Nature - USA (2020-01-02)

66 | Nature | Vol 577 | 2 January 2020

Article

and iron structures revealed a fifth metal site (site V) in addition to the
four distinct octahedral sites present in the nickel(ii) halide clusters.
Complexes at site V cap the edges of each sheet at site II and probably
represent a mixture of [MCl 4 ]2− and M(DME)nCl 2 (n = 1 or 2) complexes;
however, disorder of these species precluded unambiguous assignment
of their identity. Site occupancies for the four octahedral sites in the
cobalt and iron clusters were found to range from 60.5(12)% to 81.4(6)%
for Co and from 74.6(10)% to 88.5(5)% for Fe (Supplementary Table 1),
and the tetrahedral sites were generally found to be only one-third occu-
pied. Both structures display relatively high metal loadings (74.7(4)% for

Co and 91.6(3)% for Fe relative to a M 19 Cl 38 sheet), indicating that mini-

mizing the amount of coordinating solvent strongly promotes sheet

formation. As with the nickel(ii) chloride structure, the two frameworks

contain sheets with slightly longer average M∙∙∙M separations between

octahedral centres (Co∙∙∙Co = 3.65(2) Å and Fe∙∙∙Fe = 3.680(12) Å) com-

pared to those in the bulk (Co∙∙∙Co = 3.553 Å and Fe∙∙∙Fe = 3.603 Å)^21.

Considering that sheet formation close to the crystal exterior may

hinder further diffusion of metal(ii) halide (MX 2 ) units into the crystal,

microcrystalline samples were analysed by scanning transmission elec-

tron microscopy energy-dispersive X-ray spectroscopy (STEM-EDS) to

Zr 6 O 4 (OH) 4 (bpydc) 6 (CoCl 2 ) 14

b

Zr 6 O 4 (OH) 4 (bpydc) 6 (NiCl 2 ) 13

a

Zr 6 O 4 (OH) 4 (bpydc) 6 (FeCl 2 ) 17

c

I

II

III

IV

V

Fig. 2 | Solid-state structures. a–c, Portions of the structures of 1 (NiCl 2 ) 13 (a),
1 (CoCl 2 ) 14 (b), and 1 (FeCl 2 ) 17 (c) at 100 K as determined by single-crystal X-ray
diffraction. The five crystallographically distinct metal sites in the structure of

1 (CoCl 2 ) 14 are labelled with Roman numerals at the upper right of each site.

Yellow, green, purple, orange, light green, red, blue and grey spheres represent

Zr, Ni, Co, Fe, Cl, O, N and C atoms, respectively; H atoms are omitted for clarity.

NiX 2 equivalents per bipyridine

1.0 1.5 Excess

NiBr 2

NiCl 2

Fig. 3 | Solid-state structures monitoring the growth of nickel(ii) halide
sheets. Stages of nickel(ii) halide cluster growth based on 100 K single-crystal
structures of 1 after reaction with 1.0, 1.5 and excess equivalents of NiBr 2 (top
row) and NiCl 2 (bottom row) (Supplementary Tables 1 and 2). In the structures

obtained from the reactions with 1.5 equiv NiX 2 , sections of the clusters are

faded to illustrate their lower occupancies. Yellow, green, dark red, light green,

red, blue and grey spheres represent Zr, Ni, Br, Cl, O, N and C atoms,

respectively; H atoms are omitted for clarity.