Quatuor Diotima, a French string quartet formed in 1999, has many admirable qualities, along with some weaknesses. Although the group’s self-stated repertoire focus is a somewhat cautious mix of “the Classical period, French Romanticism, and the early 20th century,” last Friday evening at the Library of Congress it boldly dove into the most challenging mainstream repertoire — Beethoven’s Op. 131 and Bedrich Smetana’s E minor quartets, along with an early Schubert (No. 7, D. 94).

To these ears, it was an overreach.

The concert began well; the Diotima’s diaphanous, evanescent sound suited the youthful innocence of Schubert at about age 14, when the piece was written. There was a slightly forced undercurrent of darkness as the players searched for seeds of “Death and the Maiden” hidden among the artless melodies and formulaic passagework. But the sensitivity and blend were a pleasure.

The other repertoire, however, called for a far wider spectrum of emotion, instrumental technique, expression and tone — more than the Diotima currently possesses. The Beethoven bespoke great care in preparation, and special kudos to the group for their scrupulous observance of dynamics, which in late Beethoven are as technically difficult as the notes themselves. But full musical enjoyment was thwarted by the players’ limited tonal palette.

The scherzo movement was a scampering, wispy delight, but all of the slower sections were disappointing. There was fussiness where there should have been a rich forte sound. Expressive slides were both rare and unconvincing, and the musicians could not agree on how to play the very first accent in the opening fugue.

Quatuor Diotima, a French string quartet formed in 1999, has many admirable qualities, along with some weaknesses. (Thibault Stipal/Courtesy of European Artistic Services)

The group’s leader has a clean, deft bow arm, but his left hand is tight, producing a pinched vibrato and numerous intonation problems.

The Diotima seemed to lose focus even further in the Smetana. Tempos felt tentative, and the opening viola statements lacked the virility and punch they needed. The cellist was similarly bland in his slow-movement solo, and the second violinist momentarily lost his place in the finale.

This is a talented group, but it needs to pick its battles more carefully.

Battey is a freelance writer.