Heterobimetallic Coordination Polymers Incorporating [M(CN)2]-(M = Cu, Ag) and [Ag2(CN)3]-Units: Increasing Structural Dimensionality via M−M‘ and M···NC Interactions

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Abstract
A series of new heterometallic coordination polymers has been prepared from the reaction of metal−ligand cations and KAg(CN)2 units. Many of these contain silver−silver (argentophilic) interactions, analogous to gold−gold interactions, which serve to increase supramolecular structural dimensionality. Compared to [Au(CN)2]- analogues, these polymers display new trends specific to [Ag(CN)2]-, including the formation of [Ag2(CN)3]- and the presence of Ag···N interactions. [Cu(en)2][Ag2(CN)3][Ag(CN)2] (1, en = ethylenediamine) forms 1-D chains of alternating [Ag(CN)2]- and [Ag2(CN)3]- units via argentophilic interactions of 3.102(1) Å. These chains are connected into a 2-D array by strong cyano(N)−Ag interactions of 2.572(3) Å. [Cu(dien)Ag(CN)2]2[Ag2(CN)3][Ag(CN)2] (2, dien = diethylenetriamine) forms a 1-D chain of alternating [Cu(dien)]2+ and [Ag(CN)2]- ions with the Cu(II) atoms connected in an apical/equatorial fashion. These chains are cross-linked by [Ag2(CN)3]- units via argentophilic interactions of 3.1718(8) Å and held weakly in a 3-D array by argentophilic interactions of 3.2889(5) Å between the [Ag(CN)2]- in the 2-D array and the remaining free [Ag(CN)2]-. [Ni(en)][Ni(CN)4]·2.5H2O (4) was identified as a byproduct in the reaction to prepare the previously reported [Ni(en)2Ag2(CN)3][Ag(CN)2] (3). In [Ni(tren)Ag(CN)2][Ag(CN)2] (5, tren = tris(2-aminoethyl)amine), [Ni(tren)]2+ cations are linked in a cis fashion by [Ag(CN)2]- anions to form a 1-D chain similar to the [Au(CN)2]- analogue. [Cu(en)Cu(CN)2Ag(CN)2] (6) is a trimetallic polymer consisting of interpenetrating (6,3) nets stabilized by d10−d10 interactions between Cu(I)−Ag(I) (3.1000(4) Å). Weak antiferromagnetic coupling has been observed in 2, and a slightly stronger exchange has been observed in 6. The Ni(II) complexes, 4 and 5, display weak antiferromagnetic interactions as indicated by their relatively larger D values compared to that of 3. Magnetic measurements on isostructural [Ni(tren)M(CN)2][M(CN)2] (M = Ag, Au) show that Ag(I) is a more efficient mediator of magnetic exchange as compared to Au(I). The formation of [Ni(CN)4]2-, [Ag2(CN)3]-, and [Cu(CN)2]- are all attributed to secondary reactions of the dissociation products of the labile KAg(CN)2.

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