Synthesis, crystal structure and magnetic properties of the dinuclear manganese(II) complexes [Mn 2(bpym) 3(NCX) 4] (bpym = 2,2′-bipyrimidine; X = S, Se)

Abstract

The dinuclear manganese(II) compounds of formula [Mn 2(bpym) 3(NCX) 4], where bpym = 2,2′-bipyrimidine and X = S(1) and Se(2), have been prepared and their crystal structures determined by X-ray diffraction methods. 1 and 2 are isostructural. They crystallize in the triclinic P 1 space group with Z = 1, γ ( Mo Kα ) = 0.71073 A ̊ , T = 295 K and a = 9.141(2), b = 9.248(2), c = 11.733(2) A ̊ , α = 74.88(2), β = 80.29(2), γ = 61.03(2)°, V = 836.7(3) A ̊ 3, D c = 1.621 g cm −3, M r = 316.7, F(000) = 412, and μ( Mo Kα) = 10.54 cm −1 for 1 and a = 9.244(2), b = 9.278(2) A ̊ , c = 11.887(2) A ̊ , α = 75.19(2), β = 80.83(2), γ = 61.54(2)°, V = 865.7(3) A ̊ 3, D c = 1.926 g cm −3, M r = 1004.3, F(000) = 464. and μ( Mo Kα) = 49.82 cm −1 for 2. A total of 3702 ( 1) and 4219 ( 2) reflections was collected over the range 3⩽2 θ⩽54°; of these, 3317 ( 1) and 3800 ( 2)were unique and 2802 ( 1) and 2975 ( 2) were considered as observed [1>3 σ( I)] and used in the structural analysis. The final R and R w residuals were 0.027 and 0.034 for 1 and 0.032 and 0.037 for 2. Both strcutures are made up of neutral centrosymmetric dinuclear units where each metal atom is bound to six nitrogen atoms belonging to two thiocyanate ( 1) or selenocyanate ( 2) groups in cis-positions and two bpym ligands, one terminal and the other bridging. The metal environment is distorted octahedral, the MnN bonds ranging from 2.403(2) to 2.114(3) in 1 and from 2.386(3) to 2.127(4) Å in 2. The intramolecular metal-metal separations for 1 and 2 are 6.223(1) and 6.211(1) Å, respectively. The magnetic properties have been investigated in the temperature ranges 2.4–300 K ( 1) and 4.0–300 K ( 2). The manganese(II) ions in 1 and 2 interact in an antiferromagnetic fashion with J = −1.19 ( 1) and −1.20 ( 2) cm −1 ( H ̂ = −J S ̂ A ∗d S ̂ B ). The magnetic coupling through bridging bpym in 1 and 2 is very close to that observed in other bpym-bridged manganese(II) complexes. A magneto-structural comparison with bpym-bridged first-row transition metal ions is carried out.