Modular construction of 3D coordination frameworks incorporating SiF62− links: Accessing the significance of [M(pyrazole)4{SiF6}] synthon

Abstract

Rational combination of Cd2+ cations, bitopic pyrazole ligands, bridging SiF62− and terminal NCS− anions provide generation of 3D frameworks and precise control over connectedness of the net nodes: two-fold interpenetrated 4-connected NbO-like net (nbo) in [Cd(Me4bpz)2{NCS}2]·⅔CH2Cl2 (1), uninodal 5-connected noz framework in [Cd2(Me4bpz)4{SiF6}{NCS}2]·6CHCl3 (2), novel 5-connected binodal topology (with a point symbol of {42.55.62.7}{42.56.62}) in [Cd2(Me4bpz)4{SiF6}{NCS}2]·2CH2Cl2 (3) and 6-connected α-Po cubic nets (pcu) in [Cd(Me4bpz)2{SiF6}]·6H2O (4) and [Cd(Me4bpz)2{SiF6}]·1.5CH2Cl2 (5) (Me4bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole). Hexafluorosilicate anions act as bridges between Cd ions yielding further linkage of 4-connected [Cd(Me4bpz)2] subtopologies. Characteristic and specific interaction between SiF62− and the metal–organic portion is conditioned by a synergy of coordination and multiple strong NH⋯F bonds, which suggests perfect compatibility of the bipyrazole and SiF62− linkers for the construction of 3D structures, either by pillaring of 2D layers or cross-linking of 3D frameworks. Two observed motifs, 1D [M(pyrazole)4{μ-SiF6}]n (in 4 and 5) and discrete [{M{NCS}(pyrazole)4}2{μ-SiF6}] (in 2 and 3) are discussed as special supramolecular synthons for the framework solids. An improved large-scale and cost-effective procedure for the synthesis of the organic ligand Me4bpz is also described.