SYMMETRICAL AND UNSYMMETRICAL COMPOUNDS HAVING A LINEAR CO-3(6+) CHAIN LIGATED BY A SPIRAL SET OF DIPYRIDYL ANIONS

Four compounds of the type Co-3(dpa)(4)XY-where X and Y are Cl or BF4 and dpa is the anion of dipyridylamine-have been prepared and structur ally characterized. For X = Y = Cl, two significantly different types of complexes are formed. In one of them, Co-3(dpa)(4)Cl-2 . CH2Cl2, 1, there is only one crystallographically independent Go-Co distance (2. 3178(9) Angstrom). In the second type of crystal, a mononuclear Co(dpa )(2) molecule is also found in the interstices of the crystal to give Co-3(dpa)(4)Cl-2 . Co(dga)(2), 2. Compound 2 has two independent and h ighly unsymmetrical Go-Co separations (2.285(1) and 2.459(1) Angstrom) corresponding to a bonding and a nonbonding interaction. Reaction of 1 with 1 or 2 equiv of AgBF4 yields Co-3(dpa)(4)Cl(BF4). 2CH(2)Cl(2), 3, and Co-3(dpa)(4)(BF4). 2CH(2)Cl(2), 4, respectively. Similarly to 2 , compound 3 has a short and a long Go-Co separation (2.277 and 2.504( 2) Angstrom, respectively). However, 4 has independent but equal Go-Co distances of 2.253[2] Angstrom, which are similar to that of 1. We pr opose that since compounds of 1 and 2 differ only in the composition o f the interstitial molecules (CH2Cl2 and Co(dpa)2, respectively) but t he Go-Co bonding is so different, then the Co-3(dpa)(4)Cl-2 species sh ould be considered as ''stretch isomers''.