In aqueous alkaline solution, the berate ion (B(OH)(4)(-)) is Capable of forming both 1:1 and 1:2 complexes with polyhydroxy carboxylate ligands such as L-(2R,3R)-tartrate or meso-(2R,3S)-tartrate (T2-). The mode of coordination is pH dependent and has been shown in base to be exclusively via the 2,3-diol linkage on the ligand. Equilibria in this system can be described by the following two equations : B(OH)(4)(-) + T2- <-> BT3- + 2H(2)O (K-1); BT3- + T2- <-> BT25- + 2H(2)O (K-2) B-11 NMR was used to study both these equilibria and the binding of alkaline earth metal ions by the several borotartrate complex ions. Metal ion specificity (Mg2+, Ca2+, Sr2+) was studied in the M(2+)/B(OH)(4)(-)/L-tartrate systems, while the effect of absolute ligand configuration (L-tartrate vs meso-tartrate) was studied in the Ca2+/B(OH)(4)(-)/tartrate systems. The main conclusions of this work are (1) Mg2+ binds preferentially to free tartrate, T2- and shows little if any interaction with BT3- and BT25-, (2) Ca2+ and Sr2+ bind preferentially (by 3 orders of magnitude) to BT25- (L-tartrate) with Ca2+ binding being selectively favored by a factor of 5, and (3) absolute ligand (tartrate) configuration has no significant effect on Ca2+ binding to BT25-. Stability constants for the various complexation reactions are reported as well as a proposed Ca2+ and Sr2+ binding site in the MBT(2)(3-) complex ions.