Web Release Date: October 10,
Solvent-Dependent Structures of Co(NO3)2 with 1,2-Bis(4-pyridyl)ethylene. Interconversion of Molecular Ladders versus Mononuclear Complexes
Received March 12, 1998
Abstract: Studies have been carried out on two solvent-dependent structures of Co(NO3)2 with trans-1,2-bis(4-pyridyl)ethylene (bpee) and their interconversions. X-ray analyses disclose that the molecule obtained in MeOH/CHCl3
is an infinite ladder structure, [Co(NO3)2(bpee)1.5·3CHCl3]n (triclinic P Download the full text:
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and
; a = 10.415(4) Å, b = 13.425(4) Å, c
= 14.212(4) Å, 
= 110.41(3)
, 
= 109.06(3), 
= 97.20(3), Z = 2), whereas the compound afforded in
H2O/EtOH is a mononuclear structure, [Co(H2O)4(bpee)2](NO3)2·8/3H2O·2/3bpee (triclinic P; a = 9.625(3) Å, b
= 14.597(5) Å, c = 20.544(5) Å, = 87.52(3), = 83.34(2), = 75.94(3), Z = 2). For [Co(NO3)2(bpee)1.5·3CHCl3]n, the local geometry around the cobalt(II) atom approximates to a heptacoordinate environment with
four oxygens and three nitrogens. The four oxygen sites are occupied by an isobidentate and an anisobidetate
nitrate ligand. Each bpee spacer connects two cobalt(II) atoms defining a T-shaped arrangement at the metal
atom. For [Co(H2O)4(bpee)2](NO3)2·8/3H2O·2/3bpee, the cobalt atom is in a typical octahedral arrangement with
two bpee ligands and four water molecules. The bpee ligand is coordinated to the cobalt atom in a monodentate
mode with a dangling pyridine group. Thermal and IR analyses of the present two complexes show that in the
solid state the mononuclear complex is changed to the ladder structure at temperatures above 150 C. Moreover,
the ladder structure slowly shifts to the mononuclear complexes at sufficient moisture condition. Thus, either the
ladder structure or the mononuclear complex exists depending on the presence or absence of moisture.
