A small methanoato ligand in the structural differentiation of copper(II) complexes |
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| Authors: | Bojan Kozlev
ar Elizabeta Mate Zvonko Jagli
i&#x; Lea Glaar Amalija Golobi
Peter Strauch Jan Moncol Nives Kitanovski Primo &#x;egedin |
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| Institution: | aFaculty of Chemistry and Chemical Technology, University of Ljubljana, 1000 Ljubljana, Slovenia;bInstitute of Mathematics, Physics and Mechanics & Faculty of Civil and Geodetic Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia;cInstitute of Chemistry, University of Potsdam, 14476 Golm, Germany;dDepartment of Inorganic Chemistry, Slovak Technical University, 81237 Bratislava, Slovakia |
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| Abstract: | Several copper(II) methanoato complexes, namely mononuclear Cu(O2CH)2(2-mpy)2] (1) (2-mpy = 2-methylpyridine), binuclear Cu2(μ-O2CH)4(2-mpy)2] (2), and the polynuclear {Cu(μ-O2CH)2(2-mpy)2]Cu2(μ-O2CH)4]}n (3) and {Na2Cu(μ-O2CH)2(O2CH)2]Cu2(μ-O2CH)4]}n (4), have been synthesized. The mononuclear complex 1 is formed by two asymmetric chelate methanoate anions and two 2-methylpyridine molecules, giving a highly distorted ‘elongated octahedral’ coordination sphere. Complex 1 decomposes outside the mother-liquid, transforming into a regular isolated binuclear paddle-wheel complex 2 with four intra-binuclear bridging methanoates and two axial 2-mpy ligands. The polynuclear complex 3 is formed of alternate mononuclear and binuclear building blocks resembling the central cores of 1 and 2, but with significant differences, especially for the methanoates of the mononuclear units. The oxygen atom of the mononuclear unit in the octahedral axial position in 3 is simultaneously coordinated to the axial position of the binuclear paddle-wheel central core, thus enabling a chain type of structure. A chain of alternate mononuclear and binuclear building blocks, as in the neutral compound 3, are found as well in the ionic polymeric compound 4, though two types of bridges are found in 4, while there is only one type in 3. Namely, the axial position of the octahedral mononuclear unit in 4 is occupied by the methanoate oxygen atom that is already a part of the binuclear paddle-wheel unit, while one equatorial methanoate from the mononuclear unit serves as a triatomic bridge to the axial position of the binuclear building block. A very strong antiferromagnetic interaction is found for all the complexes with the paddle-wheel building blocks Cu2(μ-O2CH)4] 2–4 (−2J = 444–482 cm−1), attributed to the methanoate intra-binuclear bridges. On the other hand, this strong antiferromagnetism, found already at room temperature, reduces the intensity of the EPR S = 1 spin signals reported for the isolated paddle-wheel complex 2. For the polymeric 3, only the spin S = ½ signals are found in the EPR spectra, and they are assigned to the mononuclear building blocks. No signals with a clear origin are however seen in the room temperature EPR spectrum of the polymeric analogue 4, only the S = ½ signals in the low temperature spectra. This feature is suggested to be due to a specific influence between the adjacent S = 1 (binuclear) and S = ½ (mononuclear) species via their bridges. |
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| Keywords: | Copper(II) Methanoate Formate 2-Methylpyridine Dimer Antiferromagnet |
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