Synthesis, crystal structure, magnetic properties and DFT calculations of new dihydroxo-bridged binuclear chromium(III) based on monodentate mixed ligand

A new dihydroxo-bridged binuclear chromium(III) complex [Cr(µ-OH)(Py)2(N3)2]2•Py has been synthesized and characterized by elemental analyses, infrared spectroscopy, single crystal X-ray diffraction and magnetic measurements. This metal complex crystallizes in the monoclinic space group P21/c with two binuclear formula units in the crystal cell dimensions a = 10.114(5) A, b = 10.416(5) A, c = 17.341(5) A and β = 105.248(5)°. The Cr…Cr separation is 3.042 (2) A and the bridging Cr–O–Cr angle is 101.83(3)°. In addition, moderate O-H…N hydrogen bond and weak C-H…N and π–π stacking interactions, link the components of the structure into a three-dimensional network. The magnetic susceptibility of a powdered sample has been examined in the temperature range 1.8–300 K. The dinuclear complex exhibits an antiferromagnetic exchange interactions between the metal centers, with the best fit to the Van Vleck equation including biquadratic exchange yielding J = −6.762(9) cm−1 and (g) = 1.9938(2). DFT geometry optimizations using the two B3LYP and PBE0 hybrid functionals were carried out (spin-orbit coupling omitted) on dichromium [CrIII(μ-OH)2CrIII] complex 1 in high spin (HS) septet ground state with valence electronic 3d3α⋅⋅⋅3d3α configuration. The broken symmetry (BS) 3d3α⋅⋅⋅3d3β state was predicted slightly lower in energy than the HS one, suggesting an occurrence of weak antiferromagnetic coupling between the two Cr(III) metal spin carriers. The computed super-exchange constant J equals to −5.19 cm−1, in keeping with the experimental value. The DFT/B3LYP/BS results show that the spin density is mostly localized on the two Cr(III) metal centers. The DFT results reveal that the weak exchange coupling exhibited by the complex is due to the small spin density along the dihydroxo-bridged path [CrIII(μ-OH)2CrIII] linking the two metal spin carriers.