Bis­(di-2-pyridyl­phosphinato-[kappa]³N,O,N')copper(II) di­chloro­methane disolvate

The solid-state structure of the first reported homoleptic copper di-2-pyridyl­phosphinate complex shows an extremely large `z-out' tetragonal distortion, with an axial Cu...O distance of 2.430 (2) Å. The title complex, [Cu(C₁₀H₈N₂O₂P)₂]·2CH₂Cl₂ or Cu[py₂P(O)O]₂·2CH₂Cl₂, comprises two di-2-pyridyl­phosphinate ligands coordinated to the central copper(II) ion, which sits on an inversion center. The pyridyl rings of one ligand are trans to the pyridyl rings of their symmetry-related counterpart. The two trans py-Cu-py moieties are coplanar, as required by the inversion symmetry. A disordered dichloromethane solvent mol­ecule is cocrystallized in the asymmetric unit cell.

S1. Comment

Published examples of metal complexes of phosphinates (R₂P(O)O⁻) are limited (Annan et al., 1991; Betz & Bino, 1988; Chakraborty et al., 2000; Kongprakaiwoot et al., 2002). Their binding atoms are almost exclusively confined to O atoms. Derivation of the R groups (e.g. pyridyl) enables the development of multidentate phosphinates and opens a new field in coordination chemistry. However, there are even fewer examples of such compounds in the literature than there are of underivatized phosphinates. The N,O-bidentate mode only occurrs in {bis(4,5-di-isopropylimidazol-2-yl)phosphinic acid}- dichlorozinc monohydrate (Ball et al., 1984) and the tridentate mode in the [Ru{py₂P(O)O}{py₃PO}]⁺ cation (Keene & Stephenson, 1991). The latter is the only structurally identified example of a metal complex bearing pyridylphosphinate. During the course of a study of metal complexes with pyridylphosphines, we accidentally isolated the title compound, (I), and found it to be the first homoleptic pyridylphosphinate metal complex. The isolation of this compound may encourage further studies of possible applications for the new tridentate ligand, py₂P(O)OH, as well as other multidentate phosphinate derivatives.

X-ray structural analysis was carried out in order to elucidate the coordination mode of the bis(2-pyridyl)phosphonate (L) ligand. The molecular structure of (I) is illustrated in Fig. 1. The asymmetric unit contains half the CuL₂ complex and a dichloromethane solvent molecule. The Cu^II center sits at the inversion center and is coordinated with both pyridyl rings from both ligands. Each phosphinate ligand further provides an O atom to occupy the axial positions above and below the CuN₄ plane (Fig. 1). The Cu···O distance is extremely long [2.430 (3) Å] but falls between the sum of the covalent radii (2.11 Å) and the sum of the van der Waals radii (2.95 Å). One other notable feature is that the O1—Cu—O1ⁱ [symmetric code: (i) 1 − x, 1 − y, 1 − z] vector is tilted away from the normal of the CuN₄ plane. These facts may cast some doubt on the existence of the Cu···O interaction in the title complex. However, the existence of the interaction is evidenced by the bending (folding?) of the P1—O1 segment towards the Cu center, which is manifested by the reduction of the P—C—N angles as well as the enlargement of the P—C—C angles from their ideal (120°) angle (Table 1). The off-normal O1—Cu1—O1ⁱ vector and the extremely long Cu···O distances may very well be the result of the balance between the tendency to bond the axial O atoms (electronic attraction) and the resistance to distortion of the phosphinate ligand (steric rigidity). The elongatation of the Cu···O bond may also arise for the same reason as the often-observed Jahn–Teller distortion in Cu^II complexes. Although the ligand field in (I) hardly produces electronically degenerate state, as required by the Jahn–Teller theorem, the argument of lowering energy due to the tetragonal distortion still holds true in the case of (I).

The only other example of a metal bispyridylphosphinate in the literature, as mentioned above, is [Ru{py₃P=O}{py₂P(O)O}] [BF₄] (Keene & Stephenson,1991). The N,N,O-tridentate mode of the bispyridylphosphinate in this Ru complex is similar to that observed in the title complex but differs in its strong M—O interaction [Ru—O=2.11 (2) Å]. The strength of this interaction may be due to the electronic configuration (d⁶) for Ru^II. Because the need for electronic input from the ligand is greater for Ru^II (d⁶) than for Cu^II (d⁹), Ru^II ions are usually six coordinated, while Cu^II ions usually prefer four- (square planar) or five-coordination (square pyramid) modes. This argument may explain why the Ru^II ion forms normal Ru—O bonds in [Ru{py₃P=O}{py₂P(O)O}][BF₄] and add addtional support to the existence of elongated Cu—O bonds in (I). The distortion of the py/Ru/py moieties (mean Ru—N···X=173.5°, X is the centroid of the py ring) is more obvious than that observed in the title complex (mean Cu—N···X=176.1 (2)°), and this result is consistent with the stronger M—O interaction in the Ru complex.

Although the py/Cu/py moieties are coplanar, as required by the existence of an inversion center, all of the pyridine rings around the Cu^II center are not coplanar with the CuN₄ plane. Therefore, there are no significant pπ···dπ interactions strengthening the Cu—N bonds. The Cu—N bond lengths (Table 1) are, however, still comparable to the literature values (2.00–2.07 Å; International Tables of Crystallography, 1992, Vol. C, pp. 738–739).

Because H atoms are not always located in X-ray analysis, the possibility exists for one of the ligands to be neutral in charge. However, the distinct blue color (a common color for Cu^II complexes) of the crystal and the equality of the P—O distances in the moiety support the anionic assignment of py₂P(O)O⁻. The normal atomic displacement parameters of the two O atoms (Fig. 1) also indicate that disorder of the py₂P(O)OH group is unlikely.

The dichlomethane solvent molecule is disordered. The non-H atoms of the two major orientations (A, with an occupancy of 40%, and B, with an occupancy of 60%) were located and refined anisotropically.

S2. Experimental

The title complex was obtained by mixing an acetonitrile solution of [Cu(CH₃CN)₄][BF₄] with Ppy₃ in a 2:3 molar ratio for 24 h. After filtration, CH₂Cl₂ was added to the precipitate. Deep-blue crystals were obtained after simple evaporation of the CH₂Cl₂ solution. Elemental analysis of the crystalline powder gave satisfactory results: Calculated: C 42.98, H 3.09, N 9.55%; found: C 43.02, H 3.81, N 9.36%. During the synthesis of Ppy₃, incomplete substitution of PCl₃ by 2-pyridyl anions would lead to the formation of hydroxybis(2-pyridyl)phosphine, which would give rise to the production of bis(2-pyridyl)phosphinic acid in the subsequent air oxidation. This is believed to be the route for the generation of the pyridylphosphinate observed in the title complex.

S3. Refinement

H atoms on the pyridyl rings were placed in calculated positions, with C—H distances of 0.93 Å. Fixed positions, isotropic ADPs (0.05) and occcupancy factors (40/60%)of the H atoms of the disordered CH₂Cl₂ molecule were included in the final cycle of least-squares refinement. All other H atoms were included as riding, with U_iso(H) values equal to 1.2U_eq of the carrier atoms.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1992); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 1992–1997); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. The molecular structure of (I), with 30% probability displacement ellipsoids. For clarity, only one of the two orientations of the disordered CH2Cl2 is shown. [Symmetry code: (i) 1 − x,1 − y,1 − z.]
	Fig. 2. The molecular packing of (I), showing the space around the CH2Cl2 solvent molecules.

Bis(di-2-pyridylphosphinato-κ³N,O,N')copper(II) dichloromethane disolvate

Crystal data

[Cu(C10H8N2O2P)2]·2CH2Cl2	F(000) = 678
Mr = 671.70	Dx = 1.665 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 20 reflections
a = 8.404 (3) Å	θ = 4.3–7.1°
b = 14.392 (2) Å	µ = 1.37 mm^−1
c = 11.167 (2) Å	T = 293 K
β = 97.42 (2)°	Prism, blue
V = 1339.5 (6) Å^3	0.64 × 0.60 × 0.30 mm
Z = 2

Data collection

Rigaku AFC6S diffractometer	1664 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.024
Graphite monochromator	θmax = 25.0°, θmin = 2.3°
ω–2θ scans	h = 0→9
Absorption correction: ψ scan (North et al., 1968)	k = 0→17
Tmin = 0.425, Tmax = 0.663	l = −13→13
2647 measured reflections	3 standard reflections every 150 reflections
2358 independent reflections	intensity decay: 0.6%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.033	H-atom parameters constrained
wR(F^2) = 0.102	w = 1/[σ^2(Fo^2) + 0.3429P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max < 0.001
2358 reflections	Δρmax = 0.47 e Å^−3
197 parameters	Δρmin = −0.37 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0184 (15)

Special details

Experimental. The scan width was (1.47 + 0.30tanθ)° with an ω scan speed of 16° per minute (up to 5 scans to achieve I/σ(I) > 10). Stationary background counts were recorded at each end of the scan, and the scan time:background time ratio was 2:1.

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cu	0.5000	0.5000	0.5000	0.02675 (19)
Cl1A	0.1810 (18)	0.7474 (12)	0.6954 (14)	0.107 (5)	0.40
Cl1B	0.2187 (11)	0.7437 (6)	0.6921 (10)	0.0714 (11)	0.60
Cl2A	−0.0366 (8)	0.7395 (8)	0.4851 (9)	0.110 (3)	0.40
Cl2B	−0.0049 (7)	0.7128 (5)	0.4719 (5)	0.115 (2)	0.60
P1	0.64648 (10)	0.54520 (7)	0.74932 (7)	0.0342 (2)
O1	0.7050 (3)	0.47171 (17)	0.6702 (2)	0.0385 (6)
O2	0.7252 (3)	0.5641 (2)	0.8732 (2)	0.0529 (7)
N1	0.3584 (3)	0.50057 (19)	0.6346 (2)	0.0289 (5)
N2	0.5574 (3)	0.63285 (18)	0.5418 (2)	0.0307 (6)
C1	0.4317 (4)	0.5199 (2)	0.7473 (3)	0.0298 (7)
C2	0.3467 (4)	0.5202 (2)	0.8452 (3)	0.0407 (9)
H2	0.3978	0.5345	0.9219	0.049*
C3	0.1847 (4)	0.4989 (3)	0.8280 (3)	0.0435 (8)
H3	0.1270	0.4961	0.8936	0.052*
C4	0.1100 (4)	0.4820 (2)	0.7136 (3)	0.0436 (9)
H4	0.0005	0.4699	0.7000	0.052*
C5	0.2011 (4)	0.4833 (2)	0.6186 (3)	0.0383 (8)
H5	0.1508	0.4718	0.5409	0.046*
C6	0.6252 (4)	0.6504 (2)	0.6564 (3)	0.0334 (7)
C7	0.6645 (4)	0.7402 (3)	0.6937 (4)	0.0477 (9)
H7	0.7139	0.7517	0.7718	0.057*
C8	0.6291 (5)	0.8132 (3)	0.6129 (4)	0.0576 (11)
H8	0.6539	0.8740	0.6365	0.069*
C9	0.5579 (5)	0.7948 (3)	0.4987 (4)	0.0571 (11)
H9	0.5318	0.8429	0.4441	0.068*
C10	0.5248 (5)	0.7036 (3)	0.4650 (3)	0.0440 (9)
H10	0.4785	0.6912	0.3865	0.053*
C11A	0.1624 (13)	0.7459 (10)	0.5332 (11)	0.068 (4)	0.40
C11B	0.0889 (11)	0.7944 (6)	0.5705 (7)	0.065 (2)	0.60
H11A	0.1953	0.8097	0.5037	0.050*	0.40
H12A	0.2275	0.7031	0.4960	0.050*	0.40
H11B	0.0153	0.8357	0.5981	0.050*	0.60
H12B	0.1571	0.8294	0.5204	0.050*	0.60

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu	0.0320 (3)	0.0245 (3)	0.0238 (3)	−0.0022 (2)	0.00378 (19)	−0.0019 (2)
Cl1A	0.145 (11)	0.115 (6)	0.054 (4)	−0.002 (6)	−0.014 (5)	0.017 (4)
Cl1B	0.078 (2)	0.065 (2)	0.068 (2)	0.0036 (15)	0.0004 (15)	0.0105 (17)
Cl2A	0.044 (2)	0.137 (8)	0.145 (7)	−0.026 (3)	−0.006 (3)	0.025 (5)
Cl2B	0.168 (6)	0.112 (4)	0.064 (2)	−0.072 (4)	0.011 (3)	−0.032 (2)
P1	0.0310 (4)	0.0438 (6)	0.0262 (4)	0.0005 (4)	−0.0029 (3)	−0.0015 (4)
O1	0.0335 (12)	0.0440 (15)	0.0369 (13)	0.0073 (10)	0.0007 (10)	0.0013 (11)
O2	0.0503 (15)	0.073 (2)	0.0312 (13)	−0.0036 (13)	−0.0109 (11)	−0.0041 (13)
N1	0.0301 (12)	0.0292 (13)	0.0273 (13)	−0.0007 (11)	0.0040 (10)	−0.0019 (12)
N2	0.0379 (14)	0.0259 (14)	0.0283 (13)	−0.0014 (12)	0.0047 (11)	0.0000 (11)
C1	0.0358 (16)	0.0247 (19)	0.0288 (16)	0.0032 (13)	0.0041 (13)	0.0022 (13)
C2	0.053 (2)	0.040 (2)	0.0307 (18)	−0.0010 (16)	0.0093 (15)	−0.0025 (15)
C3	0.0467 (19)	0.0391 (19)	0.050 (2)	0.0000 (18)	0.0250 (16)	−0.0014 (19)
C4	0.0307 (17)	0.043 (2)	0.059 (2)	−0.0030 (15)	0.0154 (16)	−0.0028 (18)
C5	0.0346 (17)	0.038 (2)	0.0412 (19)	−0.0026 (14)	−0.0001 (14)	−0.0011 (15)
C6	0.0302 (16)	0.037 (2)	0.0331 (17)	−0.0062 (14)	0.0043 (13)	−0.0052 (15)
C7	0.049 (2)	0.043 (2)	0.051 (2)	−0.0126 (18)	0.0081 (17)	−0.0160 (19)
C8	0.063 (3)	0.033 (2)	0.080 (3)	−0.0152 (19)	0.021 (2)	−0.017 (2)
C9	0.078 (3)	0.030 (2)	0.065 (3)	−0.0039 (19)	0.013 (2)	0.005 (2)
C10	0.062 (2)	0.033 (2)	0.0373 (19)	−0.0024 (17)	0.0040 (16)	0.0031 (16)
C11A	0.045 (6)	0.094 (11)	0.067 (7)	0.003 (6)	0.017 (5)	0.033 (7)
C11B	0.086 (6)	0.059 (5)	0.049 (4)	−0.009 (4)	0.010 (4)	−0.002 (4)

Geometric parameters (Å, º)

Cu—N2	2.012 (3)	C3—C4	1.371 (5)
Cu—N1	2.034 (2)	C3—H3	0.9300
Cu—O1	2.429 (2)	C4—C5	1.386 (5)
Cl1A—C11A	1.80 (2)	C4—H4	0.9300
Cl1B—C11B	1.785 (13)	C5—H5	0.9300
Cl2A—C11A	1.692 (12)	C6—C7	1.386 (5)
Cl2B—C11B	1.728 (9)	C7—C8	1.392 (6)
P1—O2	1.480 (2)	C7—H7	0.9300
P1—O1	1.502 (3)	C8—C9	1.363 (6)
P1—C6	1.831 (3)	C8—H8	0.9300
P1—C1	1.838 (3)	C9—C10	1.383 (5)
N1—C5	1.334 (4)	C9—H9	0.9300
N1—C1	1.356 (4)	C10—H10	0.9300
N2—C10	1.337 (4)	C11A—H11A	1.026
N2—C6	1.356 (4)	C11A—H12A	0.954
C1—C2	1.382 (4)	C11B—H11B	0.939
C2—C3	1.384 (5)	C11B—H12B	0.989
C2—H2	0.9300
N2—Cu—N1	88.30 (10)	N1—C5—H5	118.8
N2—Cu—O1	81.56 (9)	C4—C5—H5	118.8
N1—Cu—O1	81.14 (9)	N2—C6—C7	120.8 (3)
O2—P1—O1	122.61 (14)	N2—C6—P1	112.3 (2)
O2—P1—C6	112.16 (16)	C7—C6—P1	126.8 (3)
O1—P1—C6	105.31 (14)	C6—C7—C8	119.1 (4)
O2—P1—C1	111.58 (15)	C6—C7—H7	120.5
O1—P1—C1	104.44 (14)	C8—C7—H7	120.5
C6—P1—C1	97.62 (14)	C9—C8—C7	119.5 (4)
P1—O1—Cu	95.11 (10)	C9—C8—H8	120.3
C5—N1—C1	119.1 (3)	C7—C8—H8	120.3
C5—N1—Cu	124.4 (2)	C8—C9—C10	119.1 (4)
C1—N1—Cu	116.57 (19)	C8—C9—H9	120.4
C10—N2—C6	119.3 (3)	C10—C9—H9	120.4
C10—N2—Cu	123.5 (2)	N2—C10—C9	122.1 (3)
C6—N2—Cu	117.0 (2)	N2—C10—H10	118.9
N1—C1—C2	121.0 (3)	C9—C10—H10	118.9
N1—C1—P1	112.3 (2)	Cl2A—C11A—Cl1A	105.9 (8)
C2—C1—P1	126.6 (2)	Cl2A—C11A—H11A	104.1 (9)
C1—C2—C3	119.3 (3)	Cl1A—C11A—H11A	108.7 (12)
C1—C2—H2	120.4	Cl2A—C11A—H12A	115.2 (12)
C3—C2—H2	120.4	Cl1A—C11A—H12A	117.8 (11)
C4—C3—C2	119.5 (3)	H11A—C11A—H12A	104.1 (9)
C4—C3—H3	120.2	Cl2B—C11B—Cl1B	113.0 (6)
C2—C3—H3	120.2	Cl2B—C11B—H11B	111.9 (7)
C3—C4—C5	118.6 (3)	Cl1B—C11B—H11B	111.9 (7)
C3—C4—H4	120.7	Cl2B—C11B—H12B	103.7 (6)
C5—C4—H4	120.7	Cl1B—C11B—H12B	107.3 (7)
N1—C5—C4	122.4 (3)	H11B—C11B—H12B	108.5 (8)