A Novel Bis Tridentate Bipyridine Carboxamide Ligand and Its Complexation to Copper(II): Synthesis, Structure, and Magnetism

A new bis tridentate ligand 2,2‘-bipyridine-3,3‘-[2-pyridinecarboxamide] H2L1 which can bind transition metal ions
has been synthesized via the condensation of 3,3‘-diamino-2,2‘-bipyridine together with 2-pyridine carbonyl chloride.
Two copper(II) coordination compounds have been prepared and characterized:  [Cu2(L1)(hfac)2]·3CH3CN·H2O (1)
and [Cu2(L1)Cl2]·CH3CN (2). The single-crystal X-ray structures reveal that complex 1 crystallizes in the triclinic
space group P1̄, with the unit cell parameters a = 12.7185(6) Å, b = 17.3792(9) Å, c = 19.4696(8) Å, α =
110.827(2)°, β = 99.890(3)°, γ = 97.966(3)°, V = 3868.3(3) Å3, Z = 4, R = 0.0321 and Rw = 0.0826. Complex
2 crystallizes in the monoclinic space group P21/n with the unit cell parameters a = 12.8622(12) Å, b = 9.6100(10) Å, c = 19.897(2) Å, β = 102.027(3)°, V = 2405.3(4) Å3, Z = 4, R = 0.0409 and Rw = 0.1005. In both
complexes the ligand is in the dianionic form and coordinates the divalent CuII ions via one amido and two pyridine
nitrogen donor atoms. In 1, the coordination geometry around both CuII ions is best described as distorted trigonal
bipyramidal where the remaining two coordination sites are satisfied by hexafluoroacetylacetonate counterions. In
2 both CuII ions adopt a (4 + 1) distorted square pyramidal geometry. One copper forms a longer apical bond to
an adjacent carbonyl oxygen atom, whereas the second copper is chelated to a neighboring Cu−Cl chloride ion to
afford a μ-Cl-bridged dimerized [Cu2(L1)Cl2]2 complex. The magnetic susceptibility data for 1 (2 −270 K), reveal the
occurrence of weak antiferromagnetic interactions between the CuII ions. In contrast, variable-temperature magnetic
susceptibility measurements for 2 reveal more complex magnetic properties, with the presence of a weak
antiferromagnetic exchange (J = −10.1 K) between the copper ions in each dinuclear copper complex and a
stronger ferromagnetic exchange interaction (J = 32.9 K) between the CuII ions of the Cu(μ-Cl)2Cu dimeric bridging
units.