Ligand displacement reactions from the coordination sphere of cobalt complexes .2. The displacement of ligands of [cis-Co(en)(2)Cl-2]Cl by potassium squarate. The crystal and molecular structure of a compound with idealized formula of [cis-Co(en)(2)(H2O)Br](2)[trans-(C2O42-(C2O4H-)Co-trans-(H2O)(2)(OH)(2)]Br-2(I)

Compound (I), idealized as Br4Co3O14N8C16H41 (see text), crystallizes in the triclinic space group P1 (No. 2) with cell constants of a = 7.4470(7), b = 7.9648(4), c = 15.2223(8), alpha = 96.338(4)degrees beta = 93.504(6)degrees, gamma = 112.894(6)degrees, V = 821.328 Angstrom(3), and d(calc; MW = 1065.97, z = 1) = 2.155 gm-cm(-3). Data (3880 total reflections) were collected over the range 2 degrees less than or equal to 2 theta less than or equal to 55 degrees and corrected for absorption (mu = 63.69 cm(-1)) using data from Psi scans. The unexpectedly isolated compound contains a [cis-Co(en)(2)Br(OH)](+) cation, while the anion contains a central Co(III) surrounded by two mondentate, trans-squarato ligands, two trans-hydroxo, and two waters. The waters and hydroxy ligands were identified by determining, experimentally, the presence and positions of their respective hydrogens. Given the need for overall electroneutrality, one squarato ligand must be a dianion (Sq(2-)) and the other a monoanion (SqH(-)); however, since the ion bearing the squarato ligands sits at an inversion center, the hydrogen of the latter must be disordered. Refinement of the heavy atoms with anisotropic thermal parameters and fixed hydrogen positions (B's fixed at) led to the final R(F) and R(w).(F) factors of 0.036 and 0.042, respectively. (I) was obtained during efforts to prepare [Co(en)(2)(squarate)]Br by the displacement of two chloro ligands from the coordination sphere of [cis-Co(en)(2)Cl-2]Cl by K-2 (squarate) followed by addition of NaBr. Compound (I) appears to be the first example of a coordination compound in which squarate(2-) and squarate H- anions are present as ligands to a transition metal ion. A search of the Cambridge file (to 1992) produced no known examples of Co(III) squarates. Thus, (I) appears to also be the first example of its kind.