Architecture Dependence on the Steric Constrains of the Ligand in Cyano-Bridged Copper(I) and Copper(II)−Copper(I) Mixed-Valence Polymer Compounds Containing Diamines: Crystal Structures and Spectroscopic and Magnetic Properties

A family of cyano-bridged copper(II)−copper(I) mixed-valence polymers containing diamine ligands of formula
[Cu(pn)2][Cu2(CN)4] (1, pn = 1,2-propanediamine), [Cu2(CN)3(dmen)] (2, dmen = N,N-dimethylethylenediamine),
and [Cu3(CN)4(tmen)] (3, tmen = N,N,N‘,N‘-tetramethylethylenediamine) have been prepared with the aim of analyzing
how their architecture may be affected by steric constraints imposed by the diamine ligands. In the absence of
diamine and with use of the voluminous NEt4+ cation, the copper(I) polymer [NEt4][Cu2(CN)3] (4) forms. The structure
of 1 consists of a three-dimensional diamond-related anionic framework host, [Cu2(CN)4]2-, and enclathrated
[Cu(pn)2]2+ cations. The structure of 2 is made of neutral corrugated sheets constructed from fused 18-member
nonplanar rings, which contain three equivalent copper(I) and three equivalent copper(II) centers bridged by cyanide
groups in an alternative form. The 3D structure of 3 consists of interconnected stair-like double chains built from
fused 18-member rings, which adopt a chairlike conformation. Each ring is constructed from two distorted trigonal
planar Cu(I) centers, two bent seemingly two-coordinated Cu(I) centers, and two pentacoordinated Cu(II) atoms.
The structure 4 is made of planar anionic layers [Cu2(CN)3]nn- lying on mirror planes and NEt4+ cations intercalated
between the anionic layers. From the X-ray structural results and calculations based upon DFT theory some
conclusions are drawn on the structure−steric factors correlation in these compounds. Compound 1 exhibits very
weak luminescence at 77 K with a maximum in the emission spectrum at 520 nm, whereas compound 4 shows
an intense luminescence at room temperature with a maximum in the emission spectrum at 371 nm. Polymers 2
and 3 exhibit weak antiferromagnetic magnetic exchange interactions with J = −0.065(3) and −2.739(5) cm-1,
respectively. This behavior have been justified on the basis of the sum of two contributions:  one arising from the
pure ground-state configuration and the other one from the charge-transfer configuration CuI−CN−CuII−CN−CuII
that mixes with the ground-state configuration.