Two Versatile N,N‘-Bipyridine-Type Ligands for Preparing Organic−Inorganic Coordination Polymers: New Cobalt- and Nickel-Containing Framework Materials

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Abstract
The Schiff base ligands 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (L1, monoclinic, P21/c, a = 3.856(1) Å, b = 11.032(2) Å, c = 12.738(3) Å, β = 92.21(3)°, Z = 2) and 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (L2, monoclinic, P21/c, a = 10.885(2) Å, b = 4.613(1) Å, c = 14.978(3) Å, β = 92.827(4) °, Z = 2) were used in the synthesis of four new organic−inorganic coordination polymers, each of them adopting a different structural motif. Synthesis, X-ray structural determinations, and spectroscopic and thermogravimetric analyses are presented. The reaction between Co(NO3)2·6H2O and L1 afforded a two-dimensional noninterpenetrating brick-wall structure, [Co(C12N4H10)1.5(NO3)2(H2O)(CH2Cl2)2]n (1, triclinic, P1̄; a = 10.242(7) Å, b = 10.802(7) Å, c = 15.100(1) Å, α = 70.031(1), β = 75.168(11), γ = 76.155(11), Z = 2), while Ni(NO3)2·6H2O combined with L1 yielded an interpenetrating three-dimensional rhombus-grid polymer, [Ni(C12N4H10)2(NO3)2(OC4H8)1.66(H2O)0.33]n (2, monoclinic, C2/c; a = 20.815(8) Å, b = 23.427(8) Å, c = 17.291(6) Å, β = 116.148(6), Z = 8). The reaction of Co(NO3)2·6H2O and L2 was found to be solvent-sensitive and resulted in the formation of two different noninterpenetrating compounds: [Co(C14N4H14)2(NO3)2(C6H6)1.5]n (3, monoclinic, C2/c; a = 22.760(2) Å, b = 21.010(3) Å, c = 25.521(2) Å, β = 97.151(2), Z = 8), which adopts a two-dimensional square-grid motif formed by propeller-type modules, and [Co(C14N4H14)1.5(NO3)2(CH2Cl2)2]n (4, monoclinic, P21/n; a = 14.432(2) Å, b = 14.543(8) Å, c = 15.448(4) Å, β = 96.968(0), Z = 4), consisting of T-shaped building blocks assembled into a one-dimensional ladder-type structure. These four coordination polymers all exhibit impressive thermal stability. Thermogravimetric studies showed that after complete removal of the solvents, the frameworks are stable to temperatures between 234 °C and 260 °C.

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