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

Abstract

A series of robust, thermally stable open-framework cobalt nicotinate compounds, Co(2)(H(2)O)[C(6)H(4)O(2)N](4).0.5CH(3)CH(2)OH.0.5H(2)O (1), Co(2)(H(2)O)[C(6)H(4)O(2)N](4) (2), and Co(2)(H(2)O)[C(6)H(4)O(2)N](4).C(6)H(5)CH(2)OH (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 x 4.5 A. 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 degrees 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: Co(2)(H(2)O)[C(6)H(4)O(2)N)](4).0.5CH(3)CH(2)OH.0.5H(2)O, fw = 656.33, triclinic, space group P(-)1, a = 10.5407(2) A, b = 11.8266(3) A, c = 14.1122(2) A, alpha = 106.878(4) degrees, beta = 102.411(2) degrees, gamma = 111.011(3) degrees, V = 1467.9(5) A(3), Z = 2. Crystal data for 2: Co(2)(H(2)O)[C(6)H(4)O(2)N](4), fw = 624.28, triclinic, space group P(-)1, a = 10.507(3) A, b = 11.824(2) A, c = 14.113(3) A, alpha = 107.06(2) degrees, beta = 102.39(2) degrees, gamma = 111.105(16) degrees, V = 1459.5(6) A(3), Z = 2. Crystal data for 3: Co(2)(H(2)O)[C(6)H(4)O(2)N](4).C(6)H(5)CH(2)OH, fw = 732.42, triclinic, space group P(-)1, a = 10.6671(6) A, b = 12.0063(7) A, c = 14.0658(8) A, alpha = 106.7180(10) degrees, beta = 102.2790(10) degrees, gamma = 111.1900(10) degrees, V = 1504.1(6) A(3), 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.