Assembly of a Robust, Thermally Stable Porous Cobalt(II) Nicotinate Framework Based on a Dicobalt Carboxylate Unit

A series of robust, thermally stable open-framework cobalt nicotinate compounds, Co2(H2O)(C6H4O2N)4·0.5CH3CH2OH·0.5H2O (1), Co2(H2O)(C6H4O2N)4 (2), and Co2(H2O)(C6H4O2N)4·C6H5CH2OH (3), based on rigid
dimetallic carboxylate clusters as the basic building unit have been prepared. Single-crystal X-ray crystallographic
analyses of 1 and 3 reveal the host framework possessing an effective channel area with the dimensions of 10.8
× 4.5 Å. These channels can accommodate guest molecules of various sizes and shapes such as ethanol, water,
and benzyl alcohol. Thermogravimetric analysis shows a two-step weight loss corresponding to the loss of guest
molecules followed by the loss of coordinated water. The host framework is thermally stable up to 295 °C. The
cobalt nicotinate host remains intact, even upon the removal of the guest to form compound 2 as revealed by
single-crystal X-ray diffraction analysis. Crystal data for 1:  Co2(H2O)(C6H4O2N)4·0.5CH3CH2OH·0.5H2O, fw =
656.33, triclinic, space group P1̄, a = 10.5407(2) Å, b = 11.8266(3) Å, c = 14.1122(2) Å, α = 106.878(4)°, β
= 102.411(2)°, γ = 111.011(3)°, V = 1467.9(5) Å3, Z = 2. Crystal data for 2:  Co2(H2O)(C6H4O2N)4, fw =
624.28, triclinic, space group P1̄, a = 10.507(3) Å, b = 11.824(2) Å, c = 14.113(3) Å, α = 107.06(2)°, β =
102.39(2)°, γ = 111.105(16)°, V = 1459.5(6) Å3, Z = 2. Crystal data for 3:  Co2(H2O)(C6H4O2N)4·C6H5CH2OH,
fw = 732.42, triclinic, space group P1̄, a = 10.6671(6) Å, b = 12.0063(7) Å, c = 14.0658(8) Å, α = 106.7180(10)°, β = 102.2790(10)°, γ = 111.1900(10)°, V = 1504.1(6) Å3, Z = 2. The magnetic exchange coupling between
the dicobalt centers for compounds 1 and 3 are analyzed on the basis of both the Curie−Weiss expression and
a binuclear magnetic model. The negative values of the magnetic exchange coupling constant indicate the
antiferromagnetic nature within the cobalt dimer.