Synthesis and crystal structure of NaCuIn(PO4)2.

Single crystals of sodium copper(II) indium bis-[phosphate(V)], NaCuIn(PO4)2, were grown from the melt under atmospheric conditions. The title phosphate crystallizes in the space group P21/n and is isotypic with KCuFe(PO4)2. In the crystal, two [CuO5] trigonal bipyramids share an edge to form a dimer [Cu2O8] that is connected to two PO4 tetra-hedra. The obtained [Cu2P2O12] units are inter-connected through vertices to form sheets that are sandwiched between undulating layers resulting from the junction of PO4 tetra-hedra and [InO6] octa-hedra. The two types of layers are alternately stacked along [101] and are joined into a three-dimensional framework through vertex- and edge-sharing, leaving channels parallel to the stacking direction. The channels host the sodium cations that are surrounded by four oxygen atoms in form of a distorted disphenoid. © Benhsina et al. 2020.

Chemical context

Transition-metal phosphates have been the subject of intensive research as a result of their inter­esting physical properties and potential applications in wide-ranging fields such as catalysis, electrochemistry, luminescence (Tie et al., 1995 ▸; Pan et al., 2006 ▸; Yang et al., 2016 ▸) and ion exchange (Cheetham et al., 1999 ▸; Han et al., 2015 ▸; Manos et al., 2005 ▸, 2007 ▸; Plabst et al., 2009 ▸; Stadie et al., 2017 ▸). In these materials, the anionic framework is built up from PO4 tetra­hedra linked to different kinds of transition metal (TM) coordination polyhedra of the form [TMO] (n = 4, 5 and 6), leading to a large variety of crystal structure families. This structural diversity is mainly associated with the ability of TM cations to adopt different oxidation states in various coordination polyhedra. Based on previous hydro­thermal investigations aimed at orthophosphates of general formula (M,M′′)3(PO4)2·nH2O (M and M′′ = bivalent cations), we have reported on synthesis and characterization of the phosphates Ni2Sr(PO4)2·2H2O (Assani et al., 2010 ▸), Mg1.65Cu1.35(PO4)2·H2O (Khmiyas et al., 2015 ▸) and Mn2Zn(PO4)2·H2O (Alhakmi et al., 2015 ▸). In this context, the aim of the present study was to develop new phases belonging to the series AM′′M′′′(PO4)2 where A, M′′ and M′′′ are mono-, bi- and trivalent cations, respectively. As a result, we report here on synthesis and crystal structure of the new compound NaCuIn(PO4)2.

Structural commentary

The principal building units of the crystal structure of NaCuIn(PO4)2 are two PO4 tetra­hedra linked to a [CuO5] triangular bipyramid [Cu—O bond-length range of 1.9088 (9) to 2.1939 (9) Å] and to an [InO6] octa­hedron [In—O bond lengths range from 2.1028 (10) to 2.2051 (9) Å], and is completed by a distorted [NaO4] polyhedron (Fig. 1 ▸). The P—O bond lengths in the two phosphate tetra­hedra are similar and comparable with those of similar phosphates. However, the P1—O distances, varying between 1.5035 (10) and 1.5729 (9) Å, indicate a somewhat higher distortion of this tetra­hedron than the P2—O distances [between 1.5297 (9) and 1.5488 (9) Å] of the other tetra­hedron.

Figure 1

The principal building units in the crystal structure of NaCuIn(PO4)2. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) x + , −y − , z + ; (ii) −x + 1, −y, −z + 2; (iii) −x + , y − , −z + ; (iv) x + , −y + , z + ; (v) −x + 1, −y, −z + 1; (vi) x, y, z + 1; (vii) −x, −y, −z + 1; (viii) −x + , y + , −z + ; (ix) x − , −y + , z + .]

In this phosphate, two [CuO5] triangular bipyramids share one edge to form a [Cu2O8] dimer, the ends of which are linked to two P1O4 tetra­hedra by edge-sharing. The obtained [Cu2P2O12] groups are linked together via the vertices to form sheets extending parallel to (10), as shown in Fig. 2 ▸. On the other hand, the [InO6] octa­hedra and the P2O4 tetra­hedra are inter­connected through common vertices to build up an undulating layer extending in the same direction (Fig. 3 ▸). The copper phosphate layers are sandwiched between the undulating indium phosphate layers. By sharing corners and edges, an alternating stacking of the layers along [101] leads to a three-dimensional framework structure with channels in which the Na+ cations are located (Fig. 4 ▸). The four nearest oxygen atoms around the alkali metal cation form a distorted disphenoid with Na—O distances between 2.3213 (12) and 2.4275 (11) Å (Fig. 1 ▸).

Figure 2

Projection along [001] of [Cu2P2O12] copper phosphate sheets in the crystal structure of NaCuIn(PO4)2.

Figure 3

(a) A view approximately along [101] showing the undulating layer formed by [InO6] octa­hedra linked to PO4 tetra­hedra and (b) a projection of this layer onto (101).

Figure 4

The sodium cations located in channels running parallel to [101] in the crystal structure of NaCuIn(PO4)2.

NaCuIn(PO4)2 is isotypic with KCuFe(PO4)2 (Badri et al., 2011 ▸), whereby potassium is substituted by sodium and iron by indium. However, we note a significant difference in the coordination number of sodium and potassium in the two structures. Whereas sodium has a fourfold coordination in NaCuIn(PO4)2, potassium is surrounded by nine oxygen atoms in KCuFe(PO4)2 because of its greater ionic radius.

Bond-valence-sum calculations (Brown & Altermatt, 1985 ▸) are in good agreement with the expected values (in valence units) for sodium(I), copper(II), indium(III) and the phospho­rus(V) cations, viz. NaI = 0.845 (2), CuII = 2.102 (3), InIII = 3.152 (4), P1V = 4.930 (8), and P2V = 4.992 (8). For the oxygen anions, the calculated values range between 1.940 (5) and 2.076 (3).

Database survey

Phosphate-based materials with general formula AM II M′III(PO4)2 commonly show crystal structures where channels or, more rarely, layers are formed by the [M II M′II(PO4)2]− framework to delimit suitable environments to accommodate the A + cations. A recent survey given by Yakubovich et al. (2019 ▸) revealed that all compounds of the morphotropic series AM II M′III(PO4)2, where A = Na, K, Rb or NH4, M′′ = Cu, Ni, Co, Fe, Zn or Mg and M′′′ = Fe, Al or Ga, crystallize in the monoclinic crystal system and can be classified into seven subgroups according to their structure types, viz. (i) KNiFe(PO4)2 (space-group type P21/c, Z = 4; Strutynska et al., 2014 ▸); (ii) KFeIIFeIII(PO4)2 (space-group type P21/c, Z = 4; Yakubovich et al., 1986 ▸); (iii) (NH4)FeIIFeIII(PO4)2 (space-group type C2/c, Z =16; Boudin & Lii, 1998 ▸); (iv) K(Co,Al)2(PO4)2 (space-group type C2/c, Z = 8; Chen et al., 1997 ▸); (v) (NH4)(Zn,Ga)2(PO4)2 (space-group type P21/a, Z = 4; Logar et al., 2001 ▸); (vi) KMgFe(PO4)2 (space-group type C2/c, Z = 4; Badri et al., 2009 ▸); (vii) NaZnAl(PO4)2 (space-group type P21/c, Z = 4; Yakubovich et al., 2019 ▸). NaCuIn(PO4)2 belongs to the second subgroup of this classification.

In addition, the structures of certain members of this phosphate family are similar to those of the zeolite-ABW structural type (Badri et al., 2014 ▸). When the trivalent cation is lanthanum or yttrium, the crystal structures KM IILa(PO4)2 (M II = Mg or Zn) are isotypes of the monazite monoclinic structure of LaPO4 with space-group type P21/n (Pan et al., 2006 ▸; Tie et al., 1995 ▸), while KMgY(PO4)2 turns out to be an isotype of the xenotime structure YPO4 adopting a tetra­gonal symmetry with space-group type I41/amd (Tie et al., 1996 ▸).

Synthesis and crystallization

Stoichiometric amounts of NaNO3, CuO, In2O3 and NH4H2PO4 as precursors in the molar ratio 1:1:0.5:2 were ground in an agate mortar and pre-heated at 473 and 673 K in a platinum crucible to eliminate gaseous products. The resulting powder was subsequently heated to a temperature of 1473 K. The product was then cooled to room temperature at a rate of 5 K h−1. The obtained product contained green single crystals corresponding to the title phosphate.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▸.

Table 1

Experimental details

Crystal data
Chemical formula	NaCuIn(PO4)2
M r	391.29
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	296
a, b, c (Å)	8.2563 (3), 10.1382 (4), 8.8060 (3)
β (°)	114.444 (1)
V (Å3)	671.03 (4)
Z	4
Radiation type	Mo Kα
μ (mm−1)	7.16
Crystal size (mm)	0.34 × 0.25 × 0.19
Data collection
Diffractometer	Bruker X8 APEX Diffractometer
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 ▸)
T min, T max	0.528, 0.747
No. of measured, independent and observed [I > 2σ(I)] reflections	24292, 3106, 2996
R int	0.026
(sin θ/λ)max (Å−1)	0.820
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.013, 0.033, 1.11
No. of reflections	3106
No. of parameters	119
Δρmax, Δρmin (e Å−3)	0.66, −0.59

Computer programs: APEX2 and SAINT (Bruker, 2009 ▸), SHELXT2014/5 (Sheldrick, 2015a ▸), SHELXL2018/3 (Sheldrick, 2015b ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸), DIAMOND (Brandenburg, 2006 ▸) and publCIF (Westrip, 2010 ▸).

Labelling of atoms and their coordinates were adapted from isotypic KCuFe(PO4)2 (Badri et al., 2011 ▸). Since not all atoms in the latter description are part of one unit cell, a translation by (z + 1) relative to the original coordinates brings all corresponding atoms inside one unit cell. Moreover, oxygen atoms O11 and O14 were translated by (x − , −y + , z − ) and (x, y, z − 1), respectively, to be linked directly to P1.

The maximum and minimum electron densities in the final difference-Fourier map are at 0.70 Å from O14 and 0.50 Å from Cu1, respectively.

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989020001929/wm5539sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989020001929/wm5539Isup2.hkl

CCDC reference: 1983244

Additional supporting information: crystallographic information; 3D view; checkCIF report

NaCuIn(PO4)2	F(000) = 732
Mr = 391.29	Dx = 3.873 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 8.2563 (3) Å	Cell parameters from 3106 reflections
b = 10.1382 (4) Å	θ = 2.9–35.6°
c = 8.8060 (3) Å	µ = 7.16 mm−1
β = 114.444 (1)°	T = 296 K
V = 671.03 (4) Å3	Block, green
Z = 4	0.34 × 0.25 × 0.19 mm

Bruker X8 APEX Diffractometer	3106 independent reflections
Radiation source: fine-focus sealed tube	2996 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
φ and ω scans	θmax = 35.6°, θmin = 2.9°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −12→13
Tmin = 0.528, Tmax = 0.747	k = −16→16
24292 measured reflections	l = −14→14

Refinement on F2	0 restraints
Least-squares matrix: full	w = 1/[σ2(Fo2) + (0.0139P)2 + 0.5758P] where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.013	(Δ/σ)max = 0.004
wR(F2) = 0.033	Δρmax = 0.66 e Å−3
S = 1.11	Δρmin = −0.59 e Å−3
3106 reflections	Extinction correction: SHELXL-2018/3 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
119 parameters	Extinction coefficient: 0.0093 (3)

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

	x	y	z	Uiso*/Ueq
Na1	0.51418 (10)	−0.16856 (7)	1.09748 (8)	0.01965 (13)
Cu1	0.37225 (2)	0.11940 (2)	0.45881 (2)	0.00706 (3)
In1	0.00214 (2)	0.12812 (2)	0.73403 (2)	0.00463 (3)
P1	0.12997 (4)	0.17027 (3)	0.15664 (4)	0.00494 (5)
O11	−0.03216 (13)	0.25215 (10)	0.13588 (12)	0.01037 (15)
O12	0.30223 (12)	0.24790 (9)	0.27141 (11)	0.00812 (14)
O13	0.14612 (12)	0.04925 (9)	0.27222 (11)	0.00824 (14)
O14	0.13759 (14)	0.12965 (10)	−0.00448 (12)	0.01159 (16)
P2	0.28460 (4)	−0.08358 (3)	0.66933 (4)	0.00448 (5)
O21	0.11495 (13)	−0.13653 (9)	0.52826 (12)	0.00993 (15)
O22	0.37706 (12)	−0.19241 (8)	0.79630 (11)	0.00787 (14)
O23	0.24068 (13)	0.03111 (9)	0.75876 (12)	0.00903 (15)
O24	0.41607 (13)	−0.03247 (9)	0.59836 (12)	0.00962 (15)

	U11	U22	U33	U12	U13	U23
Na1	0.0288 (3)	0.0145 (3)	0.0146 (3)	−0.0042 (2)	0.0079 (3)	−0.0035 (2)
Cu1	0.00887 (7)	0.00557 (6)	0.00492 (6)	−0.00104 (4)	0.00104 (5)	0.00126 (4)
In1	0.00517 (4)	0.00405 (4)	0.00432 (4)	−0.00022 (2)	0.00161 (3)	−0.00042 (2)
P1	0.00552 (11)	0.00490 (11)	0.00367 (11)	−0.00020 (9)	0.00119 (9)	0.00053 (8)
O11	0.0096 (4)	0.0125 (4)	0.0094 (4)	0.0054 (3)	0.0044 (3)	0.0042 (3)
O12	0.0085 (4)	0.0077 (3)	0.0063 (3)	−0.0034 (3)	0.0012 (3)	0.0008 (3)
O13	0.0091 (4)	0.0055 (3)	0.0071 (3)	−0.0028 (3)	0.0004 (3)	0.0020 (3)
O14	0.0129 (4)	0.0165 (4)	0.0043 (3)	0.0025 (3)	0.0025 (3)	−0.0014 (3)
P2	0.00536 (11)	0.00392 (11)	0.00410 (11)	0.00089 (8)	0.00189 (9)	0.00025 (8)
O21	0.0096 (4)	0.0119 (4)	0.0054 (3)	−0.0026 (3)	0.0002 (3)	−0.0013 (3)
O22	0.0109 (4)	0.0058 (3)	0.0073 (3)	0.0032 (3)	0.0041 (3)	0.0027 (3)
O23	0.0088 (4)	0.0071 (3)	0.0113 (4)	0.0018 (3)	0.0042 (3)	−0.0034 (3)
O24	0.0101 (4)	0.0092 (4)	0.0125 (4)	0.0030 (3)	0.0077 (3)	0.0056 (3)

Na1—O21i	2.3213 (12)	In1—O22viii	2.1441 (9)
Na1—O23ii	2.3496 (12)	In1—O13vii	2.1632 (9)
Na1—O22	2.4268 (11)	In1—O12ix	2.2051 (9)
Na1—O11iii	2.4275 (11)	P1—O14	1.5035 (10)
Cu1—O24	1.9088 (9)	P1—O11	1.5205 (10)
Cu1—O11iv	1.9317 (9)	P1—O13	1.5642 (9)
Cu1—O12	1.9913 (9)	P1—O12	1.5729 (9)
Cu1—O13	2.0378 (9)	P2—O23	1.5297 (9)
Cu1—O24v	2.1939 (9)	P2—O22	1.5310 (9)
In1—O14vi	2.1028 (10)	P2—O21	1.5340 (10)
In1—O21vii	2.1044 (9)	P2—O24	1.5488 (9)
In1—O23	2.1303 (9)
O21i—Na1—O23ii	108.90 (4)	O14vi—In1—O13vii	94.18 (4)
O21i—Na1—O22	71.58 (4)	O21vii—In1—O13vii	90.44 (4)
O23ii—Na1—O22	123.80 (4)	O23—In1—O13vii	96.21 (4)
O21i—Na1—O11iii	94.99 (4)	O22viii—In1—O13vii	171.80 (3)
O23ii—Na1—O11iii	88.91 (4)	O14vi—In1—O12ix	85.65 (4)
O22—Na1—O11iii	146.95 (4)	O21vii—In1—O12ix	96.23 (4)
O24—Cu1—O11iv	96.82 (4)	O23—In1—O12ix	164.87 (3)
O24—Cu1—O12	166.88 (4)	O22viii—In1—O12ix	87.16 (3)
O11iv—Cu1—O12	96.28 (4)	O13vii—In1—O12ix	91.55 (3)
O24—Cu1—O13	95.96 (4)	O14—P1—O11	114.50 (6)
O11iv—Cu1—O13	144.90 (4)	O14—P1—O13	111.94 (5)
O12—Cu1—O13	72.85 (3)	O11—P1—O13	109.89 (5)
O24—Cu1—O24v	82.35 (4)	O14—P1—O12	111.32 (5)
O11iv—Cu1—O24v	110.97 (4)	O11—P1—O12	108.72 (5)
O12—Cu1—O24v	93.34 (4)	O13—P1—O12	99.40 (5)
O13—Cu1—O24v	103.05 (4)	O23—P2—O22	108.94 (5)
O14vi—In1—O21vii	174.97 (4)	O23—P2—O21	110.57 (5)
O14vi—In1—O23	80.87 (4)	O22—P2—O21	110.58 (5)
O21vii—In1—O23	96.68 (4)	O23—P2—O24	107.97 (5)
O14vi—In1—O22viii	93.79 (4)	O22—P2—O24	108.36 (5)
O21vii—In1—O22viii	81.66 (3)	O21—P2—O24	110.35 (5)
O23—In1—O22viii	86.94 (4)