Crystal structures of three basic zinc carboxylates together with infrared and FAB mass spectrometry studies in solution

We report the X-ray crystal structures of three new basic zinc carboxylate complexes, [Zn4O(O2CR)6] where RC(CH3)3 (pivalate) or C6H5 (benzoate) and [Zn5(OH)2(O2CCHCHCH3)8]x (crotonate). The basic pivalate is orthorhombic, Cmc21, with a=18.609(1), b=11.027(1), c=22.439(1)A, Z=4; R=0.042 for 1887 unique observed reflections. The basic benzoate is monoclinic, P21/m, with a=10.818(2), b=18.527(3), c=12.170(2) A, β=110.32(1)°, Z=2; R=0.036 for 3633 unique observed reflections. The basic crotonate is monoclinic, P21/n, with a=8.723(1), b=21.957(2), c=11.302(1) A, β=90.94(1)°, Z=2; R=0.058 for 3049 unique observed reflections. The pivalate and benzoate structures possess the well-known tetranuclear structure containing a central oxygen atom, while the structure of the crotonate complex consists of a chain polymer. In solutions containing traces of water, the hydrated basic structures appear to be in equilibrium with hydrated forms of the normal 3,1 metal carboxylate structures reported previously and their interconversions have been investigated using FTIR and FAB mass spectral data.