With their often turbulent and dark-hued openings, poignant slow movements, elfin Scherzos reminiscent of the music for A Midsummer Night’s Dream, and tense, thrilling last movements of perpetual motion, Mendelssohn’s String Quartets are works of considerable emotional range and mastery of form. This first disc of the complete String Quartets ranges from the youthful No. 1, Op. 12 (actually the second of the published quartets) to the great, tragic String Quartet No. 6, Op. 80, Mendelssohn’s last major work, composed after the death of his sister.