Cymantrenecarboxylate complexes of nickel(II) and cobalt(II)

Reactions of cymantrenecarboxylic acid (CO)₃MnC₅H₄COOH (CymCOOH) with Ni(II) and Co(II) pivalates in boiling THF followed by extraction of the products with diethyl ether or benzene and treatment with triphenylphosphine gave the binuclear complexes LM(CymCOO)₄ML (M = Ni (I) and Co (II); L = PPh₃). Treatment of the benzene extract of the intermediate cobalt cymantrenecarboxylate with 2,6-lutidine (L’) yielded the trinuclear complex L’Co(CymCOO)₃Co(CymCOO)₃CoL’ (III). Complex I is antiferromagnetic; μ_eff decreases from 3.7 to 0.9 μ_B in a temperature range from 300 to 2 K. Structures I-III were identified using X-ray diffraction. The frameworks of complexes I and II are like Chinese lanterns, having four carboxylate bridges and axial ligands L (Ni-P, 2.358(1) Å; Co-P, 2.412(2) Å). The metal atoms are not bonded to each other (Ni…Ni, 2.7583(9) Å; Co…Co, 2808 (2) Å). In complex III, either terminal Co atom is coordinated to one ligand L’ (Co-N, 2.059(2) Å). The Co atoms form a linear chain showing no M-M bonds (Co…Co, 3.346(1) Å), in which either terminal Co atom is linked with the central Co atom by three carboxylate bridges (on average, Co_centr-O, 2.164 Å; CO_term-O, 2.094 Å). In one of three carboxylate groups, only one carboxylate O atom serves as a bridge, while the other is bonded to the terminal Co atom only (Co_term-O, 2.094 and 2.389 Å); so this carboxylate group is a bridging and chelating ligand.