The reaction of sodium pentaselenide with silver nitrate in dimethylformamide (DMF) was investigated. The addition of various counterions, Ph4P+, Me4N+, Et4N+, and Pr4N+, to this common reaction solution resulted in the isolation of four new soluble silver(I) pplyselenide complexes, [(Ph4P)Ag(Se4)]n (I), [(Me4N)Ag(Se5)]n (II), [(Et4N)Ag(Se4)]4 (III), and (Pr4N)2[Ag4(Se4)3] (IV), in high yield. Compound I (85% in yield) crystallizes in the monoclinic space group P21/c with unit cell dimensions a = 14.145 (3) Å, b = 7.076 (2) Å, c = 24.939 (5) Å, β = 105.23 (2)°, and V = 2408 Å3. Compound II (93% in yield) crystallizes in the monoclinic space group Cc with unit cell dimensions a = 11.350 (2) Å, b = 18.764 (3) Å, c = 7.434 (I) Å, β = 124.59 (1)°, and V = 1303 Å3. Compounds III and IV (96% and 76% in yield, respectively) belong to the monoclinic space group P21/n with unit cell dimensions a = 16.229 (3) Å, b = 11.480 (5) Å, c = 17.171 (3) Å, β = 106.06 (1)°, and V = 3074 Å3 and a = 10.493 (2) Å, b = 24.573 (3) Å, c = 17.499 (1) Å, β = 93.84 (1)°, and V = 4502 Å3, respectively. All structures were solved and refined by direct methods and Fourier techniques. All non-hydrogen atoms were refined anisotropically, and all hydrogen atoms were calculated and included but not refined. Refinement by full-matrix least-squares methods on these structures gave final R values of 7.5% for I, 5.2% for II, 2.8% for III, and 3.3% for IV. The four compounds are divided into two different structural categories: one-dimensional chains, [(Ph4P)Ag(Se4)]n and [(Me4N)Ag(Se5)]n, and discrete molecular clusters, [(Et4N)Ag(Se4)]4 and (Pr4N)2[Ag4(Se4)3]. The structures of these four silver(I) polyselenide compounds feature two types of coordination spheres for the Ag atoms, trigonal planar and tetrahedral. Compound I consists of infinite macroanionic chains separated by the cation Ph4P+, forming a unique one-dimensional structure containing five-membered AgSe4 rings. These rings are generated from each other by a 2-fold screw axis operation. Each [Ag(Se4)]nn- chain contains trigonal-planar Ag+ atoms. Similarly, compound II is a one-dimensional polymer consisting of AgSe5 as repeat units in which AgSe4 forms a five-membered ring. The [Ag(Se5)]nn- chain can be generated by a 2-fold screw axis along the chain direction. The Ag+ atoms in this structure adopt a tetrahedral coordination geometry. Compound III is molecular. The anion [Ag(Se4)]44- possesses a crystallographic inversion center. Four silver atoms are symmetrically disposed around the inversion center, forming a planar rhombus. The structure features two different kinds of Ag coordination, Ag(I) and Ag′(1) are tetrahedrally coordinated, while the other two Ag(2) and Ag′(2) possess a trigonal-planar coordination. The [Ag4(Se4)3]2- anion features a tetrahedral array of Ag atoms "glued" together by three Se42- ligands, forming a Ag4Se6 central adamantane-like core in which all Ag+ ions assume a trigonal-planar coordination. We found a correlation of counterion size and Ag coordination number in these compounds. The smaller the counterions, the higher the silver coordination number. Variable-temperature 77Se NMR spectra of I-IV are reported. The IR spectra of the compounds exhibit two absorptions at ∼265 and ∼195 cm-1. The former is assigned tentatively to the vSe·Se vibration. I-III have similar UV/vis spectra in DMF with two absorptions at ∼450 and ∼630 nm, while IV has a featureless spectrum. Thermal gravimetric analysis data are reported.
|Number of pages||12|
|Publication status||Published - 1991|
ASJC Scopus subject areas
- Inorganic Chemistry