Quasi-one-dimensional uniform spin- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:math> Heisenberg antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>KNaCuP</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mn>7</mml:mn></mml:msub></mml:math> probed by <mml:math xmlns:mml="http://www.w3.org/1998/…

We present the structural and magnetic properties of KNaCuP$_2$O$_7$ investigated via x-ray diffraction, magnetization, specific heat, $^{31}$P NMR $^{23}$Na measurements complementary electronic structure calculations. The temperature dependent susceptibility shift could be modeled very well by uniform spin-$1/2$ Heisenberg antiferromagnetic chain model with nearest-neighbour interaction $J/k_{\rm B}\simeq 58.7$ K. corresponding mapping using first principles calculations leads to $J^{\rm DFT}/k_{\rm B} \simeq 59$ K negligibly small inter-chain couplings ($J^{\prime}/k_{\rm B}$, $J^{\prime \prime}/k_{\rm < 0.1$ K), further confirming that system is indeed an one-dimensional antiferromagnet. temperature-dependent unit cell volume described Debye approximation a $\Theta_{\rm D} 294$ K, consistent heat capacity data. diverging trend spin-lattice relaxation rates ($^{31}1/T_1$ $^{23}1/T_1$) imply onset long-range-ordering at low temperatures supporting anticipated $T_{\rm N} 0.38$ from couplings. Moreover, show dominant contributions ($q=0$) staggered ($q = \pm \pi/a$) spin fluctuations in high regimes, respectively mimicking one-dimensionality spin-lattice. have also demonstrated $^{31}1/T_1$ varies linearly $1/\sqrt{H}$ reflecting effect diffusion on dynamic susceptibility. Further, frustration substantially impede ordering rendering perfect antiferromagnet over wide range.