Dynamic Motion of Organic Ligands in Polar Layered Cobalt Phosphonates

Abstract

By introducing the polar methoxy group into phenyl- or benzyl-phosphonate ligands, four cobalt phosphonates with layered structures are obtained, namely, [Co(4-mopp)(H O)] (1), [Co(4-mobp)(H O)] (2), [Co(3-mopp)(H O)] (3), and [Co(3-mobp)(H O)] (4), where 4- or 3-moppH is (4- or 3-methoxyphenyl)phosphonic acid and 4- or 3-mobpH is (4- or 3-methoxybenzyl)phosphonic acid. Compounds 1, 2, and 4 crystallize in the polar space groups Pmn2 or Pna2 , whereas compound 3 crystallizes in the centrosymmetric space group P2 /n. The layer topologies in the four structures are similar and can be viewed as perovskite type, where the edge-sharing [Co O ] rhombi are capped by the PO C groups. The phenyl and MeO groups in compounds 1-3 are heavily disordered, whereas that in 4 is ordered. Structural comparison based on the data at 296 and 123 K reveals distinct dynamic motion of the organic groups in compounds 1 and 2. The fluctuation of the polar MeO groups in these two compounds is confirmed by dielectric relaxation measurements. In contrast, the fluctuation of polar groups in compounds 3 and 4 is not evident. Interestingly, the dehydrated samples of 3 and 4 (i.e., 3-de and 4-de) exhibit one-step and two-step phase transitions associated with the motion of polar organic groups, as proven by DSC and dielectric measurements. The magnetic properties of compounds 1-4 are investigated, and strong antiferromagnetic interactions are found to mediate between the magnetic centers through μ-O(P) and O-P-O bridges.

Cobalt(II)‐dianthracene Frameworks: Assembly, Exfoliation and Properties

“…While Co2 has a distorted seesaw geometry ( C 2 v , CShM=0.476), coordinated by four oxygen atoms from four phosphonate groups (O2, O8, O6 A and O12B) [Co2−O: 1.932(4)–1.948(4) Å, O−Co2−O: 102.3(2) –114.9(2)°] (Table S4). The Co−O bond lengths are comparable to those in the other cobalt phosphonate compounds containing tetrahedrally or octahedrally coordinated Co(II) ions [32–34] . Two amp 2 H 2 2− are crystallographically distinguished, each serves as a tridentate ligand by using three phosphonate oxygen atoms from its two singly protonated phosphonate groups (Scheme 1a).…”

“…The CoÀ O bond lengths are comparable to those in the other cobalt phosphonate compounds containing tetrahedrally or octahedrally coordinated Co(II) ions. [32][33][34] Two amp 2 H 2 2À are crystallographically distinguished, each serves as a tridentate ligand by using three phosphonate oxygen atoms from its two singly protonated phosphonate groups (Scheme 1a). One phosphonate group of each amp 2 H 2 2À provides two oxygen donors (O1 and O2, O7 and O8) to bridge Co1 and Co2 atoms forming dimers of {Co 2 (PO 3 H) 2 }.…”