Synthesis , Crystal Structures , and Magnetic Properties of Ternary M ( II )-Dicyanamide-hydroxypyridine Complexes

Three two-dimensional (2D) and 3D supramolecular coordination architectures based on ternary M(II)-dicyanamide-2-hydroxypyridine systems, [Co(hmpH) 2 (dca) 2 ] (1), [Cu(hmpH) 2 (dca) 2 ] (2), and [Mn(hepH) 2 (dca) 2 ] (3) (dca = dicyanamide, hmpH = 2-(hydroxymethyl)pyridine, hepH = 2-(hydroxyethyl)pyridine), have been synthesized. 1 is a mononuclear Co(II) complex. The mononuclear units are interlinked into a 2D (4,4) hydrogen-bonded layer via O–H⋅ ⋅ ⋅N hydrogen bonds between the hydroxyl groups and the noncoordinating nitrile ends. These 2D layers are further extended into a 3D supramolecular architecture via the interlayer pyridyl-pyridyl stacking interaction. 2 has a 1D coordination chain structure formed by the double μ 1,5 -dca bridged dinuclear [Cu2(μ 1,5 -dca) 2 (hmpH) 2 ] unit and the μ 1,3 -dca bridges via weak Cu–N coordination, and these 1D coordination chains are further extended into 2D hydrogen-bonded layers via strong O–H⋅ ⋅ ⋅N hydrogen-bonding interaction between the hydroxyl groups and the noncoordinating nitrile ends. 3 is a 2D (4,4) coordination network made of 1D [Mn(hepH)(μ 1,5 -dca)] helical chain units and interchain double (μ 1,5 -dca) bridges. Pairs of [Mn(hepH)(μ 1,5 -dca)] helical chains are interlinked by the double (μ 1,5 dca) bridges into a racemic coordination layer structure, which is further extended into a 3D hydrogen-bonded network. Magnetic studies reveal that weak antiferromagnetic exchange occurs in 3.

In this work, two 2-hydroxypyridines, 2-(hydroxymethyl) pyridine (hmpH), and 2-(hydroxyethyl) pyridine (hepH) were chosen as the auxiliary ligands to the M(II)-dca-L systems to realize this rational crystal engineering for the following reasons: (1) hmpH and hepH can act as chelating ligand; (2) the hydroxyl groups of hmpH and hepH may act as the hydrogen bond donors, which generate strong hydrogen bond with the amide nitrogen atom of the dca
All empirical absorption corrections were applied using the SADABS program [77].The structure was solved using direct method, which yielded the positions of all nonhydrogen atoms.These were refined first isotropically and then anisotropically.All calculations were performed using the SHELXTL programs [78].The crystallographic data for 1-3 are summarized in Table 1.The selected bond lengths and angles are listed in Table 2. CCDC 711609-711611 contain the supplementary crystallographic data for this paper.These data can be obtained free of charge from the Cambridge Crystallographic Data Centre.

Results and Discussion
3.1.Synthesis and Characterization.Air-stable complexes 1-3 were obtained from the reactions of metal(II) salts, Na(dca), and 2-hydroxypyridine-type ligands (Scheme 2), in which the hydroxypyridines act as chelating ligands.Moreover, the products are independent of the ligand-to-metal ratios.
Analysis of the crystal packing of 1 shows that these sheets again interdigitate to form 3D supramolecular architecture (Figure 1(c)), with the average interplanar distance between pyridine rings being ca.3.55 Å.
Compound 3 crystallizes in monoclinic space group P2 1 /c with the asymmetric unit consisting of half formula unit.The manganese ion is coordinated to one chelating hepH ligand, coordinating via the pyridyl nitrogen atom donor (Mn-N = 2.291(3) Å) and hydroxyl oxygen atom (Mn-O = 2.188(3) Å) and four nitrile nitrogen atoms from four  1,5dca anions (Mn-N = 2.175(4)-2.271(4)Å), featuring a distorted MnN 5 O octahedron environment.The surrounding of manganese ion is shown in Figure 3(a).Each manganese ion is connected to another three manganese ions by means of two single (Mn⋅ ⋅ ⋅ Mn = 8.192(1) Å) and one double dca bridges (Mn⋅ ⋅ ⋅ Mn = 7.467(1) Å), in an end-to-end ( 1,5 ) coordination mode, leading to 2D (6,3) coordination layers (Figure 3(b)), which have been found in dca chemistry [30].As expected, the dca anions do not coordinate linearly to the metal centers with C-N-Mn angles of 153.4(1) ∘ -169.7(1)∘ .As a result, the topology of the coordination network is that of a herringbone-waved grid since the rings have a slight chair conformation.The bidentate hepH ligands are located on both sides of each layer.

Magnetic Properties.
The magnetic properties of 3 are shown in Figure 4 as   (inset) and    versus  plots (  is the molar magnetic susceptibility for one Mn II ion).Taking into consideration the two-dimensional structure, magnetic data are taken for one manganese ion.The value of    product at 300 K is 4.19 cm 3 mol −1 K, which is the typical value for one isolated Mn(II) ion ( = 2.0).This

Conclusion
In this study, we have demonstrated the construction of ternary M(II)-dca-2-hydroxypyridine supramolecular architectures from low to high dimensionality via both metal coordination and hydrogen-bonding interactions.
The dca ligand displays quite different coordination modes of monodentate in 1, double-bridge in 2, and single-and double-bridge fashion in 3. We are extending this strategy to construct new supramolecular architectures by using other functional coligands.

Figure 1 :
Figure 1: Coordination environments of the metal ions in 1 (a) and the hydrogen-bonded 2D layer (b).3D molecular architecture with interbilayer - interaction (c).

Figure 2 :Figure 3 :
Figure 2: Coordination environments of the metal ions in 2 (a) and the 1D chain extended by Cu-N weak interaction (b).2D layer built by N⋅ ⋅ ⋅ H-O hydrogen bond (c).

3 K mol − 1 )𝜒 M (cm 3 mol − 1 )Figure 4 :
Figure 4: Plot of the    versus .Solid lines represent the best fit with the parameters given in the text for 3.

Table 1 :
Crystal and structure refinement for compounds 1-3.FormulaC 16 H 14 CoN 8 O 2 C 10 H 7 CuN 7 O C 11 H 9 MnN 7 O two trans-dca ligands.The dca ligand is in  1 coordination mode and acts as a terminal ligand.The dca anions adopt nonlinear bonding configurations about the Co ions with C1-N1-Co1 = 162.08(3)∘.These mononuclear units are further cross-linked by strong N⋅ ⋅ ⋅ H-O