementi had 6 children, one of whom was named John (his youngest I believe) and was by his third and final wife, Emma Gisborne. The family lived in London in the late 1700s and 1800s. Also one of Muzio's granddaughters married and had a son, Arthur Clementi Lacey-Baker, my great-grandfather. I think his brother's name, too, was John, and he lived in or around London. Do you have any names of your John Clementi's father/mother? It may help me trace some of the breaks in my "tree".
Also, your note says 1889-1852; do you mean 1952?