Syntheses, Structure, and Magnetic Behavior of Two New Nickel(II) and Cobalt(II) Dinuclear Complexes with 1,4-Dicarboxylatopyridazine. MO Calculations of the Superexchange Pathway through the Pyridazine Bridge

Abstract

Two new dinuclear complexes of formula [M 2 (dcpz) 2 (H 2 O) 4 ] in which M is nickel(II) (1) or cobalt(II) (2) and dcpz is the bridging ligand 1,4-dicarboxylatopyridazine have been synthesized and characterized. The crystal structure for the nickel compound has been solved. Complex 1 crystallizes in the orthorombic system, space group Pbca(61), with FW ) 521.7, a ) 14.501(3) Å, b ) 13.169(3) Å, c ) 8.774(2) Å, V ) 1675(2) Å 3 , Z ) 4, and R ) 0.022. The cobalt compound is isomorphous to 1. The pyridazine ligand acts as a double bridge between the two paramagnetic centers. Magnetic measurements show moderate antiferromagnetic coupling, with J values of -33.6 cm -1 for 1 and -11.5 cm -1 for 2. Magnetostructural correlations have been obtained by extended-Hu ¨ckel MO calculations, and several electronic or structural factors that influence the coupling were analyzed.

Coordination Algorithms Control Molecular Architecture: [CuI4(L2)4]4+ Grid Complex Versus [MII2(L2)2X4]y+ Side‐By‐Side Complexes (M=Mn, Co, Ni, Zn; X=Solvent or Anion) and [FeII(L2)3][Cl3FeIIIOFeIIICl3]

“…[31] Of the other five nickel(ii) complexes, [26±30] with similar side-by-side structures to that of 5 a, the Ni ¥¥¥ Ni separations are in the range 3.791 ± 3.920 ä for those containing octahedral nickel(ii) ions, [26,27,29] and in the significantly lower range 3.587 ± 3.627 ä for those containing one square planar and one octahedral nickel(ii) ion. [28] No details are reported for the last of these structures and the data have not been deposited in the CCDC.…”

“…The exchange integral (J) for this high-spin dicobalt(ii) complex is À 7.6 cm , [14] and [Co 2 (dcpz) 2 . [29] The binuclear cobalt(ii) complex has a room temperature magnetic moment, m(RT) 4.54 m B , which is lower than values of mononuclear Co II , because of antiferromagnetic coupling. The value is comparable to those observed for related binuclear cobalt(ii) complexes, for example, [Co 2 (ppd) 2 [14] For the orange dimanganese(ii) complex 9, the value of c M gradually increased as the temperature was lowered, to give a maximum in c M at very low temperature (Figure 7).…”

“…Of the few structurally characterised doubly pyridazine-bridged-only nickel dimers (see above), those for which an exchange integral (J) is quoted include [Ni 2 (ppd) 2 , [27] and [Ni 2 (dcpz) 2 (H 2 O) 4 ], whereby dcpz is 1,4-dicarboxylatopyridazine and J À 33.6 cm À1 . [29] The J value observed for the doubly pyridazine-bridged dinickel complex 5 b, À 21.6 cm [27] The c M plots for 6 b show a maximum susceptibility value, at 30 K, and the corresponding m eff value decreases continuously from room temperature. The behaviour of the complex is typical of high-spin (S 3 ³2) cobalt(ii) dimers, which exhibit weak antiferromagnetic exchange between the cobalt(ii) centres.…”

Tuning of the Spin States in Trinuclear Cobalt Compounds of Pyridazine by the Second Simple Bridging Ligand

“…The strong electronegativity of oxygen results in only 1.87 and 1.962 Å for the average lengths of the bonds between the central cobalt atom and its bridging OH and pdz ligands, respectively. Differing from the pdz compounds published previously, [5][6][7][8][9][13][14][15] the bridging pdz ligands in 1 and 2 afford two nitrogen donors to the two adjacent metal atoms with quite different bond lengths, an average of 1.96 Å to the central and 2.17 Å to the terminal cobalt atoms. The bridging OH group also affords different bond lengths to the central (average 1.87 Å) and terminal cobalt atoms (average 1.98 Å).…”

“…Magnetic data and MO calculations indicate that the magnetic coupling of two metal ions in binuclear compounds of pdz always involves antiferromagnetic interactions through a short two-atom pdz exchange pathway. [8,9] However, in the trinuclear nickel() compound [Ni 3 (pdz) 6 (µ-SCN) 6 ], [10] for which the quasi Curie law magnetic behavior was published, the antiferromagnetic interaction through double pdz bridges was compensated for by the ferromagnetic interaction through a single end-on thiocyanato bridge. At that time, it was conjectured that the magnetic properties of such polynuclear bridging pyridazine ligand affords two nitrogen donors to two metal ions with different bond lengths.…”