Zinc(II) vs cadmium(II) in organic chelate-free chemistry: Synthesis and characterization of 1-D [Zn2(N3)4(MeCN)3]n and 2-D [Cd3(N3)6(MeCN)2]n coordination polymers. (1st November 2021)

• Record Type: Journal Article
• Authors: Papanikolaou, Gavriilia T.; Kourtellaris, Andreas; Pantelis, Konstantinos N.; Bekiari, Vlasoula; Tasiopoulos, Anastasios J.; Stamatatos, Theocharis C.
• Is Part Of: Polyhedron. Volume 208(2021)
• Publication Date: 2021-11-01
• Subjects: Zinc -- Cadmium -- Coordination polymers -- Single-crystal X-ray crystallography -- Azides -- Emission; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2021.115423
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: A new synthetic route to purely azido-bridged coordination polymers of Group 12 metals has led to an 1-D chain comprising {Zn4 } defective dicubane repeating units (top) and a 2-D network consisting of {Cd4 } cubane clusters linked to mononuclear {Cd(N3 )4 } tetrahedra (bottom). Abstract: The employment of a relatively unexplored reagent, namely the Me3 SiN3, in the coordination chemistry of Zn(II) and Cd(II), in the absence of any external organic chelating/bridging ligand, has led to two new, azido-bridged coordination polymers with formulae [Zn2 (N3 )4 (MeCN)3 ]n (1 ) and [Cd3 (N3 )6 (MeCN)2 ]n (2 ), respectively. The reaction between Zn(ClO4 )2 ·6H2 O, Me3 SiN3 and NEt3 in an 1:8:2 molar ratio afforded colorless needle-like crystals of the 1-D chain 1, whereas the exact same reaction but with Cd(ClO4 )2 ·6H2 O in place of the Zn II starting material resulted in the formation of colorless needles of the 2-D polymer 2 . The repeating unit of 1 consists of a [Zn4 (N3 )8 (MeCN)6 ] cluster with a defective dicubane core; the vertices of the latter are occupied by the four metal ions and the bridging ligation is provided by two μ3 -1, 1, 1 (or 3.30) and six μ-1, 1 (or 2.20) end-on N3 − groups. In contrast, compound 2 comprises a central [Cd4 (μ3 -N3 )4 (MeCN)4 ] 4+ cubane-like unit, unprecedented in the coordination chemistry of Cd II, which is linked to [Cd(N3 )4 ] 2− tetrahedra through μ-1, 1 end-on N3 − groups, eventually forming the overall layered structure of 2 . Topological analysis of 2 shows a trinodal (3, 4, 5) network with stoichiometry (3-c)2 (4-c)(5-c)2 and a very rare topological type of 3, 4, 5L6 . Terminal ligation in both 1 and 2 is solely provided by MeCN solvate molecules. Despite the optical inactivity of complex 1, the 2-D polymer 2 exhibits an intense violet-to-blue emission upon excitation at 225 or 277 nm in the solid-state, which is tentatively ascribed to an intra-ligand fluorescence from the coordinated azido groups within the robust 2-D network. Although it is strongly evidenced that the chemistry of Zn II and Cd II follows the same general trends, and thus the majority of these coordination compounds are isomorphous, the present study demonstrates the formation of two chemically, structurally and optically different compounds of divalent Group 12 metal ions, under the exact same experimental conditions. This work may pave the way to further study the chemical, structural and physicochemical properties of organic chelate-free coordination polymers and clusters using different Me3 SiX (X = OCN −, SCN −, CN − and RCO2 − ) reagents.