Linear chain complexes linked by hydrogen bonded O2H3- and O3H5- units: structural and magnetic comparison of trans-dihydroxo-, -diaqua-, and -aquahydroxo-chromium(III) complexes

The syntheses and characterization of a series of chromium(III) complexes o f the general types trans- [(A)(4)Cr(OH)(H2O)](2+), trans-[(A)(4)Cr(OH)(2)] (+), and trans-[(A)(4)Cr(H2O)(2)](3+) are described. The ligands (A)(4) use d include the tetradentate ligand 1,4,8,11-tetraazacyclotetradecane (cyclam ), its hexamethylated derivative C-meso-5,5,7,12,12,14-hexamethyl-1,4,8,11- tetraazacyclotetradecane (cyca), and the bidentate ligand 2-aminomethylpyri dine (pico). The cobalt(III) aquahydroxo complexes with cyclam and cyca are also reported. The trans-diaqua and trans-dihydroxo complexes are monomeri c, but the trans-aquahydroxo complexes form linear chains. The complexes tr ans-[Cr(cyclam)(OH)(H2O)](CF3SO3)(2) 1 and trans- [Co(cyclam)(OH)(H2O)](CF3 SO3)(2) 3 and their corresponding perchlorates (2 and 4, respectively) have been isolated and the structures of the chromium triflate salt 1 and the c obalt perchlorate salt 4 have been determined. Both of these complexes I an d 4 form infinite chains in the solid state, adjacent metal centers being b ridged by hydrogen bonds between hydroxo and aqua ligands. The Cr . . . Cr separation in 1 is 6.085 Angstrom whereas the Co . . . Co separation in 4 i s 6.078 Angstrom. The complex trans-[(pico)(2)Cr(OH2)(2)](NO3)(3).H2O 8 (wh ere pico is picolylamine, 2-aminomethylpyridine) crystallizes with only one monomeric formula in a unit cell. In contrast to the structures of 1 and 4 (and, presumably, of 2 and 3 also), the two complexes trans-[Cr(cyclam)(OH )(2)]ClO4.H2O 5 and 8 are monomeric in the solid state. The chromium comple x trans-[Cr(cyca)(OH)(H2O)](ClO4)(2).H2O 6 crystallizes with two monomeric formula units in a unit cell and the cobalt analogue 7 is isomorphous with the chromium complex. The structures of these complexes are also linear cha ins, but in this case there is an intervening water molecule between the aq ua and hydroxo ligands on adjacent chromium centers. EPR spectroscopy of th e chromium complex 1 doped in the diamagnetic cobalt host 3 reveals the pre sence of weak magnetic interactions.