Cesium hydrogen tartrate and anomalous dispersion of cesium

Cesium hydrogen (+)-tartrate is orthorhombic, P2₁2₁2₁, a = 8.076 (3), b = 11.621 (5), c = 7.692 (3) Å, Z = 4, D_x = 2.594 g cm^-3, at 22°C. Its structure, nearly the same as that of ammonium hydrogen tartrate, was refined to R = 0.016 for 2442 reflections (F² > 3σ) out to d = 0.66 Å. Our least-squares program was modified to treat anomalous-dispersion terms as independent adjustable parameters, and f" for cesium was determined as 2.22 (6) e for Mo Kα radiation. In the determination of absolute configuration or polarity, refinement of f" for a heavy atom has the advantage that one can detect inversion twinning, as well as save on computational time.