The structures of ordered defects in thiocyanate analogues of Prussian Blue

We report the structures of six new divalent transition metal hexathiocyanatobismuthate frameworks with the generic formula , M = Mn, Co, Ni and Zn. These frameworks are defective analogues of the perovskite-derived trivalent transition metal hexathiocyanatobismuthates MIII[Bi(SCN)6]. The defects in these new thiocyanate frameworks order and produce complex superstructures due to the low symmetry of the parent structure, in contrast to the related and more well-studied cyanide Prussian Blue analogues. Despite the close similarities in the chemistries of these four transition metal cations, we find that each framework contains a different mechanism for accommodating the lowered transition metal charge, making use of some combination of Bi(SCN)63− vacancies, MBi antisite defects, water substitution for thiocyanate, adventitious extra-framework cations and reduced metal coordination number. These materials provide an unusually clear view of defects in molecular framework materials and their variety suggests that similar richness may be waiting to be uncovered in other hybrid perovskite frameworks.


Synthetic Procedures
The synthesis procedures were adapted from those reported in S1 .

Synthesis of HSCN
In a 250 mL round bottom flask, NH 4 SCN (5g, 65.7 mmol) was dissolved in 5 mL H 2 O and cooled to 0 • C in an ice bath. A H 2 SO 4 solution (ca. 7 ml of H 2 SO 4 in 12 ml H 2 O) was then added dropwise to the cooled NH 4 SCN solution. The reaction mixture was stirred for 30 mins before being warmed to room temperature. The aqueous mixture was subsequently extracted with diethyl ether (2×20 ml) and the organic phase was retrieved and its volume reduced by half using a stream of N 2 .

Synthesis of H 3 [Bi(SCN) 6 ] solution
Bi 2 O 2 (CO 3 ) (0.50 g, 0.98 mmol) was suspended in ca. 12 mL H 2 O followed by the addition of the HSCN/ether solution. The resulting reaction mixture was stirred vigorously under a slight flow of N 2 until all ether had been removed and the solution had turned bright orange. Any remaining solids were filtered off and the orange solution was placed under a slight vacuum to remove any excess HSCN.

Synthesis of 1
1mL of the prepared H 3 [Bi(SCN) 6 ] was added to approximately 50 mg MnCO 3 , and left to react overnight. Any excess solids were removed by gravity filtration. The dark red solution was then left to evaporate in a watch glass covered by petri-dish for a period of approximate two weeks until diffraction quality dark orange single crystals formed.

Synthesis of 2
1mL of the prepared H 3 [Bi(SCN) 6 ] was added to approximately 50 mg (Co 5 (CO 3 ) 2 (OH) 6 ) and left to react overnight. Any excess solids were removed by gravity filtration. The dark red solution was then left to evaporate in a watch glass covered by petri-dish for a period of approximate two weeks until diffraction quality dark orange single crystals formed.

Synthesis of 3 and 4
Bi(NO 3 ) 3 · 2.5 H 2 O (3 mmol, 1.46 g) was dissolved in 1.5 mL 3M HNO 3 , and a solution of NH 4 SCN (13.1 mmol, 1.00 g) dissolved in 2 mL of distilled water was added to it, producing a vivid orange solution. Ni(NO 3 ) 2 · 6 H 2 O (7 mmol, 2.036 g) was dissolved in 2 mL of water and then added to to bismuth thiocyanate solution, which on standing produced numerous small very dark orange single crystals of 4 over a period of 15 min. The same route can be used to produce 3, substituting Co(NO 3 ) · 6 H 2 O.

Synthesis of 5 and 6
Bi(NO 3 ) 3 · 2.5 H 2 O (3 mmol, 1.46 g) was dissolved in 1.5 mL 3M HNO 3 , and a solution of NH 4 SCN (13.1 mmol, 1.00 g) dissolved in 2 mL of distilled water was added to it, producing a vivid orange solution. Zn(NO 3 ) 2 · 6 H 2 O (7 mmol, 2.082 g) was dissolved in 2 mL of water and then added to to bismuth thiocyanate solution, which on standing produced an immediate precipitate of numerous orange single crystals of 5 and 6.

Single Crystal X-ray Diffraction
Single crystals were selected and mounted using perfluorinated oil on a polymer-tipped micromount and cooled rapidly to measurement temperature 120 K or 180 K in a stream of cold N 2 using an Oxford Cryosystems open flow cryostat. To enable variable temperature measurements, the crystal used for structures 1 and 1a was mounted using varnish on a pin.
Single-crystal X-ray diffraction data for 2, 4, 5 and 6 were collected using a Nonius KappaCCD diffractometer, using graphite monochromated MoKα radiation (λ = 0.7107 Å). Data for 1 and 1a were collected using a on a Bruker D8-Quest PHOTON-100 diffractometer equipped with an Incoatec IµS Cu microsource (λ = 1.54056Å). Data for 3 were collected using Single crystal X-ray diffraction data were collected on an Oxford Diffraction GV1000 (AtlasS2 CCD area detector, mirror-monochromated Cu-K α radiation source (λ = 1.54184Å). Structure solution was carried out using SHELXT and refinement with SHELXL, within the OLEX2 graphical interface. S2-4 For crystal 1, hydrogen atoms were refined with constrained geometries and riding thermal parameters, however the disorder present in samples 2-4 meant that hydrogen atoms could not be located, aside from an NH 4 cation in 4. Disordered sites in structures 1, 2, 3 and 4 were modelled at half occupancy. ESI

Powder X-ray Diffraction
A high-resolution synchrotron X-ray powder diffraction measurement on a ground powder of Zn 3 Bi 2 (NCS) 12 was carried out at beamline 11-BM at the Advanced Photon Source (APS) using a wavelength of 0.414537 Å. The sample was loaded into a 0.8 mm diameter Kapton capillary. Rietveld refinement of the data was carried out using Topas Academic 4.1. S5, S6 Lattice parameters were allowed to refine freely along with isotropic displacement parameters for Bi atoms and terms accounting for crystallite size broadening and crystallographic strain. The presence of a minor tertiary phase was modelled using independently refining peaks, which we were unable to index as a separate phase.

ICP-OES
Inductively coupled plasma optical emission spectroscopy (ICP-OES) was recorded on a Perkin Elmer, Optima 2000 DV ICP-OES with S10 autosampler. Samples and standards were prepared with a final solution composition of 2% nitric acid. Metal content was kept below 50 mg/L for ICP measurements as at higher concentrations a precipitate would form which would not dissolve in limited volumes of acids. Found for sample 2 Bi 27.35%, Co 17.97%, Ca 0.0%, Ni 0.0% and Ti 0.0%.

STEM-EDX
Energy dispersive X-ray (EDX) spectroscopy was acquired using dark field scanning transmission electron microscopy (STEM), performed using a JEOL JEM-2100+ microscope operated at 200 kV and an Oxford Instruments XMaxN 100TLE X-ray microanalysis system. Samples were deposited onto copper grid mounted "lacey" carbon films (Agar) and the beam was condensed to areas suspended over holes of the amorphous carbon to negate the contribution to the carbon signal from the support film. Copper contributions from the grid were discounted from the analysis. The measured proportions of light atoms (C, N and O) will have contributions from the carbon film and as these measurements were carried out under high vacuum, it is likely a significant proportion of lattice water will have been lost. ESI