Influence of Pseudohalide Ions on the Molecular Structure and Magnetic Properties of the Manganese(II)−Bipyrimidine−Pseudohalide System

The compounds [Mn 2 (bpm) 3 (NCS) 4 ] ( 1 ), [Mn(bpm)(NCO) 2 ] ( 2 ), and [Mn 2 (bpm)(N 3 ) 4 ] ( 3 ) (where bpm= 2,2‘-bipyrimidine) have been synthesized and characterized. Compound 1 crystallizes in the triclinic P 1̄ space group, with a = 9.122(1) Å, b = 9.229(1) Å, c = 11.710(2) Å, α = 74.89(1)°, β = 80.30(1)°, γ = 61.04(1)°, V = 831.7(2) Å 3, Z = 2, R ( F o ) = 0.029, and w R ( F o 2 ) = 0.078. Compound 2 crystallizes in the monoclinic C 2/ c space group, with a = 7.309(1) Å, b = 14.498(2) Å, c = 10.740(4) Å, β = 99.93(4)°, V = 1121.0(5) Å 3, Z = 4, R = 0.025, and w R ( F o 2 ) = 0.060. In the case of compound 3, the crystal parameters of the monoclinic C 2/ m space group are a = 6.206(2) Å, b = 15.084(2) Å, c = 8.909(1) Å, β = 95.75(2)°, V = 829.8(3) Å 3, Z = 4, R = 0.029, and w R ( F o 2 )= 0.069. The pseudohalide ions have a dramatic influence in the molecular structures of the three compounds. Compound 1 is dinuclear, with the manganese(II) ions bridged by bpm ligands and with terminal bpm and NCS groups; compound 2 is a linear chain of manganese(II) ions bridged by bpm ligands in cis conformation, with terminal cyanate groups; compound 3 shows a two-dimensional honeycomb like structure, where the sheets consist of an infinite hexagonal array of manganese(II) ions bridged by bischelating bpm ligands and double end-on azido bridges. The manganese(II) ions have octahedral environments in all cases. Magnetic susceptibility measurements show antiferromagnetic couplings for compounds 1 and 2, while alternating ferro-antiferromagnetism is observed for compound 3 . The obtained exchange parameters are J = −0.72 K and J = −0.78 K for compounds 1 and 2, respectively. No theoretical model is available for compound 3, which represent the first two-dimensional honeycomb-like compound showing alternating signs in the magnetic interactions.