Pyrophosphate-mediated magnetic interactions in Cu(II) coordination complexes

Nadia Marino, Oluwatayo F. Ikotun, Miguel Julve, Francesc Lloret, Juan Cano, Robert P. Doyle

Research output: Contribution to journalArticle

45 Scopus citations

Abstract

The reaction in water of Cu(NO3)2·2.5H 2O with 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), or 1,10-phenanthroline-5-amine (phenam), and sodium pyrophosphate (Na 4P2O7), at various pHs, afforded three new copper(II)-pyrophosphate complexes, namely, {[Cu(bipy)(cis-H2P 2O7)]2}·3H2O (1a), {[Cu(phen)(H2O)]4(HP2O7) 2}(ClO4)2·4H2O (2), and {[Cu2(phenam)2(P2O7)] 2·25H2O}n (3). A solvent free crystalline phase of 1a was also isolated with formula {[Cu(bipy)(trans-H 2P2O7)]2} (1b), which can be regarded as a pseudo-polymorph of 1a. Single crystal X-ray analyses revealed these compounds to have uncommon molecular architectures, with 3 being an unprecedented pyrophosphate-containing two-dimensional (2D) polymer. Compounds 1a/1b and 2 are discrete di- and tetra-nuclear complexes, respectively. The cationic {[Cu(phen)(H2O)]4(HP2O 7)2}2+ unit in 2 presents a unique quasi-flat structure, held together by solely in-plane pyrophosphate bridging modes (short Oeq-P-Oeq and long Oeq-P-O-P-Oeq pathways), a coordination arrangement also not previously reported. A different tetranuclear copper(II)-pyrophosphate arrangement is found in 3, with two classically bridged dimers (Oeq-P-Oeq pathway) joined together by auxiliary equatorial-axial μ-O pyrophosphate bridges. Here, the bidimensionality is reached through bridging phenam ligands, which provide further inter-"tetramer" metal-metal connections [(N,N′) eq-(N″)ax pathway], leading to the formation of an expanded covalent network based on the [Cu2(phenam) 2(P2O7)]2 moiety. Variable-temperature magnetic susceptibility measurements on polycrystalline samples of 2 and 3 revealed net antiferromagnetic coupling between metal centers with J2a = -7.9(2) cm-1, J2b = -46.9(3) cm-1, J2c = 0 cm-1 in 2 (H = -J 2a[SCu(1)·SCu(2) + S Cu(1a)·SCu(2a)] - J2b[S Cu(1)·SCu(2a) + SCu(1a)·S Cu(2)] - J2cSCu(2)·SCu(2a)), and J3a = -87.9(2) cm-1, J3b = -5(1) cm -1 and J3c = +5(3) cm-1 in 3 (H = -J 3a[SCu(1)·SCu(2) + S Cu(1a)·SCu(2a)] - J3b[S Cu(1)·SCu(2a) + SCu(1a)·S Cu(2)] - J3cSCu(2)·SCu(2a)). For 1a, a net ferromagnetic coupling is observed with J1a = +0.86(1) cm-1 (H = -J SA·SB + S A·D·SB + βH (gASA + gBSB). This is the first example of ferromagnetic coupling in pyrophosphate-complexes reported to date. A structure-function correlation study focusing on magnetic exchange across the observed diverse pyrophosphate-bridges is described with density functional theory (DFT) calculations included to support the stated observations.

Original languageEnglish (US)
Pages (from-to)378-389
Number of pages12
JournalInorganic Chemistry
Volume50
Issue number1
DOIs
StatePublished - Jan 3 2011

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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