Synthesis, Structure, and Magnetic Properties of Regular Alternating μ-bpm/di-μ-X Copper(II) Chains (bpm = 2,2′-bipyrimidine; X = OH, F)

The preparation and X-ray crystal structure of four 2,2′-bipyrimidine (bpm)-containing copper­(II) complexes of formula {[Cu₂(μ-bpm)­(H₂O)₄(μ-OH)₂]­[Mn­(H₂O)₆]­(SO₄)₂}_<i>n</i> (<b>1</b>), {[Cu₂(μ-bpm)­(H₂O)₄(μ-OH)₂]­SiF₆}_<i>n</i> (<b>2</b>), {Cu₂(μ-bpm)­(H₂O)₂(μ-F)₂F₂}_<i>n</i> (<b>3</b>), and [Cu­(bpm)­(H₂O)₂F­(NO₃)]­[Cu­(bpm)­(H₂O)₃F]­NO₃·2H₂O (<b>4</b>) are reported. The structures of <b>1</b>–<b>3</b> consist of chains of copper­(II) ions with regular alternation of bis-bidentate bpm and di-μ-hydroxo (<b>1</b> and <b>2</b>) or di-μ-fluoro (<b>3</b>) groups, the electroneutrality being achieved by either hexaaqua manganese­(II) cations plus uncoordinated sulfate anions (<b>1</b>), uncoordinated hexafluorosilicate anions (<b>2</b>), or terminally bound fluoride ligands (<b>3</b>). Each copper­(II) ion in <b>1</b>–<b>4</b> is six-coordinated in elongated octahedral surroundings. <b>1</b> and <b>2</b> show identical, linear chain motifs with two bpm-nitrogen atoms and two hydroxo groups building the equatorial plane at each copper­(II) ion and the axial position being filled by water molecules. In the case of <b>3</b>, the axial sites at the copper atom are occupied by a bpm-nitrogen atom and a bis-monodentate fluoride anion, producing a “step-like” chain motif. The values of the angle at the hydroxo and fluoro bridges are 94.11(6) (<b>1</b>), 94.75(4) (<b>2</b>), and 101.43(4)° (<b>3</b>). In each case, the copper–copper separation through the bis-bidentate bpm [5.428(1) (<b>1</b>), 5.449(1) (<b>2</b>), and 5.9250(4) Å (<b>3</b>)] is considerably longer than that through the di-μ-hydroxo [2.8320(4) (<b>1</b>) and 2.824(1) Å (<b>2</b>)] or di-μ-fluoro [3.3027(4) Å (<b>3</b>)] bridges. Compound <b>4</b> is a mononuclear species whose structure is made up of neutral [Cu­(bpm)­(H₂O)₂F­(NO₃)] units, [Cu­(bpm)­(H₂O)₃F]⁺ cations, uncoordinated nitrate anions, and crystallization water molecules, giving rise to a <i>pseudo</i>-helical, one-dimensional (1D) supramolecular motif. The magnetic properties of <b>1</b>–<b>3</b> have been investigated in the temperature range 1.9–300 K. Relatively large, alternating antiferro- [<i>J</i> = −149 (<b>1</b>) and −141 cm^–1 (<b>2</b>) across bis-bidentate bpm] and ferromagnetic [α<i>J</i> = +194 (<b>1</b>) and +176 cm^–1 (<b>2</b>) through the dihydroxo bridges] interactions occur in <b>1</b> and <b>2</b> [the Hamiltonian being defined as <i>H</i> = −<i>J</i>∑_<i>i</i>=1^<i>n</i>/2 (<i>S</i>_2<i>i</i>·<i>S</i>_{2<i>i</i>–1} – α<i>S</i>_2<i>i</i>·<i>S</i>_2<i>i</i>+1)]. These values compare well with those previously reported for parent examples. Two weak intrachain antiferromagnetic interactions [<i>J</i> = −0.30 and α<i>J</i> = −8.1 cm^–1 across bpm and the di-μ-fluoro bridges, respectively] whose values were substantiated by density functional theory (DFT)-type calculations occur in <b>3