A new crystal structure of clarithromycin

A new crystal structure of clarithromycin single acetonitrile solvate designated "Form III'' was first determined by single crystal X-ray diffraction. The compound crystallized in the monoclinic system, P2(1) space group with a = 10.644(2) angstrom, b = 18.099(4) angstrom, c = 11.628(2) angstrom, alpha = gamma = 90 degrees, beta = 95.38(3)degrees, V = 2230.1(8) angstrom(3), Z = 2, D-c = 1.175 g/cm(3), mu = 0.087 mm(-1), F(000) = 860, R-1 = 0.034, wR(2) = 0.062, S = 0.875, (Delta/sigma)(max) = 0.001 for 2,709 observed reflections (I>2 sigma (I)). Form III of clarithromycin, contrary to Form I, is more thermodynamically stable than Form II used currently on the market.