Synthesis, Crystal Structures, and Magnetism of Cobalt Coordination Polymers Based on Dicyanamide and Pyrazine-dioxide Derivatives

Abstract

Three coordination polymers of Co(II) with dicyanamide (dca) were obtained by adding coligands of 2,5-dimethylpyrazine-dioxide (2,5-dmpdo), 2,3,5-trimethylpyrazine-dioxide (2,3,5-tmpdo), or 2,3,5,6-tetramethylpyrazine-dioxide (2,3,5,6-tmpdo) to the binary system of Co-dca. Co2(dca)(4)(2,5-dmpdo)2 (1) crystallizes in the triclinic space group P with a=7.4962(2), b=9.0364(2), c = 10.4783(4) A, alpha = 72.567(1), beta = 72.557(1), gamma = 68.814(2) degrees , V = 616.61(3) A(3), Z = 1, and R1 = 0.0345. [Co3(dca)6(H2O)4].2(2,3,5-tmpdo) (2) is in the monoclinic space group C2/c with a = 29.477(1), b = 7.3735(2), c = 17.4631(7) A, beta = 93.652(1) degrees , V = 3787.9(2) A(3), Z = 4, and R1 = 0.0532. [Co(dca)2(H2O)2].2(2,3,5,6-tmpdo) (3) is in the monoclinic space group P2(1)/c with a = 9.4739(3), b = 11.3876(3), c = 12.1778(3) A, beta = 98.967(1) degrees , V = 1297.74(6) A(3), Z = 4, and R1 = 0.0481. 1 contains an unusual (4,4) Co-dca layer, representing a rare example of metal-dca coordination polymers with mixing 1,3-mu(2)- and 1,5-mu2-dca bridges. The Co-dca (4, 4) layers are connected by 2,5-dmpdo to give an alpha-Po-type network, which displays antiferromagnetic ordering below 10.8 K. 2 is a unique 3D framework composed of 2D twinned 1,5-mu2-dca bridged layers, which are connected by Co-H2O-Co linkages. The noncoordinated 2,3,5-tmpdo units and the coordination water molecules form hydrogen-bonded chains that thread the framework. 3 has alternating stacks of usual Co-dca (4, 4) layers through 1,5-mu2-dca bridges and organic layers of noncoordinated 2,3,5,6-tmpdo. Weak antiferromagnetic and weak ferromagnetic coupling was observed in 2 and 3, respectively.

Synthesis, Crystal Structures, and Magnetism of Cobalt Coordination Polymers Based on Dicyanamide and Pyrazine-dioxide Derivatives

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