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

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) over bar space group with Z=1, lambda (Mo K alpha)=0.71073 Angstrom, T=295 K and a=9.141(2), b=9.248(2), c=11.733(2) Angstrom, alpha=74.88(2), beta=80.29(2), gamma=61.03(2)degrees, V=836.7(3) Angstrom(3), D-c=1.621 g cm(-3), M-r=816.7, F(000)=412, and mu(Mo K alpha)=10.54 cm(-1) for 1 and a=9.244(2), b=9.278(2)Angstrom, c=11.887(2)Angstrom, a=75.19(2), beta=80.83(2), gamma=61.54(2)degrees, V=865.7(3)Angstrom(3), D-c=1.926 g cm(-3), M-r=1004.3, F(000)=484, and mu(Mo K alpha)=49.82 cm(-1) for 2. A total of 3702 (1) and 4219 (2) reflections was collected over the range 3 less than or equal to 2 theta less than or equal to 54 degrees; of these, 3317 (1) and 3800 (2) were unique and 2802 (1) and 2975 (2) were considered as observed [l>3 sigma(l)] 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 structures 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) A in 2. The intramolecular metal-metal separations for 1 and 2 are 6.223(1) and 6.211(1) A, 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) over cap=-J (S) over cap(A) .(S) over cap(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.