O-Pivaloyl diphenyl­seleno­phosphinate

Cholewinski, G.; Chojnacki, J.; Pikies, J.; Rachon, J.

doi:10.1107/S1600536809009295

organic compounds

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ISSN: 2056-9890

Volume 65| Part 4| April 2009| Pages o853-o854

doi:10.1107/S1600536809009295

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O-Pivaloyl diphenylselenophosphinate

Grzegorz Cholewinski,^a Jaroslaw Chojnacki,^a ^* Jerzy Pikies ^a and Janusz Rachon ^a

^aChemical Faculty, Gdansk University of Technology, Narutowicza 11/12, Gdansk PL-80233, Poland
^*Correspondence e-mail: jaroslaw.chojnacki@chem.pg.gda.pl

(Received 23 January 2009; accepted 13 March 2009; online 25 March 2009)

The title compound, C₁₇H₁₉O₂PSe, was obtained in the reaction of the diphenylmonoselenophosphinic acid ammonium salt with pivaloyl chloride. The P—Se bond length of 2.0769 (11) Å is normal, while the P—O bond length of 1.650 (3) Å is longer than in related O-alkyl and O-aryl derivatives. One phenyl ring is periplanar to the Se—P—C plane, while the dihedral angle between the two phenyl rings is ca 73°. The carbonyl group is in a synperiplanar position [torsion angle = 8.9 (6)°] to one of the methyl groups of the pivaloyl group. This is the first O-acyl derivative of diphenylmonoselenophosphinic acid characterized by X-ray structural analysis.

Related literature

Syntheses and the chemical properties of O-acyl monoselenophosphates have already been described by Rachon et al. (2005 ). For other monoselenophosphates, such as O-alkyl or O-aryl esters, see: Lepicard et al. (1969 ); Balakrishna et al. (2002 , 2005 ); Mague et al. (2007 ). For details of the Cambridge Crystallographic Database, see: Allen (2002 ).

Experimental

Crystal data

C₁₇H₁₉O₂PSe
M_r = 365.25
Monoclinic, P 2₁ /c
a = 9.6212 (5) Å
b = 10.3914 (5) Å
c = 17.1087 (9) Å
β = 99.618 (5)°
V = 1686.45 (15) Å³
Z = 4
Mo Kα radiation
μ = 2.32 mm⁻¹
T = 120 K
0.22 × 0.2 × 0.12 mm

Data collection

Oxford Diffraction KM-4-CCD diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008 $[Oxford Diffraction (2008). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ) T_min = 0.588, T_max = 0.760
12450 measured reflections
3674 independent reflections
2596 reflections with I > 2σ(I)
R_int = 0.06

Refinement

R[F² > 2σ(F²)] = 0.057
wR(F²) = 0.147
S = 0.97
3674 reflections
193 parameters
H-atom parameters constrained
Δρ_max = 2.18 e Å⁻³
Δρ_min = −0.65 e Å⁻³

Table 1
Comparison of the geometry of the title compound with related compounds (Å, °)

CSD refcode(Allen, 2002)	P—Se	P—O	Ph–Ph dihedral	Smaller torsion	Reference
	2.0769 (11)	1.650 (3)	72.64 (14)	7.0 (4)	This work
MPSEPO	2.080	1.619	82.62	4.15	Lepicard et al. (1969)
MUMFUV	2.072	1.624	80.93	13.32	Balakrishna et al. (2002)
	2.070	1.612	75.01	22.34
RAMXEJ	2.089	1.596	78.65	8.84	Balakrishna et al. (2005)
	2.079	1.585	78.49	6.58
YIQOM	2.089	1.620	70.15	6.15	Mague et al. (2007)

Data collection: CrysAlis CCD (Oxford Diffraction 2008 $[Oxford Diffraction (2008). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ); cell refinement: CrysAlis RED (Oxford Diffraction 2008 $[Oxford Diffraction (2008). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, England.]$ ); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ) and PLATON (Spek, 2009 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809009295/ez2163sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809009295/ez2163Isup2.hkl

checkCIF report

Comment top

O-acyl monoselenophosphates were studied in a search for potential selenoacylating agents. O-pivaloyl-diphenylmonoselenophosphinate, C₁₇H₁₉O₂PSe, was obtained in the reaction of diphenylmonoselenophosphinic acid ammonium salt with pivaloyl chloride (Rachon et al., 2005). The P—Se bond length is normal for a double bond, while the P—O bond is rather long when compared with the related O-alkyl and O-aryl derivatives (see Table 1). One phenyl ring is placed periplanar to the Se—P—C plane, while the dihedral angle between the two phenyl rings is relatively small. The carbonyl group is in a synperiplanar position [torsion angle = 8.9 (6)°] to one of methyl groups in the pivaloyl group.

This compound, together with O-p-chlorobenzoyl-diphenylselenophosphinate, reported in the following paper, are the first structures determined by X-ray diffraction of O-acyl derivatives of diphenylmonoselenophosphinic acid reported. Only four related O-alkyl and O-aryl derivatives were characterized by x-ray study so far: methyl diphenylselenophosphinate (Lepicard et al., 1969), 1,4-bis(diphenyl(seleno)phosphinito)cyclohexane (Balakrishna et al., 2005); 1,1'-methylene-bis(2-((diphenylphosphoroselenoyl)oxy)naphthalene) (Balakrishna et al., 2002) and O-2-naphthyl diphenylselenophosphinate (Mague et al., 2007).

Related literature top

Syntheses and chemical properties of O-acyl monoselenophosphates have already been described by Rachon et al. (2005). For other monoselenophosphates, such as O-alkyl or O-aryl esters, see: Lepicard et al. (1969); Balakrishna et al. (2002, 2005); Mague et al. (2007).

For related literature, see: Allen (2002).

Experimental top

O-Pivaloyl diphenylmonoselenophosphinate was obtained in the reaction of diphenylmonoselenophosphinic acid ammonium salt with pivaloyl chloride with 43% yield (Rachon et al., 2005, compound numbered as 2u, melting point 63-65 °C). Relevant ¹H, ¹³C, ³¹P NMR, MS and IR spectra were recorded and are consistent with the formula anticipated - see the supporting information for the article cited.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction 2008); cell refinement: CrysAlis RED (Oxford Diffraction 2008); data reduction: CrysAlis RED (Oxford Diffraction 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON (Spek, 2009).

Figures top

Fig. 1. View of the title compound showing the atom-numbering scheme (50% probability displacement ellipsoids).

O-pivaloyl diphenylselenophosphinate top

Crystal data top

C₁₇H₁₉O₂PSe	F(000) = 744
M_r = 365.25	D_x = 1.439 Mg m⁻³
Monoclinic, P2₁/c	Melting point: 337(2) K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 9.6212 (5) Å	Cell parameters from 5361 reflections
b = 10.3914 (5) Å	θ = 2.0–32.4°
c = 17.1087 (9) Å	µ = 2.32 mm⁻¹
β = 99.618 (5)°	T = 120 K
V = 1686.45 (15) Å³	Fragment, colourless
Z = 4	0.22 × 0.2 × 0.12 mm

Data collection top

Oxford Diffraction KM-4-CCD diffractometer	3674 independent reflections
Radiation source: Mo Kα radiation	2596 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.06
ω scans (0.75° width)	θ_max = 27°, θ_min = 2.3°
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008)	h = −12→12
T_min = 0.588, T_max = 0.760	k = −12→13
12450 measured reflections	l = −21→19

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.057	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.147	H-atom parameters constrained
S = 0.97	w = 1/[σ²(F_o²) + (0.0979P)²] where P = (F_o² + 2F_c²)/3
3674 reflections	(Δ/σ)_max = 0.001
193 parameters	Δρ_max = 2.18 e Å⁻³
0 restraints	Δρ_min = −0.65 e Å⁻³

Crystal data top

C₁₇H₁₉O₂PSe	V = 1686.45 (15) Å³
M_r = 365.25	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 9.6212 (5) Å	µ = 2.32 mm⁻¹
b = 10.3914 (5) Å	T = 120 K
c = 17.1087 (9) Å	0.22 × 0.2 × 0.12 mm
β = 99.618 (5)°

Data collection top

Oxford Diffraction KM-4-CCD diffractometer	3674 independent reflections
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008)	2596 reflections with I > 2σ(I)
T_min = 0.588, T_max = 0.760	R_int = 0.06
12450 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.057	0 restraints
wR(F²) = 0.147	H-atom parameters constrained
S = 0.97	Δρ_max = 2.18 e Å⁻³
3674 reflections	Δρ_min = −0.65 e Å⁻³
193 parameters

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
P2	0.85844 (10)	0.75002 (9)	0.28847 (6)	0.0208 (2)
Se1	0.78275 (4)	0.76292 (4)	0.16772 (2)	0.02698 (17)
O1	0.8422 (2)	0.6100 (2)	0.33157 (15)	0.0243 (6)
O2	0.6042 (3)	0.6037 (3)	0.30807 (16)	0.0310 (6)
C1	0.7130 (4)	0.5607 (4)	0.3426 (2)	0.0243 (8)
C2	0.7308 (4)	0.4557 (4)	0.4043 (2)	0.0274 (8)
C3	0.7855 (5)	0.5221 (5)	0.4839 (2)	0.0424 (11)
H3A	0.8789	0.5588	0.4826	0.064*
H3B	0.7923	0.4588	0.5269	0.064*
H3C	0.7203	0.5908	0.493	0.064*
C4	0.8353 (4)	0.3542 (4)	0.3869 (3)	0.0341 (10)
H4A	0.7989	0.3118	0.3365	0.051*
H4B	0.8486	0.2903	0.4296	0.051*
H4C	0.9258	0.3953	0.3835	0.051*
C5	0.5874 (4)	0.3949 (4)	0.4078 (3)	0.0412 (11)
H5A	0.5226	0.4609	0.4212	0.062*
H5B	0.5984	0.3272	0.4482	0.062*
H5C	0.5493	0.3574	0.356	0.062*
C6	1.0474 (4)	0.7623 (3)	0.3126 (2)	0.0211 (8)
C7	1.1309 (4)	0.6520 (4)	0.3187 (2)	0.0263 (8)
H7	1.0889	0.569	0.3136	0.032*
C8	1.2769 (4)	0.6654 (4)	0.3324 (2)	0.0273 (9)
H8	1.3348	0.5908	0.3365	0.033*
C9	1.3386 (4)	0.7856 (4)	0.3399 (2)	0.0298 (9)
H9	1.4384	0.7935	0.3494	0.036*
C10	1.2550 (4)	0.8946 (4)	0.3337 (2)	0.0277 (9)
H10	1.2976	0.9773	0.3387	0.033*
C11	1.1095 (4)	0.8839 (4)	0.3203 (2)	0.0242 (8)
H11	1.0524	0.9589	0.3164	0.029*
C12	0.7863 (4)	0.8624 (4)	0.3506 (2)	0.0254 (8)
C13	0.6748 (4)	0.9438 (4)	0.3208 (2)	0.0262 (8)
H13	0.6364	0.9409	0.266	0.031*
C14	0.6194 (4)	1.0279 (4)	0.3691 (3)	0.0338 (10)
H14	0.5447	1.084	0.3476	0.041*
C15	0.6734 (4)	1.0307 (4)	0.4499 (3)	0.0357 (10)
H15	0.6343	1.0875	0.4839	0.043*
C16	0.7843 (5)	0.9505 (4)	0.4806 (3)	0.0376 (10)
H16	0.8216	0.953	0.5356	0.045*
C17	0.8406 (4)	0.8673 (4)	0.4316 (2)	0.0307 (9)
H17	0.9169	0.8128	0.453	0.037*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
P2	0.0152 (5)	0.0257 (5)	0.0208 (5)	0.0002 (4)	0.0014 (4)	0.0001 (4)
Se1	0.0227 (2)	0.0355 (3)	0.0210 (2)	0.00040 (17)	−0.00147 (16)	0.00093 (15)
O1	0.0153 (13)	0.0272 (13)	0.0289 (14)	−0.0003 (10)	−0.0002 (10)	0.0038 (11)
O2	0.0159 (14)	0.0380 (16)	0.0371 (16)	0.0016 (12)	−0.0016 (12)	0.0088 (13)
C1	0.0201 (19)	0.0271 (19)	0.026 (2)	−0.0059 (16)	0.0044 (16)	−0.0059 (15)
C2	0.0211 (19)	0.035 (2)	0.025 (2)	−0.0008 (17)	0.0007 (16)	0.0055 (16)
C3	0.050 (3)	0.050 (3)	0.025 (2)	−0.004 (2)	0.003 (2)	0.0038 (19)
C4	0.026 (2)	0.035 (2)	0.040 (2)	0.0042 (18)	0.0028 (18)	0.0097 (18)
C5	0.023 (2)	0.046 (3)	0.054 (3)	−0.0007 (19)	0.006 (2)	0.017 (2)
C6	0.0152 (17)	0.0296 (19)	0.0183 (18)	0.0002 (14)	0.0024 (14)	0.0004 (14)
C7	0.023 (2)	0.0282 (19)	0.027 (2)	−0.0011 (16)	0.0032 (16)	0.0007 (15)
C8	0.020 (2)	0.031 (2)	0.031 (2)	0.0051 (16)	0.0040 (16)	−0.0002 (16)
C9	0.019 (2)	0.041 (2)	0.028 (2)	−0.0034 (17)	0.0029 (16)	−0.0027 (18)
C10	0.023 (2)	0.033 (2)	0.025 (2)	−0.0076 (16)	0.0008 (16)	−0.0022 (16)
C11	0.022 (2)	0.0279 (19)	0.0225 (19)	0.0044 (16)	0.0031 (15)	0.0010 (15)
C12	0.020 (2)	0.0263 (19)	0.030 (2)	0.0003 (16)	0.0039 (16)	−0.0025 (16)
C13	0.0209 (19)	0.028 (2)	0.030 (2)	0.0002 (16)	0.0040 (16)	0.0016 (16)
C14	0.021 (2)	0.032 (2)	0.048 (3)	−0.0008 (17)	0.0052 (19)	−0.0006 (19)
C15	0.035 (2)	0.035 (2)	0.039 (3)	−0.0017 (19)	0.013 (2)	−0.0078 (19)
C16	0.047 (3)	0.039 (2)	0.028 (2)	0.002 (2)	0.0062 (19)	−0.0013 (18)
C17	0.030 (2)	0.034 (2)	0.026 (2)	0.0029 (18)	0.0008 (17)	0.0022 (17)

Geometric parameters (Å, º) top

P2—O1	1.650 (3)	C7—C8	1.392 (5)
P2—C12	1.795 (4)	C7—H7	0.95
P2—C6	1.801 (4)	C8—C9	1.381 (6)
P2—Se1	2.0769 (11)	C8—H8	0.95
O1—C1	1.386 (4)	C9—C10	1.383 (6)
O2—C1	1.200 (4)	C9—H9	0.95
C1—C2	1.507 (5)	C10—C11	1.384 (5)
C2—C4	1.521 (5)	C10—H10	0.95
C2—C5	1.527 (5)	C11—H11	0.95
C2—C3	1.539 (5)	C12—C13	1.394 (5)
C3—H3A	0.98	C12—C17	1.398 (5)
C3—H3B	0.98	C13—C14	1.370 (5)
C3—H3C	0.98	C13—H13	0.95
C4—H4A	0.98	C14—C15	1.394 (6)
C4—H4B	0.98	C14—H14	0.95
C4—H4C	0.98	C15—C16	1.386 (6)
C5—H5A	0.98	C15—H15	0.95
C5—H5B	0.98	C16—C17	1.377 (6)
C5—H5C	0.98	C16—H16	0.95
C6—C7	1.393 (5)	C17—H17	0.95
C6—C11	1.395 (5)

O1—P2—C12	103.55 (16)	C7—C6—P2	120.4 (3)
O1—P2—C6	97.32 (15)	C11—C6—P2	119.1 (3)
C12—P2—C6	107.07 (17)	C8—C7—C6	118.9 (3)
O1—P2—Se1	117.24 (10)	C8—C7—H7	120.5
C12—P2—Se1	116.17 (13)	C6—C7—H7	120.5
C6—P2—Se1	113.35 (13)	C9—C8—C7	120.8 (4)
C1—O1—P2	122.8 (2)	C9—C8—H8	119.6
O2—C1—O1	121.6 (3)	C7—C8—H8	119.6
O2—C1—C2	127.0 (3)	C8—C9—C10	119.9 (4)
O1—C1—C2	111.3 (3)	C8—C9—H9	120
C1—C2—C4	111.5 (3)	C10—C9—H9	120
C1—C2—C5	109.3 (3)	C9—C10—C11	120.4 (4)
C4—C2—C5	110.6 (3)	C9—C10—H10	119.8
C1—C2—C3	106.1 (3)	C11—C10—H10	119.8
C4—C2—C3	110.1 (3)	C10—C11—C6	119.6 (3)
C5—C2—C3	109.2 (3)	C10—C11—H11	120.2
C2—C3—H3A	109.5	C6—C11—H11	120.2
C2—C3—H3B	109.5	C13—C12—C17	118.5 (4)
H3A—C3—H3B	109.5	C13—C12—P2	121.9 (3)
C2—C3—H3C	109.5	C17—C12—P2	119.5 (3)
H3A—C3—H3C	109.5	C14—C13—C12	121.4 (4)
H3B—C3—H3C	109.5	C14—C13—H13	119.3
C2—C4—H4A	109.5	C12—C13—H13	119.3
C2—C4—H4B	109.5	C13—C14—C15	119.5 (4)
H4A—C4—H4B	109.5	C13—C14—H14	120.2
C2—C4—H4C	109.5	C15—C14—H14	120.2
H4A—C4—H4C	109.5	C16—C15—C14	119.9 (4)
H4B—C4—H4C	109.5	C16—C15—H15	120
C2—C5—H5A	109.5	C14—C15—H15	120
C2—C5—H5B	109.5	C17—C16—C15	120.2 (4)
H5A—C5—H5B	109.5	C17—C16—H16	119.9
C2—C5—H5C	109.5	C15—C16—H16	119.9
H5A—C5—H5C	109.5	C16—C17—C12	120.4 (4)
H5B—C5—H5C	109.5	C16—C17—H17	119.8
C7—C6—C11	120.4 (3)	C12—C17—H17	119.8

Se1—P2—O1—C1	−69.5 (3)	O2—C1—C2—C3	−108.5 (5)
C6—P2—O1—C1	169.4 (3)	O2—C1—C2—C4	131.6 (4)
C12—P2—O1—C1	59.8 (3)	O2—C1—C2—C5	8.9 (6)
Se1—P2—C6—C7	−92.1 (3)	P2—C6—C7—C8	175.9 (3)
Se1—P2—C6—C11	84.0 (3)	C11—C6—C7—C8	−0.1 (5)
O1—P2—C6—C7	31.8 (3)	P2—C6—C11—C10	−175.8 (3)
O1—P2—C6—C11	−152.1 (3)	C7—C6—C11—C10	0.3 (5)
C12—P2—C6—C7	138.5 (3)	C6—C7—C8—C9	0.0 (5)
C12—P2—C6—C11	−45.4 (3)	C7—C8—C9—C10	−0.1 (5)
Se1—P2—C12—C13	7.0 (4)	C8—C9—C10—C11	0.3 (5)
Se1—P2—C12—C17	−174.5 (3)	C9—C10—C11—C6	−0.4 (5)
O1—P2—C12—C13	−123.0 (3)	P2—C12—C13—C14	179.1 (3)
O1—P2—C12—C17	55.5 (4)	C17—C12—C13—C14	0.5 (6)
C6—P2—C12—C13	134.8 (3)	P2—C12—C17—C16	−178.3 (3)
C6—P2—C12—C17	−46.7 (4)	C13—C12—C17—C16	0.3 (6)
P2—O1—C1—O2	15.0 (5)	C12—C13—C14—C15	−1.3 (6)
P2—O1—C1—C2	−162.2 (2)	C13—C14—C15—C16	1.3 (6)
O1—C1—C2—C3	68.6 (4)	C14—C15—C16—C17	−0.5 (6)
O1—C1—C2—C4	−51.4 (4)	C15—C16—C17—C12	−0.3 (7)
O1—C1—C2—C5	−174.0 (3)

Experimental details

Crystal data
Chemical formula	C₁₇H₁₉O₂PSe
M_r	365.25
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	120
a, b, c (Å)	9.6212 (5), 10.3914 (5), 17.1087 (9)
β (°)	99.618 (5)
V (Å³)	1686.45 (15)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	2.32
Crystal size (mm)	0.22 × 0.2 × 0.12

Data collection
Diffractometer	Oxford Diffraction KM-4-CCD diffractometer
Absorption correction	Multi-scan (CrysAlis RED; Oxford Diffraction, 2008)
T_min, T_max	0.588, 0.760
No. of measured, independent and observed [I > 2σ(I)] reflections	12450, 3674, 2596
R_int	0.06
(sin θ/λ)_max (Å⁻¹)	0.639

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.057, 0.147, 0.97
No. of reflections	3674
No. of parameters	193
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	2.18, −0.65

Computer programs: CrysAlis CCD (Oxford Diffraction 2008), CrysAlis RED (Oxford Diffraction 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999) and PLATON (Spek, 2009).

Comparison of the geometry of the title compound with related compounds (Å, °) top

CSD refcode	P—Se	P—O	Ph–Ph dihedral	Smaller torsion	Reference
(Allen, 2002)			Ph–Ph dihedral	Smaller torsion
	2.0769 (11)	1.650 (3)	72.64 (14)	7.0 (4)	This work
MPSEPO	2.080	1.619	82.62	4.15	Lepicard et al. (1969)
MUMFUV	2.072	1.624	80.93	13.32	Balakrishna et al. (2002)
	2.070	1.612	75.01	22.34
RAMXEJ	2.089	1.596	78.65	8.84	Balakrishna et al. (2005)
	2.079	1.585	78.49	6.58
YIQOM	2.089	1.620	70.15	6.15	Mague et al. (2007)

Acknowledgements

GC thanks the Gdansk University of Technology for financial support (internal grant No. 014668 t. 008).

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