Magnetic Characteristics of New Cyano-Bridged Two-Dimensional Honeycomb-Like Bimetallic Assemblies Containing Ni(II)−N≡C−Cr(III) or Ni(II)−N≡C−Cr(I) Linkages

Three cyano-bridged bimetallic assemblies, [NiL1]3[Cr(CN)6]2·7H2O (1), [NiL2]3[Cr(CN)6]2·9H2O (2), and [NiL2]3[Cr(CN)5(NO)]2·9H2O (3) (L1 = 3,10-dimethyl-1,3,5,8,10,12-hexaazacycloctadecane and L2 = 3,10-diethyl-1,3,5,8,10,12-hexaazacycloctadecane), have been prepared and characterized structurally and magnetically. Complex
1 crystallizes in the monoclinic space group of C2/c with a = 25.929 Å, b = 15.442(3) Å, c = 19.553(4) Å, β
= 106.21(3)°, and Z = 4, while 2 and 3 are in the trigonal space group P3̄ with a = b = 14.919(2) Å, c =
9.5246(19) Å, γ = 120°, and Z = 1 for 2 and a = b = 14.863(2) Å, c = 9.3134(19) Å, γ = 120°, and Z = 1 for
3. The structures of 1−3 are similar and consist of cyano-bridged two-dimensional (2D) honeycomb-like neutral
Ni3Cr2 layers. In each complex, [Cr(CN)6]3- or [Cr(CN)5(NO)]3- coordinates to three trans-[Ni(macrocycle)]2+
groups using three fac-CN- ligands, providing a 2D layered network. The NO group in [Cr(CN)5(NO)]3- remains
monodentate. Magnetic studies show the existence of a short-range ferromagnetic interaction in all of the complexes.
Complexes 1 and 2 exhibit long-range antiferromagnetic ordering at 13.0 and 11.9 K, respectively, and a
metamagnetic transition with critical field of ca. 1.6 kOe for 1 and 1.5 kOe for 2 at 1.8 K. Complex 3 exhibits
long-range ferromagnetic ordering below 4.3 K.