Ligand Effects on the Structures of Extended Networks of Dicyanamide-Containing Transition-Metal Ions

The structural characterization of a series of complexes of formula [M(dca)2L]n, where dca = dicyanamide, L =
1,10-phenanthroline (phen) [1−4] and 2,9-dimethylphenanthroline (2,9-dmphen) [9−12], and M = Mn (1 and 9), Fe
(2 and 10), Co (3 and 11), and Ni (4 and 12), has revealed the effect of the presence of the methyl substituents
of L on the resulting network. The structure of [Mn(dca)2(phen)]n (1), which is identical to those of 2−4, together
with the investigation of its magnetic properties in the temperature range of 77−300 K were reported elsewhere.
The use of the 4,7-dimethylphenanthroline (4,7-dmphen) as the co-ligand yielded a series of compounds of formula
[M(dca)2(4,7-dmphen)]n [M = Mn (5), Fe (6), Co (7), and Ni (8)], which are isostructural with 1−4. Compounds
containing phen (1−4) and 4,7-dmphen (5−8) are made of two-dimensional grids of metal atoms, each metal atom
being linked to three other metal centers through single (three metal atoms involved) and double (two metal atoms
involved) dca bridges exhibiting the μ-1,5 coordination mode. The isostructural complexes [M(dca)2(2,9-dmphen)]n
(9−12) also have a sheetlike structure, the metal atoms in each layer being linked by two single and one double
μ-1,5-dca units, as in 1−8. However, the topology of the network in 9−12 is different from that in 1−8 because of
the different arrangement of the two single μ-1,5 dca bridges:  cis in 1−8 versus trans in 9−12. The magnetic study
of compounds 1−12 in the temperature range of 1.9−290 K has revealed the occurrence of weak ferromagnetic
(M = Ni) and antiferromagnetic interactions (M = Mn, Fe, and Co). The different magnetic behavior in 1−12 was
analyzed in the light of their structures, and the values of the magnetic interactions were compared to those of
related systems.