Abstract
The reaction of select copper(II) monocarboxylates Cu(RCOO)2(H2O)x (R = C4H3O, C6H5, H; x = 2, 4) with pyrazole (Hpz), carried out in protic solvents, yields mono- or dinuclear species [Cu(RCOO)2(Hpz)n]m (n = 2, 4; m = 1, 2), always accompanied by tri- or hexanuclear derivatives based on the triangular [Cu3(μ3-OH)(μ-pz)3]2+ fragment. The molecular structures of all isolated compounds have been established through XRD determinations. In some cases, the mono-, or dinuclear species act as secondary building units, self-assembling into 1D or 3D coordination polymers. The hexanuclear benzoate cluster contains coordinated and crystallization MeOH molecules, whose removal generates a crystalline 1D coordination polymer that can be reconverted into the hexanuclear cluster by soaking in MeOH. The relatively high pKb values of carboxylate anions employed in the syntheses are responsible for the preferential formation of mono- or dinuclear species rather than tri- or hexanuclear ones.
Highlights
Design and optimization of functional coordination polymers (CPs) is based on structure−property relationships that permit to foresee the contribution of building blocks, functional groups, guest molecules, and their interaction to the overall properties.[1−5] the following realization of desired structural topologies incorporating selected components is not just governed by choice of geometry, size, conformation, and number and nature of the binding sites of the building blocks,[6,7] but it critically depends on reaction conditions that control their self-assembly.[8−13] progress in the development of targeted materials requires the rationalization and generalization of the effect of fundamental parameters that may be used to a priori design and drive the synthesis
From the reactions of hydrated CuII 2-furancarboxylate, formate, and benzoate with Hpz in protic solvents two CPs based on mono- (1m2) and dinuclear (2d) secondary building units (SBUs), as well as four mono- (1m4 and 3m), tri- (1t), and hexanuclear (3h) species (Table 2) were isolated and structurally characterized
The first product isolated from the reaction of copper(II) 2-furancarboxylate with Hpz consisted in few dark-blue crystals of compound [Cu3(μ3OH)(μ-pz)3(Furc)2(Hpz)]·H2O, 1t, which were employed to achieve a Single crystal X-ray diffraction (SCXRD) structural characterization and an IR
Summary
Design and optimization of functional coordination polymers (CPs) is based on structure−property relationships that permit to foresee the contribution of building blocks, functional groups, guest molecules, and their interaction to the overall properties.[1−5] the following realization of desired structural topologies incorporating selected components is not just governed by choice of geometry, size, conformation, and number and nature of the binding sites of the building blocks,[6,7] but it critically depends on reaction conditions that control their self-assembly.[8−13] progress in the development of targeted materials requires the rationalization and generalization of the effect of fundamental parameters that may be used to a priori design and drive the synthesis.Taking into account that azolates are polytopic synthons suitable to generate CPs frameworks[14−22] and that monocarboxylate ions may bridge up to four metal ions, in recent years, we have studied the effect of reaction conditions on the interaction of copper(II) carboxylates with N-donor ligands. The reaction of some CuII monocarboxylates with pyrazole (Hpz) in dry MeCN leads to the 1D CP [Cu(pz)2],23−25 a flexible framework showing a “porosity without pore” behavior.[26] On the contrary, by performing the same reaction in protic solvents and in the presence of water, 1D and 2D CPs, where monocarboxylate ions bridge two trinuclear triangular moieties [Cu3(μ3-OH)(μ-pz)3]2+ (Chart 1), formed.[27−32] A possible reaction mechanism for the formation of the trinuclear triangular species was proposed in ref 33. We have reported that the basicity of carboxylates appears to play a primary role in controlling the formation of trinuclear triangular species in protic solvents. This result can be understood in terms of their ability to efficiently
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